Organic chemistry of aliphatic and cyclic compounds: theory and practice: educational manual 9786010436251

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AL-FARABI KAZAKH NATIONAL UNIVERSITY

R. S. Iminova

ORGANIC CHEMISTRY OF ALIPHATIC AND CYCLIC COMPOUNDS: THEORY AND PRACTICE Educational manual

Almaty «Qazaq University» 2018

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UDC 547 LBC 24.2 І-55 Recommended for publication by the decision of the Faculty of Chemistry and Chemical Technology Academic Council, RISO and Publishing Council of the Kazakh National University named after Al-Farabi (Protocol №7 dated 05.07.2018) Reviewers: Doctor of Chemical sciences, Professor G.Sh.Burasheva

І-55

Iminova R.S. Organic chemistry of aliphatic and cyclic compounds: theory and practice: educational manual / R.S. Iminova. – Almaty: Qazaq University, 2018. – 148 p. ISBN 978-601-04-3625-1 The textbook was developed in accordance with the educational program of specialties: "5В072100 – Chemical technology of organic substances", completely covers the practical material of the theoretical aspect of organic synthesis in courses "Organic chemistry of aliphatic compounds" and "Organic chemistry of cyclic compounds". This textbook consists: basic safety rules and organization of work in the laboratory, necessary chemical utensils; methods of purification and separation of organic substances; determination of physical constants of organic compounds; physical methods of identification of organic substances, driers and solvents in organic chemistry. Syntheses of organic substances of the aliphatic series and the cyclic series with the theoretical context and the type of reactions is considered in detail. The textbook is intended for students of al Farabi KazNU, the specialty 5В072100 – "Chemical technology of organic substances", taking the practical course "Organic Chemistry of Aliphatic and Compounds" and "Organic Chemistry of Cyclic Compounds", and for the course "Organic Chemistry" for the specialties "5В072000-Chemical technology of inorganic substances", "5В060600-Chemistry" with the English language of education. Published in authorial release.

UDC 547 LBC 24.2 ISBN 978-601-04-3625-1

© Iminova R.S., 2018 © Al-Farabi KazNU, 2018

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CONTENTS

INTRODUCTION ................................................................................... 7 1. SAFETY RULE AT WORKING ON LABORATORY OF ORGANIC CHEMISTRY ................................................................ 9 1.1 General Provisions ............................................................................... 9 1.2 Work with poisonous and corrosive substances ................................... 11 1.3 Safety regulations during the work with acids and alkalis ................... 13 1.4 Safety measures during the work with flammable liquids (FL) .......... 13 1.5 Security measures at leak of gas and suppression of the local fire and the burning clothes........................................................................ 14 1.6 First aid at burns and poisonings with chemicals ................................. 15 1.7 Chemical dishes for laboratory work of organic chemistry ................. 16 1.8 Rules for assembling installations for the performance of organic syntheses .................................................................................................... 18 1.9 Sample of design the experimental work performed by students ......... 19 2. METHODS OF PURIFICATION AND SEPARATION OF ORGANIC SUBSTANCES............................................................... 21 Laboratory work 1. Distillation ............................................................... 21 Simple distillation at atmospheric pressure................................................ 21 Simple distillation in vacuum .................................................................... 22 Dependence of boiling temperature of the substance from pressure .......... 25 Steam distillation ....................................................................................... 28 Fractional distillation (rectification) .......................................................... 29 Laboratory work 2. Crystallization.......................................................... 34 Crystallization ............................................................................................ 34 Recrystallization from a solution ............................................................... 34 The choice of solvent for crystallization .................................................... 35 Stimulation of crystallization ..................................................................... 37 Experimental technique ............................................................................. 38 Laboratory work 3. Sublimation ............................................................. 41 Sublimation................................................................................................ 41 Sublimation of crude benzoic acid ............................................................. 43 3. DETERMINATION OF PHYSICAL CONSTANTS. ...................... 45 Laboratory work 4. Melting point ........................................................... 45 Laboratory work 5. Boiling point ............................................................ 49 Laboratory work 6. Determination of the density ................................... 53

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Laboratory work 7. Determination of the refraction index ...................... 55 4. CHROMATOGRAPHY METHODS................................................. 59 Laboratory work 8. Preparative chromatographic separation on columns (of dyes, pigments, green leaf) .............................. 61 Laboratory work 9. Separation of amino acids by method of partition chromatography on paper. ....................................................... 64 Laboratory work 10. Separation and identification of dicarboxylic acids by TLC in an aqueous-organic mobile phases .................................. 68 5. DRYING REAGENTS AND SOLVENTS IN ORGANIC CHEMISTRY........................................................................................... 71 5.1 Drying and basic drying reagents in organic chemistry ....................... 71 5.2 Solvents and methods for their purification ......................................... 77 6 SYNTHESIZES OF ORGANIC COMPOUNDS ............................... 81 6.1 SYNTHESIZES OF ORGANIC COMPOUNDS OF ALIPHATIC SERIES ....................................................................... 81 Laboratory work 11. Saturated, unsaturated hydrocarbons ..................... 81 Obtaining methane and its properties......................................................... 81 Receiving and properties of ethylene ......................................................... 82 Receiving and properties of ethyne ............................................................ 83 Laboratory work 12. Obtaining of halogen hydrocarbons......................... 84 Synthesis of Iodoform................................................................................ 84 Synthesis of bromo-ethyl ........................................................................... 85 Synthesis of bromo-isopropyl .................................................................... 87 Synthesis of bromo-butyl ........................................................................... 88 Laboratory work 13. Synthesis of esters.................................................... 90 Synthesis of dibutyl ester ........................................................................... 90 Synthesis of ethylpropyl ester ...................................................................... 92 Laboratory work 14. Synthesis of esters by the esterification reaction ..... 95 Synthesis of ethyl ether of acetic acid .......................................................... 95 Synthesis of butyl ether of acetic acid .......................................................... 97 Synthesis of iso-amyl ether of acetic acid .................................................. 98 Laboratory work 15. Synthesis based on magnesium organic compounds.................................................................................................... 99 Synthesis of 2-methyl-2-butanol .................................................................. 99 Laboratory work 16. Oxidation reactions .................................................. 101 Synthesis of Propanal ................................................................................. 101 Synthesis of Acetone .................................................................................... 102 6.27 SYNTHESIZES OF ORGANIC COMPOUNDS OF CYCLIC SERIES ................................................................................ 103 Laboratory work 1. Synthesis of halogen containing cyclic compounds.................................................................................................... 103 Synthesis of chlorocyclohexane (cyclohexyl chloride) ................................ 103

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Laboratory work 2. Synthesis of benzene, the study of certain properties of benzene and its homologues, as well as naphthalene.............. 105 Synthesis and Analyzes in test tubes ............................................................ 105 Experiment 1. Preparation of benzene from benzoic acid and study of its properties ............................................................................................. 105 Experiment 2. Sulfurization of aromatic compounds ................................... 106 Experiment 3. Nitration of benzene and toluene .......................................... 107 Experiment 4. Nitration of naphthalene ....................................................... 107 Experiment 5. Bromination of benzene, toluene and naphthalene ............... 108 Experiment 6. Oxidation of homologues of benzene ................................... 108 Experience 7. Study of the mobility of halogen in the benzene nucleus and side chain .................................................................................. 108 Laboratory work 3. Methods of nitration aromatic compounds. Electrophilic substitution reactions .............................................................. 110 Synthesis of para-nitro acetanilide and para-nitro aniline ............................ 110 Synthesis of ortho – and para – nitrotoluenes .............................................. 112 Laboratory work 4. Methods of sulfonation of aromatic compounds. Electrophilic substitution reactions .............................................................. 115 Synthesis of Benzene sulfonic acid .............................................................. 115 Synthesis of Sulfanilic acid .......................................................................... 116 Synthesis of p-toluene sulfonic acid ............................................................. 117 Synthesis of p-xylene sulfonic acid .............................................................. 119 Laboratory work 5. Syntheses based on oxidation reactions ..................... 120 Synthesis of cyclohexanone ......................................................................... 120 Synthesis of p-benzoquinone from hydroquinone and potassium bromate.......120 Synthesis of benzophenone from benzhydrol and potassium dichromate ... 121 Synthesis of benzoic acid from toluene ........................................................ 122 Synthesis of benzoic acid from benzyl alcohol ............................................ 123 Synthesis of benzoic acid (and benzyl alcohol) from benzaldehyde............ 126 Laboratory work 6. Syntheses based on Reduction reactions of aromatic aldehydes and ketones ............................................................... 127 Synthesis of benzyl alcohol from benzaldehyde .......................................... 127 Synthesis of benzhydrol (diphenylmethanol) ............................................... 127 Laboratory work 7. Aromatic aldehydes (ketones) condensation ............. 129 Synthesis of benzalacetone ........................................................................... 129 Synthesis of dibenzalacetone........................................................................ 130 Synthesis of N-Benzylideneaniline (benzalaniline) ..................................... 131 Synthesis of Benzalacetophenon (Chalcone) ............................................... 132 Laboratory work 8. Modification reactions of aromatic compounds ........ 134 Synthesis of p-nitrobenzoic acid from p-nitrotoluene and sodium dichromate ................................................................................ 134 Synthesis of benzyl methyl ether.................................................................. 135 Synthesis of m-nitrochlorobenzene (copper chloride catalysis (1)) ............. 135 Laboratory work 9. Syntheses based on the reactions of diazotization and reactions of diazo compounds, accompanied by the release of nitrogen ............................................................................. 137

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Synthesis of bromo-aryls (catalysis copper bromide (1))............................. 137 Synthesis of Iodobenzene ............................................................................. 138 Synthesis of phenol ...................................................................................... 139 Laboratory work 10. Syntheses based on the reactions of diazotization and reactions of diazo compounds without releasing of nitrogen. Azo-coupling reactions.............................................. 141 Synthesis of Methyl orange (helianthin) ...................................................... 141 Synthesis of Naftolorange ............................................................................ 142 Synthesis of p-nitroaniline red...................................................................... 143 Synthesis of phenylazo-β-naphthol .............................................................. 144 Synthesis of chrome yellow ....................................................................... 145 REFERENCE........................................................................................... 147

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INTRODUCTION

The manual "Organic chemistry of aliphatic and cyclic compounds: theory and practice" was developed in accordance with the educational program of specialties "5В0721000 – Chemical technology of organic substances in English. The general courses "Organic Chemistry of Aliphatic Compounds" and "Organic Chemistry of Cyclic Compounds" are obligatory disciplines in state universities on the specialty "5В072100 – Chemical Technology of Organic Substances", as they constitute the theoretical basis and basis of the leading branches of the national economy and medicine, such as petrochemical, basic and subtle organic synthesis, the production of pharmaceutical and agricultural products. The present training manual prepared specially for these courses will be the main and necessary tool in the hands of students who study not only in the above-mentioned specialty, but also in the specialties "5В060600 – Chemistry" and "5В072000 – Chemical technology of inorganic substances" with the English language of instruction. The use and development of this manual and the study of courses on organic chemistry, gives the student the opportunity to understand the general patterns linking the properties of organic compounds and methods for obtaining basic classes of compounds, mechanisms for the flow of basic types of reactions; master the methodology of synthesis and identification of the main classes of organic compounds, master the methods of separation, isolation, purification, identification and methods of synthesis, handling of liquid, solid, combustible, volatile and toxic substances, instruments and equipment of the organic synthesis laboratory. In the training manual, apart from the introduction, content, bibliography and other structural elements, theoretical aspects of the synthesis of organic substances of aliphatic and cyclic series are presented and consonant with a number of techniques for performing experimental practical work, listed in the following main sections: 1) The basic safety rules and the organization of work in the laboratory, which details the main rules of work in the laboratory and the necessary chemical dishes; 7 

 

2) Methods of purification and separation of organic substances; 3) Determination of the physical constants of organic compounds; 4) Physical methods of identification of organic substances; 5) Synthesis of organic substances, which has two large subsections: 5.1) Synthesis of organic substances of the aliphatic series and 5.2) Synthesis of organic substances of the cyclic series. In Section 5, a detailed description of the progress of the main practical works on the synthesis of individual classes of organic compounds, with the theoretical context of the features of the course and conditions, and also the type of reactions is discussed in detail. Reference characteristics for some substances are given. When performing laboratory classes, students acquire practical skills and skills in working out technological parameters: the ratio of reagents, regimen, time of synthesis, methods of separation and purification of organic solvents and dry substances. Thus, the training manual "Organic chemistry of aliphatic and cyclic compounds: theory and practice" in English is developed in accordance with the educational program of specialties: "5В0721000 – Chemical Technology of Organic Substances", fully covers practical material with theoretical aspects of the synthesis on courses "Organic Chemistry of Aliphatic Compounds" and "Organic chemistry of cyclic compounds", meets all the requirements of higher education in the training of specialists of a wide range.

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1. SAFETY RULE AT WORKING ON LABORATORY OF ORGANIC CHEMISTRY

1.1. General Provisions Any experimenter, being in the laboratory, should first and foremost clearly understand where and why he is, what he has to do and what the consequences of his activities may be. A chemist (especially a beginner) should give himself up why the chemical laboratory is a place of increased danger. Getting to work in an organic workshop, first of all, it is necessary to firmly grasp the general rules of work in it and the rules of safety, to know the measures of preventing and preventing accidents, to be able to provide first aid to oneself and others. It must be remembered that non-compliance with techniques, the unreasoned use of chemical equipment and laboratory utensils, haste in the performance of work can lead to failures in the conduct of syntheses and even accidents. The practical workshop on organic chemistry is equipped in a special room, allowing simultaneous 10-12 experiments, with 6-8 workplaces equipped in fume cupboards. Each desktop has a set of tripods, legs and rubber hoses for mounting laboratory instruments. Reagents and solvents, laboratory utensils and equipment (magnetic stirrers, tiles) students receive by their applications for each individual synthesis, and after the work is handed over to the laboratory assistant. The final products of syntheses with the indication of the number and physicochemical constants are handed over to the teacher. Below are some general rules that must be fulfilled when working in a chemical laboratory: 1. In the chemical laboratory it is strictly forbidden to perform experimental work alone. 2. It is forbidden to start work without the permission of the teacher or laboratory assistant. 9 

 

3. Before beginning the experimental work, it is necessary to learn the basic rules of safety and fire safety. 4. While working in a chemical laboratory, it is necessary to observe the silence, order, cleanliness, rationally plan the order of their actions, perform them quickly, but without fuss; carefully and carefully handle chemical utensils, appliances and reagents. 5. To perform each synthesis, it is necessary to reserve a place for it in advance. The dishes and reagents required for the experiment must to be in this place. It is inadmissible to clutter this place with chemical utensils, reagents and preparations from other syntheses. 6. Before starting the experiment, the workplace must be de-energized (electric switchboard is turned off), gas and water valves are shut off. 7. Any device containing moving or heating parts, as well as intended for operation under a different from atmospheric pressure, must be pre-tested "idle", without loading solvents, reagents, reaction mixtures. The electrical current to the terminals (plugs) of electrical appliances, as well as the water current, are initially fed during the "blank" experiment. 8. When assembling instruments, care must be taken so that excessive pressure cannot be generated during operation (danger of explosion!). 9. It is highly recommended not to look from above in any open containers with chemical compounds. 10. Do not leave working laboratory equipment, or the unattended devices switched on. 11. During work, wear a lab coat, keep the work desk clean. Do not record in the laboratory journal directly under the thrust or next to the instruments for the synthesis or separation of products – for this purpose, the laboratory has written desks. 12. When starting to work with chemical utensils, you need to make sure that it is clean and dry. After performing the synthesis, the dishes should be washed and dried. 13. When preparing reagents and performing the synthesis, it is necessary to ensure that containers with reagents, solvents, reaction products are signed (preferably – labeled); Do not confuse the jams from different bottles. The flasks and glasses intended for the final product of the synthesis must be signed and weighed. It is forbidden to use reagents from containers that do not have labels. 10 

 

14. Any chemicals can only be weighed in chemical containers. 15. It is forbidden to pour into the shells the remains of aggressive inorganic reagents and any organic substances. For these purposes, there are special flasks in the hoods. 16. It is strictly forbidden to smoke in the laboratory and it is strongly discouraged to drink and eat. 1.2. Work with poisonous and corrosive substances Most chemical compounds are more or less toxic. Therefore, before carrying out each experiment, it is necessary to obtain information on the basic physical, chemical and toxic properties of the reagents and products, as well as on first aid measures for burns and poisoning by them. When working with poisonous and corrosive substances, the following rules should be observed: – It is necessary to have protective face masks, goggles and a gas mask in the laboratory. – All work with toxic and flammable gases and vapors should be carried out in a fume hood. Wherein: a) doors of the cabinet should be left at the level specified by the teacher; b) do not look inside the cabinet; c) devices containing poisonous or aggressive gases or vapors must be disassembled under traction; take out from under the traction only after the displacement of the latter by air; at the need to treat the degassing solution indicated by the teacher; d) starting to work with chlorine, bromine and other volatile toxic substances, to warn about this to nearby people; e) to know and not to clutter up the ways of emergency evacuation of the laboratory in case of release of toxic substances into the atmosphere. – Work with especially dangerous substances (bromine, concentrated acids, etc.) should only be carried out under the supervision of a teacher or laboratory assistant. – Bromine causes extremely painful and difficult to heal burns. Attention! Bromine vapor is heavier than air and drains down! When working with it: 11 

 

– Beware of inhaling vapors, eyes and hands; – When pouring and transfusing bromine wear rubber gloves, carefully remove the drop from the edge of the bottle neck about the edge of the vessel; – remember that rubber gloves are quickly corroded by bromine and are only a temporary measure of protection. – Concentrated acids, acid anhydrides and acid halides, ammonia and amines must be poured only through the funnel and under the draft. – When diluting concentrated sulfuric acid, pour acid into the water in portions and mix slightly (not vice versa!). – When dissolving concentrated sulfuric acid in water, when making chrome mix, when mixing concentrated sulfuric and nitric acids, use only thin-walled chemical glassware made of heat-resistant glass (strong heating!) When preparing concentrated alkali solutions. For the same reason, do not pour hot liquids into thick-walled dishes and appliances. – Grind caustic alkalis, iodine and other corrosive substances in a fume hood. – It is strictly forbidden to keep mercury in an open container. All devices containing mercury should be placed on trays with sufficiently high sidewalls. In the event of a breakdown of a device containing mercury, it is necessary to inform the teacher or laboratory assistant about this. Pour mercury into the sinks is prohibited. The spilled mercury is collected by means of an amalgamated copper plate into special thickwalled cans closed with a cork. Remains of mercury trapped in the slots of floor, table, etc., should be treated with a 20% aqueous solution of iron (III) chloride or sulfur powder. If, for example, when preparing the installation for the experiment, a mercury thermometer was broken, then it is necessary to immediately collect all the spreading mercury balls and open the windows, process the place to spill. In the absence of a copper plate, you can use a white paper to fold it for ease of collection and collect large drops of mercury and transfer them to a jar with a solution of ferric chloride (III) or a solution of potassium permanganate or simply water, then treat the spot with cotton wool from the above solutions and ventilate the room.

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1.3. Safety regulations during the work with acids and alkalis 1. It is necessary to store the concentrated acids and alkalis in an exhaust case in strong ware on the pallet. 2. All works with acids and alkalis need to be carried out in goggles. 3. Concentrated hydrochloric and nitric acids it is possible to pour only in an exhaust case. Dilution of acids should be carried out in heatresistant ware, at the same time acid needs to be flowed to water in the small portions, when hashing (it is impossible to flow water to the concentrated acid as in this case a large amount of warmth, waters as less dense substance is distinguished, boils on the surface of acid, and liquid can be thrown out from a vessel). 4. At dissolution of hydroxides of sodium and potassium pieces of alkali can be taken only tweezers or the pallet, but not hands; dissolution of these substances should be carried out by small portions. 1.4. Safety measures during the work with flammable liquids (FL) Classification of flammable liquids (FL) according to the degree of danger. Depending on the FL flashpoint is conventionally assigned to one of three digits which are represented in Table 1: Table 1 Classification of flammable liquids (FL) according to the degree of danger Discharge

Characteristics of liquid

I II III

Particularly dangerous Permanently dangerous Hazardous at elevated temperature

Flash point, ° С: in an open crucible Up to -18 from -18 to 23 from 23 to 61

in a closed crucible Up to -13 from -13 to 27 from 27 to 66

The third category includes: amyl acetate, anisole, acetylacetone, benzyl chloride, bromobenzene, butanol, hexyl chloride, decane, diamyl ether, diketene, N, N-dimethylaminoethanol, dimethyl sulfate, N, Ndiethylaminoethanol, diethylcarbonate isoamyl acetate, kerosines, xylene, methyl acrylate, morpholine, formic acid, octylamine, pentanol, pro13 

 

pylbenzene, propanol, turpentine, styrene, acetic acid, acetic anhydride, chlorobenzene, cyclohexanone and others. Flammable liquids (FL) are liquids that are capable of burning themselves after removing the ignition source and having a flash point not exceeding 61 °C. Combustible liquids (CL) are liquid substances having a flashpoint above 61 °C in a closed crucible or above 66 °C in an open crucible and capable of burning after removing the ignition source. Work with flammable liquids. When working with flammable liquids should be followed so basic principles: 1. Work only in a fume hood. 2. Do not allow flammable vapors to enter the atmosphere (prevent the formation of fire and explosive mixtures). 3. Works with flammable liquids (FL) should be carried out far away from fire. It is forbidden to heat flying and flammable liquids (acetone, air, alcohols, petroleum air, gasoline, benzene, carbon sulfur) on an open flame. For heating of FL it is possible to use a water bath or an electric tile with the closed spiral, at the same time the flask has to be supplied with the water refrigerator. 4. It is impossible to heat combustible substances in open vessels. It should be done in flasks with the return refrigerator. 5. It is necessary to overtake FL in the device with the water refrigerator or on the rotor evaporator. It is impossible to overtake liquids dry – it can lead to explosion or the fire. Devices which contain FL should be disassembled after removal of all sources of a flame (the lit gas burners, spirit-lamps, electric tiles with an open spiral, etc.) and full cooling of a flask. 6. It is strictly forbidden to pour out FL in the sewerage, buckets and boxes for garbage as accidentally thrown match can cause the fire. 7. FL have to be stored in metal cases in the quantities which aren't exceeding daily requirements. 1.5. Security measures at leak of gas and suppression of the local fire and the burning clothes 1. At emergence of the fire it is necessary to remove quickly all combustible substances far away from the place of ignition, to discon14 

 

nect the gas highway, all electric devices and to stop active access of air to laboratory. 2. The suppression of a flame by water can lead to expansion of the seat of fire if the substance insoluble in water (for example, ether, benzene, gasoline, turpentine metal sodium, etc.) is burning. In this case, the flame should be extinguished by sand or a fire-prevention blanket. In case of more extensive fire area it is necessary to use the fire extinguisher. 3. Soluble in water flammable substances, such as alcohol, acetone and others, can be extinguished with water. 4. If on someone the clothes light up, it is necessary densely on to cover the lit-up fabric with a fire-prevention blanket. At ignition of clothes it is impossible to run as it promotes distribution of a flame. 1.6. First aid at burns and poisonings with chemicals 1. At thermal burns of the first degree (redness and a swelling) the burned place should be processed spirit solution of tannin, 96% ethyl alcohol or solution of permanganate of potassium. At burns of the second and third degree (bubbles and ulcers) only the disinfecting lotions from potassium permanganate solution then it is necessary to see a doctor are admissible. 2. At burns acids it is necessary to wash out the struck place a large amount of flowing water, and then 3% solution of a hydrocarbonate of sodium then – again water. 3. At burns alkalis it is necessary to wash out the defeat center flowing water, and then the diluted solution of boric or acetic acid. 4. At hit of alkali or acid in eyes it is necessary to wash out their flowing water (3 – 5 min.), and then solution of boric acid (in case of alkali hit) or a sodium hydrocarbonate (in case of acid hit) then to see a doctor. 5. At burns phenol the center of defeat should be processed 70% ethyl alcohol, and then glycerin before disappearance of white spots on skin. At poisoning with vapors of phenol it is strictly forbidden to drink milk. 6. At burns bromine he needs to be washed away 96% alcohol or the diluted alkali solution then to grease the place of defeat with burns 15 

 

ointment and to see a doctor. At poisoning with vapors of bromine it is deeply necessary to inhale several times fumes of ethyl alcohol, and then to drink milk. 7. At hit on skin of caustic organic substances, not soluble in water, they need to be washed away a large amount of suitable solvent. After first-aid treatment the victim has to be sent to a first-aid post. 1.7. Chemical dishes for laboratory work of organic chemistry Flasks, glasses, test tubes, cups, funnels, refrigerators, dephlegmators and other vessels of various designs belong to the main laboratory chemical glassware. Most often chemical ware is made of glass of various brands. Such ware differs in resistance to influence of the majority of chemical reagents, is transparent, easily washes. Below are the images and names of the basic chemical utensils, often used in the organic laboratory:

a

b

c

Adapters: Wurz's (b) and Claisen (b), to a round bottom flask for distillation. Vacuum and simple (c) receiving adapters connect the outlet of a condenser to a receiving flask.

. a

b

c

Flasks: The Kleisen flask (a) with a refrigerator is used for distilling organic compounds under reduced pressure; Wurz flask (b) is used for distillation; the flasks (c) are used for distillation and synthesis of chemicals.

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a

b

Three-(a) and Two-neck (b) distilling flasks with angled necks allow to connect three components for complex distillations.

a

b

c

d

Complex for vacuum filtration (a): A Buchner funnel (b), Filtering flask (c), Schott's laboratory funnel (d)

a

b

c

Condensers: Liebig (a) and a Graham (or reflux) (b) condenser are used to cool and condense hot vapor as part of a distillation and synthesis apparatus. Deзрhlegmators (c) – reflux condensers serve for more careful separation of fractions of the mixture during its fractional distillation.

Separatory funnels are used in a variety of inorganic and organic chemistry processes

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Сonical or flat bottom flask

Glass laboratory beakers

Desiccators allow to cool and store objects in a lowhumidity atmosphere.

Laboratory funnel

The commonly accessory tools

Assorted solid, 1-hole and 2-hole stoppers

used

Bunsen Laboratory Stand. An extension clamps and rings are very versatile in setting up distillation or other laboratory equipment.

1.8. Rules for assembling installations for the performance of organic syntheses The choice of the device (equipment’s) for synthesis is determined, first of all, by the task facing the experimenter, the reaction conditions, and also by the properties of the starting materials and final products. Assembly of the installation should be carried out with great care and accuracy, as this is an indispensable condition for successful and safe operation. The assembled units must be not only literate in design, but also have an attractive appearance. General rules for assembling instruments. Separate parts of the installation must be connected with each other carefully, picking up plugs, tubes and other parts even before the device is fixed to a tripod. If 18 

 

the device is assembled on thin sections, they should be pre-lubricated. The dishes are selected in such a size that the reacting substances occupy not more than half the volume (or no more than 2/3 of the volume). If the reaction mixture is heated, a round-bottomed flask of the appropriate size is necessarily used. After assembling the individual parts of the installation, they are fixed in the legs of the tripod. The installation is always assembled, beginning with its supposed "top" or from the main unit. For example, when assembling a plant for simple distillation, first fix the Wurz flask on the tripod, then attach a descending refrigerator to it, then an allonge, and finally bring the receiver under it. The entire installation should be assembled in one plane or along one line (except in some cases), without distortions or stress of the glass parts of the device. This is especially important when working with standard sections, when they should be connected to each other without much effort on the part of the experimenter. At the same time, it must be ensured that the sealing conditions are met when connecting the individual parts of the device. If the glass parts of the installation are heavy enough (for example, a flask with a reflux condenser, a stirrer, a dropping funnel, a thermometer, etc.), then a few paws should be attached to the tripod. At the same time, reflux condensers, agitators, reflux coolers are fixed strictly vertically, and descending refrigerators are sloped so that the liquid flows into the receiver without getting into the plugs. If the unit is designed for operation at atmospheric pressure, it is necessary that it is freely communicated with the atmosphere in order to avoid increasing the pressure in the system. To protect the reactants from the action of air moisture (if necessary), use a calcium chloride tube. Getting started, you should once again carefully inspect the device and make sure of the correctness of its assembly. 1.9. Sample of design the experimental work performed by students Number of laboratory work, No. _______________ Name of synthesis __________________________ The main reaction (with all the coefficients): Adverse Reactions: 19 

 

The recalculation of the number of starting materials for synthesis and the filling of the table 2-4. Table №2 Amount of starting materials for synthesis Substance

Quantity in accordance with the methodology mole g ml

Quantity proposed by the teacher moles

g

ml

Table №3 Physico-chemical characteristics of the starting materials and reaction products (reference data) Name and formula of substance

Mr

Tb°С

Tmelt°С

nD20

d

Solubility

Table №4 The characteristics and yields of the reaction products obtained as a result of the experimental process Name and formula of substance g

Yield % of the theoretical

% of the practical

Output Characteristics established during the experiment Tmelting description or nD20 (color, odor, Tboiling °С liquid, oily, solid, etc.)

In the case of a low yield of the reaction product (below 50-60%), it is necessary to give an explanation and to presume the reasons for this result. Signature of the head ________________ Date _____________ "___" ______ 20 ___.

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2. METHODS OF PURIFICATION AND SEPARATION OF ORGANIC SUBSTANCES

Laboratory work 1. Distillation The distillation (distillation) – a process in which the distilled substance is heated to boiling, the resulting vapor is condensed and discharged as a distillate. Separation by distillation of a mixture based on differences in the composition of liquid and vapor. This method is applicable, provided the thermal stability of the substance being distilled, ie material should not decompose during the distillation. By means of distillation can be: – Divide the mixture of liquids with different boiling points, Separate liquid substance dissolved therein by solid or resinous impurities. – To drive off the volatile solvent from the material to be cleaned. Depending on the properties of substances separated by distillation is carried out under different conditions: – At atmospheric pressure, – In vacuum – Steam. Based on the differences in the boiling points of the mixture components used simple (direct flow) or fractionation (countercurrent) distillation at atmospheric pressure and under vacuum. Simple distillation at atmospheric pressure Simple distillation is used for liquids boiling in the range of 40150 °C, so at low temperatures there are certain difficulties in ensuring the full condensation of the vapor, and above 150 °C many compounds are significantly decomposed. 21 

 

High-boiling liquids are distilled under reduced pressure – in a vacuum created by a water jet (8-15 mm Hg) or rotary oil (1-0.01 mmHg) pump. Simple distillation is widely used for distilling off the organic solvent from the non-volatile impurity or separating a mixture of liquids greatly differ from each other in their boiling points. Satisfactory separation is possible, provided that the difference in boiling point is distilled liquid is at least 80 °C. Fig. 1. provides for simple distillation device, consisting of a distillation flask, Würz nozzle fitted with a thermometer, a cooler, alonge and receiver. By simple distillation vapors of boiling liquid from coming into the distillation flask cooler where the condensate is converted. In this process, vapor and condensate move in the same direction, so called a co-current distillation. Separation of mixtures of liquids can occur only at the stage of evaporation.

Fig. 1. Installation for simple distillation

Simple distillation in vacuum Some organic substances may not be distilled at atmospheric pressure, since they decompose partly or completely. Others have very high boiling points that make it difficult distillation. In such cases, the distillation should be performed under reduced pressure as vacuum vapor pressure becomes lower when the outside temperature. For distillation in a vacuum, similar instruments are used – only instead of a round-bottomed flask with a nozzle, it is preferable to use a 22 

 

Claisen or Favorsky flask (Fig. 2). This is due to the fact that when heated, the lubricant of the section between the bulb and the nozzle becomes liquid, flows through the sections, air begins to penetrate, and the pressure in the device increases (and the boiling of the substance, respectively, ceases). This is one of the reasons for the convenience of using distillation flasks in which there is no grinding transition between the bulb and the condenser.

Fig. 2. The flasks of Claisen (1) and Favorsky (2) for distillation in a vacuum

Also, apparatus for vacuum distillation has several significant differences from the plant for distillation at atmospheric pressure (Fig. 3).

Fig. 3. Installation for vacuum distillation

Two neck distillation flask provided with Claisen attachment, one of which is designed for the throat of the thermometer, and the other for 23 

 

a capillary, through which the air or inert gas, when the system is under vacuum. The capillary is required to achieve uniform boiling liquid, without shocks and bounce. The amount of air flowing into the flask through a capillary, can be adjusted using the clamp on the hose piece is fitted on the upper end of the capillary. The hose must be inserted into a piece of thin wire, which prevents it from sticking under vacuum system and thus ensures the smooth flow of air into the flask. When choosing a refrigerator governed by the same considerations as for distillation at atmospheric pressure. In order to make the process of vacuum distillation it was possible to select the individual fractions using different modifications rider. The simplest, so-called "spiders". Instead of "spider" is also used forshtos Anshyutts-Thiele, which allows you to change receivers, without breaking the vacuum in the device and without interrupting the distillation. This nozzle is used in large volume distillation fractions. During vacuum distillation, the following rules must be observed: – Protective goggles or a mask must always be worn before distillation; – Initially, completely assemble the instrument, attach a pressure gauge, vacuum hoses and water hoses. Then, the pump is turned on, the tap connecting the manometer to the atmosphere is closed, and after a while the U-tube with mercury is opened. After 1-2 minutes the pressure gauge should show a pressure approximately corresponding to the saturated vapor pressure of water at a water pipe temperature (10-26 mm Hg); – The distillation rate is maintained at a level of 1 to 2 drops of distillate per second; – At the end of the distillation, the pressure gauge should first close the U-tube with mercury, then stop heating, allow the device to cool and remove the vacuum; – Vacuum removal is performed either by opening the valve connecting the pressure gauge to the atmosphere, either by disconnecting the vacuum hose from the device, or by carefully removing the thermometer. Do not disconnect the water jet for this! The inevitable, in the latter case, suction of water into the device will lead to its entry into the receivers with the substance, into the manometer (where it is difficult to extract) and, if it gets into the insufficiently cooled distillation flask, to its explosion. 24 

 

– All operations related to the evacuation of the device, the distillation and the removal of vacuum can only be carried out after the device is inspected by the teacher and under his supervision. Dependence of boiling temperature of the substance from pressure The vapor pressure of the liquid increases with increasing temperature. When it becomes equal to the total pressure of the gases above the liquid, boiling begins. In other words, the liquid boils in an open vessel when, when heated (to a certain temperature, called the boiling point), its pressure becomes 760 mm Hg. If the vessel maintains a reduced pressure, the substance will boil at a lower temperature. Let us assume, at room temperature, that the saturated vapor pressure of the compound is 20 mm Hg. This means that in a vacuum of 20 mm Hg, this compound will boil – and further lowering the pressure will cause the boiling point of the substance to drop below room temperature. The latter phenomenon is widely used for drying compounds from traces of organic solvents using vacuum plants. Based on the same considerations, it is easy to explain the lower efficiency of water jet pumps in the summer, and also the fact that the minimum pressure achieved with these simple devices is ~ 5 mm Hg. This is just the pressure of water vapor having a temperature of 1 °C. The dependence of the vapor pressure on temperature is approximately described by the Clausius-Clapeyron equation: or, after integration: where p is the vapor pressure, ΔvH is the molar enthalpy of evaporation; T is the temperature (K); R is the gas constant. The equation is valid for ideal gases, in addition, ΔvH should not vary with temperature. Those. in the ideal case, in the graphical representation, the dependence of the logarithm of the vapor pressure on the reciprocal temperature is a straight line. Incline 25 

 

The straight line is determined by the quantity ΔvH. If this value is known, the dependence of the boiling point on the pressure can be calculated. If the boiling point is known at a certain pressure, its value at a different pressure can be calculated or approximately determined using an appropriate nomogram (Fig. 4).

Fig. 3. The nomogram pressure – fluid boiling point

In practice, it looks like this: a short ruler is placed on the nomogram in such a way that it crosses the right scale at the point corresponding to the known pressure, and the left one at the point corresponding to the boiling point. The intersection point of the line with the middle scale gives the approximate boiling point of the substance at atmospheric pressure. Rotating the ruler relative to this point on the middle scale, we get the values of the boiling point of the substance at different pressures. For example, we need to determine the boiling point at 760 mm Hg (scale B) for a sample that boils at 100 °C (scale A) at 1 mm Hg (scale C). In order to bring the boiling point at a certain pressure to 760 mm Hg, 26 

 

the corresponding values on the scales A and B are connected by a straight line. The desired value of the boiling point is determined on the scale B. If then the direct found value of the boiling point is combined with any pressure value on the scale B, then the point of intersection of it with the scale A gives an approximate boiling point corresponding to this pressure. So, we need to draw a line from 100 °C on scale A (left side, observed boiling point) to 1.0 mm Hg on scale C (right side, pressure "P" mm). We can then read off the boiling point at 760 mm on line B, it is about 280 °C (Fig. 5).

Fig.5. Using a pressure nomograph: Determining the boiling point at 760 mm Hg (scale B) for a sample that boils at 100 °C (scale A) at 1mm Hg (scale C)

For a rough estimate of the boiling point under reduced pressure, you can use the following rule of thumb: the reduction of the external pressure by half, the boiling temperature is lowered by about 15 °C. Thus, a substance with a boiling point of 200 °C at a pressure of 760 mm Hg. at 380 mm Hg. It will boil about 185 °C. 27 

 

Steam distillation In organic chemistry, steam distillation is used for separation, purification, or separation of substances which are not miscible or little miscible. This process, which is co-distillation with water, consists of passing a jet of steam through the hot mixture was distilled substances and water. The method is based on the fact that the high boiling point substance having a volatility, and is transferred from the steam is condensed together with it in the refrigerator. The collected distillate in the receiver in the form of two immiscible liquid layers then separated in a separatory funnel. Immiscible substances vapor pressure independent of each other, in contrast to what is observed for the soluble substances in each other. The total vapor pressure P equal to the sum of the mixture of the vapor pressures of the two components. PA and PB is not dependent on the ratio of the components: P = PA + PB. The boiling point of a heterogeneous mixture is achieved when the total pressure becomes equal to atmospheric vapors. When steam distillation a mixture of water and high boiling point substances boil at temperatures below the boiling point of water. It allows you to clean high-boiling substances are sensitive to heat, do not withstand conventional distillation. Steam distillation is of great importance in the separation of volatile products from the tarry impurities. Often this method is used in the allocation of organic matter from natural objects, especially those that are part of the essential oils. In order to determine whether the steam volatile substance, a small amount must be heated in a tube with two milliliters of water. Above this second test tube holding the bottom of the tube, which put ice. If condensing on the cold bottom of the second tube turbid drop, the volatiles steam. Instead of water vapor and vapors can be used other substances with the following properties: low mutual solubility with the secreted substance vapor pressure close to the water vapor, and a low molecular weight. Apparatus for steam distillation is shown in Fig. 6. It consists of a steam generator, a tube through which the steam enters the distillation flask and the refrigerator. As the steam generator can be round or flatbottomed flask. 28 

 

Fig. 6. Apparatus for steam distillation

Fractional distillation (rectification) Simple distillation method is not effective for the separation of liquids with a difference in boiling points of less than 80 °C. In this case use by fractional distillation (rectification), based on the multiple repetition of the evaporation and partial condensation of the vapor mixture of liquids, which results in their separation. Distinguish distillation at atmospheric pressure and under vacuum (applied to separate high boiling and thermally unstable liquids). Similarly, the behavior of a pure liquid, a binary mixture of two completely miscible with each other liquids starts to boil at a temperature at which the total vapor pressure of both components is equal to the external pressure. The total vapor pressure of the mixture equals the sum of the partial vapor pressures of each component. According to Raoult's law the partial pressure of one of the mixture components depends on the mole fraction of the substance in the mixture. When the total vapor pressure of the mixture reaches 760 mm Hg. Art., it starts to boil. Since the partial pressure of volatile components makes up most of the total pressure, the original condensable vapor consists mainly of a volatile component and contains only a small 29 

 

amount of high boiling material which accumulates in the residue. However, this leads to the fact that according to Raoult's law the partial pressure of a high boiling component was increased. As the concentration of the residue of the substance increases the boiling point, and its share in the vapor increases. Progress in this distillation by the example of ethanol, butanol is depicted in Figure 7.

Fig. 7. Diagram of ethanol – butanol boiling

An equimolar mixture of ethanol, butanol boils at about 93 °C and at atmospheric pressure (pure ethanol boils at 78 °C, pure butanol at 117.5 °C). The lower curve shows the temperature dependence of the boiling mixture of ethanol and butanol from their composition (in mole percent). The upper curve expresses the appropriate vapor composition defined by Raoult's law. Distillation takes place with a gradual increase in the boiling temperature according to curve towards the lower point 1. Separation of this mixture can only be achieved by repeating multiple distillation fractions collected. Separation efficiency can be markedly improved by using a fractional distillation (rectification) method (Fig.8). Distillation was carried out using a special speaker – reflux condensers (dephlegmators). Dephlegmator consists of a set of vertical tubes bulb distillation (column) filled with a material with a large surface area on which the partial condensation of the vapor. The dephlegmator and steam condensate (reflux) move in opposite directions that is based on the action column countercurrent principle couples rising upwards is removed from the reflux flowing down low-boiling components and vapor reflux extracts high boiling component. The process is repeated several times 30 

 

throughout the column height. This type is called countercurrent distillation. It is necessary to establish the closest contact between rising vapor and descending condensate, which flows into the distillation flask. Under these conditions, an equilibrium is established in a dephlegmator, wherein the vapor in the upper part composed mainly of the more volatile component. The process efficiency depends on the surface area of the falling reflux. In the best cases it is possible to divide the liquid boiling temperature which differs by only a few degrees.

Fig. 8. Installation for rectification

There are several types dephlegmator (Fig. 9). The first type includes those columns in which a high surface area is achieved by filling a loose material of the cylindrical tube, which is called "nozzle" (Fig. 9b).

a – Vigreux column, b – with a nozzle, c – with a revolving belt, d – tree shape Fig. 9. Reflux condenser (dephlegmators)

31 

 

As the nozzles used glass beads, glass or porcelain rings (Raschig rings), glass and metal spiral, cutting short glass tubes. The columns of the second type are liners made of pre-cast stainless steel meshes. The third type is represented by open columns with respect to the internal space. These include Vigreux column representing glass tube with projections pointing downwards (Fig. 9a), «Christmas tree» reflux condenser (Fig. 9d). The most effective of these are the columns of concentric tubes, in such columns vapor rises through the narrow annular space between the two walls through which the condensate flows. There is also a column with a rotating belt, where in the condensate and vapor is mixed by means of rapidly rotating the twisted tape. The distillation column should be insulated to processes occurring in it proceeded in the conditions maximally approximate to adiabatic. With significant external cooling and overheating of the walls speakers correct her work is impossible. When the distillation of substances with a boiling point up to 80 °C as the insulation can wrap the cord column asbestos, glass wool, put on her "shirt" or foam placed in a glass tube, to thereby create an air shirt. Column type is selected based on the difficulty of separation of the mixture. The closer the boiling point separated liquids, the more effective shall be the column, i.e. have a greater internal surface area. In addition, it is necessary to take into account the amount of product being distilled, and the value of the pressure at which distillation should be carried out. The amount of each component being recovered in pure form from a feed mixture shall be at least 10 times the column operating capacity. For the distillation of small quantities of substances used column with the least possible labor capacity (hollow tube, Vigreux column). However, not all liquid mixtures can be separated into individual components, even when using the most efficient distillation columns. There azeotropic mixtures boiling at a constant temperature. They cannot be separated by distillation, since the resulting vapor has the same composition as the liquid. In this case we speak about the positive or negative deviation from Raoult's law. In practice one often encounters azeotrope formed by water and an organic liquid such as ethanol (96%) – water (4%). Water separation is performed in such cases by means of drying agents such as anhydrous calcium chloride or oxide, sodium sul32 

 

fate, sodium or potassium hydroxide, phosphorus oxide (V) and others. Ethanol for dehydration, for example using refluxing over calcium oxide for 6-8 hours, after which the alcohol is distilled, preventing moisture from air drying calcium chloride tube attached to a alonge tube. Experimental technique. The flask was filled with a mixture of 2/3 shared heated on a hot plate (or bath, depending on the nature of the components of the mixture) to boiling and set the rate of distillation 1-2 drops per second (Fig. 8). Too rapid distillation of steam enters the refrigerator, without having to enrich low-boiling component, and therefore the separation of the mixture becomes impossible. During the distillation, several fractions were collected and their number depends on the number of the substances in the mixture. The temperature range of the collection of each fraction is selected empirically. Control questions 1. What process is called simple distillation? 2. What types of flasks do you know? What are they used for? 3. Why does the distillation flask, when distilled at atmospheric pressure, are filled with no more than 2/3, and with vacuum distillation – no more than 1/2? 4. What determines the nature of the boiling of the liquid? What is a "kipelki" and what are they used for? 5. What are the principles for choosing a descending refrigerator? 6. What is rectification? How does this process differ from simple distillation? 7. Explain the principle of the dephlegmator. What types of dephlegmators do you know? Why should the reflux condenser be isolated from heat loss? 8. What is an azeotropic mixture? How to separate ethanol from water, if these substances form an azeotrope? 9. In what cases is distillation applied under reduced pressure? Which flasks are used for vacuum distillation? Why? 10. What is steam distillation used for? What properties should the substance possess so that it can be distilled with water vapor? 11. The liquid organic substance decomposes above 150 °C and boils at atmospheric pressure at 174 °C. What kind of distillation should I choose to clean it? 12. Predlozhite method of purification of toluene from resinous impurities. 13. How can the mixtures be separated: a) acetone and ethyl acetate, b) pentane and decane?

33 

 

Laboratory work 2. Crystallization Crystallization – is the process of formation and growth of crystals from a solution, melt or gas phase. Crystallization and recrystallization from a solution or substance melt and crystallization from the gaseous phase (sublimation, volatilization) are widely used in laboratories and in the industry to be effective methods of cleaning contaminants from solid compounds. The process generated organic synthesis «raw» (crude) products can be released in a more or less pure form by cooling the reaction mixture, or after evaporation of the solution, but require further purification, so subjected to recrystallization. Often the «raw» product manages to clear only by repeated recrystallization, leading to large losses of substance. It is therefore desirable pre-treatment of the substance or the use of another method of treatment. Recrystallization from a solution Recrystallization from a solution is based on the fact that the solubility of compounds in solid hot solvents is much higher than in the cold, as well as on the difference in the solubility of substances in the same solvent. Recrystallization from a solution in two cases applied when the crude material contains a readily soluble or, alternatively, the insoluble impurities. If the impurity solubility greater solubility of the basic substance, after recrystallization, the primary material will be in the solid phase and impurity – in the mother liquor. When the solubility of impurities is less solubility of the basic substance by heating the crude product of the saturated solution is prepared in a suitable solvent, the solution was filtered hot to remove insoluble impurities and the filtrate was then cooled. As a result, drop crystals whose impurity content is less than in the starting material. Sometimes the crude material contains impurities, which are soluble in the solvent to a very small degree and thus partially precipitated 34 

 

together with a basic substance. Then quite a pure substance can be obtained only by repeated recrystallization (fractional crystallization). Dissolution – a physicochemical interaction process gas, liquid or solid matter from the liquid (the solvent), whereby a solution is formed as a transparent homogeneous liquid. At the same time under the influence of liquid molecules is the distribution of solute throughout the volume of the solvent. This process is known to the saturation limit. The solution which is in equilibrium with a solute and contains the maximum possible amount of material at a given temperature, called a saturated solution. The saturated solution of a dynamic equilibrium in which at a time so the molecules pass into solution as separated from the solution. The saturated solution at this temperature contains the maximum possible amount of material. The concentration of a saturated solution of a substance is a measure of the solubility under these conditions. Reserve solubility of the substance at a given temperature coefficient is characterized by a solubility that shows the number of grams of a substance that is soluble in 100 g of solvent at a given temperature. The unsaturated solution contains less material and in a supersaturated – more than saturated. For the first time received supersaturated solutions T.E. Lovitz (1794). This solution having a high concentration of solute than a saturated solution under the same conditions. They can be prepared by slow cooling of saturated solutions. Supersaturated solution is thermodynamically unstable. Introducing these crystal mixing solute or promote the precipitation of excess substance from the solution. On the dissolution rate affects the degree of grinding of the solute. With increasing fineness increases the contact surface between the liquid and solid phases, which speeds up the process. The choice of solvent for crystallization Crystallization success largely depends on the correct choice of solvent. The solvent used for crystallization, should have the following properties: a) be chemically inert with respect to the cleaning substance at room temperature and the boiling temperature of the solution; 35 

 

b) the solubility of the substance in the chosen solvent should increase significantly during heating and cooling at – decrease; c) dissolving the impurity well even at a lower temperature, or to dissolve them virtually at boiling; g) the solvent must be easily removed from the surface of crystals by washing or by drying. To select the solvent used reference data on the solubility of the substance being purified, or carried out by the selection of an experienced. The tube is placed, and a few grains of substance added 2-3 drops of solvent. If a substance is easily soluble at room temperature, the solvent is not suitable for purification from soluble impurities, but can be used for removal of insolubles. In the case where dissolution at room temperature is bad, the tube was gently heated until complete dissolution of the sample. If, after cooling, the crystals fall, the suitable solvent for recrystallization. It is desirable that the solvent boiling temperature was 10-15 °C below the melting temperature of the substance. Otherwise, the agent may be allocated as an oil (melt). The substance in the result is dirtier than before recrystallization. This can be explained by the formation of two-phase system with a large contact surface, as a result of removing the substance from the solution is an impurity as dopant distribution ratio between the solvent and the molten material tends to be in favor of the molten material. If the substance is recrystallized very low melting point and is not possible to select an appropriate solvent, the dissolution should be conducted at a lower temperature and to provide a strong solution of cooling agent. When unable to pick up an individual solvent, crystallization is carried out from a solvent mixture. For compounding, usually choose two solvents: «good» (good dissolving substance) and «bad» (non-solvent). Cleansing agent is dissolved under heating in a «good» solvent, then reduce its solubility, adding dropwise a hot solution of «poor» solvent nonvanishing until turbidity. The solvents used in the mixture must be mixed well with each other. The following solvent mixtures are typically used: water-alcohol; alcohol-benzene; alcohol, glacial acetic acid; acetone-water; ether-acetone-benzene; chloroform-petroleum ether and the like. When choosing the solvent guided empirical rule «like dissolves like» (hydrocarbons – hydrocarbon, carbonyl compounds – in acetone, etc.). In other words, for dissolving substances used solvents with simi36 

 

lar or the same chemical properties, also recorded their polarity, characterized by the value of the dielectric constant ε (value ε given in reference literature), which for different solvents varies in a fairly wide range (for ε hexane = 1, 9 for ε = 25, ethanol, etc.). Polar substances are readily soluble in polar solvents (high value of ε), and the non-polar – nonpolar (low value of ε). When choosing the solvent should be considered its freezing point, the possibility of regeneration after recrystallization, toxicity and availability. Most used solvents – water, alcohols, acetone, diethyl ether, dioxane, ethyl acetate, chlorinated (chloroform, carbon tetrachloride, dichloroethane, chlorobenzene), carbon disulfide. Often, solvents are aliphatic and aromatic hydrocarbons, petroleum ether (mixture of liquid alkanes, mainly C5 and C6 branched chain), gasoline (a mixture of liquid hydrocarbons containing in the molecule an average of from 5 to 9 carbon atoms), cyclohexane, benzene, toluene, xylenes. Other commonly used solvents should be noted nitrobenzene, acetonitrile, formamide and solvents possessing the basic amine properties – pyridine and quinoline. Similar properties are to diethyl ether, tetrahydrofuran (THF) and dioxane. All solvents are characterized by certain physical constants (boiling point, distillation range, density, refractive index). Purified solvents containing no water are referred to as absolute. There are various methods of purifying organic solvents. Thus, for example, diethyl ether absolutizes repeated shaking with a concentrated solution of calcium chloride and subsequent distillation over sodium metal. Ether is very dangerous to use – highly flammable, it forms explosive mixtures with air. Dehydration of ethanol – boiling with calcium oxide rectified in a few hours. Ethanol is easily ignited, forms explosive mixtures with air. Stimulation of crystallization Often the crystalline substance is not out of solution, even on prolonged cooling. In order to accelerate the crystallization process creates artificial crystallization centers. It is often used two passes. 1. Introduction «seed». This technique consists in the fact that a solution is made of the same substance crystals (seed), i.e. artificially 37 

 

create the crystallization centers. If a pure substance, there can be moistened with a glass rod and abruptly cool it by placing an empty tube cooled externally. The thin films of liquid crystals are formed on the surface of the glass rod. It is also possible to leave the solution for several days at low temperature. 2. Rubbing a glass rod to the vessel wall. This technique consists in the fact that taking glass rod, making it into the solution and gently rubbing against the vessel wall. This creates a fine glass dust; some dust particles may be suitable crystallization centers. The same crystallization centers and may be dust particles contained in the air. Crystallization always starts from the walls and from the surface to the center, on hard surfaces or at the interface. The electric and magnetic fields, ultrasound, and sometimes strong cooling (e.g. with liquid nitrogen) – all contribute to the process of crystallization. Experimental technique Recrystallization from a solution includes the following main steps: a) dissolving the substance with heating; b) hot filtering to separate insoluble impurities; c) crystallization upon cooling of the mother liquor; g) filtering under vacuum. When choosing a solvent for an unknown substance should always be first to experience its solubility in water. For this small amount of material to be placed in a test tube, add 1 ml of water (solvent) and observe the dissolution at room temperature. If the substance is not dissolved at room temperature, the tube with the material must be heated to boiling. If a solvent suitable for crystallization on cooling tubes under cold running water must fall crystals. In the presence of activated carbon to be added in the material colored impurities. It should be borne in mind that the addition of coal causes a sharp boiling, therefore it cannot be added to the superheated liquid. It should be somewhat cool the solution, and then adding carbon. After selecting the solvent for the crystallization agent is weighed and placed in a conical flask, adding small portions of pre-heated water (solvent). If the substance is not dissolved, then add a little water and 38 

 

the solution was again brought to boiling and etc. Scheme of experimental technique of recrystallization shown on Fig. 10.

Fig. 10. Recrystallization process

When the substance is completely dissolved, saturated hot solution rapidly filtered (Fig. 10), making sure that during the filtration did not drop crystals. To crystallization does not start on the funnel, it is necessary to heat and to avoid saturation of the solution. If the solution is cooled slowly, large crystals were formed. For a more complete separation of crystals flask must be cooled under running cold water. The crystallization may be accelerated by friction of the glass rod sides of the flask. The crystals were filtered off from the mother liquor under water pump vacuum on a Buchner funnel, using a Bunsen receiver flask (stock solution if many) or a small tube of sidearm. After separation of the crystals they were dried in air, weighed and the yield of pure substance in percent by weight taken for crystallization. Control questions 1. Give the definition of recrystallization and dissolution, what are these processes? 2. What do you know about the most commonly used solvents? 3. Indicate the main requirements for the solvent in recrystallization. 4. What factors determine the rate of crystallization? 5. How can the crystallization process be accelerated? 6. In what units are solubility expressed?

39 

 

7. Why can not a solvent with a good dissolving power be used for crystallization? 8. Why are alcohols not suitable for the recrystallization of carboxylic acids? 9. Which of the solvents – alcohol, benzene or water – is suitable for the recrystallization of glucose? 10. What are the ways of expressing the concentration of solutions?

40 

 

Laboratory work 3. Sublimation Sublimation is the process of evaporation of a solid substance, followed by the condensation (sublimation) of vapors into the solid phase, by passing the liquid phase. When the vapor condenses, the solid phase forms directly in the form of crystals settling on the cold surface. Only those substances whose vapor pressure in the solid state are sufficiently high at a temperature below their melting point are subjected to sublimation. The temperature at which the vapor pressure above the solid is equal to the external pressure is called the sublimation temperature. Vapor pressure increases with heating, so the rate of sublimation increases with increasing temperature. However, raise the temperature with caution to avoid decomposition of the substance. Reduce the sublimation temperature by conducting the process in a vacuum. The dependence of the vapor pressure of a solid on temperature (sublimation pressure) is shown graphically in the form of a sublimation pressure curve (a) in the phase diagram (Fig. 11).

a – the sublimation pressure curve; b – melting point curve; c – steam pressure curve Fig.11. Phase diagram of water

41 

 

This curve is located below the so-called triple point T, in which the liquid and the solid have the same vapor pressure. Substances having a relatively high vapor pressure can, upon heating, acquire vapor pressure equal to atmospheric pressure at a temperature lower than the melting point. In this case, the melting point when the substance is heated is not reached, and it directly passes into the vapor state, i.e. sublime. Organic compounds with a relatively high vapor pressure can sublimate at atmospheric pressure at a temperature below their melting point. They are relatively few, and the vast majority is sublimated only under strongly reduced pressure. This method is best suited for nonpolar compounds that are usually more volatile than polar ones with similar molecular weight; The method is especially valuable for compounds that are hygroscopic or melt. Sublimation is an effective way of purifying substances in cases where the pollutants have a different volatility than the substance itself. The advantages of sublimation are simplicity, ease of execution and minimal loss of matter. From recrystallization this method is advantageously distinguished by the absence of contact with an extraneous substance (solvent) and a good yield. There are often cases when the yield of a pure product reaches 98-99%. The use of sublimation is particularly desirable when working with small quantities of substances as the final operation in obtaining samples for analysis. The main disadvantage of sublimation is that the separation process depends on the difference in vapor pressure, so compounds with similar volatility will sublimate together, that is, the solid can be purified by sublimation only if it has a higher vapor pressure than the impurities. The substance thus purified is free from impurities. The distillation can be carried out at normal pressure or in a vacuum. The most common laboratory instruments for sublimation are shown in Fig. 12. Often in a laboratory, a porcelain cup with a funnel is used (Fig.12, b). Porcelain cup with a substance is slowly heated on a sand bath. Do not increase the rate of sublimation due to increased heating. In case of overheating, the sublimated substance can melt, and then evaporation will proceed from the liquid phase. In fact, the substance will be distilled with the conversion of condensate into a solid. In this case, significant losses of material are possible, so it is recommended to heat the substance slowly so that the sublimation on 42 

 

the walls of the funnel appears only after 15-20 minutes, and then only maintain the temperature of the sand bath at this level until the sublimation ends, periodically switching off the tile.

а

b

c

Fig. 12. Devices for sublimation: a – device for sublimation using hour glasses; b – porcelain cup with funnel; c – for vacuum sublimation.

To increase the speed of sublimation, the funnel walls can be cooled with filter paper moistened with a small amount of water. In addition, the substance must first be ground into a fine powder, since the sublimation occurs from the surface, and the speed of the process depends on its area. The device can only be disassembled after full cooling, avoiding a concussion. Sublimation of crude benzoic acid Reagents: crude benzoic acid, camphor – on the instructions of the teacher. Instruments and materials: porcelain cup, conical funnel, cotton wool, filter paper, thermometer, sand bath, electric tile, Petri dish. The task. Purify the crystalline substance from impurities by sublimation, determine the melting point of the pure substance. Oder of work: 1. Weigh 2 g of crude benzoic acid, place it in a porcelain dish. 2. Cut out a circle from the filter paper (its diameter should be slightly larger than the diameter of the porcelain cup), make frequent small holes throughout its area. Cover the porcelain cup with a circle. 43 

 

This circle is needed so that the overlooked substance does not get back into the unpurified mass. 3. Place the mug with the substance in a sand bath heated by electric tiles. Cover the cup with a conical funnel and cover the spout with cotton wool. In the process of sublimation, the walls of the funnel can be covered with filter paper and periodically moistened with cold water so that condensation of the vapors of the sublimated substance passes more fully. 4. Place a thermometer in the sand bath, fix it in the foot of the tripod. Make sure that the temperature of the bath is about 10 °C below the melting point of the sublimated substance. 5. At the end of the sublimation, allow the appliance to cool, remove the crystals of the purified substance with a scalpel from the walls of the funnel into a Petri dish and weigh. A small amount of purified refined substance is used to determine the melting point. Control questions 1. When the sublimation of substances is used, what is its essence? 2. Define the sublimation temperature. Can all substances sublimate? Answer explain. 3. What is the triple point, where the sublimation pressure curve should be located on the phase diagram of water? 4. How do I heat the substance in sublimation to avoid significant losses? 5. What needs to be done to increase the speed of sublimation?

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3. DETERMINATION OF PHYSICAL CONSTANTS

Laboratory work 4. Melting point Melting point (m.p) is the major constant characterizing solid matter. Melting point of compound call temperature at which its crystal phase is in equilibrium with characteristic melt. Melting point corresponds to temperature at which steam tension over solid matter is equal to steam tension over liquid. It is possible to define melting point in the course of melting or in the course of a crystallization of a melt as if overcooling is excluded, crystallization temperature coincides with melting temperature. Usually mean an interval of temperatures between emergence of the first drops of liquid and the complete transition of solid matter of liquid state by melting point. For pure individual substances this interval is measured by degree shares. It is possible to define a temperature band of melting by repeated melting of an exemplar after its hardening more precisely. In the presence of impurity melting point of substances always goes down according to a Raoul's law. Thus, mixtures of substances have to melt at lower temperature, than the individual substances making them. Absence of a depression of melting point of mix of the studied substance with the standard is considered as the proof of their identity (or their complete relative insolubility). Use it for identification of chemical combinations. For this purpose, mix in equal quantities (on 0,05 or 0,1 g) the studied substance and chemically pure standard substance (reference substance) and define melting point of mix. If test of mixture melts at the same temperature, as each component separately, identity of the studied substance with standard is considered proved. If test of mixture melts at lower temperature, than each component separately, it means that the studied substance not to the identically standard. 45 

 

Determination of melting point of mixture is the most widely used and easily applicable criterion of identity which, however, should use with caution. Existence of a depression indicates distinction of substances, but absence of a depression is observed sometimes in case of two rather difficult compounds having slight structural distinctions. Technology of experiment. The most widespread of all methods of determination of melting point of organic matters is determination of melting point by a capillary method. For this purpose, a small amount is thin the pounded and well dried up preparation place the thin-walled capillary soldered since one end which attach to the thermometer and place in the heating block. Use a capillary 45-50 mm in length, with a diameter of 1.0-1.2 mm for colorless substances and 0.8-1.0 mm for the painted. For waxy and fibrous substances, it is possible to use capillary tubes of a few larger sizes. When filling a capillary its open end is pressed several times into the powdery substance placed on a clock glass. After that the capillary is struck several times with the filled end about a table surface. The filled capillary is thrown the soldered end down by 10-15 times through a glass tube 800 mm high and with a diameter of 15-20 mm, put upright on a glass or tiled plate, before consolidation of substance into a layer of 2-3 mm. Melting point of hygroscopic substances is defined in the capillaries soldered since both ends; thus the capillary has to be shipped entirely in a heating bath (the heating block). The capillary is fixed on the thermometer a rubber ringlet (a ring cut off from the rubber hose suitable by the sizes), a copper wire or paste top end a drop of sulfuric acid. Test of substance has to be at the level of the mercury tank of the thermometer. Upon transition from solidity in fluid in routine conditions of heating in a capillary it is possible to observe the following phenomena: contraction of substance (the column of substance changes the form, contracting and lagging behind capillary walls, without visible transition to liquid state); a steam (on an internal surface of a capillary there are liquid droplets, the substance bakes, without losing the compendency); partial melting (in a capillary along with solids the liquid meniscus on all section of a capillary is formed). After that at a little higher temperature there comes the condition of the complete fusion. To avoid a rather large and sometimes not enough reliable amendments on extending the mercury, thermometers are recommended for shorter set of TL-6. 46 

 

Some organic substance melts with decomposition (color appearance, gas evolution). The decomposition temperature is usually not clearly expressed, and often not able to accurately reproduced. Melting point determination in a capillary can be performed very precisely, if at the preliminary experiment to determine the approximate melting point material, and then the capillary with the substance placed in the device, heated a few degrees below this approximate value. The simplest of these is the DDMP instrument (Fig. 13). This device consists of a round bottom flask with 100-150 ml of throat 90 mm long and 30 mm in diameter. The flask was poured on 2/3 of its volume of coolant, which is used as the concentrated sulfuric acid, paraffin or silicone oil. The neck of the flask is inserted into a special tube length of 150 mm and a diameter of about 15 mm, which is fixed in the neck of the bulb ring with a special slot (to avoid an explosion, possibly by heating a sealed container); moreover, the tube has an opening for communication with the atmosphere.

1 – Flask 2 – coolant 3 – test-tube 4 – thermometer 5 – capillary substance 6 – ring for fixing the capillary 7 – ring for fixing the tubes 8 – Hole in vitro Fig. 13. The device for determining the melting point of the

The tube was sealed with a cork stopper inserted into it a shorter thermometer, a lower end of which must be a few millimeters above the bottom of the tube. The flask contents were heated to about 10-15 °C below the anticipated melting point of the drug, the instrument 47 

 

measuring the temperature with a thermometer, and then placed in a test tube with a capillary thermometer shortened so that no thermometer or capillary not touch the bottom and walls of the tube. Then continue to heat apparatus, raising the temperature at a rate of 0.5 °C per minute. If the substance decomposes during melting, the heating rate is increased to 2-3 °C in the mine, or the capillary is placed in the drug unit, preheated to a temperature of approximately 5 °C below the anticipated melting point. The beginning of melting is the appearance of the first drops of molten material, or the appearance of the meniscus in the capillary, and the end – moment of complete melting of the substance. Both temperatures note and consider melting range of the substance. In determining the melting point of substances that melt below 170 °C is used without the rinsed vial flask. Sulfuric acid, the use of which requires great care, it can be used in the determination of the melting temperature of 250 °C. If concentrated sulfuric acid in the process becomes brownish tint, the bleach is added thereto a few crystals of potassium nitrate or sodium nitrate. A mixture of concentrated sulfuric acid (7 parts) and potassium sulfate (3 parts) after 5 minutes boiling under vigorous stirring, became a clear liquid which can be used as a heating medium to 320 °C (a mixture of hygroscopic, and it must be protected from moisture).

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Laboratory work 5. Boiling point In the process of evaporation of liquids equilibrium between liquid and vapor. The vapor pressure above a liquid is determined by the temperature and the nature of the liquid. At the moment when the vapor pressure becomes equal to the external pressure, the liquid begins to boil. The temperature at which the vapor pressure of the liquid becomes equal to the outside is called boiling point. Boiling point unlike the melting temperature is strongly dependent on external pressure, so it is necessary to indicate the pressure at which measurements were made. If the pressure is not specified, it means that the boiling point is measured under a pressure of 760 mm Hg. Moreover, at its value significantly affected by the presence of even small amounts of impurities. Therefore, the boiling point is rarely used to identify characteristics of the fluid and its purity, more reliable performance pure liquid substance is the index of refraction. Table 5 shows the boiling point and refractive index of certain organic liquids. With low vapor pressure deviation from the normal rule is executed: ΔТ= С0 (760–р) Т, where ΔT – a deviation from the normal boiling point, K; C0 – empirical coefficient; p – pressure at which the measured temperature T. The coefficient C0 has the following meanings: – Substances with very low boiling points 0.00014. – The majority of substances 0.00012. – Substances associated by hydrogen bonds. In most cases, a boiling point is determined by a thermometer immersed in the vapor phase (Fig. 14). Boiling point defined in pairs, always lower than the true, as several pairs of sub-cooled and it takes time to reach thermal equilibrium and phase liquid – vapor. Therefore, any liquid is distilled, first drops of distillate distills at lower temperatures. Conversely, the end of the distillation flask when there is little 49 

 

liquid as a result of overheating, the distillate is distilled at a high temperature. Table 5 Boiling point and refractive indices Some organic substances Substance Acetone Benzene Butanol-1 Dimethylformamide Diethyl ether 2-propanol Petroleum ether Toluene Chloroform Carbon tetrachloride Ethyl acetate

Т. boil., °С

n

20

D

56 80 117 153 34,6 82 40 – 65 110 61 76 77

1,3580 1,5010 1,3985 1,4303 1,3520 1,3774 1,3660 – 1,3700 1,4960 1,4460 1,4600 1,3725

In this regard, according to the existing standard boiling point is defined as the interval between initial and final boiling points at atmospheric pressure (760 mmHg, or 1013 kPa). Wherein initial boiling point is the temperature at which the receiver is distilled in the first five drops of fluid, and the ultimate – the temperature at which a receiver moves 95% of the liquid. But, strictly speaking, the boiling point of the liquid is such a temperature that the thermometer in contact with both the liquid and vapor phases – in this case the temperature is measured at equilibrium conditions. The value of boiling point of substance largely depends on its molecular size and intermolecular interactions contribution. So, for normal alkanes (C4-C12) is characterized by an increase in boiling temperature to 20-30 °C for each subsequent member of the homologous series. Strengthening of intermolecular interactions (with the same number of carbon atoms) in the series: ethers