CHEM1102

Organic Chemistry

Laboratory Manual

2010

Discipline of Chemistry

School of Biomedical, Biomolecular and Chemical Sciences

Name: ________________________________________________________ Student ID: ________________________________________________________ Lab: ________________________________________________________

TABLE OF CONTENTS General information Laboratory regulations i Whos who? iii Safety in the laboratory iv Activities in the laboratory v In case of accident vi Attendance and assessment of laboratory sessions vii Laboratory manual viii The periodic table of the elements ix Experiments 1. Molecular models 1 2. Acid/base separation and recrystallisation 13 3. The reduction of diphenyl ketone to diphenylmethanol 25 4. Carboxylic acids and esters (Part 1 Synthesis) 30 5. Carboxylic acids and esters (Part 2 Purification) 38 6. Aromatic chemistry 44

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LABORATORY REGULATIONS 1. Each student is allocated a bench, locker and associated set of apparatus and

must work at their allocated place. 2. Students are responsible for their benches and apparatus. All apparatus must

be cleaned before being returned to the locker. Broken apparatus must be replaced.

3. Keys to lockers are available in the laboratory. Each set of keys is labelled

with the laboratory room (A-D), bench number (1-36) and locker colour. (e.g. B9 red is laboratory B, bench 9, red locker). The appropriate key should be taken at the beginning of the laboratory session and returned to the correct place at its conclusion. If you have taken the wrong key, return it immediately to avoid confusion.

4. Lockers must be checked immediately on entering the laboratory. Any dirty,

broken or missing apparatus should be reported to the Laboratory Technician in the Preparation Room.

5. It is compulsory for students to wear safety glasses in the laboratory.

Prescription glasses are not adequate protection. Contact lenses should never be worn in the laboratory. Safety glasses are stored in the laboratories and must be returned at the conclusion of the session. Students who persistently infringe the safety glasses requirement will be asked to leave the laboratory.

6. It is compulsory for students to wear enclosed footwear in the laboratory.

Inadequate footwear equates to no admittance to the laboratory. 7. It is compulsory for students to wear laboratory coats in the laboratory.

Laboratory coats are purchased from Uniprint in the Guild Village. No laboratory coat equates to no admittance to the laboratory.

8. A variety of gloves are stored in the laboratories. Students may choose to

wear gloves at any time. It is compulsory to wear gloves for some manipulations. The laboratory demonstrator will inform you in these instances.

9. Mobile telephones are not permitted in the laboratory. All telephones must be

switched off on entering the laboratory. If this causes hardship, speak to the Laboratory Supervisor and arrangements may be made.

10. Smoking in the building is not permitted. 11. Consumption of food or beverages in the laboratory is prohibited. 12. Students must not perform unauthorised or unsupervised experiments. 13. All operations involving the evolution of poisonous or obnoxious fumes must

be carried out in a fumehood.

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14. Reagent bottles must be returned to their designated places. Reagents must be kept free from contamination (e.g. solutions once removed must not be returned and stoppers must not be interchanged).

15. Sinks are for the disposal of liquid waste only. Concentrated acids and bases

must be washed down a fumehood sink with copious amounts of running water. Use the rubbish bins for solid waste.

16. Bunsen burners must only be lit with the lighter provided. When in use, they

must rest on a heat resistant mat. When not in use, they must be turned off. 17. The removal of chemicals, including samples prepared by students, from the

laboratory is prohibited.

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WHOS WHO? Staff supervisors will visit the laboratory and are available to discuss course work, laboratory techniques and any other problems pertaining to the unit. They oversee the demonstrators. Dr Scott Stewart (room 3.30) Laboratory demonstrators supervise you in the laboratory and are available to answer your questions. Their role is to teach you and show you laboratory techniques. They oversee and assess your work. The Laboratory Technician is the person to see if you have any problems with your apparatus. Mr Kim Foo (room 1.14)

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SAFETY IN THE LABORATORY General Never work in the laboratory alone. Do not use mouth suction to fill pipettes. Confine long hair and loose clothing while working in the laboratory. Learn the location of the safety shower, eye wash and first aid kit and be prepared to give help to others. Fire Avoid unnecessary flames. Check the area near you for volatile solvents before lighting a Bunsen burner. Check the area near you for flames if you are about to begin working with a volatile solvent. Care must be observed when handling or distilling flammable liquids. Vessels containing flammable liquids must not be heated over a naked flame. Learn the position of the nearest fire-fighting appliances. Chemicals Many chemical substances are irritants and others cause severe burns (e.g. glacial acetic acid). Handle every chemical with care, avoid contact with skin and clothing and avoid the inhalation of organic vapours. Unless you know otherwise, assume all substances are poisonous by inhalation, skin absorption or mouth ingestion. Replace stoppers on reagent bottles as soon as possible and wipe up spills immediately. Glassware Most cuts in the laboratory are the result of breakage of glassware when being forced into tubing. Learn the correct method of carrying out these procedures from the demonstrator. Return any damaged glassware to the Preparation Room for replacement as sharp edges can cause cuts. Electrical equipment Students must not make internal adjustments to electrical equipment. Should a piece of apparatus appear to be malfunctioning, it should be switched off, the plug pulled out from the mains and the Laboratory Technician must be informed immediately.

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ACTIVITIES IN THE LABORATORY Throughout the laboratory course, the demonstrator will show you laboratory techniques and additional information can be found in such texts as Vogels Textbook of Practical Organic Chemistry, available in the Preparation Room. However, commonsense considerations are important in laboratory manipulations and you should consider each step from this point of view. In particular, pay attention to the following points, which concern the safety of everybody in the laboratory. 1. Think before lighting a Bunsen burner. Most organic liquids are flammable. 2. Never heat glassware suddenly or directly. If heating under reflux, use a

gauze mat or, where possible, a water or steam bath. 3. Never heat an organic liquid in an open vessel over or near a naked flame. 4. Periodically check to ensure water is running through a condenser. 5. Avoid skin contact with organic materials and minimise the inhalation of

organic vapours. Use the fumehood for reactions that evolve poisonous or foul-smelling vapours.

6. Always use boiling chips when refluxing, but never add boiling chips to a

near boiling liquid. If the liquid is superheated and boiling chips are added, the liquid will suddenly boil and be propelled out of the vessel. Note: Boiling chips lose their activity when in a liquid which is allowed to cool. If you wish to reheat the liquid you must add new boiling chips.

Make efficient use of your time. Never be idle because you are waiting for apparatus, chemicals or a reaction to be completed. Do something else (e.g. Attend to your laboratory write-up, clean your glassware or proceed with a later section of the experiment). Do not leave cleaning your glassware to the end of the laboratory session. Cleaning of most glassware can be achieved with a bottlebrush and detergent.

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IN CASE OF ACCIDENT Accidents can be avoided by working carefully and intelligently. However, in case of an accident, notify the demonstrator immediately. All accidents must be reported to the Staff Supervisor. Fire Burning clothing: Prevent the person from running and fanning the flames. Rolling the person on the floor helps extinguish the flames and prevents the inhalation of flames. If a safety shower is nearby hold the person under the shower until the flames are extinguished. Do not use a fire blanket if a shower is nearby. The blanket does not cool and smouldering continues. Remove contaminated clothing. Wrap the person in a blanket to avoid shock. Get prompt medical attention. Burning reagents: Extinguish all nearby Bunsen burners and remove combustible material and solvents. Small fires in flasks and beakers can be extinguished by covering the vessel with a heat mat, a large beaker, or a watch glass. Do not use water. Use a dry chemical or carbon dioxide fire extinguisher directed at the base of the flames. Be very careful if using a carbon dioxide fire extinguisher as it can cause suffocation. Burns (thermal or chemical): Flush the burned area with copious amounts of running water for at least 15 minutes. Resume if pain returns. If chemicals are spilled on a person over a large area, quickly remove the contaminated clothing while under the safety shower. Seconds count and time should not be wasted because of modesty. Get prompt medical attention. Chemicals (on the skin or in the eye): Flush the affected area with copious amounts of running water for 15 minutes. Hold the eye open to wash behind the eyelids. It is University regulation that in all cases of suspected eye injury, prompt medical attention must be obtained. Contact details of eye specialists are found in the first aid kit. Cuts Minor cuts: This type of cut is most common in the organic laboratory and usually arises from broken glass. Wash the cut, remove any pieces of glass, and apply pressure to stop the bleeding. Get medical attention. Major cuts: If blood is spurting, place a pad directly on the wound, apply firm pressure, wrap the injured to avoid shock, and get prompt medical attention. Never use a tourniquet. See the University of Western Australia, School of Biomedical, Biomolecular and Chemical Sciences, Discipline of Chemistry "Safety Notes", available in the laboratory.

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ATTENDANCE AND ASSESSMENT OF LABORATORY SESSIONS

Attendance at laboratory sessions is compulsory. The demonstrator marks an attendance sheet at each session. The sessions contribute 25 % toward the final course mark for Biological Organic Chemistry CHEM1103. For this reason, an absentee form must be filled in and handed to Laboratory Technician Kim Foo (Rm 1.14), immediately after any absence. Absentee forms are obtained from the Laboratory Technician in the Preparation Room. A medical certificate must accompany an absentee form for illness. Satisfactory excuses for absences from laboratories do not include mechanical problems with cars or bikes, sporting engagements, meeting relatives, or part time work. There is no practical examination in chemistry, but students are expected to be familiar with the content of the laboratory course. The final examination for Organic Chemistry CHEM1103 may include questions on the experiments. In addition, the laboratory mark is considered when deciding borderline cases. Assessment in the laboratories will focus on your prework, laboratory performance (e.g. punctuality, enthusiasm, willingless to learn, understanding and progress) and your samples. Grading scheme description: Grade

Grade name

Mark range

HD Higher distinction 80-100 D Distinction 70-79 CR Credit pass 60-69 P Pass 50-59 F Fail 0-49

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LABORATORY MANUAL There will be prework to prepare you for the laboratory experiment each week. You should do this in the laboratory manual prior to attending the laboratory session. A permanent, dated record of observations and interpretations must be made directly into your laboratory manual as you go. Use a pen, not a pencil. Do not use correction fluid. If you want to change something, cross it out. We do not expect a thing of beauty. Rather, we want a true and accurate record of what you did, what you saw and what you thought. Sometimes you realise later that you need what you deleted earlier. Do and observe individually. Discuss and make sense of things cooperatively if you wish, but write up individually. Inferences should be recorded where possible (e.g. a white precipitate of benzoic acid formed is preferred over a white precipitate formed), but always record what you observe. Write equations for every reaction. Equations must include the following information. (i) The dominant species of substances dissolved in aqueous solution (e.g. a

sodium chloride solution contains Na+ and Cl- ions, not NaCl). (ii) Structures of organic starting materials and products indicated

unambiguously (e.g. CH3CH2CH2OH not C3H7OH). (iii) Names of organic participants. (iv) Any catalysts or special conditions used.

e.g. Br2

hvC6H13Br HBr

hexane bromohexane(various isomers)

Plagiarism is perhaps the greatest crime in science. Record nothing that you have not done yourself. Do not include what other students in your laboratory have done unless advised to do so by the demonstrator, and even then you should acknowledge the source of your data. To copy a write-up from a previous student is a serious breach of practice. If there is a sin worse that plagiarism, it is to record false data. Negative test results are just as significant as positive ones and should be recorded, along with inferences arising from them. Experiment write-ups are collected by the demonstrator at the conclusion of each laboratory session.

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1

Experiment 1

MOLECULAR MODELS Read about the following topics in your text: (a) Constitutional isomerism in alkanes (Brown &LeMay 2nd Ed., pp. 802-9). (b) Cycloalkanes (Brown &LeMay 2nd Ed., pp. 809-12). (c) Chirality (Brown &LeMay 2nd Ed., pp. 825-839). Introduction An appreciation of the 3-dimensional arrangement of atoms in molecules is important in order to rationalise and understand many of the physical and chemical properties of organic compounds. In this experiment you will: (i) construct models of a number of simple molecules. (ii) draw a reasonable 3-dimensional representation of the resulting structures. (iii) answer some questions regarding these structures. The FlexibleStereoChemistryTM model kit utilises lengths of plastic tubing to represent chemical bonds. While this is useful for many purposes, note that the models do not give a good indication of the effective size of atoms or groups of atoms. Space-filling models are required for that purpose. Name: _____________________________ Date: ____________________ Student ID: _____________________________ Lab: ____________________

PREWORK Q1. Draw the line structures of: 2-Methyl-1-propanol

1-Isopropyl-1-cyclohexanol

trans-1,2-Dichlorocyclopentane

2

Q2. Draw a sawhorse representation and a Newman projection for 2-methyl-1-propanol

Sawhorse representation

Newman projection

Q3. Indicate with an asterix (*) the stereogenic centres in menthol.

OH

Menthol

3

EXPERIMENTAL Section A Constitutional isomerism Construct a model of methane by clicking together two pieces of black tubing

to create a tetrahedral carbon atom. Place a white ball on each bond to represent H atoms. Note the equivalence of all four bonds.

Q1. What is the H-C-H bond angle and 3-dimensional shape of methane? H-C-H Bond angle = 3-Dimensional shape = Construct a model of all the constitutional isomers of C3H6Br2. Q2. Draw the line structures and name all the constitutional isomers of C3H6Br2.

4

Section B Staggered and eclipsed conformations Construct a model of ethane. Note that rotation about the C-C bond can lead

to an infinite number of arrangements of the 6 hydrogen atoms (i.e. an infinite number of conformations).

Q3. Draw the Newman projections of the staggered and eclipsed conformations

of ethane.

Staggered

Eclipsed

Construct a model of butane. Note the conformational changes resulting from

rotation about the C2-C3 bond. Q4. Draw the Newman projections of the two eclipsed conformations of butane

and indicate which conformation has the higher energy and which has the lower energy.

Higher energy / Lower energy

Higher energy / Lower energy

5

Q5. Draw the Newman projections of the two staggered conformations of butane and indicate which conformation has the higher energy and which has the lower energy.

Higher energy / Lower energy

Higher energy / Lower energy

Section C Cycloalkanes Construct a model of cyclopentane. Note that the five carbon atoms are

essentially coplanar. Cyclopropane and cyclobutane, the smallest cycloalkanes, are highly strained and difficult to construct with the present model kit without causing damage to the plastic tubing.

Q6(i). Draw the line structures of cyclopropane, cyclobutane and cyclopentane.

Determine the C-C-C bond angle and hence, the deviation from the normal tetrahedral angle.

Cyclopropane

Cyclobutane

Cyclopentane

C-C-C Bond angle =

C-C-C Bond angle =

C-C-C Bond angle =

Deviation =

Deviation =

Deviation =

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(ii). What are the implications of this deviation in regards to reactivity? Construct a model of all the possible isomeric dimethylcyclopentanes. Q7. Draw and name all the possible isomeric dimethylcyclopentanes. Draw the

structures so that you can indicate geometric (cis-trans) isomerism. One of the isomers is given as an example.

1,1-Dimethylcyclopentane

Section D Cyclohexane Construct a model of cyclohexane. Note that the ring is not planar and that

the ring strain present in the smaller cycloalkanes is absent. Put the ring into a chair conformation.

7

Q8. Draw the resulting structure of cyclohexane in chair conformation, being careful to distinguish between axial and equatorial C-H bonds. Label one axial H and one equatorial H.

View the chair conformer along one of the C-C bonds. Q9. Which conformer (i.e. staggered or eclipsed) of butane has a similar

arrangement of atoms? Hint: See Section B Q4 and Q5. Put the ring into a boat conformation and view it along one of the two C-C

bonds which make up the side of the boat.

Q10. Which conformer (i.e. staggered or eclipsed) of butane has a similar

arrangement of atoms? Hint: See Section B Q4 and Q5.

8

Section E Stability of conformers Construct a model of methylcyclohexane in the chair conformation. Convert

the chair conformer into the boat conformer, and finally to the other chair conformer.

Q11. Draw the three different conformers and indicate their relative order of

stability.

Chair 1 conformer Boat conformer Chair 2 conformer

Most/medium/least

stable

Most/medium/least

stable

Most/medium/least

stable

Q12. Draw and name all the constitutional and geometric (cis-trans) isomers of

dimethylcyclohexane. For each isomer, draw the two different chair conformations and indicate the preferred conformation, if any. One of the isomers is given as an example. (Leave the chirality column for Section G Q16).

Isomers

Chair 1 (Boat) Chair 2

Chirality

axial

equatorial

equatorial

axial

Chiral

Achiral

Meso

1,1-Dimethylcyclohexane

Only one conformation exists. No preference.

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Chiral

Achiral

Meso

Chiral

Achiral

Meso

Chiral

Achiral

Meso

Chiral

Achiral

Meso

10

Chiral

Achiral

Meso

Chiral

Achiral

Meso

Section F Geometric (cis-trans) isomerism Construct a model of ethylene (C2H4) using two grey trigonal carbon atoms.

Note that a double bond prevents rotation about the axis joining the two bonded atoms.

Construct a model of all the possible isomers of dichloroethylene. Q13. Draw the line structures and name all the possible isomers of

dichloroethylene.

Q14(i). Two of the above isomers can be interconverted chemically by irradiation

with ultraviolet light. Which are they?

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(ii). How does this interconversion occur? Draw line structures to illustrate. Section G Optical isomerism Construct a model of CHBrClF by attaching four different coloured balls to a

tetrahedral carbon atom. This will be structure A. Place structure A on the bench and construct structure B, which is the mirror image of structure A.

Q15(i). Draw structures A and B using bold and hashed bonds.

Structure A

Structure B

(ii). Are structures A and B the same (i.e. superimposable)? Non-superimosable mirror-image molecules are called enantiomers. Enantiomers are chiral. Compounds that have two or more stereogenic centres and a plane of symmetry are called meso compounds. A meso compound is achiral and does not have an enantiomer (i.e. its mirror-images are superimposable). Q16. For each isomer of dimethylcyclohexane in Section E Q12, indicate whether

the molecule is chiral or achiral, and identify any meso forms. Section H Stereochemical analysis Construct a model of all the possible stereoisomers of tartaric acid (HOOC-

CHOH-CHOH-COOH) and identify any chiral or achiral species.

12

Q17. Draw Fischer projections of each of the stereoisomers of tartaric acid. Indicate any chiral or achiral species. Also indicate which Fischer projections represent enantiomers and which Fischer projection represents meso-tartaric acid.

13

Experiment 2

ACID/BASE SEPARATION AND RECRYSTALLISATION Separation In this experiment you are going to separate benzoic acid from a mixture with quinine (an anti-malaria drug), based on their acidic and basic properties, respectively. Both chemicals are soluble in organic solvents so you cannot separate them in their present forms. You must convert one of them into an ionic form so that it becomes water-soluble. For example, when you add a base (e.g. NaOH), benzoic acid forms the benzoate ion (C6H5COO-), which is water soluble, while quinine, with no COOH groups, will not react and will remain unchanged in the organic solvent. By using a separatory funnel, you can now separate them.

COOH

N

NHHO

H3CO

Benzoic acid (-)-Quinine Recrystallisation The crude product of a reaction is rarely of high purity. For example, if benzoic acid is prepared by oxidation of benzyl alcohol, the crude benzoic acid obtained from the reaction might contain unreacted benzyl alcohol, benzaldehyde, water, and other impurities. Usually, the crude product of a reaction must be purified before it can be used in another reaction, or before it can be properly analysed (e.g. by melting point). If the compound you wish to purify is a solid then one of the most convenient methods used is recrystallisation. The technique of recrystallisation is an art that requires much practice. In this experiment, you have the opportunity to explore the technique of recrystallisation. What is a recrystallisation? Usually, the solubility of a compound increases with temperature. For example, benzoic acid is soluble in hot water, but only sparingly soluble in cold water. For recrystallisation, a useful solvent is one that will dissolve a reasonable amount of the your compound at high temperatures (usually the boiling point) and very little at low temperatures.

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In recrystallisation, the crude product is dissolved in hot solvent, and the hot solution is filtered. Any insoluble impurities are removed by this filtration step. The filtered solution is then allowed to cool. Because the product is only sparingly soluble in the cold solvent (the choice of solvent is important), it crystallises as the solution cools. The crystals are then collected in a second filtration step, and washed with a little pure, cold solvent. Any soluble impurities stay in solution, and so are separated from your product during this second filtration step. Your crystals should be pure product. To summarise, there are several steps in a recrystallisation: 1. Dissolution of the crude product, 2. Filtration of the hot solution, 3. Crystallisation of the product, 4. Isolation of the crystals. The notes below describe these steps in general terms. Read the notes carefully, and then have a go at recrystallising your benzoic acid. Take care! Good technique can lead to some beautiful crystals, but poor technique will lead to a soggy filter paper caked with white gunge! 1. Dissolution of the crude product, The mixture to be purified should be placed in a conical flask and just covered with the solvent of choice. The mixture is then heated to the boiling point and more boiling solvent is added until all the sample has dissolved. CAUTION: BUNSEN BURNERS MAY ONLY BE USED WHEN WATER IS THE SOLVENT. FOR ORGANIC SOLVENTS, A STEAM BATH MUST BE USED. Once the product has just dissolved, add about 20 % more boiling solvent, and then filter the hot solution by gravity filtration through a fluted filter paper. Occasionally there are small amounts of insoluble impurities and these should not be mistaken for product. If 50% of the sample dissolves in 10 mL of the solvent then the whole sample should dissolve in 20 mL of solvent. Attempting to dissolve small amounts of solid impurities results in excess solvent being added. This must be boiled away before crystallisation will occur, and so it is preferable to avoid too much solvent in the first place. An ideal solvent should: (a) dissolve a reasonable amount of the organic compound at high temperatures

(usually the boiling point) and very little at low temperatures. (b) dissolve impurities readily or not dissolve them at all. (c) not react chemically with the compound being recrystallised. (d) be readily removed from the purified product. (i.e. should be volatile/low

boiling).

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If the structure of your compound is known, a good guess on a suitable recrystallisation solvent can be made, remembering that polar solvents dissolve polar compounds and non-polar solvents dissolve non-polar compound (like dissolves like). Frequently, a compound will be either too soluble or too insoluble in any one solvent. Usually such compounds can be recrystallised from a mixture of two or more solvents. Mixtures commonly used are ethanol-water, ether-hexane and acetone-water. 2. Filtration of the hot solution, The key to successful recrystallisation is the hot-filtration step. Because the compound being purified is not very soluble in cold solvent, the solution must remain hot throughout this filtration step, or the product will crystallise in the filter paper and/or funnel. The best way of avoiding this blockage is by warming the filter paper and funnel, either by pouring some hot solvent through just before use, or by warming the funnel and filter paper in an oven. As well, throughout the filtration, the conical flask into which the solution is being filtered should be kept hot by a steam bath so that boiling solvent helps to keep the funnel warm. Use of a fluted filter paper also helps to prevent crystallisation during filtration. There are different was of preparing fluted filter paper. The following outlines one method. The demonstrator may show you another method. The filter paper is first folded in half and again in quarters, and opened up as shown in Figure (a). The edge 2,1 is then folded on to 2,4 and edge 2,3 on to 2,4, producing, when the paper is opened, new folds at 2,5 and 2,6. The folding is continued, 2,1 to 2,6 and 2,3 to 2,5, thus producing folds at 2,7 and 2,8 respectively [Figure (b)]; further 2,3 to 2,6 giving 2,9, and 2,1 to 2,5 giving 2,10 [Figure (c)]. The final operation consists in making a fold in each of the eight segments - between 2,3 and 2,9, between 2,9 and 2,6, etc. in a direction opposite to the first series of folds, (i.e. the folds are made outwards instead of inwards as at first). The result is a fan arrangement [Figure (d)], and upon opening, the fluted filter paper [Figure (e)] is obtained.

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3. Crystallisation of the product, The filtered solution is allowed to cool to room temperature. As the solution cools, crystallisation should commence. Once the mixture has cooled to room temperature, it can be further cooled in an ice bath. Crystallisation is a beautiful thing. Sometimes, it occurs rapidly, and large magnificent crystals grow before your eyes. At other times, only small crystals form. The size of crystal is not usually important, but large crystals are more aesthetically pleasing than small ones. Formation of large crystals is encouraged by slow cooling of your hot solution. If you take your conical flask containing the hot filtered solution and plunge it in an ice bath, crystals are likely to be small. If crystallisation does not set in, it may be induced by the following methods. (i) Scratching the bottom and sides of the container with a glass stirring rod.

This makes rough edges on which crystals tend to form. (ii) Adding a small seed crystal, if available. If these methods fail to bring about recrystallisation there is probably too much solvent present. The solvent should then be evaporated further and the above steps repeated. 4. Isolation of the crystals. When crystallisation is complete, the crystals are collected by vacuum filtration using a Hirsch funnel for small amounts, or a Bchner funnel of appropriate size for large quantities. In order to remove adhering mother liquor which will contain soluble impurities, the crystals are rinsed on the funnel with small amounts of cold solvent. Finally, the crystals are dried by drawing air through the filter for a few minutes. It is important that all solvent be removed, since the melting point and yield will be inaccurate otherwise. The crystals are then stored in a stoppered container.

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Name: _____________________________ Date: ____________________ Student ID: _____________________________ Lab: ____________________

PREWORK Q1. Besides the normal neutral forms for benzoic acid and quinine, will there be

any other chemical form(s) present in the dichloromethane solution? (benzoic acid, pKa 4.2; quinine, pKa 8.5)

Q2. What is the purpose of: a separatory funnel? recrystallisation?

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Q3. Complete the following flowchart.

OH

O

N

NHHO

O

Dissolve in CH2Cl2 and add 2 M NaOH

Organic layer Aqueous layer

add 2 M NaOH

Organic layer Aqueous layer

add CH2Cl2

Organic layer

Aqueous layer

add HCl

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EXPERIMENTAL Separation Weigh out approximately 1 g of benzoic acid/quinine mixture on the top-

loading balance. Record the exact mass (e.g. 1.06 g). m(benzoic acid/quinine mixture) = Transfer the mixture to a 100 mL conical (Erlenmeyer) flask. Add 20 mL of

dichloromethane. Clamp a separatory funnel by its ground glass joint to a retort stand, making sure the separatory funnel tap is closed. Transfer the mixture into the separatory funnel, using a filter funnel. Pour 10 mL of 2 M NaOH solution into the separatory funnel using a filter

funnel. Two layers will form. Stopper the separatory funnel and shake the mixture gently. CAUTION: DO

NOT SHAKE VIGOROUSLY HEAT FROM YOUR HANDS WILL CONVERT SOME OF THE DICHLOROMETHANE INTO ITS GASEOUS FORM, RESULTING IN PRESSURE BUILD-UP. To release the pressure, you must vent the system by holding the separatory funnel upside-down and opening the tap after you shake it CAUTION: BE CAREFUL WHERE YOU POINT THE TAP. Shake and vent three times.

Allow the contents to separate into two layers. Secure the separatory funnel

to the retort stand and remove the stopper. Q1. Which layer is the organic (dichloromethane) layer? How did you determine

this?

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Q2. Why cant ethanol or acetone be used as the organic solvent? Q3. What ions or compounds are present in each layer? Write a chemical

equation for any transformation that has occurred. Water layer

Organic layer

Open the tap and drain the organic layer into a dry conical flask. Label it. Q4. Again, what is present in this organic layer? Drain the aqueous layer into another labelled conical flask. Q5. Again, what is present in this aqueous layer? Pour the organic layer back into the separatory funnel using a filter funnel

and pour in another 5 mL of 2 M sodium hydroxide solution. Repeat the above 'extraction' (stoppering, shaking and releasing of pressure) steps. Drain the organic layer into the conical flask containing the original organic extract.

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Drain the aqueous layer into the conical flask containing the original aqueous 'extract'.

Q6. What is the purpose of this repeat addition of sodium hydroxide? Place the combined aqueous layers back into the separatory funnel, add 1-2

mL of dichloromethane, swirl gently, then drain the two separated layers back into their respective conical flasks.

Q7. Why would you bother with this seemingly trivial operation? Q8. Where is the benzoic acid now? In what form is it? Q9. Where is the quinine now? In what form is it? Recovering the quinine The quinine is dissolved in dichloromethane. As the solvent has a low boiling

point (40C), boil off the dichloromethane using a steam bath in the fumehood.

Solid quinine will result. Weigh a clean, dry, labelled sample vial. Transfer

your quinine into the sample vial and reweigh it when the sample seems free of residual solvent (dichloromethane). Determine the mass of quinine and yield as a percentage of the weight of material with which you started.

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m(sample vial) = m(sample vial + quinine) = m(quinine) = % Yield = Recovering the benzoic acid To the combined aqueous layers, add concentrated hydrochloric acid

dropwise until a white precipitate is seen, and then until the precipitation is complete (i.e. until the solution is acidic). Use litmus paper to determine when precipitation is complete.

Q10. What is happening here? Write an equation. Use vacuum filtration with a Hirsch funnel and filter paper to separate the

white precipitate. Disconnect the vacuum and wash the crystals with approximately 5 mL of distilled water.

Re-apply the vacuum and dry the crystals. Weigh a dry watch glass. Transfer

the crystals onto the watch glass and reweigh it. Determine the mass of the impure benzoic acid.

m(watch glass) = m(watch glass + impure benzoic acid) = m(impure benzoic acid) =

23

Purifying the benzoic acid The benzoic acid is now ready to be recrystallised. The notes on recrystallisation are found at the beginning of this experiment. Recrystallise your benzoic acid from about 50 mL of water. The graph below

shows that solubility (particularly of benzoic acid) drops off rapidly with temperature. CAUTION: BENZOIC ACID IS VOLATILE IN STEAM AND SOME MAY BE LOST IF THE SOLUTION IS BOILED FOR TOO LONG. THEREFORE, ADD THE BENZOIC ACID TO THE ALREADY BOILING WATER WITH CARE.

0

1

2

3

4

5

6

0 20 40 60 80 100

Solu

bilit

y (g

/100

mL)

Temperature (C)

Q11. How does a fluted filter paper help prevent crystallisation during filtration? Q12. Hirsch or Bchner funnels should not be used for filtration of the hot

solution. Why?

24

Q13. The crystals should not be collected by gravity filtration. Why? Weigh a clean, dry, labelled sample vial. Transfer the purified benzoic acid

crystals into the sample vial and reweigh it. Determine the mass of benzoic acid recovered after recrystallisation as a percentage of the weight of material with which you started (benzoic acid/quinine mixture).

m(sample vial) = m(sample vial + benzoic acid) = m(benzoic acid) = % Yield = Q14. Do your two recovered yields of benzoic acid and quinine add up to 100%?

Explain any differences.

25

Experiment 3

THE REDUCTION OF BENZOPHENONE TO DIPHENYLMETHANOL

Read about the following topic in your text: (a) Reduction (Brown &LeMay 2nd Ed., pp.939-940 ). Introduction Aldehydes and ketones can be reduced to primary and secondary alcohols respectively. One of the most common laboratory reagents fr the reduction of a carbonyl group of an aldehyde or a ketone to a hydroxyl group is sodium borohydride (NaBH4). Sodium borohydride is a source of hydride ions, which are very strong nucleophiles. In this experiment you will be preparing diphenylmethanol from the reduction of benzophenone using sodium borohydride.

O H OH1. NaBH4, EtOH

2. H2O, OH-

Benzophenone Diphenylmethanol

26

Name: _____________________________ Date: ____________________ Student ID: _____________________________ Lab: ____________________

PREWORK Q1. Give the molecular mass (g mol-1) for: M(benzophenone) = M(diphenylmethanol) = Q2. Draw the product of each of the following reduction reactions.

CH3

O1. NaBH4

2. H+

H

O1. NaBH4

2. H+

OCamphor

1. NaBH4

2. H+

27

EXPERIMENTAL Preparation Set up a water bath using a 250 mL beaker with 120-150 mL of hot water

over a gauze mat on a tripod. Arrange a retort stand and clamp to be able to suspend a 50 mL round bottom flask in the beaker. Using a Bunsen burner, heat the water bath to boiling.

Into the 50 mL round bottom flask, put 2.8 g of benzophenone and 10 mL of

ethanol. Record the exact mass and calculate the number of moles it corresponds to.

m(benzophenone) = n(benzophenone) = Add 0.3 g of sodium borohydride and a boiling chip to the round bottom flask

and place a reflux condenser on top.

Water outCondenser

Clamp

Water in

Water bathGauze mat

Heat resistant mat

Reflux the mixture gently in a water bath for 10 minutes. CAUTION:

SODIUM BOROHYDRIDE IS STRONGLY CAUSTIC. HANDLE IT CAREFULLY AND DO NOT PERMIT IT TO TOUCH THE SKIN.

28

Q1. What is the purpose of the reflux condenser? Cool the flask under running water briefly. Isolation To decompose the boric acid complex, add 20 mL of 2 M aqueous sodium

hydroxide and swirl the reaction mixture. Add 10 mL of dichloromethane, swirl again and transfer the mixture to a

separatory funnel. Into a dry flask, run off the organic layer and keep it, extract the remaining

aqueous layer with a further 10 mL portion of dichloromethane (shake gently to avoid an emulsion) and combine both of the organic extracts.

Place the combined dichloromethane extracts back into the separatory funnel

and separate from any remaining water. Dry the extracts over a little anhydrous magnesium sulfate (the demonstrator must be consulted here).

Filter the combined extracts into a dry 100 mL conical flask using a filter

paper and funnel. Place a boiling stick into the conical flask and boil off most of the dichloromethane using a steam bath in the fume hood.

On cooling the residue in ice, it should crystallise. Purification Add 30-40 mL of hexane, warm using a steam bath until the product

dissolves, and filter through a small plug of cotton wool into a conical flask in the fumehood.

As the flask cools, crystals of diphenylmethanol will form. Cooling the flask

in an ice water bath will maximise the amount of crystals. Recover your product by vacuum filtration. Record the mass of your product, taking care to dry the diphenylmethanol

well, and calculate the percentage yield obtained.

29

m(sample vial) = m(sample vial + diphenylmethanol) = m(diphenylmethanol) = n(diphenylmethanol) = % Yield = In the above experiment you have converted a colourless, crystalline solid into another colourless, crystalline solid. Q2. How could you use 13C N.M.R. spectroscopy to distinguish between the

ketone and the alcohol?

30

Experiment 4

CARBOXYLIC ACIDS AND ESTERS PART 1 - SYNTHESIS

Read about the following topics in your text: (a) Esterification (Brown &LeMay 2nd Ed pp. 975-980). (b) Reaction with alcohols (Brown &LeMay 2nd Ed., pp. 904-907). Introduction Esters can be prepared via what is known as esterification. This involves the treatment of a carboxylic acid with an alcohol, with the aid of an acid catalyst, most commonly, concentrated sulfuric acid. Another way of preparing esters is by the reaction between acid anhydrides and alcohols to form one equivalent of ester and one equivalent of carboxylic acid. In this experiment, you will be using both methods to prepare two different esters. You will be synthesising isoamyl acetate, also known as banana oil, by the esterification process using the corresponding isoamyl alcohol and acetic acid. The liquid product obtained will be purified via distillation in the following experiment.

O

O

OH HO

O H2SO4H2O

isoamyl alcohol acetic acid isoamyl acetate(banana oil)

You will also be making aspirin from salicylic acid and acetic anhydride. The crude asprin will be stored for recrystallisation in the following experiment.

OH

OH

O

salicylic acid

O

O O

O

OH

O

O

OH

OH3PO4

o-acetylsalicylic acid (aspirin)

acetic anhydride

31

Name: _____________________________ Date: ____________________ Student ID: _____________________________ Lab: ____________________

PREWORK Q1. Give the molecular mass (g mol-1) for: M(isoamyl alcohol) = M(acetic acid) = M(isoamyl acetate) = M(salicylic acid) = M(aspirin) = Q2. Draw the product of each of the following reactions.

OH

OH

O

CH3OHH2SO4

O

OH HOH2SO4

HOOH

O

HH2SO4

32

Q3. Draw the mechanism for the following reaction.

O

O

OH HO

O H2SO4H2O

33

EXPERIMENTAL CAUTION: THIS EXPERIMENT UTLISES CONCENTRATED ACIDS. TAKE SPECIAL CARE WHEN HANDLING THESE ACIDS OR WHEN ADDING THEM TO OTHER CHEMICALS. IF THESE ACIDS COME INTO CONTACT WITH YOUR SKIN, WASH THE AFFECTED AREA COPIOUSLY WITH WATER AND SEEK FIRST AID TREATMENT. Preparation of isoamyl acetate Into a dry 50 mL round bottom flask place 5 mL of isoamyl alcohol (d =

0.809 g/mL) and 4 mL of acetic acid (d = 1.049 g/mL). Note: Isoamyl alcohol has a strong odour and you should ensure that the concentration of the vapour in the laboratory is kept to a minimum.

Q1. Using the densities provided, calculate the mass and number of moles of

isoamyl alcohol and acetic acid used. Which is the limiting reagent and which is in excess? Make a note of the molar quantity of isoamyl alcohol in Experiment 5 in the space provided as you will need it for the percentage yield calculation next week.

m(isoamyl alcohol) = n(isoamyl alcohol) = m(acetic acid) = n(acetic acid) = Limiting reagent = Excess reagent = Carefully add 1 mL of concentrated sulfuric acid dropwise with gentle

swirling to mix the contents thoroughly. You may feel the flask warm up.

34

Q2. What is the function of the sulfuric acid? Add a boiling chip to the round bottom flask, equip the flask with a reflux

condenser, and reflux the mixture using a water bath for 1.5 hours (Use a 250 mL beaker with 120-150 mL of hot water over a gauze mat on a tripod and a Bunsen burner).

Proceed with the preparation of aspirin while the mixture is refluxing. Note:

The yield of ester can be increased substantially by using a longer reflux time.

Preparation of aspirin Place 2 g of salicylic acid into a dry 100 mL conical flask. Record the exact

mass. Make a note of the molar quantity in Experiment 5 in the space provided as you will need it for the percentage yield calculation next week.

m(salicylic acid) = n(salicylic acid) = Add 5 mL of acetic anhydride and 5 drops of 85 % phosphoric acid to the

conical flask. Swirl the mixture and then heat the flask on the steam bath for 5 minutes. Isolation of aspirin Remove the flask from the steam bath and, while it is still hot, cautiously add

2 mL of water in one portion CAUTION: THE SOLUTION MAY BOIL FROM THE HEAT OF DECOMPOSITION OF THE EXCESS ACETIC ANHYDRIDE.

35

Q3. Why add water to the reaction mixture while it is still hot? Write the appropriate equation.

Follow by adding 50 mL of water and stir the solution until crystals begin to

form. Cool the mixture in an ice bath to complete the crystallisation and collect the

crystals on the Hirsch funnel, using vacuum filtration. Wash the crystals with two 10 mL portions of cold water, and dry them well.

Record the mass of impure aspirin. m(sample vial) = m(sample vial + impure aspirin) = m(impure aspirin) = Isolation of isoamyl acetate Cool the flask and pour the mixture into a separatory funnel containing about

20 mL of cold water. Shake the mixture and, when the layers separate, run out the aqueous layer out into a labelled conical flask.

Q4. Which layer is the aqueous layer and which layer is the organic layer? How

can you tell?

36

Q5. What is in the aqueous layer? Q6. What is in the organic layer? Slowly, add about 20 mL of saturated sodium bicarbonate solution to the

separatory funnel with the organic layer. Before replacing the lid back onto the separatory funnel, gently swirl the layers together until gas evolution has ceased CAUTION: THE ADDITION OF SODIUM BICARBONATE MAY CAUSE A VIOLENT REACTION. DO NOT REPLACE THE LID ON THE SEPARATORY FUNNEL UNTIL GAS EVOLUTION HAS CEASED.

Stopper the separatory funnel and shake gently, taking care to vent the funnel.

Drain out the aqueous layer into a labelled conical flask. Q7. What is the function of the sodium bicarbonate wash? Write the appropriate

equation.

37

Using litmus paper as a guide, continue to wash the organic layer with 20 mL portions of saturated sodium bicarbonate solution until the organic layer is neutral.

Collect the organic layer in a dry conical flask and dry over a little anhydrous

MgSO4. Filter the organic layer through a plug of cotton wool into a pre-weighed

labelled sample vial. Record the mass of the impure isoamyl acetate. m(sample vial) = m(sample vial + impure isoamyl acetate) = m(impure isoamyl acetate) = Isoamyl acetate smells strongly of bananas. Smell your product cautiously

(the demonstrator must be consulted here) and note down any odours you detect.

Stopper the sample vial and give it to your demonstrator, making sure your

name is on the label. Your sample will be stored for you until the next laboratory experiment when you will purify your product via distillation.

38

Experiment 5

CARBOXYLIC ACIDS AND ESTERS PART 2 - PURIFICATION

Purification In the previous experiment you prepared isoamyl acetate and aspirin. It is most likely that the products collected were not of high purity. In this experiment you will purify your products using two different purification techniques, recrystallisation and distillation. You have had experience recrystallising an organic solid before, and you will also learn the basic set up for distillation by performing a simple distillation. In this distillation, the vapour arising from heating the crude product will pass through a condenser that will cool and condense the vapour back to liquid phase, leaving the high boiling and involatile impurities behind. From Experiment 4 n(isoamyl alcohol) = n(salicylic acid) =

39

Name: _____________________________ Date: ____________________ Student ID: _____________________________ Lab: ____________________

PREWORK Q1. What is the purpose of a recrystallisation? Q2. What is the purpose of a distillation? Q3. Would you perform a recrystallisation or a distillation on aspirin for its

purification? State your reasons. Q4. Would you perform a recrystallisation or distillation on isoamyl acetate for its

purification? State your reasons.

40

EXPERIMENTAL Purification of isoamyl acetate Clamp a 50 mL round bottom flask containing your impure isoamyl acetate

product halfway up a retort stand and add a boiling chip to it. Place a stoppered distillation head on top of the 50 mL distillation flask

Distillation head Q1. What is the purpose of adding a boiling chip to the distillation flask? Attach a condenser to the distillation head and set up another retort stand and

clamp to support it. Place a distillation adaptor at the end of the condenser and secure it with a

clip. Finally, attach a clean dry round bottom flask to the distillation adaptor and secure this receiving flask with another clip.

Distillation adaptor

41

Retort stand

Distillation flask

Receiving flask

Distillation head

Distillation adaptor

Condenser

Stopper

Clamp

Clamp

Water inWater out

Clip

Clip

Ask the demonstrator to check your completed set up before proceeding to

the next step. CAUTION: DO NOT PROCEED TO THE NEXT STEP UNTIL THE DEMONSTRATOR HAS CHECKED YOUR SET UP AND SIGNED OFF IN YOUR LAB MANUAL.

Demonstrators signature: _______________________________________________ Carefully, heat the distillation flask gently with a Bunsen burner so that the

isoamyl acetate slowly distils over. If the vapours are condensing back into the distillation flask before passing through the condenser, you may have to use the Bunsen burner to warm the distillation head sufficiently so that the vapours do not condense until it passes through the condenser. CAUTION: ISOAMYL ACETATE IS A FLAMMABLE LIQUID. ENSURE THAT THE VAPOURS ARE PROPERLY CONDENSED AND DO NOT ALLOW VAPOUR OR DISTILLATE TO BE NEAR YOUR FLAME OR YOUR NEIGHBOURS FLAME.

Q2. Why does it help to keep the distillation head warm? Continue slow distillation until a small residue remains. CAUTION: DO

NOT DISTIL UNTIL THE DISTILLATION FLASK IS DRY. THIS CAUSES THE GLASS TO OVERHEAT AND ANY FLAMMABLE GASES MAY IGNITE.

42

Q3. What is the purpose of distilling slowly? When the distillation is complete, allow the distillation flask and distillation

head to cool to room temperature before disassembling the apparatus. Proceed with the recrystallisation of aspirin while the glassware is cooling.

When the set up has cooled to room temperature, transfer the isoamyl acetate

distillate into a pre-weighed labelled sample vial. Determine the mass of isoamyl acetate and yield as a percentage from the isoamyl alcohol starting material from the previous laboratory experiment.

m(sample vial) = m(sample vial + isoamyl acetate) = m(isoamyl acetate) = n(isoamyl acetate) = % Yield = Purification of aspirin Recrystallise your aspirin from about 50-75 mL of water. Use a steam bath to

heat the water to 80 C. CAUTION: DO NOT HEAT THE WATER ABOVE 80 C AS BOILING WATER HYDROLYSES ASPIRIN.

43

Q4. Explain the meaning of boiling water hydrolyses aspirin by the use of an equation.

Once your product has completely dissolved, filter it through a fluted filter

paper and allow the filtrate to cool so that crystals can begin to form. Place the flask in an ice-water bath to complete crystallisation.

Collect the crystals by vacuum filtration, allow the crystals to air-dry, and

transfer them to a pre-weighed sample vial. Determine the mass of aspirin and yield from the salicylic acid starting material from the previous laboratory experiment.

m(sample vial) = m(sample vial + aspirin) = m(aspirin) = n(aspirin) = % Yield =

44

Experiment 6

AROMATIC CHEMISTRY

Read about the following topics in your text: (a) Nitration (Brown &LeMay 2nd Ed . 1017-1026). (b) Hydrolysis of amides (Brown &LeMay 2nd Ed pp 1063). Introduction The nitro group is a very important functional group in aromatic chemistry, since it is readily introduced into an aromatic ring. It can be reduced to the amino group and diazotisation of a primary aromatic amine yields a diazonium salt. The diazo group (N2+) can be replaced by a variety of other functionalities such as Br, Cl, F, I, OH, etc. This experiment involves the preparation of 4-nitroaniline. If aniline is nitrated directly, only a low yield of nitro compounds is obtained since much of the aniline is destroyed through oxidation by the nitric acid. This problem is overcome by carrying out the nitration on acetanilide, which can readily be prepared from aniline and acetic anhydride. The acetamido group (NHCOCH3) directs the incoming electrophile (NO2+) primarily into the para position and the resulting 4-nitroacetanilide can be hydrolysed to give 4-nitroaniline.

NH

O

NH

NO2

O

NH2

NO2

HNO3

H2SO4

1. HCl, H2O

2. NH3

acetanilide 4-nitroacetanilide 4-nitroaniline

45

Name: _____________________________ Date: ____________________ Student ID: _____________________________ Lab: ____________________

PREWORK Q1. Give the molecular mass (g mol-1) for: M(acetanilide) = M(4-nitroaniline) = Q2(i). Draw the mechanism for the reaction between sulfuric acid and nitric acid. (ii). Draw the electron dot diagram for the product of the above reaction. Q3. Draw the mechanism for the nitration of benzene and indicate the elecrophilic

and nucleophilic species.

46

EXPERIMENTAL Section A Preparation of 4-nitroacetanilide

NH NH

NO2

O O

HNO3H2SO4

H2O

acetanilide 4-nitroacetanilide CAUTION: THIS EXPERIMENT UTLISES CONCENTRATED ACIDS. TAKE SPECIAL CARE WHEN HANDLING THESE ACIDS OR WHEN ADDING THEM TO OTHER CHEMICALS. IF THESE ACIDS COME INTO CONTACT WITH YOUR SKIN, WASH THE AFFECTED AREA COPIOUSLY WITH WATER AND SEEK FIRST AID TREATMENT. Prepare a nitrating mixture by cooling 5 mL of concentrated sulfuric acid in a

small dry flask in an ice-water bath. Cautiously add 2 mL of concentrated nitric acid to the cold sulfuric acid and keep the nitrating mixture in the ice-water bath.

Q1. What is the function of the sulfuric acid in the nitrating mixture? In a dry 100 mL conical flask dissolve 3.2 g of acetanilide in 5 mL of glacial

acetic acid by warming gently on the steam bath. Record the exact mass. m(acetanilide) = n(acetanilide) = Q2. What is the function of the acetic acid?

47

Cool the solution for a minute in an ice-water bath and, after removing the solution from the ice-water bath, add 5 mL of concentrated sulfuric acid dropwise with swirling.

Q3. What is the function of the sulfuric acid in the acetanilide/acetic acid

solution? Hint: The melting point of acetic acid is 16.2 C. Cool the resulting acetanilide solution in an ice-water bath and add the

nitrating mixture, 4 drops at a time, from a dry pipette. Swirl the viscous mixture thoroughly during the addition and keep its temperature low by cooling in the ice bath.

Q4. Why is the reaction temperature kept low? When the addition of the nitrating mixture is complete, allow the resulting

mixture to stand at room temperature for 10 minutes. Q5. Why is the resulting mixture left to stand at room temperature for 10

minutes? Pour the mixture slowly with stirring into a 250 mL beaker containing 100

mL of water and a handful of crushed ice. Q6. Why is the mixture poured into ice-water?

48

Collect the product by on the Bchner funnel and wash the product with about 100 mL of water.

Section B Hydrolysis of 4-nitroacetanilide

NH

NO2

O

H2O

4-nitroacetanilide

HCl

NH3

NO2

Cl

CH3COOHNH3

NH2

NO2

4-nitroaniline Transfer the crude 4-nitroacetanilide to a 250 mL round bottom flask and add

60 mL of water. Swirl the flask until the mixture becomes a slurry. Add 15 mL of concentrated hydrochloric acid and two boiling chips. Q7. What is the function of the hydrochloric acid? Equip the flask with a condenser and reflux the mixture gently over a gauze

mat using a Bunsen burner until all the solid material has gone into solution. This should take about 15 minutes.

Cool the flask and pour the solution of 4-nitroaniline hydrochloride with

stirring into a 400 mL beaker containing about 100 g of crushed ice. Liberate the free 4-nitroaniline by slowly adding concentrated ammonia

solution with stirring until the mixture is basic. You will need at least 10 mL of ammonia solution. CAUTION: AMMONIA SOLUTION MUST BE USED IN THE FUMEHOOD.

49

Q8. Why is it necessary to add ammonia solution to precipitate the product? Write the appropriate equation.

Collect the precipitate on a Bchner funnel and wash the filter cake with two

100 mL portions of water. Recrystallise the crude product from water. About 150-200 mL of water is

required. Transfer the air-dried recrystallised 4-nitroaniline into a pre-weighed labelled

sample vial. Determine the mass of 4-nitroaniline, and yield from the acetanilide starting material.

m(sample vial) = m(sample vial + 4-nitroaniline) = m(4-nitroaniline) = n(4-nitroaniline) = % Yield =

Q7. Why would you bother with this seemingly trivial operation?