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CHEM1102
Organic Chemistry
Laboratory Manual
2010
Discipline of Chemistry
School of Biomedical, Biomolecular and Chemical Sciences
Name: ________________________________________________________
Student ID:
________________________________________________________ Lab:
________________________________________________________
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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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i
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
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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
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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.
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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
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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.
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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.
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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
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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.
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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.
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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?
-
20
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.
-
21
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.
-
22
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
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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
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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?