THE UNIVERSITY OF EDINBURGH SCHOOL OF CHEMISTRY CHEMISTRY 3

THE UNIVERSITY OF EDINBURGH
SCHOOL OF CHEMISTRY
CHEMISTRY 3
ORGANIC CHEMISTRY
LABORATORY MANUAL
2013-2014
1
GENERAL ORGANISATION OF THE COURSE
This manual contains just the information you need at the bench. You must read and use the
information on LEARN in addition to this manual. On LEARN you will find:
General safety information
Course aims and outcomes
Advice on how to write a report
Pre-lab exercises for all the experiments
Resources relevant to each experiment such as reference spectra etc.
Information on the Unknowns exercise
Also there are useful videos and helpful lab tips on www.kirsoplabs.co.uk
Organiser: Dr. Peter Kirsop (room 281, Tel. 50 4719, email [email protected]).
The lab work takes place over twenty-four laboratory sessions and consists of two types of
exercise:
Experiments: Each student is assigned experiments by bench:
BENCH A
Experiments: 1,2,3,4,5,7,10
BENCH B
BENCH C
1,2,6,7,8,9,11
1,2,5,6,7,9,10
You must all start with Ex. 1. After that the order is up to you. Note that some
experiments are shorter than others. There is a compulsory pre-lab quiz on LEARN for
each experiment. This must be done before before staring the experiment and is worth
10% of the individual experiment mark.
Unknowns: Each of you are allocated two unknowns to identify. These are listed in the lab
and on LEARN. There are no set sessions for this, you complete these whenever convenient to
you. Resources for this are in the computer room at the rear of the lab. All information about
this, including the report sheet, a pre-printed form, is available on LEARN.
Total lab mark is 7 x 20 for the experiments and 2 x 20 for the unknowns. Total 180.
It is not necessary to complete all the experiments to pass the lab course. If you feel you
are struggling then talk to a demonstrator or staff member about your progress as they will be
able to give you guidance as to the best way to maximise your remaining time in the lab.
You will be issued with one laboratory notebook for recording experiments throughout all three
(inorganic, physical and organic) labs. Your lab book must be inspected and initialled by a
demonstrator or staff member at the end of every session.
The week following the six weeks of lab sessions is for writing up and no lab
work may be done during that week.
It is in your interests to hand in reports soon after you complete the experiment as this will allow
you to take into account feedback from the marked reports before writing the next report. All
reports are due in by:
Lab / tutorial groups A, B and C:
Lab / tutorial groups D, E and F:
5pm Friday of Semester 1 week 8
5pm Friday of Semester 2 week 4
Without prior agreement by Dr. Peter Kirsop no reports will be accepted after this time
and a mark of zero will be recorded for the missing reports.
2
EXPERIMENT 1
Synthesis of Sulfanilamide from Aniline.
Have you done the pre-lab?
Sulfanilamide was the first substance to be used systematically and effectively as a
chemotherapeutic agent for the prevention and cure of bacterial infection in humans. You will
hear much more about these compounds in the third year medicinal chemistry course.
This is a multi-step synthesis starting from aniline, and is almost identical to the method used
industrially for sulfanilamide production.
RISK ASSESSMENT
Substances Used
Aniline
Acetic anhydride
Sodium acetate
Chlorosulfonic acid
Ammonium hydroxide
Conc. Hydrochloric acid
Hazards Identified
Toxic. Possible carcinogen. Possible
mutagen. Possible sensitizer. Readily
absorbed through the skin
Flammable, causes burns on contact
with skin, harmful by inhalation
Irritant
Causes severe burns, irritant, toxic.
Fumes on contact with air
Corrosive, causes burns, irritant to skin,
eyes and respiratory system
Causes severe burns
Safety Procedures:
Safety glasses, gloves and laboratory coats should be worn at all times.
3
Emergency Procedures:
Spillage: Wipe up wearing gloves.
Fire: CO2 extinguisher
Waste Disposal:
Waste solvents should be placed in appropriate waste bottles located in fume cupboards
First Aid: The nearest first aid workers are in the Technicians area.
Step 1 – Preparation of acetanilide from aniline
First, make up a solution of sodium acetate (8.5 g in 30 mL of water) and put to one side.
Dissolve aniline (8.0 g) in a mixture of water (135 mL) and concentrated hydrochloric acid (7.5
mL) in a 250 mL round bottom flask. The solution should be colourless – if it is not add around
4 spatula’s of activated charcoal and stir for a few mins. Remove the charcoal by filtering
through a celite layer.
Add acetic anhydride (10 mL) to the solution whilst stirring with a stirrer bar and then add the
sodium acetate solution. Stir for a few minutes then cool in an ice bath where a solid should
form. Collect the solid (which should be colourless) by filtration.
The product must be dry before moving on, so dissolve the solid in dichloromethane and add
some anhydrous magnesium sulphate. Stir, then remove the magnesium sulphate by filtration.
Recover the solid acetanilide by removing the solvent on a rotary evaporator.
Record the yield, melting point and an IR spectrum. Confirm with a demonstrator that the step
has been successful before starting the next step.
Step 2. Chlorosulfonation of Acetanilide
Place acetanilide (5.0 g) in a dry 100 mL conical flask and heat, with occasional swirling, on a
hotplate until it liquefies (Do not boil). Remove from the hotplate and allow to cool and solidify,
then chill in an ice bath. Add chlorosulfonic acid (13 mL, in portions with a pipette CARE –
reacts violently with water) whilst still in the ice bath and allow to warm slowly to room
temperature, with occasional swirling. Most of the solid material should dissolve before
proceeding.
Heat the liquid on a boiling water bath for a 10 minutes with occasional swirling. Initially there
will be effervescence as the reaction completes. Allow to cool to room temperature. Slowly
poor the contents, with vigorous stirring, into a 250 mL beaker containing approx. 75 mL of ice
water. This hydrolysis is exothermic and a milky white precipitate will form. Collect the solid by
suction filtration. Press the solid with a spatula and, using vacuum, suck off as much of the
water as possible.
Transfer the wet solid to a weighed 100 mL conical flask. You should have around 8 – 10 g of
crude wet solid.
Do not stop at this stage – the product of this step will deteriorate over time. Go straight
on to the next step.
4
Step 3. Preparation of p-Acetamidobenzenesulfonamide
Add concentrated ammonia solution (20 mL) and water (20 mL) to the conical flask with the
product from the previous stage. Swirl the flask until the reaction mixture forms a solid mass –
this should take about one minute. Warm the flask on a hotplate for 10 – 15 minutes but do not
allow to boil. Allow to cool to room temperature and then chill in an ice bath.
Collect the solid by suction filtration and wash the solid with approx 10 mL of water. Allow the
solid to remain under suction for a few minutes to remove most of the water.
Dry a sample of the product overnight in a desiccator to allow determination of the melting point
and to obtain an IR. Use the rest to proceed onto the next step.
Step 4. Conversion to Sulfanilamide
Place the crude product from the last step in a 100 mL conical flask and add a solution of
hydrochloric acid made up of bench concentrated HCl (5 mL) in water (10 mL). Boil the mixture
gently on a hotplate until all the solid has dissolved (5 – 10 min). If the solid does not dissolve
after this time add another 10 mL of the acid / water mixture. Continue to heat at boiling point
for a further 10 mins, but do not evaporate to dryness.
Allow to cool to room temperature. Transfer the cooled liquid to a 250 mL beaker and slowly
add saturated sodium bicarbonate solution with stirring until the solution is no longer acidic
(litmus). Cool in an ice bath and collect the white precipitate of sulfanilamide using suction
filtration.
Recrystallise the product from ethanol or water. Record the yield (based on the quantity of
acetanilide used at the start of stage 2) melting point and IR spectrum.
Sample of the final product only is required.
Questions
1. In your report give mechanisms for all the reaction steps. (3 marks)
2. Why is an acetyl group added to aniline, and then later removed to regenerate the amine
in the final product? (1 mark)
3. What happens when the product of step 2, p-acetaminobenzenesulfonyl chloride, is
allowed to stand for some time in contact with moisture from the atmosphere? (1 mark)
5
EXPERIMENT 2
Stereospecific Reduction of Benzoin with Sodium Borohydride; Determination of
the Stereochemistry by NMR spectroscopy
Have you done the pre-lab?
The stereochemical course of ketone reductions can be influenced by the presence of hydroxyl
groups close to the carbonyl function. This experiment illustrates the stereoselective reduction
of benzoin using sodium borohydride as a reducing agent, followed by the conversion of the
resulting 1,2-diol into its acetonide (isopropylidene) derivative catalysed by anhydrous iron (III)
chloride, a reaction commonly used for the protection of 1,2-diols during a synthetic sequence.
NMR spectroscopic analysis of the acetonide permits the determination of its relative
stereochemistry and hence that of the diol.
Ph
O
Ph
OH
NaBH4
EtOH
Ph
OH
Ph
OH
Ph
OH
Ph
OH
Ph
O
Me2CO
Ph
O Me
FeCl3
Ph
O
Me
Ph
O
Me
Me
RISK ASSESSMENT:
1. Preparation of 1,2-diphenylethane-1,2-diol
Substances Used
Hazards Identified
Benzoin (FW 212.3)
Sodium borohydride (FW 37.3)
Ethanol
Light petroleum (bp 60-80oC)
Hydrochloric acid (6M)
2. Preparation of acetonide derivative
Substances Used
Irritant
Corrosive, flammable, toxic, reacts violently with
water
Flammable, toxic
Flammable, harmful by inhalation
Corrosive
Hazards Identified
Acetone (pure)
Flammable
Iron (III) chloride (anhydrous)
Corrosive, hygroscopic
Dichloromethane
Irritant, toxic
Light petroleum (bp 60-80oC)
Flammable, harmful by inhalation
Potassium carbonate solution (10%) Corrosive
Safety Procedures:
Safety glasses, lab coats and gloves must be worn for all chemical manipulations.
Reaction and work-up must be carried out in a hood.
Emergency procedures:
Spillage: Wear gloves and wipe up with copious amounts of water. In the event of a sodium
borohydride spillage, do not use water to clean up the area until you have removed the bulk of
the material.
Fire:
CO2 extinguisher
6
Waste Disposal
Waste solvents to bottles in fume hoods.
First Aid: The nearest first aid workers are in the Technicians area.
PROCEDURES
1. Preparation of 1,2-diphenylethane-1,2-diol
Dissolve benzoin (2.00 g, 9.4 mmol) in 20 mL of ethanol in a 100 mL conical flask (dissolution
need not be complete). Stir the solution magnetically, and add sodium borohydride (0.40 g, 10.6
mmol) in small portions over 5min using a spatula (CARE!, exothermic reaction). If necessary,
rinse in the last traces of sodium borohydride with 5mL of ethanol. Stir the mixture at room
temperature for a further 20min, and then cool it in an ice bath whilst slowly adding 30 mL of
water followed by 1 mL of 6M hydrochloric acid. Some foaming will occur at this stage.
Add a further 10 mL of water, and stir the mixture for a further 20 min. Collect the product by
suction filtration, and wash it thoroughly with 100 mL of water. Dry the product by suction for 30
min, and record the yield. This material is sufficiently pure to be used, so set aside 1.00 g of the
product to be left drying until the next period for use in the next stage.
Recrystallise the remainder (ca. 0.50 g) from hexane. Add acetone dropwise to the hot hexane
until the solid just dissolves. On cooling crystals will form. Record the mp and IR spectrum of
the product after one recrystallisation. Record an IR spectrum of benzoin for comparison. Make
sure that this step has been successful (IR) before attempting the next stage.
2. Preparation of acetonide derivative (2,2-dimethyl-4,5-diphenyl-1,3-dioxolane)
Dissolve 1.00 g of the diol in 30 mL of pure acetone, and add anhydrous iron (III) chloride (0.30
g). Transfer this reagent rapidly, as it is hygroscopic. Heat the mixture under reflux with a silica
gel guard tube for 20 min, and then allow it to cool to room temperature. Pour the mixture into a
100 mL beaker containing 40 mL water, and add 10 mL potassium carbonate solution.
Transfer the mixture to a 250mL separating funnel and extract with 3 x 20 mL portions of
dichloromethane. Wash the combined organic extracts with 25 mL water, and then dry them
over MgSO4. Evaporate the solvent on the rotary evaporator, and purify the crude acetonide by
dissolving it in 15 mL boiling petroleum (bp 40-60 oC), and filtering whilst hot to then cool the
solution in ice, whereupon the acetonide crystallised out.
Collect the product by suction at the filter pump for 10 min. Record the yield, mp and IR
spectrum of the product. Record the NMR spectrum (CDCl3) of your purified material for
assignment of stereochemistry. Do not delay NMR analysis, as the product slowly decomposes
at room temperature.
Submit a sample of the final product only with the report.
Questions:
1.
Assign your NMR spectrum of the acetonide derivative; including its stereochemistry,
and hence that of the diols. (2 marks)
2.
Give the mechanism and stereochemistry of the reduction of benzoin; propose a
transition state for the reaction which accounts for the stereochemistry. (2 marks)
3.
Give the mechanism of acetonide formation. What is the role of the FeCl3? (2 marks)
7
EXPERIMENT 3
Catalytic Hydrogenation
Have you done the pre-lab?
Catalytic hydrogenation is a valuable method for the reduction of various functional groups and
is used widely in the synthesis and structure elucidation of organic molecules. It involves
agitating the compound to be reduced, in an inert solvent, at or above atmospheric temperature
and pressure, in an atmosphere of hydrogen in the presence of a suitable catalyst. Typical
hydrogenation catalysts are transition metals (e.g. Pt, Pd, Ni) on different inert ‘supports’
(carbon, BaSO4, CaCO3), the nature of the support determining the activity of the catalyst.
Catalytic hydrogenation has the advantages over other comparable types of reduction that it is
simple in practice, often proceeds under mild conditions, and that the products are usually
readily isolated. One of the most important applications of catalytic hydrogenation is in the
reduction of carbon-carbon double bonds and this reaction is illustrated in the present
experiment by the conversion of cinnamic acid (3-phenylpropenoic acid) into hydrocinnamic acid
(3-phenylpropanoic acid).
In the first part of this experiment the cinnamic acid is prepared using the Perkin reaction. This
reaction has been known for many years and is a variation on the aldol reaction.
The second part is the hydrogenation of the cinnamic acid to hydrocinnamic acid:
1. Preparation of Cinnamic Acid.
RISK ASSESSMENT
Substances Used
Benzaldehyde
Acetic anhydride
Potassium carbonate
Hazards Identified
Irritant, flammable
Flammable, causes burns on contact
with skin, harmful by inhalation
Irritant
PROCEDURE
Place benzaldehyde (5.0 mL) and anhydrous potassium carbonate (7.0 g) in a dry 100 mL
round-bottomed flask with a stirrer bar. Then add acetic anhydride (8.2 mL) and fit a condenser
with drying tube. Heat slowly to 180 oC whilst stirring in an oil bath. At approximately 100 oC
foaming should be observed. Allow the mixture to reflux for 90 minutes.
8
Allow the mixture to cool, then add 40 mL of water. Transfer the reaction mixture to a 500 mL
beaker ensuring that no solid material remains in the flask. Add bench sodium hydroxide
solution dropwise until alkaline (test with red litmus). Add 150 mL of diethyl ether to the beaker
and stir rapidly to try and dissolve as much of the solid material as possible.
Transfer the mixture, without any remaining solid material, to a 250 mL separating funnel.
Shake well, then transfer the aqueous layer into a beaker. Acidify with bench concentrated HCl
until acidic with a pH of between 2 to 3 (universal indicator paper). A precipitate of cinnamic
acid will form; remove this using suction filtration. Wash the solid with water then dry the
product in a desiccator overnight. Record the yield, melting point and IR of the dried product.
2. Hydrogenation of Cinnamic Acid.
RISK ASSESSMENT
Substances Used
Cinnamic acid
Ethanol
5% Palladium on charcoal
Hydrogen
Celite
Petrol (bp 60-80oC)
Hazards Identified
Irritant
Highly flammable
Flammable
Extremely flammable
Harmful by inhalation, irritating to eyes
and
respiratory system
Extremely flammable, harmful
Equipment used and Hazards Identified:
Hydrogen cylinder, water pump pressure, danger due to use of highly flammable gas.
First Aid: The nearest first aid workers are in the Technicians area.
Safety Procedures:
Instructions on use of hydrogen cylinder must be followed carefully; if unsure ask a technician,
postgraduate demonstrator or a member of staff for assistance.
Emergency Procedures:
Fire: IF THERE IS A FIRE NEAR THE CYLINDER EVACUATE THE AREA IMMEDIATELY,
SOUND THE ALARM, DO NOT ATTEMPT TO EXTINGUISH THE FIRE.
PROCEDURE
1.
Dissolve cinnamic acid (1.0 g) in ethanol (30 ml), add water (6 ml) and place the
solution, together with a magnetic stirrer bar, in the 100 ml RB reaction flask. This reaction is
very sensitive to any trace contaminants, so you will need to use the specially clean flask and
stirrer bar provided by the technician, which should be returned at the end of the session. Add
5% palladium on charcoal catalyst (0.1 g). Seal the flask with the provided B24 septum. Clamp
the flask above a magnetic stirrer in the fume cupboard.
2.
Remove the plunger from a 5 mL plastic syringe and attach a balloon to the open end.
With the assistance of a demonstrator fill the balloon with hydrogen from the cylinder at the far
end of the laboratory. Place your finger over the end of the syringe to prevent the gas from
escaping.
9
3.
Back at your fume cupboard remove your finger and quickly fit a needle. Push the
needle through the septum and into the flask.
4.
Start the magnetic stirrer and set it to the highest speed. Position the flask slightly to one
side of the stirrer to cause the solution to “splash” whilst stirring. This helps the uptake of the
hydrogen.
5.
Push a second needle into the septum for ten seconds or so to allow the hydrogen to
displace some of the air in the flask.
6.
The balloon will slowly deflate as the hydrogen is taken up. After approximately one hour
the balloon should have deflated by a significant amount. Remove the balloon and allow it to
completely deflate in the fume cupboard. Switch off the stirrer and remove the septum.
7.
Filter off the catalyst through a Buchner funnel in which the filter paper has been covered
with a layer (ca. 5 mm) of Celite. Deposit the layer by filtering an ethanol-Celite slurry.
Evaporate the filtrate on a rotary evaporator until the oily residue of hydrocinnamic acid is clear
and free from droplets of water. Dissolve the oil, while still hot, in light petroleum (bp 60-80oC)
(ca. 2 ml), pour the solution into a conical flask, and allow it to cool. Scratching with a spatula or
glass rod may be necessary to initiate crystallisation of the acid. When crystallisation is
complete, filter off the acid, wash it with a small volume of pentane and allow it to dry in air.
Record the yield, m.p, IR and 1H NMR spectrum of the acid (consult a demonstrator on the
procedure to be used for recording the 1H NMR spectrum). Obtain a sample 1H NMR spectrum
of the starting cinnamic acid from the laboratory technician and compare it to the 1H NMR
spectrum of your product, noting significant differences in absorption. Assign your NMR
spectrum.
Submit a sample of your product with the report.
EXERCISES AND QUESTIONS
1.
Using the proton NMR (available on LEARN) determine if the cinnamic acid produced in
the first step is cis or trans. Justify your decision. (1 mark)
2.
Calculate the theoretical requirement, and the volume, of hydrogen for complete
hydrogenation of your sample of cinnamic acid to hydrocinnamic acid. (1 mark)
3.
Predict the product of the catalytic deuteration of your cinnamic acid, paying particular
attention to its stereochemistry. (1 mark)
4.
What would be the expected product from the reduction of your cinnamic acid with
lithium aluminium hydride? (1 mark)
10
EXPERIMENT 4
Preparation of 7-Trichloromethyl-8-bromo-1-p-menthane by Radical Addition of
Bromotrichloromethane to -Pinene
Have you done the pre-lab?
Free radical additions to alkenes are examples of chain reactions, with each cycle of addition
generating more radical species. Although the reaction should be self-sustaining once initiated,
continuous production of radicals is necessary to maintain the reaction due to quenching
processes taking place, in which two radicals combine and are removed from the reaction
sequence.
Benzoyl peroxide is used in the following experiment as the initiator of the reaction, but radical
species may also be generated conveniently in the laboratory using UV light.
CCl3
CH2
BrCCl3
Me
Me
(PhCO2)2 cat.
Me
Me
Br
RISK ASSESSMENT:
Substances Used
Hazards Identified
-Pinene (FW 136.2)
Flammable, irritant
Bromotrichloromethane (FW 198.3) Toxic, irritant
NOTE: bromotrichloromethane is highly toxic. Always handle in the hood
Benzoyl peroxide (FW 242.2)
Explosive
NOTE: benzoyl peroxide is an oxidising agent and liable to explode if heated or ground
as the dry solid. Handle with extreme caution.
Cyclohexane
Flammable
Methanol
Flammable, toxic
Safety Procedures:
Safety glasses, lab coats and gloves must be worn for all chemical manipulations.
Reaction and work-up must be carried out in a hood. Bromotrichloromethane must be handled
in a hood at all times. Any waste residues should be transferred to the chlorinated solvent
waste, rinsing with dichloromethane if necessary.
Emergency procedures:
Spillage: wear gloves and wipe up with copious amounts of water
Fire:
CO2 extinguisher
Waste Disposal
Waste solvents to bottles in fume hoods.
First Aid: The nearest first aid workers are in the Technicians area.
11
PROCEDURE:
Place the -pinene (1.2 mL = 1.02 g, 7.5 mmol), bromotrichloromethane (0.85 mL, 8.2 mmol)
and benzoyl peroxide (CARE!) (approx. 5 mg, catalytic quantity) in a 100 mL three-necked flask
equipped with a reflux condenser with nitrogen bubbler and a nitrogen inlet. The third neck is
stoppered. Add 30 mL cyclohexane, taking care to wash down all the material that may be
adhering to the walls of the flask. Heat the mixture under a nitrogen atmosphere under reflux for
40 min, taking care not to apply heat above the surface of the liquid.
Add 5 mL of water to the mixture and remove the solvent and excess bromotrichloromethane on
the rotary evaporator in a fume hood. It will be necessary to heat the water bath (ca. 40 oC) to
remove the solvents, if bumping is a problem transfer the mixture to a larger flask using a further
5 mL of water. Cool the aqueous residue in an ice bath until the oil solidifies (ca. 15 min), break
up the solid with a spatula and filter it with suction.
Collect the solid and wash it with 10 mL of water followed by three 5 mL portions of ice-cold
methanol. Dry the residue with suction and record the yield of the crude product. The material is
fairly pure, and should be analysed at this stage by TLC (referencing to the -pinene starting
material) and 1H NMR (CDCl3). Try the TLC in a light petroleum 40/60 : ethyl acetate mixture
and vary the ratio, if required, to get good separation of the product and starting material.
Assign the NMR spectrum.
The product may then be purified further by recrystallisation from methanol (avoid prolonged
heating as this can lead to decomposition). Record a melting-point of your recrystallised
compound.
Submit a sample of your product with the report.
Questions:
1.
Draw out the mechanism which occurs in the radical chain reaction that you have just
carried out. (2 marks)
2.
Explain which structural features of benzoyl peroxide make it a useful means of
generating radicals thermally in the laboratory (1 mark)
3.
Predict the major products (if any) of the following reactions and explain your
reasoning: (4 marks)
12
EXPERIMENT 5
Asymmetric Synthesis:
Sharpless Epoxidation of Geraniol
Have you done the pre-lab?
The term asymmetric synthesis is applied to a reaction which produces two enantiomers or
diasteromers in unequal amounts. Since the reaction of a non-chiral substrate with a non-chiral
reagent must give an optically inactive product [either a meso-compound or an equal mixture of
(+) and (-) enantiomers], it is necessary to have a chiral influence somewhere - either in the
substrate or the reagent. In recent times there has been an active search for new chiral
reagents which can accomplish asymmetric syntheses using a wide variety of substrates with
high degrees of optical purity. One of the most successful has been the chiral epoxidation of
allylic alcohols developed by Professor K.B. Sharpless at M.I.T. The actual oxidising agent is tbutylhydroperoxide (ButOOH), but the reaction is catalysed by a mixture of titanium
tetraisopropoxide [Ti(OiPr)4] and diethyl tartrate. The latter compound is conveniently available
in optically active form, and acts as a chiral catalyst in transferring its asymmetry to the final
product.
OH
OH
HO
Me
Me
CO2Et
Ti(OiPr)4
CO2Et
tBuOOH
Me
+
Me
HO
Me
O
Me
RISK ASSESSMENT
Substances Used
Geraniol
Molecular sieves
Dichloromethane
L-(+)-Diethyl tartrate
Titanium (IV) isopropoxide
t-Butylhydroperoxide
Acetone
Solid CO2
30% Aqueous sodium hydroxide
Sodium chloride
Magnesium sulphate
Hazards Identified
Irritant
Irritant
Possible risk of irreversible effects
Flammable, irritant
Highly flammable, causes burns,
harmful,
possible risk of irreversible effects
Highly flammable
causes burns
Causes burns, harmful
Irritant
Harmful
Equipment used and Hazards Identified:
Assembly of hot apparatus; hazards due to high temperatures; use of solid CO2-acetone bath;
hazards due to low temperatures; addition of harmful materials using syringes.
Safety Procedures:
Procedure must be carried out in a fume hood.
Gloves must be worn when using extremes of temperature and when handling dangerous
materials (titanium isopropoxide, tert-butylhydroperoxide).
Wear safety glasses and a laboratory coat.
13
Emergency Procedures:
Spillage: Wear gloves; if dangerous materials are involved (dichloromethane, tertbutylhydroperoxide) wear suitable protection to guard against inhalation; wipe up using plenty of
water.
Fire: CO2 extinguisher.
First Aid: The nearest first aid workers are in the Technicians area.
Waste Disposal:
Give syringe used for titanium isopropoxide to technician for cleaning immediately after use,
place waste solvents in appropriate bottles in fume hoods.
PROCEDURES
(2S,3S)-EPOXYGERANIOL
The following preparations should be carried out in the laboratory period BEFORE the
experiments:
(a)
Dry, overnight in an oven at 125 °C:
100 ml 3-necked RB flask
Magnetic stirrer bar
Screw cap thermometer holder (glass portion only)
25 ml measuring cylinder
50 ml conical flask
Powdered molecular sieves
(b)
Make sure that the following reagents are available:
dry dichloromethane
solution of t-butylhydroperoxide
(fridge)
First, remove the sieves from the oven and allow to cool in a desiccator. Then assemble
the hot apparatus. To avoid condensation of moisture on apparatus on cooling, do not remove
from the oven too soon before assembly.
Place the magnetic stirrer bar in the flask, and attach a low-temperature thermometer (available
from the technician) in the screw-cap adapter, a nitrogen bubbler (see a demonstrator), and a
rubber septum to the necks, and allow the apparatus to cool down to room temperature under
an atmosphere of nitrogen (be sure to use pressure tubing to connect the nitrogen line). Then
add the powdered molecular sieves (0.28 g) and dry dichloromethane (15 ml) to the flask, start
the magnetic stirrer, and cool the flask in a dry ice-acetone bath to -10°C. Temperature control
is VERY important in this experiment – put the acetone in the bath first and slowly add the dry
ice until the required temperature is reached.
Using plastic syringes, add L-(+)-diethyl tartrate (0.13 ml) and titanium (IV) isopropoxide (0.15
ml) to the flask through the septum, followed by the solution of t-butylhydroperoxide in
dichloromethane (6M, ca 2.5 ml) using a 5 ml plastic syringe. (Plastic syringes can be obtained
from the technician and should be rinsed with ethanol and returned immediately after use).
The mixture is stirred at -10 °C for 10 min and then cooled to -20 °C by the addition of more dry
ice to the acetone bath. Dissolve geraniol (1.54 g) in dry dichloromethane (1 ml) in the 50 ml
conical flask and add this solution dropwise via a syringe to the vigorously stirred mixture, so
that the temperature does not rise above -15 °C. After the addition is complete, the mixture is
stirred for a further 60 min at -15 to -20 °C. It is important to ensure that the temperatures
stated in the procedure are closely adhered to.
14
Next, allow the mixture to warm up to 0 °C, and add water (3ml). Allow the mixture to
warm to room temperature - two phases may be visible - and add a solution of sodium
hydroxide (30%, 0.7 ml) saturated with sodium chloride to hydrolyse the tartrates. Continue to
stir the mixture vigorously for another 10 min. Allow to settle, separate the organic (lower) layer,
and extract the aqueous layer twice with bench dichloromethane (2 x 10 ml).
Dry the combined organic layers (MgSO4) and evaporate the solvent (rotary evaporator).
The crude product is purified by flash chromatography on silica gel. Record a tlc of the product
using ethyl acetate/hexane mixtures as eluent, referenced to geraniol. Vary the eluent until the
product epoxide has an RF of 0.3; this will be the eluent you will use for chromatography. It may
be necessary to try a number of different solvent systems before an acceptable separation is
obtained on the tlc plate. You need to use a permanganate dip to visualise the spots.
Set up the flash chromatography equipment (see video on LEARN or kirsoplabs.co.uk), and
purify the crude epoxygeraniol. Record an NMR spectrum (CDCl3), yield and IR spectrum of the
final product. Analyse the NMR spectrum to assess the purity of the epoxygeraniol. Sample 1H
NMR of the starting geraniol are available for comparison purposes and are fixed to the glass
windows of the staff area.
OPTICAL ROTATION OF (2S,3S)-EPOXYGERANIOL
Optical rotation is a useful method for determining the enantiomeric purity of a compound and
hence allows you to determine the extent to which you have successfully transferred asymmetry
from the diethyl tartrate to the epoxide in the course of this reaction. Record the optical rotation
[]D of your epoxygeraniol using an accurately known concentration of around 0.3 g in
chloroform made up to 10 ml in a volumetric flask.
Calculate the []D according to the following equation:
[]D = 100 x 
lxc
 = measured rotation
l = path length (i.e. length
of cell) in dm
c = concentration in
g/100ml
The optical rotation should be presented in the form []D = 22.4º
(c 4.3 g/100 ml in CHCl3), where you have substituted your values for []D and c.
Do not submit a sample of your product.
EXERCISES AND QUESTIONS
1.
Assign your NMR spectrum and comment on the purity of your product. (4 marks)
2.
Draw the correct stereochemical structure for (2S,3S)-epoxygeraniol. (2 marks)
3.
Suggest a method of making the (2R,3R) isomer. (1 mark)
15
EXPERIMENT 6
A Knoevenagel Initiated Annelation Reaction
Have you done the pre-lab?
The Hagemann ester (1) has been used extensively in recent years as a building block for a
wide variety of important natural products. It is commonly made by allowing ethyl acetoacetate
and formaldehyde to react in the presence of piperidine catalyst followed by dehydration and
partial deethoxycarboxylation with sodium ethoxide in ethanol.
O
O
1. piperidine / EtOH
O
O
O
+
H
H
2. EtOH / EtO-
1
COOEt
The reaction initially involves a Knoevenagel condensation, a subset of the general aldol
condensation. Typically an amine such as piperidine is used as the catalyst in this
condensation rather than hydroxide or ethoxide.
The three stages are summarised below:
The reaction you will perform is similar to the formation of the Hagemann ester with an
additional stereochemical component. It involves the reaction of two moles of methyl
acetoacetate and one mole of acetaldehyde with a piperidine catalyst from which two
stereoisomers are produced, namely, the trans isomer (2) and the cis isomer (3).
O
O
O
O
O
+
1. piperidine
O
H
+
+
H3O
COOMe 2
COOMe
3
It is possible to use the proton NMR spectrum of the mixture of products to identify the two
isomers. The Karplus curve shows the relationship between the coupling constant and the
angle between two adjacent carbon-hydrogen bonds, and the value of J, the coupling constant,
is different for the hydrogen atoms on carbons 4 and 5 in the cis and trans products as the
angle between the two hydrogen atoms will be different.
16
O
1
6
5
O
2
3
6
4
5
COOMe
1
2
3
4
COOMe
The Karplus curve, showing how the coupling constant varies with the dihedral angle:
15
J / Hz
10
5
45
90
Angle / deg
180
In this experiment the proton NMR spectrum clearly shows two different signals for the
hydrogens on carbon 4 for the two isomers.
RISK ASSESSMENT
Substances Used
Acetaldehyde
Methyl acetoacetate
Piperidine
Methanol
Hydrochloric acid
Ether
Hazards Identified
Highly flammable, harmful
Irritating to the eyes
Harmful by ingestion, inhalation or through
skin contact.
Highly flammable, toxic
Causes burns
Volatile, highly flammable
Safety Procedures:
Safety glasses, lab coats and gloves must be worn for all chemical manipulations.
Reaction and work-up must be carried out in a hood.
First Aid: The nearest first aid workers are in the Technicians area.
Emergency procedures:
Spillage: Wear gloves and wipe up with copious amounts of water.
Fire:
CO2 extinguisher
17
Waste Disposal:
Place waste solvents in appropriate bottles in fume hoods.
PROCEDURE
A mixture of 0.88 g (0.02 mol) of acetaldehyde, 4.65 g (0.04 mol) of methyl acetoacetate and
1.7 g (0.02 mol) of piperidine in 25 mL of 50% aqueous methanol is allowed to stand stirring at
room temperature in a 250 mL conical flask covered with parafilm for at least 48 hours. At the
end of this time the reaction 10 mL of 6M hydrochloric acid (fume hood) is slowly and carefully
added. The reaction mixture bubbles at this point.
The solution is then extracted twice with 30 mL portions of ether, Use TLC to confirm that the
reaction has gone to completion, by comparing your product with a sample of methyl
acetoacetate in solvent. In this case a good solvent system to try is 4 parts light petroleum 4060 to 1 part ethyl acetate. If TLC indicates that all or most of the starting material has been
consumed then a flash chromatography column should be used to separate the products from
remaining starting materials. Note the RF values of the product(s) and starting material.
First dry the combined ether extracts over anhydrous magnesium sulfate for 10 minutes. The
solution is then gravity filtered to remove the magnesium sulfate and the ether removed using a
rotary evaporator leaving a yellow oil. Record the weight of the oil for calculating the crude yield
of the reaction.
Then set up the flash chromatography equipment (see video on LEARN or kirsoplabs.co.uk),
and purify the crude product. Record an NMR spectrum (CDCl3), yield and IR spectrum of the
final product. Analyse the NMR spectrum to assess the purity of the product.
Do not submit a sample of your product.
EXERCISES AND QUESTIONS
1. Draw Newman projections for the cis and trans isomers 2 and 3. Use the Karplus
relationship to predict the J coupling constants for the two isomers. (2 marks)
2. You should be able to see two doublets on your NMR between 3 and 3.5 ppm. These
doublets correspond to the hydrogen on carbon 4 on the product. One doublet is for
the trans- isomer, the other for the cis- isomer. Use your answer to question 1 to determine
which doublet corresponds to which isomer, and so work out the ratio of the two isomers in
the products. Label the cis and trans isomers on your NMR. (2 marks)
3. Draw a mechanism for the reaction, including the intermediates. (4 marks)
18
EXPERIMENT 7
Diazotisation of Aminocyclohexanol
Have you done the pre-lab?
This is a two-step synthesis. In the first stage an epoxide used as a precursor to the
amino alcohol. Upon diazotisation the two possible products are shown below. It is not trivial to
isolate the product so in this experiment it is derivatised with Brady’s reagent. Brady’s reagent
contains 2,4 dinitrophenylhydrazine and, as you should remember from the second year lab, it
reacts with aldehydes and ketones to give a precipitate which is easily recovered.
Measurement of the melting point of this derivative and examination of NMR spectra give
evidence for the products.
1.
Preparation of 2-Amino-cyclohexanol
RISK ASSESSMENT
Substances Used
Cyclohexene oxide
Concentrated ammonia soln.
Methanol
2-Aminocyclohexanol
Hazards Identified
Flammable, irritant, harmful by
inhalation.
Corrosive, causes burns, irritant to skin,
eyes and respiratory system
Flammable, harmful by ingestion
Irritant, harmful by ingestion and
inhalation
Equipment used and Hazards Identified:
Standard glassware/equipment used; hazards associated minimal provided good laboratory
practice is observed
Safety Procedures:
Carry out procedure in a fume hood
Wear safety glasses and a laboratory coat
First Aid: The nearest first aid workers are in the Technicians area.
Waste Disposal:
Place any waste solvents in the appropriate labelled bottles in the fume hood
19
PROCEDURE
Place of cyclohexene oxide (10 mL) and of concentrated ammonia solution (25 mL) into a 100
mL round bottomed flask with stirrer bar. Add methanol (25 mL) and stir the mixture at room
temperature for at least 24 hours. Weigh the empty flask before you start.
Remove the water, methanol and remaining ammonia using a rotary evaporator with the water
bath set to at least 60 oC and the pressure set initially to 150 mbar then down to 20 mbar.
Leave it on the evaporator until a viscous clear liquid remains. After removing from the
evaporator and allowing to cool a solid should form. If a solid does not form add ethanol and
then dilute with light petroleum (60 – 80). Poke the mixture with a glass rod and a solid should
result. If in doubt consult a demonstrator.
Record IR, melting point and yield. Check the IR with a demonstrator before moving on to the
next stage.
2. Diazotisation and derivitisation of aminocyclohexyl alcohol
RISK ASSESSMENT
Substances Used
Sodium nitrite
Sulphuric acid
Urea
Brady’s reagent
Glacial acetic acid
Hazards Identified
Toxic by ingestion, irritant, oxidising
agent
Causes severe burns
No significant hazard
Toxic by ingestion, causes burns,
flammable.
Causes severe burns
Equipment used and Hazards Identified:
Use of standard glassware; hazards associated with this are minimal providing good laboratory
practice is used
Heating under reflux; hazards associated with the use of running water and electricity
Safety Procedures:
Carry out in fume hood;
Wear safety glasses and a laboratory coat at all times
Emergency Procedures:
Spillage: Wear gloves, wipe up using plenty of water
Fire: CO2 extinguisher
Waste Disposal:
Place waste solvents in bottles provided in the fume cupboard
First Aid: The nearest first aid workers are in the Technicians area.
20
PROCEDURE
Add 2-aminocyclohexanol (1.2 g) to glacial acetic acid (10 mL) in a 100 mL round
bottomed flask with a stirrer bar and cool in an ice bath. Dissolve sodium nitrite (3.5 g) in water
(10 mL) and add dropwise to the acetic acid / aminocyclohexanol solution whilst stirring in the
ice bath. Brown fumes should be seen. Allow to stir vigorously for 30 mins, the add urea (1.3 g)
and allow to warm to room temperature.
When the foaming has stopped (approx 1 hour) add Brady’s reagent (25 mL). A yellow
precipitate should form. Warm the mixture to 70 oC and keep at this temperature for 10 minutes
Suction filter the mixture and transfer the yellow solid to a conical flask. Add acetone (50 mL) to
the flask. This will dissolve much of the solid and leave a residue of white powder. Remove the
powder from the solution by filtration. Put the orange solution on a rotary evaporator to recover
a bright orange powder.
Record the melting point, yield and an IR spectrum.
Submit a sample of your final product only with the report.
EXERCISES AND QUESTIONS
1.
Consult the 1H NMR spectrum of the aminocyclohexanol (lab or LEARN) and measure
the coupling constants for the protons at H 2.5 and 3.2 ppm. These are the protons
adjacent to the NH and OH respectively. Use these coupling constants to provide
evidence that the that the product is in the conformation shown below:
NH2
OH
This is the trans di-equatorial product. Typical J values are:
Jaxial – axial = 8 to 13 Hz
Jequatorial – equatorial = 2 to 6 Hz
Explain, with a mechanism, how this product is formed.
2.
(4 marks)
Examine the carbon DEPT and 1D NMR of the DNPH derivative (LEARN). Use this
information to determine which product you have obtained after diazotisation. Provide a
mechanism for the formation of the product but no mechanism is needed for the
derivitisation step.
(4 marks)
HN
NH2
NO2
2,4 dinitrophenylhydrazine
(DNPH)
NO2
21
EXPERIMENT 8
The Sharpless Asymmetric Dihydroxylation of Stilbene
Have you done the pre-lab?
The cis-dihydroxylation of an olefin with osmium tetroxide is a racemic reaction, but if the same
reaction is carried out in the presence of a chiral catalyst the production of one enantiomer can
be favoured over the other. Such catalysts have been developed in the laboratories of Nobel
Laureate Professor K. Barry Sharpless at MIT in the USA. In this experiment the Sharpless
asymmetric dihydroxylation (abbreviated to AD) uses the enantiomerically pure chiral ligand
(DHQD)2PHAL (1) which is derived from the natural product quinine; DHQD stands for
dihydroquinidine (2) and PHAL which is an abbreviation for phthalazine (3).
Et
N
O
H
Et
N N
N
O
H
MeO
N
N
N N
OH
H
OMe
MeO
Et
N
N
1
2
3
The catalyst is available as part of a commercially available mixture which contains the
necessary osmium, the chiral ligand and potassium ferricyanide as a co-oxidant, to re-oxidise
the osmium after each catalytic cycle. The catalyst with the ligand shown above is sold as ADmix Dihydroxylation of the other face of an olefin can be performed using AD-mix  which
uses a different chiral ligand. This is discussed in detail in the asymmetric synthesis lectures.
In this experiment the dihydroxylation reaction is to be carried out using trans-stilbene as the
olefin. Determination of the enantiopurity of the product, 1,2 diphenyl-ethane 1,2 diol, will be by
measurement of optical rotation using a polarimiter.
H
Ph
Ph
AD-mix 
H
OH
Ph
H
22
OH
Ph
H
RISK ASSESSMENT
Substances Used
AD-mix 
trans-Stilbene
tert-Butanol
Sodium sulfite
Ethyl acetate
Hazards Identified
Hygroscopic, toxic
Irritating to the eyes
Flammable
Irritant
Highly flammable
Safety Procedures:
Safety glasses, lab coats and gloves must be worn for all chemical manipulations.
Reaction and work-up must be carried out in a hood.
Emergency procedures:
Spillage: Wear gloves and wipe up with copious amounts of water.
Fire:
CO2 extinguisher
First Aid: The nearest first aid workers are in the Technicians area.
Waste Disposal:
Place waste solvents in appropriate bottles in fume hoods.
PROCEDURE
5 mL of tert-butanol, 5mL of water and 1.4 g of AD-mix ** are added to a 50 mL round bottom
flask. It is capped with a septum and put under a nitrogen atmosphere using a balloon. The
mixture is cooled to 0O C in an ice-water bath and 0.18 g (1mmol) of trans-stilbene is added.
The reaction is left to stir for at least 24 hours.
Sodium sulfite (1.5 g) is then added and the mixture is stirred for 40 min at room temperature.
The mixture is extracted 4 times with ethyl acetate (10 mL the first time, then 3 × 5 mL). The
combined organic extracts are dried over MgSO4 and the solvent removed using a rotary
evaporator to give the diol.
** NOTE: 1.4 g of AD–mix  is composed of 0.980 g of K3Fe(CN)6, 0.410 g of K2CO3, 0.0078 g
of (DHQD)2PHAL and 0.00074 g of K2OsO2(OH)4. In your report show the relative ratios of
these ingredients.
Using thin-layer chromatography to check that the reaction has gone to completion by running a
sample of the product against stilbene (both need to be in solvent for this). A good solvent for
running the TLC for these compounds is light petroleum 40-60. If the TLC of your product
shows the product to be impure you will need to perform flash-column chromatography to purify
the products. Note the quantity of product and calculate the yield. Submit a sample for 1H NMR
analysis. Run an IR spectrum and obtain the melting point.
23
OPTICAL ROTATION
Optical rotation is a useful method for determining the enantiomeric purity of a compound and
hence allows you to determine the extent to which you have successfully transferred asymmetry
from the chiral catalyst to the product in the course of this reaction. Record the optical rotation
[]D of your 1,2 diphenyl-ethane 1,2 diol, using an accurately known amount of your product in
ethanol made up to 10 ml in a volumetric flask.
Calculate the []D according to the following equation:
[]D = 100 x 
lxc
 = measured rotation
l = path length (i.e. length
of cell) in dm
c = concentration in
g/100ml
The optical rotation should be presented in the form []D = xx.xº
(c x.xx g/100 ml in CHCl3), where you have substituted your values for []D and c.
Do not submit a sample of your product.
Questions
1.
Find the literature value for the optical rotation of your product. Does this agree with
your observed value? If not, can you think of any reasons for the discrepancy. State
where you found your literature value. (4 marks)
2.
Draw the correct stereochemical structure for your 1,2 diphenyl-ethane 1,2, diol, stating
if the chiral centres are R or S. (2 marks)
3.
Assign the NMR and IR spectra of your product and comment on purity (2 marks)
24
EXPERIMENT 9
Heterocyclic Ring Expansion – Reaction of a Dimethylpyrrole with
Dichlorocarbene.
Have you done the pre-lab?
Carbenes are a very reactive species, and a typical reaction of a carbene is to insert itself into a
pi or sigma bond. This is driven by the extreme electrophilicity of the carbene – a carbon atom
with only six electrons will do almost anything to get another two. Carbenes will undergo
insertion into cyclic compounds and this can be used to increase the number of carbon atoms in
the ring; this is known as a ring expansion and an example is shown below:
EtOOC
N
N
COOEt
heat
This is a very useful reaction as it is an example of forming carbon-carbon bonds as well as
enabling the formation of rings that would be difficult to synthesise by any other means. In this
experiment a carbene is generated from sodium trichloroacetate and reacted with a five
membered heterocycle, 2, 5 dimethylpyrrole, to give a six membered heterocycle. Heterocycles
are a very important class of organic compounds, particularly in biological systems, and their
synthesis is very important in the drug industry.
The starting material for this ring expansion, 2,5-dimethylpyrrole, is a reactive compound and
has a short shelf-life. Fortunately synthesis is quite straightforward from inexpensive starting
materials. Here it is synthesised it from 2,5-hexanedione (acetonylacetone):
Me
Me
O O
(NH4)2CO3
Me
H
N
Me
heat
The 2,5-dimethylpyrrole is isolated by distillation and can be stored for up to few days in the
refrigerator in readiness for the expansion reaction, shown overleaf.
25
RISK ASSESSMENT
Substances Used
Acetonylacetone
Ammonium carbonate
Sodium trichloroacetate
1,2-Dimethoxyethane
Dilute Hydrochloric acid
Diethyl ether
Sodium hydroxide
Hazards Identified
Irritating to the eyes, do not inhale vapour
Eye, skin and respiratory irritant. May be
Harmful if inhaled
Irritant
Toxic, flammable
Causes burns
Extremely flammable, may form
explosive peroxides
Causes burns
Safety Procedures:
Safety glasses, lab coats and gloves must be worn for all chemical manipulations.
Reaction and work-up must be carried out in a hood.
Emergency procedures:
Spillage: Wear gloves and wipe up with copious amounts of water.
Fire:
CO2 extinguisher
First Aid: The nearest first aid workers are in the Technicians area.
Waste Disposal:
Place waste solvents in appropriate bottles in fume hoods.
1. Preparation of 2,5-dimethylpyrrole
Place ammonium carbonate (10 g) and acetonylacetone (5 g) in a 100 mL B24 round bottom
flask. Fit a B24 water jacket condenser and reflux gently for one hour in an oil bath at 115 OC.
After this time all the solid material should have disappeared.
Transfer the oil formed to a 50 mL round bottom flask and distil at a reduced pressure of max
25 mbar. If the fume cupboard pump will not go down this low consult a demonstrator. The
dimethylpyrrole should distil at a temperature of approx 75 OC at 25mbar, but will be lower at
lower pressure. Make a note of the exact temperature and pressure used in your distillation and
include this in your report. The distillate should be a clear oil. Take an IR spectrum of the oil
and then transfer it in a labelled stoppered flask into the refrigerator until you are ready to use it
in the next stage. Confirm with a demonstrator that your IR spectrum is the target compound
before proceeding with the next step.
26
2. Preparation of 3-chloro-2,6-dimethylpyridine
Sodium trichloroacetate ( 11.0 g, 0.06 mol) and dimethoxyethane (25 mL) are added to a 100
mL round bottom flask, along with a magnetic stirrer follower bar. A reflux condenser and
nitrogen bubbler are fitted and the apparatus is flushed through with nitrogen. The condenser is
briefly removed and 2,5-dimethylpyrrole (1.9 g, 0.02 mol) added. This addition should be done
as quickly as possible to minimise contact with the atmosphere.
The reaction mixture is refluxed gently in an oil bath at around 100 OC, whilst stirring, for 3 to 4
hours. This is best done by setting up the reaction and starting the reflux in a morning session
and leaving the reaction refluxing over lunch. If you are not returning for the afternoon session
you should notify a demonstrator or staff member so that they can have the stirrer hotplate
switched off at the appropriate time and you can move onto the next stage at your next session.
The reaction mixture should be a dark brown colour at this stage. Using thin layer
chromatography, in a 4:1 mixture of light petroleum to ethyl acetate, run a spot of the reaction
mixture against a solution of 2,5-dimethylpyrrole to confirm that all the starting material has
been consumed. Note the RF values and record them in your report.
Remove any solid material using suction filtration and transfer the filtrate to a 250 mL round
bottom flask. Remove the volatile components of the mixture on a rotary evaporator. After
cooling add 20 mL of dilute hydrochloric acid, shake well and then thoroughly extract the
mixture with diethyl ether (3 × 30 mL). Discard the ethereal extract.
Add sufficient bench (2 molar) sodium hydroxide solution to the aqueous component of the
above procedure to make the pH alkaline, using red litmus or universal indicator paper to
monitor this. Once again extract the mixture with diethyl ether (3 × 30 mL). Combine the
ethereal extracts and dry them over magnesium sulfate. Remove the magnesium sulfate using
filtration, and then remove the diethyl ether on a rotary evaporator. You should be left with a
quantity of yellow oil. Note the yield. Record an IR spectrum and submit a sample for 1H NMR
spectroscopy. Assign your NMR spectrum
Do not submit a sample of your product.
Special note on washing glassware for this experiment.
The second part of this experiment produces a brown residue that can be tricky to remove from
your glassware. The best way to do this is by using lots of the green washing up liquid and
plenty of hot water along with a brush. The washing-up liquid is stored in a large glass bottle on
the sink near the window.
Questions
1. Draw the mechanisms for both parts of the experiment. (4 marks)
2. Deduce the product you would obtain on using 2,3-dimethyl indole (below) rather than the
pyrrole in part 2. (1 mark)
Me
Me
N
27
EXPERIMENT 10
Synthesis of 6-Methylquinoline
Have you done the pre-lab?
This experiment benefits from being run over two laboratory sessions on the
same day.
Quinoline 1 was first isolated from coal tar in 1834 and its name is derived from quinine, which
is extracted from quina, the South American name for the bark of quinine containing cinchona
species. Substituted quinolines have interesting biological properties, quinoline motif is present
in several therapeutical compounds i.e. quinidine. The well known Skraup synthesis of
quinoline from aniline and glycerol is shown in Scheme 1.
Substituted anilines can be employed in the Skraup synthesis to give substituted quinolines; for
instance methyl anilines produce methylquinolines with a methyl substituent in the benzene ring
of quinoline.
In this experiment you will carry out a Skraup synthesis of a substituted quinoline. It is a wellknown method for synthesizing simple heterocyclic compounds in one pot.
RISK ASSESSMENT:
Substances Used
Hazards Identified
4-Toluidine
Glycerol
Iodine
Acetic Anhydride
Celite
Conc. Sulfuric acid
5 M Sodium Hydroxide
Diethyl Ether
1 M Hydrochloric Acid
Ethyl Acetate
Toxic
Irritating to eyes
Harmful, don’t inhale vapour
Flammable, causes burns
Irritating to eyes and lungs
Corrosive, causes severe burns
Corrosive, causes burns
Extremely flammable, may form explosive
Corrosive
Highly flammable, irritant
Safety Procedures:
Safety glasses, lab coats and gloves must be worn for all chemical manipulations.
Reaction and work-up must be carried out in a fume hood.
Emergency procedures:
Spillage: Wipe up wearing gloves.
Fire:
CO2 extinguisher
First Aid: The nearest first aid workers are in the Technicians area.
28
Waste Disposal
Place waste solvents in bottles provided in the fume hood.
PROCEDURES
Add 4-toluidine (750 mg, 5.8 mmol), glycerol (2 mL, 27 mmol) and iodine (3-4 crystals) to a 25
mL round bottomed flask containing a stirrer bar. Attach a reflux condenser and cool the
mixture in an ice bath, with stirring, before adding concentrated sulfuric acid (2 mL) dropwise.
The resulting mixture is heated to 100-110 °C in an oil bath, stirring for 1 hour.
Allow the reaction mixture to cool and then add ice water (10 mL). Transfer the reaction mixture
to a 100 mL conical flask and cool it in an ice bath. Wash the reaction vessel with ice water (5
mL), add the washings to the cold conical flask and make the reaction mixture basic with 5 M
sodium hydroxide. Add ether (25 mL) to the flask and vacuum filter the biphasic mixture with
the aid of a Celite pad. Wash the conical flask with ether (2 x 20 mL) and pour the organic
solution through the filter pad. Separate the biphasic filtrate using a separating funnel, wash the
aqueous layer with ether (20 mL) and then combine all the organic fractions.
Using TLC analysis (ethyl acetate/pet. ether 60-80 (1:4) of the ethereal solution, check for the
presence of any starting materials.
Dry the ethereal solution over magnesium sulphate, filter under suction and concentrate on the
rotary evaporator. Add acetic anhydride (1 mL) and leave the resulting solution to react for 30
minutes. Add 1 M hydrochloric acid (20 mL) dropwise and stir for a further 10 minutes.
Transfer the solution to a separating funnel and wash the reaction flask with ethyl acetate (20
mL), before adding the solvent to the separating funnel. Separate the two layers, wash the
aqueous layer with more ethyl acetate (20 mL) and neutralise the aqueous layer with 2 M
NaOH. Finally, extract the aqueous solution with ether (2 X 20 mL) and keep the ethereal
solution. Dry the ethereal solution over magnesium sulphate, filter under suction.
Fill a small sinter funnel with an ethereal silica gel slurry. Carefully pour the ethereal solution of
the product onto the silica and apply suction until level of liquid is just above the top of the silica.
Add more ether (20 mL) to the top of the silica and pass it through the filter using suction. Pour
the filtrate into a pre-weighed RBF and then concentrate it to give the product.
Record the yield and IR. Submit a sample for 1H NMR spectroscopy.
Do not submit a sample of your product.
Questions:
1.
Assign 1H and 13C NMR spectra of the 6-methylquinoline (LEARN). You are advised to
refer to cosy spectrum of 6-methylquinoline (LEARN) for correct analysis. (4 marks)
2.
Compare your 1H NMR spectrum with the reference spectrum (LEARN). Comment on
the purity of your product. (4 marks)
3.
Give the mechanism for the Skraup synthesis of 6-methylquinoline. (2 marks)
4.
What is the acetic anhydride for? How does it aid in the purification of the product? (2
marks)
29
EXPERIMENT 11
A Diels- Alder Reaction
Have you done the pre-lab?
The Diels-Alder reaction is a cycloaddition of an electron rich diene and an electron poor
dienophile (alkene or alkyne). In this experiment, diene is 1,3-cyclohexadiene, which is locked
in its “s-cis” conformation. The dienophile is N-phenylmaleimide which possesses a strong
electron withdrawing carboximido group also held in a cis geometry.
RISK ASSESSMENT
Substances Used
1,3-Cyclohexadiene
N-Phenylmaleimide
Ethanol
Hazards Identified
Flammable
Toxic, irritant
Flammable, irritant
Equipment used and Hazards Identified:
Microwave oven, the biggest concern is the proper assembly of the microwave reaction vials.
Students need to assemble the microwave reaction vials with extreme care specifically the final
tightening of the cap on the reaction vials before these are placed into the slots.
Standard glassware/equipment used; hazards associated minimal provided good laboratory
practice is observed.
Safety Procedures:
Carry out procedure in a fume hood.
Wear safety glasses and a laboratory coat.
Waste Disposal:
Place any waste solvents in the appropriate labelled bottles in the fume hood.
First Aid: The nearest first aid workers are in the Technicians area.
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PROCEDURES
1.
Synthesis of endo-N-phenylbicyclo[2.2.2]-oct-5-ene-2R, 3S-dicarboximide (a
Diels-Alder adduct) using microwave oven
Ask demonstrator about the use of microwave and related equipment i.e microwave reaction
vials, caps and magnetic stirrers (microwave magnetic stirrers are different than the normal
magnetic stirrers)
Weigh N-phenylmaleimide (0.20 g) directly into the microwave vial (2-5 mL vial). Add 1,3cyclohexadiene (0.12 mL) to the vial. Add absolute ethanol (5 mL) and the magnetic stirrer,
swirl the vial to dissolve the N-phenylmaleimide. Complete the assembly for microwave heating
At this stage ask a demonstrator to check it. Place your sealed vial into a slot on the
turntable (record your slot number).
Microwave reaction parameters are as follow;
Time: 10 minutes
Temperature: 130 °C
Prestirring: 2 minutes
Absorption: High
Vial type: 2-5 mL
At the end of the heating period, recover you vial and vent it in your fume hood, then cool the
reaction mixture first to RT and then place the vial in an ice bath. Suction filter the crystals,
wash them with chilled ethanol (3 mL). Place the sample in the desiccator for 1 h.
Determine the yield, melting point of the product.
Record IR of you sample. Submit a sample for 1H, 13C NMR spectroscopy.
2.
Synthesis of endo-N-phenylbicyclo[2.2.2]-oct-5-ene-2R, 3S-dicarboximide (a
Diels-Alder adduct) using traditional chemistry
Weigh N-phenylmaleimide (0.20 g) directly into the 10 mL RBF. Add ethanol (5 mL) and a
stirbar. Swirl to dissolve the maleimide. Add 1,3-cyclohexadiene (0.12 mL) to the reaction
mixture and gently swirl. Complete a reflux set-up and heat for 1.5 hours. The product will
precipitate out of solution as a white solid.
At the end of the reflux period, cool the reaction mixture first to RT and then in an ice bath.
Suction filter the crystals and wash them with chilled ethanol (3 mL). Place the sample in the
desiccator for 1 h.
Determine the yield, melting point of the product.
Record IR of you sample. Submit a sample for 1H NMR spectroscopy.
Do not submit a sample of your product.
Questions
1. Draw the mechanism for Diels-Alder cycloaddition reaction to afford endo-Nphenylbicyclo[2.2.2]-oct-5-ene-2R, 3S-dicarboximide. (2 marks)
2. Assign 1H and 13C spectra of the endo-N-phenylbicyclo[2.2.2]-oct-5-ene-2R, 3Sdicarboximide. (4 marks)
31
THE IDENTIFICATION OF UNKNOWN ORGANIC COMPOUNDS
In this exercise you have been assigned two unknown compounds to identify on the basis of
their spectra. Check the laboratory notice board to find your allocated unknowns. All the
spectra are on the PCs in the instrument room. There is a card for each compound which are in
boxes in the instrument room. The cards have elemental analysis data, some notes and the
DEPT spectra, but all this information is also loaded onto the computers. The reports for the
two unknowns is completed by filling in the form available on LEARN.
To access the spectra go to Computer, select C(OS) and open the folder “Unknowns”, then
“Third Year Unknowns”. Open the folder for your compound and you can view the infra red,
mass spec and DEPT NMR spectra. The FID’s are also here, for use in the ACD/NMR
program.
The first job is to find the molecular formula. Use the elemental analysis data to find the
empirical formula. How to do this is described on the report sheet.
You can use the molecular formula to find out more about the compound by calculating the
number of “double bond equivalents”.
For CaHbOc
dbe = [(2a + 2) – b]/2
For CaHbOcNd
dbe = [(2a + 2) – (b – d)]/2
Halogens count as hydrogen for this purpose and you will see that the number of oxygen atoms
is immaterial. The dbe value is the sum of the number of multiple bonds of all kinds (C=C, CC,
C=O, C=N, CN, N=O, etc) and rings (each ring counts as 1 dbe) in the molecule, and must
always have an integral value. Note that for triple bonds the dbe = 2, and that for an aromatic
ring the dbe = 4 (3 double bonds and one ring). Obviously, if you can identify securely by
spectroscopic or other means the number of multiply bonded functional groups, e.g. carbonyl,
present, the remainder will be rings. It is therefore possible to decide if the compound is acyclic,
monocyclic, bicyclic, etc. and this is extremely helpful in determining a structure.
Example Calculation of dbe:
for C4H8O2 a = 4, b = 8, c = 2; dbe = [(2 x 4 + 2) - 8]/2 = 1
for C4H6NCl a = 4, b = 7 (6H + 1Cl), c = 0, d = 1; dbe = [(2 x 4 + 2) - (7 - 1)]/2 = 2
The 1H and 13C NMR spectrum of each compound has been recorded and should be processed
using the ACD/NMR software available on the lab computers (see below). The spectra have
been run at 250 MHz for proton, and 62.5MHz for carbon. Enough information is provided for
complete identification.
Remember that there will be a signal in the carbon NMR due to the deuterated solvent.
CDCl3 appears as three peaks at around 77 ppm, so ignore these.
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1. OPENING A FILE using ACDLABS NMR processor (on lab PC’s )
Go to File > Import > From 1D NMR Directory. In the ‘Look in’ box go to Computer > C(OS) >
unknowns > chem3 and locate in this folder the folder bearing the allocated spectra number.
Open this folder and click on ‘fid’. Go to the bottom of the box and click ‘Open’. The FID will now
appear in the window of the program.
If the program has just been opened there may be a window on the program starting up asking
to open an existing file or create a new one. If this dialog box does appear click ‘Cancel’ and
continue as above.
2. OBTAINING THE NMR SPECTRA FROM THE FID (Preforming a Fourier Transform)
Go to ‘Process’ and then to ‘Fourier Transform’ and finally click on ‘Default Transform’. The
‘Default Transform’ function provides the most appropriate Fourier transform for the input data.
A recognisable NMR spectrum should now have appeared in the window, replacing the FID.
Now click on the ‘Phase’ button that lies on the third from the top command line and click on
‘Auto Simple’ then the green tick to correct the phase of the NMR spectra.
3. ANALYSING THE SPECTRA
 To zoom into areas of interest:
Click on the image of a magnifying glass with a + in the middle of it and a double headed
arrow above it on the second from the top command line. Now click the mouse at one
side of the area of interest and drag the magnifying glass to the other side of this area,
then release.
 To zoom out:
To zoom out and show the whole spectrum, click on the image of a magnifying glass
with a – in the middle of it. However, to undo a zoom, click on the magnifying glass with
a green arrow on it.
 To obtain the chemical shift of the peaks – listing the peaks:
Click on the ‘Peak Picking’ button that can be found on the same command line as
‘Phase’ and then on ‘Auto’. There should now be numbers above each peak indicating
their chemical shift in ppm. It may be helpful to zoom into areas with the peaks to make
sure that all of the peaks have their chemical shift denoted. If the ‘Auto’ function has
missed some peaks out, these can be picked out manually by clicking on ‘Peak by Peak’
and then on the individual peaks in the spectra. If no numbers appear above the peaks
in the spectra or to check that all of the peaks have been listed, then click on the image
of an NMR spectrum with a box above it that can be found on the same command line
as the zooming functions. Once all of the peaks have their chemical shift denoted click
on the green tick.
 To view the peak list:
Click on the image of a table with a small NMR spectrum in front of it that can be located
on the same command line as the zooming functions. A small dialog box will then open
which will show the number of peak and the chemical shift in ppm and Hz. This box can
be closed as it is included with the spectrum when it is printed.
 To integrate the spectrum:
Click on ‘Integrate’ and then on ‘Manual’. Now click on one side of a singlet or multiplet
and drag the cursor to the other side of the singlet or multiplet, then release. Do this for
each singlet/multiplet in the spectra. Once all peaks have been integrated, click on the
green tick.
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4. PRINTING THE SPECTRUM AND PEAK LIST
It is often helpful to zoom into the area of interest if all peaks lie in one portion of the spectrum
before printing as this can make analysing the printed off spectrum much easier. If the peaks in
the spectrum are such that they lie quite far apart from each other, then zooming in is not
particularly useful. Once zoomed into the area of interest if this is applicable, go to File > Print >
Standard.
On the window that opens make sure that under the ‘Spectrum’ tab the following are ticked:
1. ‘Always Landscape Orientation’
2. Units: ppm
3. Display mode: Normalised Intensity
4. Spectrum Region: Zoomed Region (or for whole spectrum NMR, select ‘Whole
Spectrum’ instead)
Under the ‘Tables’ tab, make sure that the Table of peaks as well as the corresponding ppm
AND Hz are ticked but leave ALL other options un-ticked.
Under the ‘View’ tab, makes sure that only the following are ticked:
1. Integrals
2. Horizontal and Vertical Scale as well as the Vertical Scale Factor
Under the ‘Text’ Tab, tick the option for ‘Page Title’ and give the spectrum and meaningful title.
The option for ‘Current Date’ may also be helpful.
Click on the ‘OK’ button to print the spectrum off and close the programme by clicking File > Exit
and do not save the transformed spectrum.
Having obtained 1H and 13C NMR spectra of your three unknowns, in each case record your
results on the data sheets provided. First look at the IR spectrum to see if you can pick out
functional groups (OH, C=O, etc). Then consider the NMR spectra, molecular formula, mass
spec and double bond equivalents. Information on interpretation of NMR, DEPT, Mass and IR
spectroscopy are given on LEARN.
Use the information to identify the unknown compound. Ensure that you describe fully the
logical deduction processes needed to identify the compound. The majority of the marks are
for the correct interpretation of the spectra, and not for just identifying the compound.
Doing this from home
You can, if you wish, do this exercise from home. You will need a USB flash memory stick to
transfer the files from the lab computers. The folders with each unknown are in C:OS
>unknowns > third year unknowns. Copy across the folders with your unknowns. The folders
contain the information on the cards in the lab as well as NMR and mass spec data.
You will also need to download and install the ACD software which is free for students. Go to:
http://www.acdlabs.com/resources/freeware/
and follow the instructions to set up the NMR processor on your PC.
MARKS for each unknown
Molecular formula / dbe
Proton NMR interpretation
Carbon / DEPT NMR interpretation
IR interpretation
Mass spec. interpretation
Structure
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2
5
5
1
4
3