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Unit 14 Learning Aim D – Investigate organic chemistry reactions in order to gain skills in

preparative organic chemistry.

Practical 1 – Preparation of a non-carbonyl compound: 1-bromobutane from butan-1-ol

Aim & Introduction

The purpose of this experiment is to prepare 1-bromobutane from butan-1-ol via a substitution reaction.

You will also familiarise yourself with several practical techniques employed in organic chemistry.

Butan-1-ol reacts with hydrobromic acid (HBr) when heated to form 1-bromobutane and water. The HBr

in this experiment shall be made during the reaction, when KBr reacts with concentrated sulphuric acid. In

this experiment, you shall be using a reflux set-up to react the butan-1-ol with hydrobromic acid, followed

by a distillation set-up to separate the product. The 1-bromobutane shall then be further purified with an

aqueous wash using a separating funnel.

Safety assessment

Hazard I understand this!

Butan-1-ol and 1-bromobutane are flammable and may give off harmful vapours. Keep

stoppers on bottles and away from naked flames.

Potassium bromide is an irritant in case of skin and eye contact. In case of eye contact,

flush eyes with plenty of cold water for 15 minutes.

Concentrated sulphuric acid is extremely corrosive and reacts vigorously with water.

Handle with care. If it comes into contact with skin, wipe it off with a dry paper towel

then wash the area with cold water. Clean up spillages immediately with sodium

carbonate solid and a dry paper towel.

All liquids must be disposed of in the labelled waste bottle and not down the sink.

As we shall be using a Bunsen burner, long hair must be tied back.

You must be stood up during the practical. Bags and coats should be placed at the front

of the classroom and stools tucked under the desks.

You must wear safety glasses and lab coats throughout the practical.

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Method

PART 1 – reaction of butan-1-ol with HBr under reflux.

1. Weigh 14 g of potassium bromide (KBr) using a weighing boat and a top pan balance. Place the KBr

into a 100 cm3 flat bottom flask. To this, add 12 cm3 of distilled water.

2. Pour ~10 cm3 of butan-1-ol into a clean, dry measuring cylinder. Weigh this measuring cylinder

containing the butan-1-ol and pour the butan-1-ol into the flat bottom flask containing the potassium

bromide. Re-weigh the empty measuring cylinder. Record the weights below.

Mass of measuring cylinder containing butan-1-ol (g)

Mass of empty measuring cylinder (g)

Mass of butan-1-ol used (g)

3. Measure out 10 cm3 of concentrated sulphuric acid into a clean dry measuring cylinder. Put this on a

white plastic tray with the flat bottom flask before carrying out the next step.

4. Slowly add to the flask, over the tray, the concentrated sulphuric, a small amount at a time using a

pipette. This may take a few minutes, be patient! Swirl the flask between additions and cool under

running water if necessary. Take care not to spill any acid and ensure that any spillages are cleaned

up immediately.

5. Add a few anti-bumping granules to the flask and set it up for reflux as shown in the diagram below.

You must have your apparatus checked for leakages before proceeding to the next step.

6. Once the apparatus has been setup for reflux and checked by a teacher, heat the flask using a Bunsen

burner for ~20 minutes. After 20 minutes, switch off the Bunsen burner and allow the glassware to cool

for ~5 minutes.

Water out

Condenser

Water in Flask is clamped to a stand

Flat bottom flask containing ~10 cm3

butan-1-ol, ~14 g KBr, ~10 cm3 H2SO4

and anti-bumping granules. Grease the

joint. Bunsen burner on a heat proof mat,

with a tripod and gauze.

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PART 2 – distillation of 1-bromobutane.

7. Once the glassware has cooled, carefully rearrange the apparatus for distillation as shown in the diagram

below. Have your apparatus checked before proceeding to the next step.

8. Warm the flask gently allowing the organic liquid to distil over. You should be able to collect ~12 cm3

of liquid distillate in a small beaker. Record the boiling point below.

Boiling point of 1-bromobutane (0C)

PART 3 – further purification of 1-bromobutane

9. Pour the distillate (using a funnel) into a separating funnel that is clamped to a stand (ensure that the tap

is closed). Add in twice the volume of water, stopper the separating funnel, remove from the clamp and

shake the mixture. Re-clamp the separating funnel, allow the two layers to separate and discard the aqueous

layer. (Which layer contains the 1-bromobutane? Hint - density of 1-bromobutane = 1.27 g cm-3).

10. To the 1-bromobutane in the separating funnel, add an equal volume of sodium hydrogen carbonate

portion wise to neutralise any excess sulphuric acid. Shake the funnel carefully, releasing the pressure

of carbon dioxide frequently by loosening the stopper. Care needs to be taken here as solution may

squirt out of the separating funnel, so wash carefully over a sink, not pointing the funnel at class

mates. Allow the layers to separate and discard the aqueous layer (you should repeat this process if carbon

dioxide is still being produced).

11. Run off the organic layer into a small dry flat bottom flask. Add a chunk of anhydrous calcium chloride

to dry the organic liquid. Stopper and swirl the flask occasionally for 5 minutes. Alternatively, leave in

the fume-hood to dry overnight.

12. Carefully pour off the dried organic liquid from the solid calcium chloride into a clean, dry sample tube

which has previously been weighed.

Thermometer

Thermometer pocket

Clamped condenser

Still head

Clamped flat bottom flask from the

reflux step. Water in

Water out Delivery tube held in

place with a green clip Bunsen burner on a heat proof mat,

with a tripod and gauze.

Small beaker to collect

the 1-bromobutane

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Mass of empty sample tube (g)

Mass of sample tube + 1-bromobutane (g)

Mass of 1-bromobutane obtained (g)

Q1 [PASS]. Identify the reactants, products and functional groups involved. Include a balanced

equation for the reaction.

Q2 [PASS]. Draw the reaction mechanism

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Q3 [MERIT]. Identify the reagents used and why. Can these be changed?

Q4 [MERIT]. Identify the temperature chosen and why. Could these be changed?

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Q5 [DISTINCTION]. Calculate the percentage yield of 1-bromobutane made.

Q6 [DISTINCTION]. Find the actual boiling point of 1-bromobutane – how does it compare to

your value and how pure do you think your product is? How else could you check the purity of

product made? Strengths and weaknesses of reaction conditions chosen? Improvements

recommended? Comment on yield.

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Practical 2 – Preparation of a carbonyl compound: the oxidation of ethanol to ethanal

Aim & Introduction

Ethanol is a primary alcohol and can be oxidised to either an aldehyde or a carboxylic acid: Ethanol to ethanal CH3CH2OH + [O] CH3CHO + H2O (equation 1) Ethanol to ethanoic aid CH3CH2OH + 2[O] CH3COOH + H2O (equation 2) The purpose of this experiment is to oxidise ethanol to ethanal (equation 1) and then to test the product to determine whether it has been oxidised to ethanal or oxidised to ethanoic acid.

Safety assessment

Sodium dichromate is toxic & corrosive. Avoid skin contact, use gloves when handling the solid.

Concentrated sulphuric acid is corrosive. Wipe any spillages off your skin with a dry paper towel

then wash with water. Clean up spillages immediately.

Ethanol is flammable. Avoid skin contact. Keep away from naked flames. Keep in fume-

cupboard when not in use.

Ethanal is flammable & harmful. Avoid skin contact. Keep away from naked flames, drain fumes

to down the sink during preparation. Dispose of into waste bottle not down the sink.

Method

To 6 cm3 of water in the pear-shaped flask, add 2 cm3 of concentrated sulphuric acid, and set up the apparatus as shown below, but with a stopper in place of the dropping funnel. Ensure that all of the glass joints are greased.

5 g Na2Cr2O7 in 5 cm3 of

water and 4 cm3 of ethanol

6 cm3 of water and 2 cm

3 of

concentrated H2SO4

ice/water mixture

water out

water in

Make up a solution containing 5 g of sodium dichromate in 5 cm3 of water, add 4 cm3 of ethanol and

pour the mixture into the dropping funnel. Warm the acid in the pear shaped flask until it is almost boiling and turn off the bunsen burner. Carefully remove the stopper and put the dropping funnel in position, as shown in the diagram. Add the mixture containing the ethanol at such a rate as to maintain the boiling of the mixture in the

pear shaped flask. Collect the distillate and record the appearance and weight in the space below.

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Carry out the following three tests on the distillate and record your observations.

Test 1. Test for the presence of a carbonyl group to find out whether ethanal had been formed. Put approx. 5 drops of 2,4-dinitrophenylhydrazine in a test tube and cautiously add 5 drops of the distillate. Record your observations below. Test 2. Test for the presence of an aldehyde group using Tollens reagent. Record your observations

below.

Test 3. Perform an infra-red analysis on your sample. Comment on your spectra.

Q1 [PASS]. Identify the reactants, products and functional groups involved. Include a balanced

equation for the reaction.

Q2 [PASS]. Draw the reaction mechanism

N/A for this reaction!

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Q3 [MERIT]. Identify the reagents used and why. Can these be changed?

Q4 [MERIT]. Identify the temperature chosen and why. Could these be changed?

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Q5 [DISTINCTION]. Calculate the percentage yield of ethanal made.

Q6 [DISTINCTION]. How else could you check the purity of product made? Strengths and

weaknesses of reaction conditions chosen? Improvements recommended? Comment on yield.

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Practical 3 – Preparation of an aromatic compound: nitration of methyl benzoate

Aim & Introduction

In this reaction, you shall nitrate the ester methyl benzoate to make methyl 3-nitrobenzoate. The

temperature of the reaction must be carefully controlled and be kept below 100C. You shall use vacuum

distillation and also check the melting point of the product formed.

Safety assessment

Safety glasses & lab coats must be worn. Long hair must be tied back

Conc. acids are very corrosive - take care not to spill when dispensing them. If spillage occurs it must

be diluted with water and treated with dry sodium carbonate solid.

Conc. Sulphuric should be wiped off the skin with a dry paper towel then washed off with water.

Ethanol is flammable therefore it must be kept in the fume cupboard and the lid remain on the bottle

when not in use. It must be kept away from naked flames.

Methylbenzoate is harmful and should be dispensed in the fume cupboard. Avoid contact with skin.

At the end of the experiment, place all used glassware in washing up trays provided. Wipe the bench with

a paper towel. Wash your hands with soap & water.

Method

Wear gloves whilst carrying out the nitration and keep glassware on a white bench tray.

Add 10cm3 of conc. sulphuric acid (CORROSIVE) to a clean, dry boiling tube. Stand the boiling

tube in a 400cm3 beaker.

Put about 4 cm3 of methylbenzoate in a clean measuring cylinder and use a balance to find the overall

mass. Add this to the acid in the boiling tube and stir carefully using a thermometer. Find the mass of

the empty measuring cylinder by weighing after it has been emptied and calculate the mass of

methylbenzoate used.

Mass of measuring cylinder containing methyl benzoate (g)

Mass of empty measuring cylinder (g)

Mass of methyl benzoate used (g)

Place the empty measuring cylinder in the fume cupboard as soon as you have reweighed it.

Add 6cm3 of nitrating mixture (50:50 conc. nitric acid HNO3 and conc. Sulphuric acid H2SO4 -

CORROSIVE) to a clean test tube. Place a dropping pipette inside.

Stand the test tube in the 400cm3 beaker, along with the boiling tube, and pack around with ice.

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When the contents of the boiling tube are below 10°C, slowly (using the dropping pipette) add the

nitrating mixture to the methylbenzoate solution in the boiling tube, gently stirring with the

thermometer and controlling the addition so that the temperature stays in the range of 5 – 15°C. Keep

the dropper in the test tube until all the nitrating mixture has been added.

After the addition, place the boiling tube in a rack and allow to stand at room temperature for 10 mins.

Keep the ice water. Rinse thermometer, test tube and dropper carefully before putting in washing-up.

Pour the liquid from the boiling tube onto approx. 40g of crushed ice in a 100cm3 beaker and stir until

the product solidifies.

Collect the product by vacuum filtration. Re-filter the filtrate if necessary to collect as much product

as possible.

Wash the solid with 3 portions of water, sucking dry each time.

Transfer the solid to a clean, dry 100cm3 conical flask.

Heat water in a water bath to almost boiling point, switch off the Bunsen

Add 20cm3 of ethanol (Flammable) to the solid in the conical flask and swirl in the water bath until

all the solid has dissolved

Allow the contents of the flask to cool to room temperature.

Filter the re-crystallised solid, wash with a little ethanol and allow to dry in the oven.

Record the appearance, weight and melting point in the space below.

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Q1 [PASS]. Identify the reactants, products and functional groups involved. Include a balanced

equation for the reaction.

Q2 [PASS]. Draw the reaction mechanism

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Q3 [MERIT]. Identify the reagents used and why. Can these be changed?

Q4 [MERIT]. Identify the temperature chosen and why. Could these be changed?

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Q5 [DISTINCTION]. Calculate the percentage yield of methyl 3-nitrobenzoate made.

Q6 [DISTINCTION]. Find the actual melting point of methyl 3-nitrobenzoate – how does it

compare to your value and how pure do you think your product is? How else could you check the

purity of product made? Strengths and weaknesses of reaction conditions chosen? Improvements

recommended? Comment on yield.

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MARKSCHEME Unit 14 Learning Aim D – Investigate organic chemistry reactions in order to gain skills in

preparative organic chemistry.

You must include your notes and results from these practicals in your write-up. You also must include:

P5/P6 – perform the practical and a write-up.

Results and notes from practicals

Safety assessment for at least two practicals.

Include information on reactants, products, functional groups involved and a balanced equation.

Reaction mechanisms.

M5 – assess the importance of the conditions chosen

Identify the reagents used and why. What happens if these are changed?

The temperature and time chosen and why. What happens if these are changed?

D4 – Evaluate the results obtained and the importance of the reaction conditions chosen

Conclusions from results to include strengths and weaknesses of the reaction conditions chosen.

Assessment criteria Essential information for assessment decisions D.P5 Carry out practical examinations of organic chemical reactions safely and in order to

produce the predicted products. D.P6 Explain the chemical reactions carried out in terms of the functional groups and reaction conditions involved.

For pass standard, learners will provide the results/notes from a portfolio of practical work, a witness testimony of working safely and a safety

assessment of at least two of the practical exercises undertaken. They will provide relevant information at least three of the reactions carried out to include the reactants, products, balanced equations and the functional groups involved in the reactions and the appropriate reaction

mechanisms.

D.M5 Assess the importance of the conditions chosen for the reactions carried out practically.

For merit standard, learners will identify the reagents used and the temperature and time chosen in the given reaction methods, providing evidence and giving reasons why these have been chosen for at least three reactions.

D.D4 Evaluate the results obtained and the importance of the reaction conditions chosen for the reactions carried out practically.

For distinction standard, learners will draw valid conclusions from the results obtained to include strengths and weaknesses of the reaction conditions chosen for the reactions carried out practically.