Examination questions
on acylating agents - acyl chlorides/anhydrides
AQA
Question 1.
Phenylethanone can be prepared by the reaction between ethanoyl chloride and benzene.
In a preparation, with an excess of benzene, the mass of ethanoyl chloride ( Mr = 78.5) used was 5.7 × 10 -2 kg.
The percentage yield of phenylethanone was 62%.
What mass, in grams, of phenylethanone was produced?
A. 35 g B. 54 g C. 87 g D. 102 g
The answers can be found here.
Question 2.
(a) Give the IUPAC name of the alcohol below.
Give the reagent needed for this reaction and name the mechanism.
(b) This alcohol reacts with ethanoyl chloride to form an ester.
Describe what would be observed when the alcohol reacts with
ethanoyl chloride.
Name the mechanism for the reaction to form the ester.
Draw the structure of the ester.
The answers can be found here.
Question 3.
Paracetamol is a medicine commonly used to relieve mild pain.
Traditionally, paracetamol has been made industrially in a three-step synthesis from phenol
(a) Name the mechanism of the reaction in Step 1.
(b) Complete the equation for the reaction in Step 2.
In theory, either ethanoyl chloride or ethanoic anhydride could be used in Step 3. Complete the mechanism for the reaction of 4-aminophenol with ethanoyl chloride.
RNH2 is used to represent 4-aminophenol in this mechanism.
(d) In practice, ethanoic anhydride is used in the industrial synthesis
rather than ethanoyl chloride.
Give one reason why ethanoyl chloride is not used in the industrial
synthesis
(e) In Step 3 other aromatic products are formed as well as paracetamol.
Draw the structure of one of these other aromatic products.
(f) Chemists have recently developed a two-step process to produce
paracetamol from phenol.
In the first step, phenol is oxidised to hydroquinone.
In the second step, hydroquinone reacts with ammonium ethanoate to form paracetamol. Complete the equation for this second step.
(g) Calculate the mass, in kg, of hydroquinone ( Mr = 110.0) needed to
produce 250 kg of paracetamol.
The answers can be found here.
Question 4.
The reaction between propanoyl chloride and benzene is an example of acylation. Which is a correct representation of part of the mechanism of this reaction?
The answers can be found here.
Question 5.
Which compound forms a white precipitate when added to
aqueous silver nitrate?
A. bromoethane
B. ethanal
C. ethanoic anhydride
D. ethanoyl chloride
The answers can be found here.
Question 6.
Benzene reacts with methanoyl chloride (HCOCl ) in the presence of a catalyst.
(a) Give an equation for the overall reaction when benzene reacts with
methanoyl chloride. Name the organic product.
(b) Identify the catalyst needed in this reaction.
Give an equation to show how the catalyst is used to form the
electrophile, [HCO] +
(c) Outline the mechanism for the reaction of benzene with the
electrophile, [HCO] +
The answers can be found here.
OCR
Question 1.
Acid anhydrides react in a similar way to acyl chlorides with phenols.
Benzoic anhydride is the acid anhydride of benzoic acid, C6H5COOH.
Benzoic anhydride reacts with butan-2-ol to form an ester.
Suggest an equation for this reaction. Show structures for organic compounds. Use C6H5 for any phenyl groups.
The answers can be found here.
Question 3.
A chemist prepares and analyses some esters.
The chemist prepares an ester of propan-2-ol, CH3CH(OH)CH3, by reacting CH3CH(OH)CH3 with ethanoic anhydride, (CH3CO)2O.
Using structural formulae, write an equation for the reaction of
propan-2-ol and ethanoic anhydride.
The answers can be found here.
Question 4.
Acid anhydrides are organic compounds that can be reacted with alcohols to form esters and carboxylic acids.
Compound F , shown below, is an acid anhydride used in the perfume industry as a starting material in the production of esters.
Compound F is a ‘mixed’ acid anhydride, formed from two different carboxylic acids.
(a) A chemist reacts compound F with an alcohol, G.
(i) Name alcohol G .
(ii) The reaction between F and G forms a mixture of four organic
compounds.
Two of the compounds are esters, and two are carboxylic acids.
One of the esters is shown below.
Draw the structures of the other three organic compounds formed.
(b) After the reaction in part (a) , the chemist wished to analyse the
mixture by separating the compounds using gas chromatography (GC),
and measuring their retention times.
(i) State what is meant by retention time .
(ii) What are the possible limitations of this analysis by GC?
The answers can be found here.
Question 2.
Aspirin and paracetamol are commonly available painkillers.
Aspirin and paracetamol can be prepared using ethanoic anhydride, (CH3CO)2O.
Some examples of the reactions of ethanoic anhydride are shown below.
reaction 1 (CH3CO)2O + CH3OH → CH3COOCH3 + CH3COOH
reaction 2 (CH3CO)2O + CH3NH2 → CH3CONHCH3 + CH3COOH
reaction 3 (CH3CO)2O + C6H5OH → CH3COOC6H5 + CH3COOH
(a) Draw the structure of a compound that could react with ethanoic
anhydride to form aspirin.
(b) Ethanoic anhydride can react with 4-aminophenol to produce
paracetamol.
(i) Write an equation, showing structural formulae, for this formation
of paracetamol.
(ii) An impurity with molecular formula C10H11NO3 is also formed.
Draw the structure of this impurity.
(iii) Explain why it is necessary for pharmaceutical companies to ensure
that drugs and medicines are pure.
(c) Name the functional groups in aspirin and in paracetamol.
d) A student carried out some reactions with samples of aspirin and
paracetamol in the laboratory. Their structures are repeated below.
The student tried to react each of the reagents A , B and C with aspirin and paracetamol.
• Reagent A reacted with aspirin and with paracetamol.
• Reagent B reacted only with aspirin.
• Reagent C reacted only with paracetamol.
Suggest possible identities of reagents A , B and C and the organic products that would be formed.
The answers can be found here.
Question 5.
A student plans a two-step synthesis starting with phenylamine.
The steps of the synthesis are shown below.
(i) In step 1 , phenylamine reacts with ethanoic anhydride to make
compound A and one other organic product.
Draw the structure of ethanoic anhydride, with the functional group
displayed, and suggest the structure of the other organic product
formed in step 1.
(ii) Calculate the mass of compound A that can be synthesised from
3.00 g of phenylamine in step 1 .
The percentage yield of this reaction is 61.0%.
Mr (phenylamine) = 93.0
Give your answer to three significant figures.
The steps of the synthesis are shown again below.
(iii) In step 2 , compound A is converted into compound B using a mixture
of concentrated nitric acid and concentrated sulfuric acid.
Outline, with the aid of curly arrows, the mechanism for the conversion
of compound A into compound B.
Use equations to explain how sulfuric acid acts as a catalyst in
this reaction.
The answers can be found here.
EDEXCEL
Question 1.
Phenylethanone is an ingredient in many types of chewing gum.
One method for the production of phenylethanone involves the reaction of benzene with ethanoyl chloride, CH3COCl.
(i) Write the equation for the formation of the electrophile, CH3CO+,
from ethanoyl chloride using the catalyst aluminium chloride.
(ii) Complete the diagram, including curly arrows, to show the mechanism
for the reaction between this electrophile and benzene to produce
phenylethanone. Include the regeneration of the catalyst.
The answers can be found here.
Question 2.
Phenylethene, commonly known as styrene, is an important substance in the production of polystyrene which is used for some types of plastic packaging.
Phenylethene can be made from benzene in a three-step synthesis.
(a) Some of the following compounds can be used to make phenylethene
from benzene.
Selecting only from these compounds, devise a synthetic pathway for converting benzene into phenylethene, clearly identifying compounds A and B and stating the appropriate conditions for each step.
(b) Which reagent could produce a diol from phenylethene?
A. acidified potassium dichromate(VI)
B. acidified potassium manganate(VII)
C. aqueous sodium hydroxide
D. steam
The answers can be found here.
Question 3.
Compound T, C4H10O, is oxidised by acidified potassium dichromate(VI) to form compound U, C4H8O.
U gives an orange precipitate with 2,4-dinitrophenylhydrazine (Brady’s reagent) but does not give a red precipitate when heated with Fehling’s solution.
T reacts with ethanoyl chloride to form compound V, C6H12O2.
Deduce the structures of compounds T , U and V. Justify your answers.
The answers can be found here.
Question 5.
Ethyl ethanoate can also be formed by reacting ethanol with ethanoyl chloride, CH3COCl.
Identify three differences in the esterification reaction when ethanoyl chloride is used instead of ethanoic acid.
The answers can be found here.
Question 6.
Butylamine, C4H9NH2, reacts with ethanoyl chloride.
2C4H9NH2 + CH3COCl → C4H9NHCOCH3 + C4H9NH3+Cl–
Explain how this equation illustrates that butylamine acts as a nucleophile and as a base.
The answers can be found here.
Question 7.
This question is about the preparation and analysis of paracetamol.
(a) In Stage 1 , phenol is nitrated using dilute nitric acid.
The nitration of benzene requires concentrated nitric acid at 55°C with a catalyst of concentrated sulfuric acid.
Both these reactions are electrophilic substitution.
(i) Explain why phenol can be nitrated using milder conditions than benzene.
(ii) A mixture of 2-nitrophenol and 4-nitrophenol is produced in Stage 1.
They are separated by steam distillation.
The boiling temperature of 2-nitrophenol is 215°C and that of 4-nitrophenol is 279°C.
Explain, in terms of intermolecular forces, why 4-nitrophenol has a higher boiling temperature than 2-nitrophenol.
You may include a diagram in your answer.
(b) State the type of reagent needed to convert
4-nitrophenol into 4-aminophenol in Stage 2.
(c) The outline procedure for Stage 3 is:
• place 1.0 g of 4-aminophenol in a conical flask. Add 9 cm 3 of distilled water and stir the mixture
• add 1 cm 3 of ethanoic anhydride to the flask and shake the mixture until a precipitate of impure paracetamol forms
• remove the paracetamol by filtration under reduced pressure
• recrystallise the paracetamol using water as the solvent
• determine the melting temperature of the pure, dry paracetamol.
(i) Draw a labelled diagram of the apparatus used for filtration under reduced pressure.
(ii) Describe the recrystallisation process to obtain a pure, dry sample of paracetamol.
(iii) The melting temperature of pure paracetamol is 170°C.
Describe what happens to the melting temperature if the paracetamol is not pure.
The answers can be found here.