Carboxylic Acids & Esters (OCR A Level Chemistry)

Esters are responsible for various sweet, flowery and fruity smells. Some confectionery products use synthetic esters to achieve their aroma.

A student reacted acids and alcohols together to form ethyl methanoate (raspberry essence) and ethyl butanoate (pineapple essence).

Write word and symbol equations to show the reactions that would produce these esters.

Propan-2-ol reacts with ethanoic acid in the presence of a suitable catalyst

The same organic product, from part (b), was synthesised using an alternative method. 

Name an alternative reagent to react with the alcohol to form the organic product in part (b) and name the other product formed as part of the reaction.

Stearic acid, C₁₇H₃₅COOH, is an example of a naturally occurring fatty acid. It has the systematic name octadecanoic acid.

Sodium stearate is the salt formed when stearic acid reacts with sodium hydroxide solution. 
Write an equation for the formation of sodium stearate.

Write a balanced equation to show the formation of the following tri-ester, shown in Figure below. 

Esters can undergo hydrolysis reactions. 

Hydrolysis is performed on the cyclic ester shown in Figure below.

This question is about aromatic carboxylic acids and their derivatives.
The flowchart below shows some reactions of compound H.
In the boxes, draw the organic products of these reactions.

Compound H can be converted into an acyl chloride.

Draw the structure of the acyl chloride and state the formula of the reagent(s) required.

Carnauba wax is found in automobile waxes and can be extracted from the Brazilian wax palm tree. A component of carnauba wax is shown in Figure.

Components such as this can be synthesised via esterification, according to the general equation:

ROH + R’COOH ⇌ R’COOR + H₂O

The reagents are typically heated with an acid catalyst. Explain the effect that using excess alcohol will have on the overall yield of the ester. 

Butan-1-ol can be used to make the same ester using either ethanoic acid or ethanoyl chloride. Both reactions can be described as condensation reactions.

Write equations for both reactions, including the name of the organic product, and explain why both reactions can be classified as condensation reactions.

Triglycerides are triesters and are found in fats and oils.

The structure of a triglyceride found in some goats’ milk is shown below.

This triglyceride is hydrolysed with hot aqueous sodium hydroxide.
Give the systematic name and displayed formula of the alcohol that is formed by this hydrolysis. 

Draw the structures of the other organic products of this hydrolysis.

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

Draw the structure of a compound that could react with ethanoic anhydride to form aspirin.

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 paracetamol
• Reagent B reacted only with aspirin
• Reagent C reacted only with paracetamol

Suggest the possible identify of reagent A and the organic products that would be formed with aspirin and paracetamol

Suggest the possible identify of reagent B and the organic products that would be formed with aspirin 

Suggest the possible identify of reagent C and the organic products that would be formed with paracetamol

E numbers are codes for substances used as food additives used in countries in Europe. Sorbitan monooleate is used as an emulsifier and has the E number E494.

sorbitan monooleate

Suggest a type of reaction that could break down sorbitan monooleate.

Explain your answer and state the type of organic products formed.

When ethyl methacrylate, CH₂C(CH₃)COOC₂H₅, is heated under reflux with aqueous dilute acid, a hydrolysis reaction takes place forming compound C and ethanol.
When compound C is heated with steam in the presence of an acid catalyst, an addition reaction takes place forming two organic products D and E.
Compounds D and E are structural isomers with the molecular formula C₄H₈O₃.
Draw the structures of compounds C, D and E.

Mandelic acid, C₆H₅CH(OH)COOH, has anti-bacterial properties and is used in some skin creams. A cosmetic chemist used mandelic acid to prepare two different esters that might be suitable for new skin creams. The structures of the two esters are shown below.

This question is about lactic acid.

When heated strongly, lactic acid forms a cyclic ‘diester’. The diester has the molecular formula, C₆H₈O₄.

Draw the structure of the cyclic diester.

This question is about esters.

Outline a method, using esterification, to test for the suspected presence of an alcohol in an unknown sample.

Ester A is responsible for a raspberry scent and has the molecular formula C₅H₁₀O₂.

Ester A can be produced by the reaction of an acid with a branched primary alcohol.

Identify the acid and alcohol used to prepare ester A.

Draw and name ester A.

Suggest why the solubility of esters in water decreases as the chain length of the ester increases.

Compare the structures and bonding of butanoic acid, ethyl ethanoate and pentan-1-ol then place them in order from most to least volatile.

This question is about esters.

Ethyl methacrylate, CH₂C(CH₃)COOC₂H₅, can form an addition polymer that is used to make artificial fingernails. 

[1]

[1]

Ethyl methacrylate can undergo a hydrolysis reaction by being heated under reflux with dilute sulfuric acid.  

The products from this hydrolysis are compound A and ethanol.  

Compounds B and C both have the molecular formula, C₄H₈O₃. These are formed when compound A is heated with steam in the presence of sulfuric acid, undergoing an addition reaction.  

Draw the structures of compounds A, B and C.

Mandelic acid (2-phenyl-2-hydroxyethanoic acid), C₆H₅CH(OH)COOH, is used in some skin creams due to its antibacterial properties.  

Using mandelic acid, two different esters were prepared for potential use in other skin creams. 

Their structures are shown below:

[1]

[1]

Compare the reactions of mandelic acid and an acid anhydride with an alcohol to form an ester.  

Esters have important commercial uses, such as artificial flavourings in food. 

They can be prepared in several ways, including through the reactions of alcohols with carboxylic acids, as well as the carboxylic acid derivatives, acid anhydrides and acyl chlorides.

Ester Z, CH₃CH₂COOCH₂CH(CH₃)₂ is used in rum flavouring. 

Outline how you could obtain a sample of ester Z, beginning with a named alcohol and carboxylic acid. 

Include any essential reaction conditions and write an equation for the reaction. 

You do not need to include details of the separation or purification methods involved. 

Another ester, phenyl ethanoate, can be used as a starting material for the formation of a variety of other organic compounds. 

[2]

Phenyl ethanoate can also be formed from ethanoyl chloride.  

Describe the steps involved to form phenyl ethanoate, starting with the synthesis of ethanoyl chloride. 

Give one condition needed. 

Give two advantages of using ethanoyl chloride instead of ethanoic acid in the laboratory preparation of pentyl ethanoate from pentan-1-ol. 

Give two advantages of using ethanoic anhydride instead of ethanoyl chloride in the industrial manufacture of pentyl ethanoate from pentan-1-ol.

Acyl chlorides are commonly used carboxylic acid derivatives. 

Ethanoyl chloride reacts with an excess of ammonia. 

A student proposes the following equation to represent the reaction:

CH₃COCl + NH₃  →  CH₃CONH₂ + HCl

Correct and explain the student's error.

N-methylethanamide can also be formed from ethanoyl chloride. 

[1]

[2]

Ethanoyl chloride will react with 2-methylpropan-1-ol to form an ester. 

Draw the displayed formula of the ester formed.