Carboxylic Acids & Derivatives (A-level only) (AQA 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.

Octyl ethanoate can be manufactured or extracted from oranges and grapefruits. It is a flammable ester with a boiling point of 211 ^oC, a flash point of 86 ^oC and a density of 0.87 g/cm³.

A student reacted an acid and an alcohol in the presence of concentrated sulphuric acid to make an immiscible sample of octyl ethanoate. They added warm, aqueous sodium carbonate solution to remove any excess acid.

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

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

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

Write a balanced equation to show the formation of the following tri-ester, shown in Figure 1 below.

Esters can undergo hydrolysis reactions.

 Hydrolysis is performed on the cyclic ester shown in Figure 2 below.

Vegetable oils are often reacted with methanol in the manufacture of biodiesel.

Write the equation for the reaction of the vegetable oil shown in Figure 3 with methanol.

The vegetable oil shown in Figure 3, from part (c), was used to make soap.

State the reagent and conditions for the saponification reaction and draw the structure of one possible soap product formed. 

Aspirin and paracetamol are two of the most common pharmaceutical drugs. They are both manufactured using acylation reactions.

Paracetamol can be made by the reaction of ethanoyl chloride with 4-aminophenol, shown in Figure 1. 

Figure 1

Name and outline the mechanism for this reaction.

In the manufacture of paracetamol and aspirin, ethanoic anhydride is usually used instead of ethanoyl chloride. 

State two reasons, other than cost, that ethanoic anhydride would be used.

Aspirin and paracetamol are recrystallised to purify the solids while removing any unwanted impurities.

Describe the process of recrystallisation, including steps to minimise early crystallisation of the solid.

The purity of a solid can be checked by determining its melting point. Typically a melting point range of 2 ^oC suggests that the solid is fairly pure.

Describe how to measure the melting point range of a solid.

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 1.

Figure 1

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.

A student used ethanoyl chloride in two separate condensation reactions.

Reaction 1 involved the addition of ethanol; while reaction 2 saw the addition of ammonia. Both reactions were vigorous and white fumes were observed in both reactions.

Figure 2

Reaction 1 was set up as shown in Figure 2 to confirm the identity of the chemical responsible for the white fumes.

A student reacted propanoic acid with ethylamine.

Draw and name the structure of the organic product.

A common method for esterification is to react an alcohol with an acyl chloride.

Name and outline the mechanism for the reaction of butan-2-ol with ethanoyl chloride.

Another method for esterification is the reaction of an alcohol with an acid anhydride.

Write an equation to show the formation of propyl ethanoate using this method.

Acyl chlorides undergo various reactions with water, alcohols, ammonia and primary amines.

Ethanamide is the product of a chemical reaction.

Identify the necessary reactants and name the other product.

Ethanoyl chloride can react with primary aliphatic and aromatic amines to produce different amides.

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.

Explain why the solubility of esters in water decreases as the chain lengths of the ester increase.

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

3-oxocyclopentane-1-carbaldehyde, shown in Figure 1, reacts with Tollens’ reagent to give a weakly acidic product, compound A.

Figure 1

Draw the structure of compound A and state any observations that occur in this reaction.

Explain why compound A does not readily undergo nucleophilic addition elimination with propylamine to produce an amide.

3-oxocyclopentanecarboxylic acid, from part (a), reacts with thionyl chloride, SOC₂. 

The products of this reaction are two acidic gases and compound B, which is a functional group isomer of 3-oxocyclopentane carboxylic acid with a molecular mass of 146.5 g mol^-1.

Write the equation for this reaction using displayed formulae for the organic compounds.

Compound C shown in Figure 2 can undergo acid hydrolysis.

Figure 2

Draw the skeletal formulas of the three carboxylic acid containing compounds that are produced in this reaction.

There is a group of compounds called acid derivatives, which can be represented by the general structure shown in Figure 1.

Figure 1

Outline the mechanism for the general reaction of an acid derivative, RCOZ, with a nucleophile, Nu^-.

State three factors that affect how readily the acid derivative, shown in part (a), reacts with a nucleophile.

In a reaction, ethanoyl chloride reacts with an excess of ammonia.

A student proposes the following equation to represent the reaction.

CH₃COC + NH₃ → CH₃CONH₂ + HC

Correct and explain the student’s error.

The naturally occurring triester, shown in Figure 1, was heated under reflux with excess aqueous sodium hydroxide. The resulting reaction mixture was then distilled.

Figure 1

Give the correct IUPAC name for the first compound to be distilled from the reaction mixture.

Name the three chemicals that remain in the distillation flask after the first product has distilled off and give a use for these chemicals.

Describe the reaction conditions required to produce biodiesel from the triester shown in part (a).

Glycerol is a by-product of the formation of biodiesel and the process of saponification.

Explain why glycerol is often used in medicinal creams and ointments.