Chemistry 9701 · AS & A Level · Carboxylic acids and derivatives

Carboxylic acids and derivatives — practice question

(a)[3]

Compare the acid strengths of benzoic acid ($\text{C}_6\text{H}_5\text{COOH}$), phenylmethanol ($\text{C}_6\text{H}_5\text{CH}_2\text{OH}$), and phenol ($\text{C}_6\text{H}_5\text{OH}$). Give your explanation.

(b)[3]

Nine separate experiments are shown in Table 5.1. Finish the table by entering a tick ($\checkmark$) in the appropriate box when a reaction takes place. Put a cross ($\times$) in the box when no reaction takes place.

(c(i))[1]

Benzoyl chloride, $\text{C}_6\text{H}_5\text{COCl}$, may be made by reacting benzoic acid with either $\text{PCl}_5$ or $\text{SOCl}_2$. Complete the equations for these reactions. Reaction 1: $\text{C}_6\text{H}_5\text{COOH} + \text{PCl}_5 \rightarrow \text{C}_6\text{H}_5\text{COCl} + \ldots + \ldots$ Reaction 2: $\text{C}_6\text{H}_5\text{COOH} + \text{SOCl}_2 \rightarrow \text{C}_6\text{H}_5\text{COCl} + \ldots + \ldots$

(c(ii))[1]

Using your answer to part (c)(i), suggest why it is simpler to isolate $\text{C}_6\text{H}_5\text{COCl}$ in pure form from reaction 2 than from reaction 1.

(d(i))[4]

Benzoyl chloride is hydrolysed by water at room temperature to make benzoic acid. Complete the diagram so that it shows the mechanism for the reaction between $\text{C}_6\text{H}_5\text{COCl}$ and $\text{H}_2\text{O}$. Include charges, dipoles, lone pairs of electrons and curly arrows where needed.

(d(ii))[1]

Name the mechanism type you showed in (d)(i).

(e(i))[2]

Acyl chlorides react with sodium carboxylates to make acid anhydrides as shown in Fig. 5.1. The condensation polymers, polyanhydride and polyester, are prepared by similar routes. The repeat unit for a polyanhydride is shown in Fig. 5.2. Use Fig. 5.1 and Fig. 5.2 to suggest the structures of the two monomers used to prepare this polyanhydride.

(e(ii))[1]

Polyanhydrides are biodegradable polymers. Suggest how this polyanhydride can be degraded.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: relative acidity: benzoic acid > phenol > phenylmethanol

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