Q-21-21-9P - Organic Chemistry (Mcmurry)

Question

How might you prepare the following esters using a nucleophilic acyl substitution reaction of an acid chloride?

(a) ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CO}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{3}}$

(b) ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CO}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{3}}$

(c) Ethyl benzoate.

Step-by-Step Solution

Answer

(a) Propanoyl chloride + methanol forms the given ester molecule.

(b) Acetyl chloride + ethanol forms the given ester molecule.

(c) Benzoyl chloride + ethanol.

Nucleophilic acyl substitution

The carbonyl carbon in acyl group attains electrophilic character when the leaving group departs from it. The leaving group is replaced with the nucleophile.

Subpart (a)

The starting reaction synthesis can be denoted as,

$$\begin{gathered} \mathrm{propanoyl} \mathrm{chloride}+\mathrm{methanol}\stackrel{\mathrm{Pyridine}}{\to }\mathrm{methyl} \mathrm{propanoate}+\mathrm{HCL} \\ {\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{COCl}+{\mathrm{CH}}_3\mathrm{OH}\to {\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{COOCH}}_3+\mathrm{HCl} \end{gathered}$$

The pyridine will stabilize HCl for the formation of pyridium hydrochloride. The alcoholysis through nucleophilic acyl substitution on acid chloride will convert it into ester. The reagents used are methanol and propanoyl chloride. 

Subpart (b)

The pyridine will stabilize HCl for the formation of pyridium hydrochloride. The alcoholysis through nucleophilic acyl substitution on acid chloride will convert it into ester. The reagents used are ethanol and acetyl chloride.

$$\begin{gathered} \mathrm{Acetyl} \mathrm{chloride}+\mathrm{ethanol}\to \mathrm{ethylacetate}+\mathrm{HCl} \\ {\mathrm{CH}}_3\mathrm{COCl}+{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\to {\mathrm{CH}}_3{\mathrm{CO}}_2{\mathrm{CH}}_2{\mathrm{CH}}_3+\mathrm{HCl} \end{gathered}$$

Subpart (c)

The reagents used are Ethanol and Benzoyl chloride. The entire reaction is as shown below: