Question

Grignard reagents add to carbonate esters as they add to other esters.

(a) Predict the major product of the following reaction.

(b) Show how you would synthesize 3-ethylpentan-3-ol using diethyl carbonate and ethyl bromide as your only organic reagents.

(c) Diethyl carbonate is a liquid reagent that is easy to handle. In contrast, phosgene is a highly toxic and corrosive gas. Show how you might use diethyl carbonate instead of phosgene to make Lexan®. Also, show how you might use diethyl carbonate instead of methyl isocyanate to make Sevin® insecticide.

Short answer

(a)

Formation of desired products

(b)

Formation of3-ethyl-pentan-3-ol

(c)

Foramtion of lexan polycarbonate

(d)

Formation of Sevin insecticide

Step-by-step solution

The reaction of Diethyl carbonate with Grignard reagent

(a) Diethyl carbonate has two leaving groups. On reaction with Grignard reagent, the ethoxy group is replaced by an alky group of Grignard reagent following two nucleophilic substitution reactions and one nucleophilic addition.

Formation of products in the given reaction

Esters react with a Grignard reagent to form the following products as follows:

Formation of desired products

Preparation of 3-ethyl pentan-3-ol

(b) The reaction of an alkyl halide with Mg in the presence of ether Grignard reagent is prepared. The ester, particularly diethyl carbonate reacts with 3 moles of Grignard reagent to form 3-ethyl pentan-3-ol replacing the two ethoxy groups with an alkyl group.

Formation of 3-ethyl pentan-3-ol

The two reactants are ethylmagnesium bromide and diethylcarbonate. The name of the product is 3-ethyl-pentan-3-ol.

The formation of Grignard reagent and 3-ethyl-pentan-3-ol is represented as follows:

Formation of3-ethyl-pentan-3-ol

Preparation of Lexan

(c) Lexan is used to prepare bisphenol A into carbonate ester and is a polycarbonate as acid chloride reacts faster than esters phosgene reacts faster than diethyl carbonate. An acid catalyst speeds up this transesterification process.

Formation of lexan polycarbonate from BPA

Preparation of seven insecticide

Sevin insecticide is formed when diethyl carbonate undergoes sequential addition with methylamine and 1-naphthol. The amide should be prepared first because nitrogen is a poor leaving group.

The two reactants diethyl carbonate and methylamine.

The reaction is represented as follows:

Formation of Sevin insecticide