Question

Propyl ester reacts with isopropyl magnesium bromide to give ${{2}^{\circ }}$ alcohol. The ester is:
(A) propyl methanoate
(B) isopropyl formate
(C) propyl ethanoate
(D) isopropyl ethanoate

Answer 1

Hint: Secondary alcohol is a hydroxyl group which is attached to a secondary carbon atom. The carbon atom that is attached to the other two carbon atoms is called a secondary carbon atom. The structure of the isopropyl group is as shown below.


Complete step by step solution:
Let’s see how these all esters will react with the given Grignard reagent one by one.
- Any ester will react with the Grignard reagent to first give a ketone and then the ketone will further react with the Grignard reagent to give alcohol as a final product.
i) Propyl methanoate

Thus, here we can see that propyl stands for the n-propyl group and it will react with two moles of the given Grignard reagent to give tertiary alcohol as a product. We can see that the hydroxyl group bearing carbon is attached with other three carbon atoms, hence the product is a tertiary alcohol.
ii) Isopropyl formate

Here, we can see that as a hydrogen atom is bonded to the carbonyl carbon, the resulting alcohol bearing carbon will have one carbon atom less than the first example, so here the carbon-bearing hydroxyl group is bonded with only two carbon atoms, so it can be categorized as secondary alcohol.
iii) Propyl Ethanoate

Here, we can see that as the ethyl group is bonded with the carbonyl carbon, the resulting alcohol will have a hydroxyl group which will be bonded to a carbon atom which is a tertiary carbon. Hence, alcohol is a tertiary alcohol.
iv) isopropyl Ethanoate

Here, also the resulting alcohol will be tertiary alcohol as the carbon attached to it is a tertiary alcohol.

Thus, we can conclude from the above discussion that option (B) is correct.

Note: Note that any ester that is derivative of formic acid means it is formate, then it will always give secondary alcohol upon its reaction with two moles of Grignard reagent. Any ester that is not formatted, will always give tertiary alcohol as a final product with the reaction with the Grignard reagent.