Question

Complete the mechanism for the reaction of butanone with NaBH4 followed by the addition of aqueous acid.

Answer 1

General guidance

Concepts and reason

The problem is based on the concept of reduction reaction. The reducing reagent is Sodium Borohydride $\\left( {{\\rm{NaB}}{{\\rm{H}}_4}} \\right)$and the substrate is aldehyde or ketone. The substrate is converted into analogous alcohol after reduction.

Fundamentals

The reducing agent ${\\rm{NaB}}{{\\rm{H}}_4}$reduces aldehydes and ketones to analogous alcohols. It is not a very strong reducing agent as it does not reduce carboxylic acids or esters. The reduction takes place in two parts. One is attack of nucleophile and other is proton transfer.

Step-by-step

Step 1 of 2

First step is nucleophilic attack on carbonyl substrate

The charged organic intermediate is

The agent ${\\rm{NaB}}{{\\rm{H}}_4}$ has attacks in carbonyl with nucleophile${{\\rm{H}}^ - }$. The double bond of carbonyl shifts towards O and thus nucleophilic addition takes place.

Step 2 of 2

Next step is proton transfer

The final product is

The negatively charged O acts as nucleophile and attacks ${{\\rm{H}}_3}{{\\rm{O}}^ + }$and a proton transfer takes place from ${{\\rm{H}}_3}{{\\rm{O}}^ + }$ to O. hence the final product formed is butanol that is an alcohol.

Answer

The charged organic intermediate is

The final product is

Answer only

The charged organic intermediate is

The final product is