Q21-21P - Organic Chemistry (Mcmurry)

Question

How would you use the reaction of an amide with LiAlH₄ as the key step in going from bromocyclohexane to (N,N-dimethylaminomethyl)cyclohexane? Write all the steps in the reaction sequence.

Step-by-Step Solution

Answer

Step involved are:

1. Conversion of bromo benzene to Grignard reagent
2. Reaction of the Grignard reagent with CO₂ followed by hydrolysis to give benzoic acid
3. Benzoic acid reaction with SOCl₂ to give benzoyl chloride
4. Benzoyl chloride reaction with an amine to give N,N-Dimethyl benzamide
5. Reduction of N,N-Dimethyl benzamide to give (N,N-dimethylaminomethyl)cyclohexane

Step 1: Conversion of bromobenzene to benzoic acid

First of all, prepare Grignard reagent by the addition of bromobenzene with magnesium metal and then convert it to Phenyl magnesium bromide. After the addition of carbon dioxide in an acidic medium. It leads to the formation of benzoic acid.

Conversion of bromobenzene to Benzoic acid

Step 2: Conversion of benzoic acid to amide

Benzoic acid first reacts with $\mathrm{SOC}{\mathrm{l}}_2$  and gets converted into benzoyl chloride which on further reaction with secondary amine can be converted to N,N-Dimethylbenzamide amide.

 

Conversion of benzoic acid to amide

Step 3: Reduction of Amide

Amides on reduction with  ${\mathrm{LiAlH}}_4$ convert to amines. So, N,N-Dimethyl benzamide on reduction with  $LiAl{H}_4$ converts to (N,N-dimethylaminomethyl)cyclohexane.

Reduction of amide