Question

Phenyl magnesium bromide reacts with methanol to give
A) A mixture of anisole and \[{\text{Mg(OH)Br}}\]
B) A mixture of benzene and \[{\text{Mg(OMe)Br}}\]
C) A mixture of toluene and \[{\text{Mg(OH)Br}}\]
D) A mixture of phenol and\[{\text{Mg(Me)Br}}\]

Answer 1

Hint: This is the reaction of the Grignard reagent with alcohol. It is known as the Zerewitnoff reaction. The reaction of phenyl magnesium bromide with methanol is an acid-base reaction. Methanol behaves as acid while phenyl magnesium bromide behaves as a base.

 Complete step by step answer:
Phenyl magnesium bromide is a Grignard reagent.

The Grignard reagent is an organometallic compound.

This is an acid-base reaction when methanol acts as an acid and donates its proton. While phenyl magnesium bromide acts as a base and accepts the proton and is converted into benzene.

Thus, Phenyl magnesium bromide reacts with methanol and gives a mixture of benzene and\[{\text{Mg(OMe)Br}}\].
Therefore, option (B) is correct.

Additional Information:
1) The Grignard reagent is a good nucleophile. It acts as a nucleophile in reaction with a carbonyl compound. It can form a new carbon-carbon bond. It behaves as a base in reaction with alcohol. The reaction of an alcohol with Grignard reagent is different than the reaction with a carbonyl compound.
2) In phenyl magnesium bromide, phenyl has a partial negative charge and magnesium has a partial positive charge. In methanol, the methoxide group has a partial negative charge while hydrogen has a partial positive charge. So phenyl attacks the acidic hydrogen of methanol and gives benzene as the product.

Note:Zerewitnoff reaction used to determine the active hydrogen in an organic compound. Alkyl magnesium bromides react with alcohol and give alkane as the product. While phenyl magnesium bromide reacts with alcohol and gives benzene as the product.