Question

Benzene is often produced as a side product during Grignard reactions using phenylmagnesium bromide. How can its formation be explained? Give a balanced equation for its formation.

Answer 1

It will happen if there is any water in the reaction system. Grignard regents are very reactive towards water.

Ar -Mg-Br + H2O ---> Ar-H + HOMgBr

Answer 2

if there is any water in the reaction system. Grignard regents are very reactive towards water.

Ar -Mg-Br + H2O ---> Ar-H + HOMgBr

Answer 3

Grignard reagents behave essentially as a carbanion, and are extremely reactive. Therefore they cannot be carried out while acidic hydrogens, or other positive reactive centers are present (carbonyl compounds such as acetone) in the reaction mixture because there is no way to stop the Grignard from reacting with these other compounds rather than the desired reactant. If phenylmagnesium bromide were prepared, and ANY water was present in the reaction mixture phenylmagnesium bromide would not hesitate to react with water--stealing one of its hydrogens. This hydrogen would therefore replace the attached --MgBr to form benzene.