REACTION OF BENZYLMAGNESIUM CHLORIDE WITH FORMALDEHYDE

The reaction of benzylmagnesium chloride with both monomeric formaldehyde and paraformaldehyde has been studied by varying the concentration of the aldehyde systematically. The three principal products of the reaction with monomeric formaldehyde are 2-phenylethanol, o-tolylcarbinol, and o-(2-hydroxyethyl)benzyl alcohol. 2-Phenylethanol is a minor product and is relatively insensitive to concentration changes. The major products, o-to-lylcarbinol and o-(2-hydroxyethyl)benzyl alcohol, are extremely concentration dependent. At low aldehyde concentrations, o-tolylcarbinol predominates, but at high aldehyde concentrations this product virtually disappears in favor of o-(2-hydroxyethyl)benzyl alcohol. With paraformaldehyde, o-tolylcarbinol is always the major product regardless of concentrations. Only small amounts of o-(2-hydroxyethyl)benzyl alcohol are even formed and then only at very high aldehyde concentrations. The latter results would indicate that the polymer itself does not react directly but serves to supply a steady but low concentration of reactive monomer, a situation which disfavors formation of o-(2-hydroxyethyl)benzyl alcohol. The intermediate leading to the latter product was trapped by trimethyl-chlorosilane and characterized. Despite many conflicting and erroneous reports in previous literature and textbooks, the formaldehyde reaction with benzylmagnesium chloride is not a paradox but has many features in common with other aldehyde-benzyl Grignard reactions. Copyright © 1979, American Chemical Society. All rights reserved.