Ethyl benzoate reaction with Grignard reagents

Esters react with 2 mol of Grignard reagent to give the salt of an alcohol. For example, reaction of ethyl benzoate with 2 mol of phenylmagnesium bromide gives a salt of triphenylmethanol. The first addition gives an intermediate, 3-7, which is unstable under the reaction conditions. 

One year later, in 1934, Vavon and co-workers [5] determined the relative reactivities of Grignard reagents with a different type of substrates benzoic acid esters. Steric requirements played a role when the alcohol component of the ester was changed from primary, to secondary, to tertiary the relative rates of reactions of ethylmagnesium bromide were 400 40 1, respectively. The relative rates of reaction of ethyl-, isopropyl-, n-butyl-, and phenylmagnesium bromide with ethyl benzoate decreased in this order. The reaction with rert-butylmagnesium chloride was reported to be extremely slow."... 

Methyl, ethyl, isopropyl, and r-butyl magnesium bromides were compared in enolization reactions [Eq. (11)]. The relative rates were Et>/-Pr> Me>f-Bu, which reflects a combination of steric and electronic effects. The bulkier Grignard reagents react slower, whereas the more substituted Grignard reagents are stronger bases. With more-hindered ketones, steric effects predominate over electronic. The structures of magnesium enoiates were confirmed by reaction with benzoyl chloride to form enol-benzoates [14,15]. 

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