Final answer:
When an ester reacts with two equivalents of a Grignard reagent, it undergoes a reduction reaction, resulting in the formation of an alcohol and a magnesium salt.
Step-by-step explanation:
When an ester reacts with two equivalents of a Grignard reagent, a reduction reaction occurs. The Grignard reagent, which is an organometallic compound, donates its electron pair to the carbonyl group of the ester. This results in the formation of an alcohol and a magnesium salt. The overall reaction can be represented as follows:
R-CO-OR' + 2R''-MgX -> R-COH + R'-OH + MgXOR''
For example, if methyl acetate (CH3COOCH3) reacts with two equivalents of ethylmagnesium bromide (C2H5MgBr), it will yield ethanol (CH3CH2OH) and methanol (CH3OH).
An ester reacts with two equivalents of a Grignard reagent to form a tertiary alcohol. The first equivalent converts the ester into a ketone intermediate, and the second equivalent reacts with this ketone to produce the tertiary alcohol.
Reaction of an Ester with Grignard Reagents
When an ester reacts with two equivalents of a Grignard reagent, the result is a tertiary alcohol. The first equivalent of the Grignard reagent attacks the carbonyl carbon of the ester, resulting in a ketone intermediate. This ketone is then attacked by the second equivalent of Grignard reagent, forming the tertiary alcohol after workup.
Esters have a polar bond (C=O) with two polar C-O groups, which makes them susceptible to nucleophilic attacks, such as those from Grignard reagents.
Product Formation
During the reaction, the ester's carbonyl carbon is the target for nucleophilic attack because of its partial positive charge. The first Grignard reagent performs a nucleophilic acyl substitution, converting the ester to a tetrahedral intermediate which then collapses to form a ketone. The newly formed ketone itself is reactive toward Grignard reagents and undergoes a second nucleophilic addition, giving rise to a new tetrahedral intermediate which, upon protonation during workup, yields the tertiary alcohol.