One mole of the anhydride shown is treated with a large excess of methylmagnesium bromide, followed by aqueous acid work-up. Assume that each acyl group that is attacked proceeds to the tertiary alkoxide, the carboxylate leaving group is not attacked, and no enolisation occurs. How many moles of $CH X_{3} MgBr$ are consumed per mole of the anhydride? Give the answer as an integer.

Numerical answer type, tolerance 0.5.

Answer: 2

Ethanoic anhydride is attacked by CH3MgBr at one carbonyl carbon; ethanoate is expelled and propanone forms. Propanone reacts with a second equivalent of CH3MgBr to give the tertiary alkoxide of 2-methylpropan-2-ol. The ethanoate that left is unreactive, so 2 mol are consumed.

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Answer: 2

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