Methyl propanoate, $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{COOCH}{}_3$, is treated with excess $\mathrm{CH}{}_3\mathrm{MgBr}$ and then $\mathrm{H}{}_3\mathrm{O}{}^{+}$. The organic alcohol product is

An ester takes two equivalents of Grignard reagent: the first gives a ketone ($\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{COCH}{}_3$) after loss of $\mathrm{CH}{}_3\mathrm{O}{}^{-}$, the second adds to it. The tertiary alcohol is $\mathrm{CH}{}_3\mathrm{CH}{}_2-\mathrm{C}(\mathrm{CH}{}_3){}_2-\mathrm{OH}$, 2-methylbutan-2-ol, with methanol as by-product.