Butanoic acid is converted as follows: (i) $\mathrm{SOCl}{}_2$; (ii) excess $\mathrm{NH}{}_3$; (iii) $\mathrm{P}{}_2\mathrm{O}{}_5$, heat; (iv) $\mathrm{CH}{}_3\mathrm{MgBr}$ (1 equiv), dry ether; (v) $\mathrm{H}{}_3\mathrm{O}{}^{+}$. The final product is

(i) gives butanoyl chloride; (ii) gives butanamide; (iii) dehydrates it to butanenitrile, $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{CN}$. (iv) The Grignard adds once to the nitrile to give the magnesium imine salt, which (v) hydrolyses to the ketone $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2-\mathrm{CO}-\mathrm{CH}{}_3$, pentan-2-one.