Chapter 23, Problem 23.8P

When ethyl acetoacetate $\left({\text{CH}}_{\text{3}}{\text{COCH}}_{\text{2}}{\text{CO}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{3}}\right)$ is treated with one equivalent of ${\text{CH}}_{\text{3}}\text{MgBr}$, a gas is evolved from the reaction mixture, and after adding aqueous acid, ethyl acetoacetate is recovered in high yield. Identify the gas formed and explain why the starting material was recovered in this reaction.