Chapter 18.21, Problem 46P

Interpretation Introduction

Interpretation: Reason behind the formation of acetone containing ${}^{\text{18}}\text{O}$ when enzymatic decarboxylation of acetoacetate is carried out in ${\text{H}}_{\text{2}}{}^{\text{18}}\text{O}$ has to be stated.

Concept introduction: Decarboxylation of acetoacetate is initiated by an enzyme named acetoacetate decarboxylase.  Enzyme forms protonate imine with substrate acetoacetate. It loses carbon dioxide in presence of a ${\text{H}}_{\text{2}}{}^{\text{18}}\text{O}$ to form an enamine.  The reaction proceeds further and undergoes hydrolysis to regenerate the enzyme.