Chapter 21.2, Problem 4P

When phenylacetaldehyde $\left({\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{CH}}_{\text{2}}\text{CHO}\right)$ is dissolved in ${\text{D}}_{\text{2}}\text{O}$ with added $\text{DCl}$, the hydrogen atoms $\alpha$ to the carbonyl are gradually replaced by deuterium atoms. Write a mechanism for this process involves enols as intermediates.