Please only answer part b

$*14\mathrm{.}36$ Barbiturates are prepared by treating diethyl

malonate or a derivative of diethyl malonate with urea in the

presence of sodium ethoxide as a catalyst. Following is an

equation for the preparation of barbital from diethyl $2,2-$

diethylmalonate and urea $($barbital$,$ a long$-$duration hypnotic

and sedative, is prescribed under a dozen or more trade

names$)$:

vienny$$

urea

$2,2-$diethylmalonate

$5,5-$Diethylbarbituric acid

$($Barbital$)$

$($a$)$ Propose a mechanism for this reaction.

$($b$)$ The $p{K}_a$ of barbital is $7\mathrm{.}4.$ Which is the most acidic

hydrogen in this molecule, and how do you account for

its acidity?C