Solution:
Solution
I-propyne reacts with methyl magnesium bromide to form prop-1-ynylmagnesium bromide which is compound A. Methane is the byproduct. The prop-1-ynyl anion acts as a nucleophile and attacks carbon dioxide. This is followed by hydrolysis to form but-2-ynoic acid which is compound B.
$$\displaystyle CH_{3}-C\equiv C-H\xrightarrow{CH_{3}MgBr}CH_{4}+ \underset {\left ( A \right )} {CH_{3}-C\equiv C-MgBr}\xrightarrow[\left ( ii \right )H_{2}O/H^{\oplus } ]{\left ( i \right )CO_{2}}\underset {\left ( B \right )} {\displaystyle CH_{3}-C\equiv C-COOH}$$
