Question

Complete the following sequence of reactions and write structures for A, B, C.

\[\ce{Dry ice ->[i. Dry ether][ii. Hydrolysis] A ->[PCl5] B ->[H2(gas)][Pd - BaSO4] C}\]

Answer 1

\[\ce{\underset{\text{Alkyl magnesium halide}}{R - Mg - X} + \underset{\text{dry ice}}{O = C = O} ->[dry ether] \underset{\text{complex}}{R - COOMgX} ->[HOH][dil.HCl] \underset{\text{Carboxylic acid (A)}}{R - COOH} + Mg(X)OH}\]

\[\ce{\underset{\text{Carboxylic acid}}{R - COOH} + PCl5 ->[\Delta] \underset{\text{Acyl chloride (B)}}{R - COCl} + POCl3 + HCl}\]

\[\begin{array}{cc}
\phantom{}\ce{O}\phantom{....................}\ce{O}\phantom{.......}\\
\phantom{}||\phantom{....................}||\phantom{.......}\\
\ce{\underset{\text{Acyl chloride}}{R - C - Cl} ->[H2(gas)][Pd - BaSO4] \underset{\text{Aldehyde (C)}}{R - C - H} + HCl}
\end{array}\]