question_answer

The reaction sequence\[C{{H}_{3}}C{{H}_{2}}COOH\xrightarrow{SOC{{l}_{2}}}A\]\[\xrightarrow{Pd/BaS{{O}_{4}}}B\xrightarrow{HOC{{H}_{2}}C{{H}_{2}}OH}C\]C is most likely to be

A)   

B)  

C)  \[C{{H}_{3}}-C{{H}_{2}}-CHO\]

D)  

Correct Answer: B

Solution :

                 \[\underset{propionic\text{ }acid}{\mathop{C{{H}_{3}}C{{H}_{2}}COOH}}\,\xrightarrow{SOC{{l}_{2}}}\underset{\begin{smallmatrix}  \left( A \right) \\  propanoyl\text{ }chloride \end{smallmatrix}}{\mathop{C{{H}_{3}}C{{H}_{2}}COCl}}\,\]              \[\xrightarrow[\begin{smallmatrix}  Rosenmund \\  reaction \end{smallmatrix}]{Pd/BaS{{O}_{4}}}\underset{\begin{smallmatrix}  (B) \\  propanal \end{smallmatrix}}{\mathop{C{{H}_{3}}C{{H}_{2}}.CHO}}\,\]          When propionic acid reacts with thionyl chloride \[(SOC{{l}_{2}})\], then \[-OH\] group of carboxylic acid replaced by \[-Cl\] group and propanoyl chloride  is formed which reacts with \[Pd/BaS{{O}_{4}}\] and compound , ie, propanal is obtained (Rosenmund reaction). This compound , ie, propanal reacts with ethylene glycol, gives a cyclic acetal compound .