Question

Select the reagents needed to effect the transformation from the carboxylic acid to the aldehyde. draw the structure of the intermediate.

Answer 1

Carboxylic Acids can be converted into the Aldehydes in following two steps,

1) Converting Carboxylic Acid into Acyl Halide;
                                                                          Carboxylic is first reacted with Thionyl chloride in order to replace a weak leaving group (-OH) with a good leaving group i.e. -Cl.

2) Converting Acyl Halide into Aldehyde;
                                                                The Acyl Halide formed in first step is treated with  Lithium tri tert-butoxy aluminum hydride, which acts as a source of Hydride and prevent further resuction of Aldehyde into Alcohols.

Reactions are as follow,