other than acetylene gives ketones CH C CH + H OH CH C = CH HgSO H SO Isomerises enol propanone CH C CH prop - - yne . From calcium salts of carboxylic acids Aldehydes and ketones may be prepared by the dry distillation of calcium salts of carboxylic acids. a) Aldehydes are obtained when the mixture of calcium salt of carboxylic acid and calcium formate is subjected to dry distillation. Ca H C H + CaCO Dry distillation Calcium methanoate methanal H C O H C O Ca + Ca dry distillation CH C H + 2CaCO Calcium ethanoate Calcium methanoate ethanal CH C O CH C O O C H O C H b) Symmetrical ketones can be obtained by dry distillation of the calcium salt of carboxylic acid (except formic acid) dry distillation CH + CaCO Calcium ethanoate Ca propanone XII U12-Carbonyl XII U12-Carbonyl - - - - B.
Preparation of aldehydes ) Rosenmund reduction a) Aldehydes can be prepared by the hydrogenation of acid chloride, in the presence of palladium supported by barium sulphate. This reaction is called Rosenmund reduction . Example CH C Cl + H CH C H + HCl Pd/ BaSO Acetyl chloride Acetaldehyde In this reaction, barium sulphate act as a catalytic poison to palladium catalyst, so that aldehyde cannot be further reduced to alcohol. Formaldehyde and ketones cannot be prepared by this method.
. Stephen's reaction When alkylcyanides are reduced using SnCl / HCl , imines are formed, which on hydrolysis gives corresponding aldehyde. H O SnCl /HCl (H) CH C CH CH=NH CH CHO + NH . Selective reduction of cyanides Diisobutyl aluminium hydride (DIBAL –H) selectively reduces the alkyl cyanides to form imines which on hydrolysis gives aldehydes.
Example CH CH CN i) AlH (iso-butyl) ii) H O CH CH CHO hex - - ennitrile hex - - enal C) Preparation of benzaldehyde . Side chain oxidation of toluene and