Alkynes undergo hydration according to Markovnikov's rule
in the presence of catalyst HgSO4 and H2SO4 to give ketones.
Exception : Ethyne gives aldehyde instead of ketones.
From acid chlorides
Acid chloride is hydrogenated over catalyst Pd on BaSO4 and partially poisoned by the addition of Sulphur or quinoline to
Important points regarding Rosenmund's reaction
Sulphur (or quinoline) acts as poison for catalyst and prevent further reduction into alcohol.
Formaldehyde cannot be prepared by this method because formyl chloride (HCOCl) is unstable at room temperature.
Ketones cannot be prepared by this reaction.
Preparation of ketones
Treatment of acid chloride with dialkylcadmium [(R)2Cd] gives ketones.
Nitriles are first reduced to corresponding imines with SnCl2 in
the presence of HCl, which on hydrolysis give corresponding aldehydes. Preparation of aldehydes by this method is known as
Imines contain carbon-nitrogen double bond and have the following structure :
Nitriles can alternatively be reduced by diisobutylaluminium hydride (DiBAL-H) to imines, which on hydrolysis gives corresponding
Similarly, esters are also reduced to aldehydes with (DiBAL-H).
Treatment of nitriles with Grignard's reagents followed by hydrolysis yield ketones.
Exception : HCN reacts with Grignard's reagents to form aldehyde (not ketone).