Rosenmund reaction hydrogenolysis

Catalytic hydrogenation is often chosen as a method for reduction because of its chemoselectivity for C=C double bonds and benzylic C-X bonds over C=0 groups. The most important hydrogenation involving a carbonyl compound is not actually a reduction of the C=0 double bond. Hydrogenation of acyl chlorides gives aldehydes in a reaction known as the Rosenmund reaction—really a hydrogenolysis of a C-Cl bond. 

The Pd-catalyzed hydrogenoiysis of acyl chlorides with hydrogen to give aldehydes is called the Rosenmund reduction. Rosenmund reduction catalyzed by supported Pd is explained by the formation of an acylpalladium complex and its hydrogenolysis[744]. Aldehydes can be obtained using other hydrides. For example, the Pd-catalyzed reaction of acyl halides with tin hydride gives aldehydes[745]. This is the tin Form of Rosenmund reduction. Aldehydes are i ormed by the reaction of the thio esters 873 with hydrosilanes[746,747]. 

Acid chlorides can be selectively hydrogenated in the presence of a catalyst (palladium deposited on a carrier, which is usually barium sulphate but is occasionally charcoal). The reaction, which involves the hydrogenolysis of the carbon-halogen bond, is known as the Rosenmund reduction and has been widely used for the synthesis of aromatic and heterocyclic aldehydes. 

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