Hydrogenolysis of Acid Chlorides to Aldehydes the Rosenmund Reduction

6 Hydrogenolysis of Acid Chlorides to Aldehydes (the Rosenmund Reduction) 

The catalytic hydrogenolysis of acid chlorides to aldehydes over Pd-BaSO. has been 

The reduction may be accompanied by side reactions such as ester, acid, or acid anhydride formation, which result from overreduction of aldehydes to alcohols or to hydrocarbons and water(eq. 13.135). Thehydrogen to be used should be dry and contain no oxygen. 

The reduction of acid chlorides may proceed at lower temperatures in the presence of a tertiary amine or sodium acetate. Peters and van Bekkum improved the method of Sakurai and Tanabe,260 using ethyldiisopropylamine, instead of A(7V-dimethylaniline, as a HC1 acceptor.261 Ethyldiisopropylamine had the advantage of forming an acetone soluble hydrochloride, and workup of the reaction mixture was easier when acetone was used as solvent. Reductions in the presence of these basic substances have been found to be especially effective when the acid chlorides are labile to decarbonylation. Examples of the use of base are shown in eqs. 13.139261 and 13.140.262 When the original procedure of the Rosenmund reduction was applied to 1 -/-bulylcyclohcxanc-carbonyl chloride, f-butylcyclohexanc was the sole product, compared to greater than 95% yield of the corresponding aldehyde in the presence of ethyldiisopropylamine or sodium acetate.261 

Many examples have been described in the literature where selective transformation of acid chlorides to aldehydes was successful in the presence of other functional groups. Cinnamoyl chloride was transformed to cinnamaldehyde in 54-60% yields over Pd-BaS04 with addition of quinoline-S or thioquinanthrene.263 o-Chloroben-zoyl chloride gave o-chlorobenzaldehyde in 70% yield in reduction over 2% Pd-kie-selguhr in toluene in the presence of quinoline-S.249 Similarly, 4-chloro- and 

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