Triphenylacetyl chloride

In certain sensitive compounds, such as triphenylacetyl chloride, decar-bonylation may be the major reaction (59). Palladium, the preferred catalyst for the Rosenmund reduction, is also an excellent catalyst for decarbonylation of aldehydes (27,28,65), and decarbonylation may occur after aldehyde formation. 

The acyl-alkyl rearrangement becomes a main path with some acyl halides. Actually, formation of the decarbonylation product has been reported in several cases as an abnormal reaction of the Rosenmund reduction. Sterically hindered acyl halides such as diphenylacetyl and triphenylacetyl chlorides and naphthoyl chloride undergo decarbonylation in attempted Rosenmund reduction (Scheme... 

Several observations indicate that this is reasonable. When a mixture of benzaldehyde and wo-butyryl chloride is treated with the organotin hydride, benzyl iro-butyrate is formed, but iro-butyl benzoate is not. Similarly when a mixture of benzoyl chloride and wo-butyraldehyde is reduced wo-butyl benzoate is formed, but benzyl iso-butyrate is not. Ethyl chloro-formate is reduced very slowly at 80° C by tri-n-butyltin hydride, but the addition of 2 mole-% of azobisisobutyronitrile leads to facile reduction. When triphenylacetyl chloride is reduced at 100° C with the same hydride the products include triphenylacetaldehyde, triphenylmethane, and carbon monoxide, but little, if any, j8,j8,j3-triphenylethyl triphenylacetate. The formation of carbon monoxide and triphenylmethane can be attributed to decarbonylation of the intermediate acyl radical to the more stable trityl radical, Eq. (61), which subsequently abstracts a hydrogen atom from the... 

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