Reduction of Benzaldehydes with Raney Alloys in an Alkaline Solution

Abstract

Abstract The reduction of benzaldehyde (1a) with Raney alloys in a 10% aq NaOH solution afforded benzyl alcohol (2a) in various yields (17—81%). In this reaction benzoic acid was also obtained as a by-product at the same time. This suggests that a Cannizzaro reaction competes with the reduction. In a 10% aq Na2CO3 solution the reduction of 1a with Raney alloys proceeded under ultrasonic irradiation to give almost exclusively 2a. In addition, we almost could not observe a Cannizzaro reaction in these experiments based on a comparison with a reduction in a 10% aq NaOH solution. A crossed Cannizzaro reaction between formaldehyde and benzaldehyde did not occur in a 10% aq NaOH solution/THF/MeOH, but afforded the reductive coupling compound hydrobenzoin.