91 



Chemistry. — ''On the reduction of aromatic Ketones". By 

 Prof. J. BOeseken and W. D. Cohen. (Coiiinuiiiicated by Prof. 

 A. F. Holleman). 



1. This research originated in the observation by one of ns that 

 in the reduction of benzophenone by ahmiinium amalgam in 80 % 

 alcohol, therefore in a neutral medium, are formed considerable 

 quantities of benzopinacone in addition to benzhydrole. As according 

 to statements in the literature which are SLi[)ported by our own 

 observations, benzophenone may be quantitatively converted into 

 benzhydrole by zinc dust in a faintly alkaline alcoholic solution, 

 whereas reduction in an acid solution causes the formatioji of pina- 

 cone^) (or of the pinacoline secondarily resulting there from) it struck 

 us that a systematic i-esearch as to the progressive change of this 

 reduction would not be devoid of interest. 



In the reduction of benzophenone may. be formed, besides alcohol 

 and pinacone, also diphenylmethane. Klages and Allendokf") have 

 even succeeded in obtaining a quantitative yield of this hydrocarbon 

 by means of sodium and ethyl alcohol. Evidently this total reduction 

 takes place owing to a powerful aclion in a concentrated alkaline 

 medium. Presumably, stress nnist be laid here on the nature of Ihe 

 reduction agent because on usijig zinc dust in a strongly alcaline 

 alcoholic solution benzhydrole is formed almost exclusively, whereas 

 on using aluminiun) amalgam diphenylmethane may be detected. 

 Working according to Montagne's ^) directions with zinc dust we 

 have obtained from 25 grams of benzoi)henone 25 grams of crude 

 hydrole which was practically odourless consequently free from 

 di))henylmetliane. 



With magnesium amalgam (obtained by heating 2 grams of Mg 

 with 200 grams of Hg) was obtained, in absolute alcohol solution, 

 mainly benzhydrole besides a little dii)henylmethane, but no pinacone. 



As magnesium and aluminium stand nearer to sodium than zinc, 

 this result is not astonishing. 



In order not to complicate the reaction too much we have tried 

 to avoid the formation of diphenylmethane as much as possible. 



As reduction agents we have chosen : zinc dust and aluminium, 

 the latter in the form of amalgam in so far as it concerned the 

 reduction in a neutral or acid medium. 



Again, when using the latter metal we have avoided a too power- 



1) LiNNEMANN Anil 133, 6. 

 3) Berichte 31. (1898). 

 3) Recueil 25, ^02 (1906). 



