448 



tliis reaction aiul tlie keloii lediictioii were primarily the same, and 

 that it is, therefore, illogical to assume that water wonid he an 

 anti-cataljsl in the ketone reduction. It has really appeared in a 

 new investigation, that there would be no question at least of a 

 considerable anti-catalytic action of water, but that the error made 

 before, which has, unfortunately, already been ado|)ted in the hand- 

 books '), must be attributed to a wrong interpretation of the 

 experiments made at the time. 



It seems to me of use to discuss this a little more at length, if it were only 

 to point out how easily certain phen(imena are overlooked in the study of a 

 reaction. For at lirst I made my experiments on the photochemical ketone reduc- 

 tion in such a way that 1 illuminated the 96"/,, alcoholic solution in a thin layer 

 in ope)i flasks, but did not observe then anything of the crystallisation of 

 the sparingly soluble pinacone already described by Uiamician '). This succeeded 

 however without any difficulty when 1 used absolute alcohol — as Ciamician 

 also did - , and besides worked in closed apparatus, hence with exclusion of 

 oxygen. I then drew the very plausible conclusion, which proved erroneous after- 

 wards, that water would be a strong anti-catalyst, and quite overlooked the 

 interesting photo -catalytic alcohol oxidation in which — the results of this paper 

 are a convincing proof of this — aldehyde does appear, but no pinacone'), and 

 which was not discovered until a few years later. 



c. In order to be able always to have a great excess of oxygen 

 at our dis|)Osal, the reaction vessel after addition of 5 C(^ of the 

 solution to be examined, is filled with oxygen which is saturated 

 with alcohol vapour in a washing bottle. Under these circumstances 

 the solution always remains more than sufficiejilly saturated with 

 0X3'gen ; it is, however, without influence on the result of the 

 measurements, if the gas in the reaction vessel is air or oxygen; 

 for the sake of safety oxygen was, however, always taken. 



The measurements, the results of which are combined in the 

 following table, extend chiefly over the following series of ketones: 



a. tienzophenon and its hydration products in the nucleus, 



b. acetophenon and some alkyl-, and also phenyl substitution pro- 

 ducts in the CH,-group, 



c. the phenyl substitution products of acetone, 



d. the simplest aliphatic, aromatic, and fat aromatic «-pf-diketones, 



e. some «-fi-y-trikelones. 



The figures over the horizontal division line indicate the molar 



1) HouBEN — Weyl. Die Methoden der organischen Chemie '2te Aufl. (1922), 

 Band 11 pag. 983. 

 ^ 2) GiAMiciANandSiLBER, Ber. 33 2911 (1900); 34 1530 (1901); 44 1288(1911). 



^) BöEöEKEN and Cohen, I.e. 



■ 



