36 GENERAL AND PHYSICO-CHEMICAL. 



ions, which transform benzaldehyde into benzoin according to the following 

 equation: 



2C 6 H 5 .COH = C 6 H 5 .CO.CH(OH).C 6 H 



If those bodies which accelerate a reaction are to be considered as catalysts, 

 then certainly the solvents must belong to the catalytes. Attention must be 

 called to the enormous influence which the solvent can exert upon the velocity 

 of a reaction under otherwise equal conditions. Thus MENSCHUTKIN 2 found for 

 the reaction 



(C 2 H 5 )3.N+C 2 H 6 .I = (C 2 H 6 ) 4 .N.I., 

 the following velocity in different solvents: 



Hexane 0.00018 



Heptane . 000235 



Xylene 0.00287 



Benzene 0.00584 



Ethyl alcohol 0.03660 



Benzyl alcohol f . .0. 13300 



Recently BREDIG and FAJANS 3 have been able to show that an optically active 

 solvent can help in the decomposition of optical antipodes to a varying extent. 

 Of the optical antipodes 'of campho-carboxylic acid, the d-form is 17 per cent 

 more quickly decomposed than the /-form, when they are dissolved in nicotine 

 or when nicotine is present, dissolved with the catalyte, while in an optically 

 indifferent solvent and without any nicotine the catalyte decomposes both forms 

 with equal rapidity. The reaction proceeds differently with or without catalyst, 

 and hence the catalyst brings about changes in reaction other than those of velocity. 

 It is apparent that this does not conform with OSTWALD'S definition of a catalyst 

 (page 33). It must be mentioned that BREDIG and FISKE have been able to 

 perform the asymmetric synthesis of benzaldehyde and hydrocyanic acid by means 

 of quinine and quinidine as catalysts (page 60). 



Catalysis in Heterogeneous Systems. The above-treated catalytic 

 processes all occur in homogenous systems, i.e., the systems which by 

 mechanical means cannot be separated into different constituents. In 

 heterogeneous systems with phases which can be separated from each 

 other by mechanical means, catalytic reactions can also occur, and 

 indeed, in such cases the substances taking part [in the reaction and 

 the catalyst occur in different phases. Such a reaction is the union of 

 detonating gas, the synthesis of SOs (from 862 and 0), and the decom- 

 position of H202 by platinum. In case the system is two-phased, and 

 the reaction takes place only at the boundary between both phases, or 

 in the one we can differentiate two simple limits: 



1. The accumulation of the bodies which are necessary for the 

 reaction at the proper place takes such a short time that in comparison 



1 Stern, ibid., 50, 513 (1905). 



*/6w2., 6,41 (1890). 



8 Ber. d. d. chem. Gesellsch., 41, 752 (1908). 



