270 L. A. NIKOLAEV 



experimental data. At the same time, the catalytic activity of simple ions of the 

 transition metals, both in their catalase-like and oxidase-like aspects, are, without 

 the slightest doubt, associated with the setting up of chains of reactions in which 

 free radicals take part. Thus, the question of the way in which complex com- 

 pounds act as catalysts, i.e. whether they form intermediate products, or whether 

 they only initiate a chain process, is obviously of fundamental importance in 

 regard to the problem of the parallelism between the action of active groups 

 and that of the models. 



In many cases the catalytic action of comparatively simple anions, e.g. those 

 of chromic, timgstic and molybdic acids, brings about the formation of inter- 

 mediate products (see review of the work of E. I. Shpital'skii, N. I. Kobozev 

 and G. A. Bogdanov [12]). Detailed analysis of the catalytic action of catalase- 

 like catalysts has shown that they form intermediate compounds with two 

 molecules of peroxide [13, 14]. It is in this compound that the process of re- 

 combination occurs, leading to the formation of a molecule of oxygen. 



On this basis we postulated that the catalytic activity of complex compounds 

 of copper like those with ammonia was brought about by the entry of two 

 molecules of hydrogen peroxide into the sphere of co-ordination of the ion. In 

 doing so the molecules of the hydroxide must have driven two molecules of water 

 out of this sphere. This hypothesis received some confirmation from the fact 

 that the rate of the reaction catalysed by the copper-ammonium complexes first 

 increased in proportion to the increase of concentration of hydrogen peroxide ; 

 the increase then fell off and the order of the reaction becomes null in relation 

 to peroxide [14]. 



It was also shown that the rate of destruction of hydrogen peroxide increases 

 as the pH rises, reaches a very spread-out maximum and, at high pH (13-14), 

 decreases somewhat. 



This sort of dependence on the concentration of hydrogen peroxide and on 

 pH is completely out of accord with the equation obtained on the basis of the 

 radical-chain theory [15]. On the other hand the kinetic picture obtained falls 

 satisfactorily within the framework of the theory of intermediate products. 



A well known way of indicating free radicals is provided by the study of the 

 influence of methyl methacrylate (and, according to our evidence, also benzene) 

 on the rate of decomposition of H2O2 [12]. 



Into a solution of hydrogen peroxide containing the catalyst, we introduced 

 a small quantity of methyl methacrylate, with the idea that, owing to competition 

 between the hydrogen peroxide and the methyl methacrylate for free radicals, 

 the rate of the reaction would fall off if the process was brought about by the 

 development of a chain. In fact, the catalytic activity of ions of copper and iron 

 was very strongly depressed by the presence of methyl methacrylate. This was 

 also to be expected as, in this case, the setting up of chains with the participation 

 of OH and HO2 radicals itself determines the whole course of the decomposition 

 of peroxide. The presence of methyl methacrylate or benzene has no effect on 

 the catalytic activity of complex compounds of copper. 



From this we may conclude that the catalytic activity of complex compounds 



