Hydrogenation bulk phase, solvent-free systems

In solvent-free systems one usual component of the liquid reaction mixture is missing hence, all the interactions of this component with the other components in the system are also missing. At the beginning, the bulk phase consists only of the substrate or of several substrates during the reaction, hydrogenation products accumulate in the reaction mixture. At first glance the system seems to be simpler than the one with solvent, but consequences of the absence of the solvent must not be forgotten. 

In a competitive hydrogenation of two substrates in a solvent-free system the relative reactivity is again given by Eq. (8). On the other hand, however, the properties of the bulk phase vary with each change in the substrate, and this change may of course variously affect the rate constants and the adsorption coefficients. Moreover, the rate constant of A cannot be directly measured in the presence of an unsaturated compound B. As a consequence, substitution of /cah and knu into Eq. (8) instead of and k, yields the values Ka/Kb subjected to the same inaccuracy. In this case, therefore, the re-... 

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