Free radical reactions at high pressures (Modern aspects of physical chemistry at high pressure : the 50th commemorative volume)

Abstract

In this article the author does not present the complete review of the works concerning free radical reactions at high pressures. He aims at the presentation of the principles, conclusions, and explanations which are the most inetresting from his point of view. Thus the author dwells upon two domains viz. Free radical reactions in the liquid phase and solid-phase reactions initiated by shear. These two divisions considerably differ in the amount of experimental data as well as in the level of theoretical development. The review includes in particular the following points. The rate of radical "cage" reactions may be determined by that of the rotational diffusion and consequently may decrease as the pressure increases. The chain termination in thermal polymerization of styrene seems to proceed in kinetical area because the reaction is characterized by a negative activation volume. There exist quantitative relations between the rate constant and activation volume of the radical substitution reactions involving the transfer of H atom from organic compounds to the Free radical. The existence of the relations is stipulated by different lengthening of valence bonds in the transition state. Deformation of organic substances at high pressure gives rise to new chemical and kinetical phenomena which can not be interpreted from the known points of view on high pressure effects.