The kinetics of the interaction of atomic hydrogen with olefines I. Apparatus and use of para-hydrogen techniques

Abstract

It is shown in this paper that the normal techniques and methods of approach to an investigation of radical reactions are not applicable in dealing with reactions involving the addition of a hydrogen atom to an olefine, since this type of reaction is so fast that even the exchange conversion of para-hydrogen by hydrogen atoms is inhibited by very small amounts of olefines. A new type of reaction has been utilized to provide a means of competing with the olefine for a hydrogen atom, namely, the removal of a hydrogen atom on a layer of molybdenum oxide or tungsten oxide. In order to adapt the system to the measurement of reactions over a wide range of collision efficiency, a special reaction vessel is described in which the path length offered to a hydrogen atom before removal on the oxide layer can be varied. A colorimetric technique has been devised for measuring the rate of addition of hydrogen atoms to the oxide surface. This technique is shown to be very sensitive, and the addition of a very small amount of hydrogen atoms can be detected. The para-hydrogen conversion technique has been applied to illustrate how the collision efficiency of a hydrogen atom with a saturated hydrocarbon molecule can be obtained. The reaction H +RH = H2+Rhas approximately the same collision efficiency as the reaction H +p-H2=n-H2+ H, and hence in the presence of a saturated hydrocarbon there is no inhibition of the para-conversion, only retardation. A further application of the para-conversion has been to demonstrate the efficiency of the removal of a hydrogen atom on the oxides of molybdenum and tungsten.