THE MERCURY-PHOTOSENSITIZED DECOMPOSITIONS OF PROPANE AND ETHANE

Abstract

The mercury-photosensitized decompositions of propane and ethane have been studied at pressures of 300 and 600 mm, at 24 °C, at very low conversions. Hydrogen was the only product identified and measured. The hydrogen yield fell rapidly at first, with increasing time of irradiation, and finally became constant. This behavior is attributed to the accumulation in the system of propylene or ethylene formed by the disproportionation of propyl or ethyl radicals, and the constant rate of hydrogen production finally achieved is thought to correspond to a steady-state concentration of the unsaturate. Previous values of the quantum yields of these decompositions were probably measured in this steady-state region, and must be corrected upwards.Relative values have been estimated for the various rate constants involved in this mechanism. There is some evidence that energy-rich radicals, formed by the addition of hydrogen atoms to the unsaturates, tend to disproportionate rather than dimerize.