Thermal decomposition of ethylbenzene, styrene, and bromophenylethane: UV absorption study in shock waves

Abstract

Shock wave studies of the pyrolysis of ethylbenzene, isopropylbenzene, tert-butylbenzene, styrene, and 1-bromo-1-phenylethane were performed using UV molecular absorption spectroscopy. By extensive spectral studies over the range 190-330 nm the overlapping absorption continua could be separated. Key observations in ethylbenzene pyrolysis were the dominance of a primary C-C bond split, the comparable fast fragmentation of benzyl radicals in agreement with observations from other benzyl sources, and the evidence for nonnegligible styrene formation. The following rate constants were derived: ethylbenzene ..-->.. CH/sub 3/ + benzyl, k/sub 1/ = 10/sup 15.55/ exp(-306.7 kJ mol/sup /minus/1//RT) s/sup +/minus/1/; styrene ..-->.. benzene + acetylene, k/sub 15/ = 10/sup 11.2/ exp(-244.5 kJ mol/sup /minus/1//RT) s/sup /minus/1/; 1 bromo-1-phenylethane ..-->.. HBr + styrene, k/sub 22/ = 10/sup 12.5/ exp(-160 kJ mol/sup /minus/1//RT) s/sup /minus/1/; benzyl fragmentation rates were identical with results from toluene, benzyl iodide, benzyl chloride, and other benzyl precursors. There is evidence for a dominant C-C bond split in isopropylbenzene and tert-butylbenzene pyrolysis as well.