ADDITION AND CYCLIZATION REACTIONS IN THE THERMAL-CONVERSION OF HYDROCARBONS WITH ENYNE STRUCTURE .2. ANALYSIS OF RADICALS AND CARBENES FROM ETHYNYLBENZENE

The pyrolysis of ethynylbenzene (1) in helium was studied in a tubular flow reactor at 10.7 mbar/1030 degrees C and reaction times ranging f rom 5 to 30 ms. Reactive intermediates such as radicals and carbenes w ere scavenged with dimethyl disulfide (DMDS). Qualitative and quantita tive analysis of the scavenging products and of the stable pyrolysis p roducts were carried out by GC-MS analysis. - The radicals phenyl (2a) , o-, m-, and p-ethynylphenyl (1c, d, e), 2- and 1-phenylvinyl (1a, b) 1- and 2-naphthyl (3a, b), methyl, hydrogen atoms, and radicals resul ting from the addition of phenyl and ethynylphenyl radicals to the tri ple bond of ethynylbenzene were detected. Carbenes, such as phenylviny lidene, occur only in small traces and obviously play no role in the o verall pyrolysis. Concentration profiles of the radicals and of some i mportant pyrolysis products are presented and discussed. Based on the detected radicals, a reaction scheme for the pyrolysis of ethynylbenze ne is proposed. Results of pyrolyses of mixtures of ethynylbenzene and ethyne show that naphthalene (3), acenaphthylene (12), and other comp ounds are produced by a sequence of ethyne addition and cyclization re actions.