COMPETITIVE REACTIVITIES OF VINYLTHIYL RADICALS THERMALLY GENERATED FROM HALOETHYLENES AND HYDROGEN-SULFIDE

Acetylene and its derivatives have been used for the first lime as ''t raps'' for vinylthiyl radicals generated in situ from hydrogen sulfide and haloethylenes in gas-phase processes. The competitive reactivity of the vinylthiyl radicals has been studied at 500-570 degrees C in th e presence of two chemical ''traps''. The efficiency of chemical ''tra ps'' for the vinylthiyl radicals decreases in the following sequence: HC=CPh > HC=CH > MeC=CH > CH2=CHCl. Acetylene is a more efficient ''tr ap'' for the vinylthiyl radicals than 1,2-dichloroethylene. from which they have: been generated. The beta-phenylvinylthiyl radicals generat ed during cothermolysis of halostyrene-hydrogen sulfide-acetylene comp onent ternary systems undergo first of all intramolecular ring closure to give benzothiophene, which is a thermodynamically favorable system ; the reaction of these radicals with acetylene and its derivatives oc curs much more slowly than heterocyclization. Phenylacetylene is a mor e efficient ''trap'' than acetylene. alpha-Phenylvinylthiyl radicals m ostly react with acetylene to yield 2-phenylthiophene.