Abstract
The pyrolysis of thiophene in a nitrogen carrier has been studied between 866 and 1233K in a quartz vessel in static and flow apparatuses. The reaction appears to be homogeneous and gas phase. The major products of the reaction are hydrogen,methane,acetylene,hydrogen sulphide,butadiene, carbon disulphide,benzene,naphthalene, benzothiophene,phenylthiophene and the bithiophenes. The disappearance of thiophene is given by the rate equation: -d [Thiophene]/dt = 10[12.8] [Thiophene] exp (-323.3/RT) The rate of evolution of hydrogen is given by d[H2]/dt = 10[9.5] [Thiophene] [3/2] exp(-223.8/RT) and the rate of evolution of bithiophene was similar. Individual rate equations for the evolution of the bithiophene isomers were obtained. The results may be explained by a free-radical mechanism initiated by fission of the thiophene ring. Two distinct chains seem to be involved,one leading to bithiophenes and hydrogen and the other to ring fission products such as methane,acetylene,carbon disulphide and benzothiophene. The reactions of phenyl radicals generated by pyrolysis of benzil were also investigated. Benzil decomposes at a rate given by: -d [Benzil]/dt = 10[14.0] [Benzil] exp (-210.4/RT) When phenyl reacts with benzene the yield of biphenyl increases with temperature. A chain length of about five was obtained. This cannot be explained by quadratic chain termination or diffusion of radicals to the wall and the mechanism is uncertain. The reaction of phenyl with thiophene follows a similar pattern. A number of experiments were performed on the pyrolysis of benzene, 2-iodothiopheneand 2-bromothiophene. The relative rates for the addition of phenyl radicals to chlorobenzene and thiophene were measured.