Thermal transformations of 1,4-dichlorobenzene: effects of temperature, time and presence of iron species

Abstract

The pyrolysis of 1,4-dichlorobenzene (1,4-DCB) was carried out in sealed Pyrex ampoules under various conditions and with different additives. In the absence of additives, no products were formed below 380°C, but at 400°C, addition of HO· to the benzene ring of 1,4-DCB took place. The principal source of HO· was the interaction of pyrolyzed H· and ambient O 2. At 500°C to 600°C, the principal reactions were chlorine transfer and biphenyl formation. At 500°C, in early stages of reaction, HO· reacted as before to produce chlorinated phenols, but in the later stages of reaction, dechlorination predominated. In the presence of Fe 2O 3, a potential electron acceptor, electron transfer reactions led to reduced metal ions, oxidized aromatic radicals, and halogen gas in the presence of O 2. The principal thermal reaction observed at 200°C to 300°C was chlorine transfer. At a temperature around 380–400°C, increasing amounts of chlorinated phenoxy phenols suggested that reactions between oxygen and chlorinated benzene became important. At 500°C to 600°C, continuing dechlorination reactions led to biphenyl and triphenyl. With added FeS 2, at 500°C, dechlorination occurred more efficiently than reactions with Fe 2O 3.