Investigations into the Mechanism of the Photodechlorination of Pentachlorobenzene
Abstract
Several experiments were undertaken to investigate the mechanism of photodechlorination of pentachlorobenzene. The thermal methoxydechlorination reaction of pentachlorobenzene was studied. In DMSO at 50 C sodium methoxide reacts smoothly with pentachlorobenzene to give three tetrachloroanisole isomers. A second-order kinetic plot for this reaction is linear to high precision, indicating that the reaction is second order overall. The proposed structure of the pentachlorobenzene radical anion formed by photolysis in the presence of triethylamine is analogous to the sigma-complex intermediate in the SNAr reaction. The regiochemistry of these two types of dechlorination was compared and showed a fair correlation. Tetrachlorophenyl radicals were generated by thermal decomposition of 1,2,4,5- tetrachlorobenzeneazotriphenylmethane in the presence of CCl4 and a hydrogen atom donor. The results support the hypothesis that, in the photolysis of pentachlorobenzene in the presence of triethylamine, the intermediate tetrachlorophenyl radical exists as an unencumbered free radical rather than in a solvent caged pair with triethylamine. It was anticipated that the rate of photodechlorination would increase in micellar solutions if triethylamine was added. Experiments showed no such expected increase in rate, and showed regiochemistry similar to that of the same reaction in the absence of triethylamine.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 31, 1991
- Accession Number
- ADA245264
Entities
People
- Robert D. Schmidt
Organizations
- Oregon State University