Photochemical reactions of chloroaromatic compounds

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Konstantinov, Alexandre
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University of Guelph

A novel reaction of successive photocyanation common for various classes of highly chlorinated aromatic compounds was discovered. The products of photolysis of polychlorinated aromatics in the presence of sodium cyanide were polycyanated hydroxychlorocompounds with various degrees of chlorine replacement. Products from some substrates were isolated, identified and characterized. The quantum yields of disappearance in the presence of sodium cyanide were determined for a number of structurally diverse chloroaromatic compounds. The quantum efficiency of photocyanations was found to increase with the number of chlorine substituents on a substrate. Sensitization and quenching experiments established the triplet excited state to be reactive for all tested compounds, consistent with the suggested SN2Ar* mechanism for the successive photocyanation. To date, the synthetic potential of the reaction is low because of low selectivity. In related work, a method for on-site destruction of dioxins in small quantities of liquid laboratory. waste using UV light was developed and applied to both standard congeners and waste samples from an analytical laboratory. The novel feature was the use of a low power, low pressure mercury arc as the radiation source. The problem of poor material balance in photolysis of dioxins was resolved by photolyzing tritiated 2,3,7,8-TCDD as a tracer compound and locating the missing material in the polar fractions. These products were identified by ES-MS as hydroxylated aromatic compounds, indicating that as much as 80% of the photolysis, proceeds by C-O rather than C-Cl homolysis. Biological assays demonstrated that the products formed upon photolysis of 2,3,7,8-TCDD lost the toxic effects associated with dioxins' receptor binding ability and did not bind to the estrogen receptor. This information is very important for the practical applications of the UV treatment methods, because it shows that the photolysis products are likely to have low toxicity, and can therefore be disposed of by conventional means.

photochemical reactions, chloroaromatic compounds, photolysis, photocyanation