Catalytic hydrodechlorination of 2,4,4′-trichloro-2′-hydroxydiphenylether under mild conditions

More than 99% of 2,4,4'-trichloro-2'-hydroxydiphenylether (TCPE) by the catalytic hydrogenation over palladium/carbon was firstly dechlorinated under mild conditions. Used molecular hydrogen as the reducing agent, TCPE was completely hydrodechorinated to 2-hydroxydiphenylether (PE) at 50degreesC and under normal pressure. The solvents affected not only the rate of the dechlorination, but also the selectivity of the hydrogenation. In general, the rate of the dechlorination decreased in the order of alcohols > alkanes > arenes > heterocycles. Addition of the bases (such as sodium hydroxide, sodium carbonate, sodium bicarbonate, triethylamine and pyridine, etc.) to the reaction systems also changed the rate of the reaction and the selectivity of the dechlorination. Except for pyridine, the other bases obviously accelerated the rate of the dechlorination. When the mixture of ethanol-water was used as the reaction solvent instead of ethanol, the rate of the dechlorination was remarkably improved. When a stoichiometric amount of sodium hydroxide was utilized as the proton acceptor in ethanol-water solvent, the catalytic life and the stability of the palladium/carbon were dramatically enhanced and promoted. The dechlorination process worked well in either organic solvents or aqueous solution and thus had potential application in the remediation of contaminated industrial waste water as well. (C) 2003 Elsevier Science B.V. All rights reserved.