Chlorination of Irgasan DP300 and formation of dioxins from its chlorinated derivatives

Irgasan DP300 (2,4,4'-trichloro-2'-hydroxydiphenyl ether) (I), an antimicrobial agent for use with fabrics, was easily chlorinated with sodium hypochlorite to give 2',3,4,4'-tetrachloro-2-hydroxydiphenyl ether (II), 2',4,4',5-tetrachloro-2-hydroxydiphenyl ether (III) and 2',3,4,4',5-pentachloro-2-hydroxydiphenyl ether (IV). Irgasan DP300 and its chlorinated derivatives were readily converted into polychlorinated dibenzo-p-dioxins (PCDDs) by heating: Irgasan DP300 was converted into dichlorodibenzo-p-dioxin(s) (di-CDD, 42%); II into two trichlorodibenzo-p-dioxins (tri-CDDs, 22%) and three tetrachlorodibenzo-p-dioxins (tetra-CDDs, 46%); III into two tri-CDDs (44%), more than two tetra-CDDs (25%) and pentachlorodibenzo-p-dioxin(s) (penta-CDD, 1%); and IV into two tetra-CDDs (16%), trace amounts of penta-CDD(s) and four hexachlorodibenzo-p-dioxins (hexa-CDDs, 40%). Although UV irradiation of Irgasan DP300, II and III gave PCDDs, the amounts of PCDDs formed were much smaller than those obtained by heating. Moreover, PCDD was not detected in the UV irradiation of IV. The identified products suggested that disproportionation of chlorine atom(s) occurred in the photolysis.