Free-radical chlorination reactions of iodobenzene dichloride

Thiyl Radical Abstraction. A Mechanism for the Free Radical Substitution Reactions of Pentachlorobenzenesulfenyl Chloride

“…One explanation considered for this was a displacement reaction analogous to that observed by Miller and Walling for displacement of bromine atoms from bromobenzene by chlorine atoms (9), and by Tanner and Van Bostelen for displacement of iodine from iodobenzene by chlorine atoms (10). The yield of hexachlorobenzene did not increase in the reactions using mixtures of chlorine and PBSC, thus discounting the feasibility of proposing a displacement reaction on PBSC by chlorine atoms.…”

“…The reaction mixtures were degassed and irradiated at 40" in the same way as the cyclohexane reactions (runs [1][2][3][4][5][6][7][8][9][10][11][12]. Irradiation times of 7-10 h were required for complcte reaction as shown by con~plete disappearance of The isomer ratios were determined by n.m.r.…”

On the chemistry of iodonyl radicals. The oxidation of iodobenzene by t-butyl hypochlorite

“…The radical chain nature of the photo-initiated formation reaction was substantiated by its initiation by light, the inhibition of the reaction by small amounts of added p-cresol and galvinoxyl, and by the induced halogenation of added cyclohexane. The intermediacy of (1) by analogy to the radical addition intermediates proposed for phosphorus (1)(2)(3)(4) and sulfur (1, 6-8) compounds with t-butoxy radicals and because of the precedented involvement of iodonyl radicals in the halogenation reactions of IBBC (see discussion on chlorination reactions), iodobenzene dichloride (12,13), and the polymeric t-butyl hypoiodite reagent (14).…”

“…analysis of the product mixtures from these chlorinations. Values for the primary: secondary :tertiary reactivities of 1 :13 : 144 per hydrogen in IBBC halogenations at 40 "C were calculated from these analyses in the usual manner (12).…”

“…Sinceiodobenzene dichloride has been shown to undergo photo-initiated radical chain halogenation where phenyl iodonyl chloride is the abstracting species (1 1) the sequence of reactions [1 1, [2], [3], [5], [6], [7], and [8] must be considered in any evaluation of the halogenation reactions of IBBC. The primary :secondary:tertia.ry selectivities for hydrogen abstraction by PhICl radicals has been reported as 1 :2 1 :368 (12). The selectivity values for IBBC are clearly lower than the values reported for iodobenzene dichloride and infer that if P~I C~ radicals were operative as an abstracting species in the chain halogenation reactions of IBBC they could not be the sole chain-carrying radicals and must by necessity be involved in a mixed chain with radicals of lower selectivity, i.e.…”