Radical-induced deiodination of aryl iodides in alkaline methanol

Abstract

m-Chloroiodobenzene is cleaved to chlorobenzene and iodide ion when exposed to the combination of a source of reactive radicals and a high concentration of sodium methoxide in methanol. Effective radical sources include 1-phenyl-2-benzenesulfonhydrazide (3) (with atmospheric oxygen), peroxydisulfate ion, benzenediazonium ion, phenylazotriphenylmethane, and azobisisobutyronitrile. The chlorobenzene formed in CHsOD solution is substantially free of deuterium and m-chlorobiphenyl is formed in a benzene-rich solvent; the intermediacy of rn-chlorophenyl radicals is indicated. Nitrobenzene, even in small amount, largely inhibits deiodination. The cyclic mechanism of eq 6-11 is proposed. Its unique features are formation of aCH20-from -CHzOH in an acid-base reaction and electron transfer from .CHzO-to the aryl iodide, with concomitant or subsequent ejection of iodide ion and formation of aryl radical.he reaction of 1-(2-iodo-4-chlorophenyl)-2-ben-T zenesulfonhydrazide (1) with sodium methoxide in methanol was found to produce chlorobenzene, an ~~--@H--KH-SO,C,H, ' I 1 unexpected product, in addition to m-chloroiodobenzene and other products which were anti~ipated.~ Happer, who performed that experiment, obtained evidence that the chlorobenzene resulted from deiodination of the m-chloroiodobenzene under the conditions of the reaction. Moreover, his experiments suggested that for deiodination to occur, it was necessary to provide both a high concentration of sodium methoxide and a 1-aryl-2-benzenesulfonhydrazide.Thus, m-chloroiodobenzene underwent deiodination on treatment with l-(o-chlorophenyl)-2-p-toluenesulfonhydrazide in 2 M methanolic sodium methoxide, but not in the alcoholic base alone or with benzenesulfonamide in alcoholic base.Hydrazide-Induced Deiodinations. Our investigation of the deiodination reaction therefore began with the system m-chloroiodobenzene (2)-phenyl-2-benzenesulfonhydrazide (3)-sodium methoxide-methanol. A series of experiments was performed to reveal the 2 3 effects of several variables. In these experiments, 240 mg (0.001 mole) of m-chloroiodobenzene was treated

Sensitized photolysis of polychlorobiphenyls in alkaline 2-propanol: dechlorination of Aroclor 1254 in soil samples by solar radiation

“…The chain reaction can be terminated if intermediates such as (CH,),C'OH and (CH3),CO'-are removed from the reaction by either reacting with each other or with other quenchers such as oxygen and nitrobenzene. The suggested mechanism is in line with a universal mechanism proposed by Bunnet and co-workers for the photoreduction of aromatic halides by alkoxide ions (18), which predates the proposal of Nishiwaki (13) and Bunce (22).…”

“…Photolysis of Aroclor 1254 (1000 mg/L) in an NaOH (0.1 M)/2-propanol solution at 254 nm was found to proceed with an apparent high dechlorination quantum yield (Ip = 35) ( Table I) similar to that which has been observed in the photodechlorination of Kanechlor, KC-300, (Ip = 36) at 298 nm (13). Bunnet and co-workers (18) reported earlier that aromatic halides are photodehalogenated in the presence of ionic metal alkoxides through a radicalchain reaction. We found that the reaction could be thermally initiated using peroxides (described later) and that photolysis was strongly quenched by either oxygen or nitrobenzene (0.1 M).…”

Photoreduction of 1,1,2-Trichlorotrifluoroethane Initiated by TiO2 Particles

“…Earlier studies have shown that efficient reductive dehalogenations of organic halides take place in deoxygenated alcohols through free radical chain reactions. − Chain reductions of fluoro halides in homogeneous solution have been observed occasionally. ,− Only a few heterogeneous photoreductive dehalogenations have been investigated. Reductions of CCl 4 and CHBr 3 occurred in suspensions of TiO 2 -containing electron donors; , halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) was photoreduced in aqueous solutions of alcohols containing platinized TiO 2 particles .…”

Regioselective alkali metal reduction of dibenzocyclooctadiene lignan derivatives, demethoxylation followed by dehalogenation

“…Cleavage of the aryl halide then occurs to form a halogen anion and an aromatic radical. This aromatic radical would prefer another electron from the alkali metal to afford an aromatic anion rather than trigger a cycle of difficult radical reactions because the aromatic radical is unlikely to abstract a hydrogen atom from t -butanol [ 33 ]. Such a two-electron transfer cycle could occur again to remove an additional methoxy group.…”