In situ formation of arenediazonium salts and aryl radicals by aprotic nitrosation of 1,3-diaryltriazenes: dual halogen abstraction from bromotrichloromethane, and radical arylation of aromatic compounds

Abstract

Nitrosation of 1,3-diaryltriazenes (XC6H4·NHN2·C6H6X; X = H, 4-Me, 4-MeO, 4-Cl, 4-NO2, 2-Me, 2-Cl, or 3-Cl) by pentyl nitrite in benzene at 80 °C, and subsequent in situ decomposition of the resulting N-nitroso-1,3-diaryltriazenes, gives biaryls (XC6H4Ph)(54–142 mol per 100 mol of triazene). 1-(4-Chlorophenyl)-3-phenyltriazene gives a mixture of 4-chlorobiphenyl (66 mol per 100 mol) and biphenyl (65 mol per 100 mol). That aryl radicals are involved follows (a) from the formation of 2-(18.5%), 3-(49.5%), and 4-(32%) t-butylbiphenyls (total yield 106 mol per 100 mol) on nitrosation of 1,3-diphenyltriazene in t-butylbenzene, and (b) from the relative extents of reaction of this nitrosated triazene with benzene and chlorobenzene (excess of an equimolar mixture; ratio 1 : 1.6, respectively). Reaction of pentyl nitrite with 1,3-diphenyltriazene in bromotrichloromethane at 15 °C gives a precipitate of benzenediazonium chloride (80 mol per 100 mol). Also formed are bromobenzene (33), chlorobenzene (21), carbon dioxide (10), and pentyl carbanilate (10) mol per 100 mol). At 50 °C the reaction gave chlorobenzene (61) and bromobenzene (49); addition of 1,1-diphenylethene led to an almost complete reversal of these proportions. These results provide another example of anomalous dual halogen abstraction from bromotrichloromethane and support the general mechanism for this type of reaction outlined in the preceding paper.