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The thermal reaction of phenylazotriphenylmethane and naphthylazotriphenylmethane derivatives with sulphur dioxide

1969; Elsevier BV; Volume: 25; Issue: 15 Linguagem: Inglês

10.1016/s0040-4020(01)82832-5

1464-5416

Hiroshi Takeuchi, T. NAGAI, N. Tokura,

Sulfur-Based Synthesis Techniques

The thermal reaction of phenylazotriphenylmethane, (I), with SO2 in benzene or n-heptane gives triphenylmethyl phenyl sulphone (II) in good yield. This reaction is suppressed by a radical scavenger such as n-butylmercaptan to give n-butyl triphenylmethyl sulphide. The kinetic data obtained from the decomposition of I in liquid SO2 does not differ much from the data in toluene. However, when two crossed reactions were carried out using two chemically labelled azo compounds in each case, the respective crossover compounds were not observed, although the two azo compounds chosen decomposed at approximately the same rate. Moreover, the intermolecular coupling product, diphenyl disulphone, was not formed. These facts suggest that the formation of II is not a 4-center type configuration or an intermolecular radical mechanism, but through an intramolecular radical reaction due to a special cage of SO2. The evidence that II could be derived from the phenylsulphonyl radical rather than from the triphenylmethylsulphonyl radical was obtained from the fact that the triphenylmethyl radical (π-character radical) formed from 1-diphenylmethylene-4-trityl-2,5-cyclohexadiene (Gomberg's trityl) does not react with SO2, but does react with O2 to give bis-triphenylmethyl peroxide. On the other hand, the reaction of I with SO2 in the presence of O2 yields p-hydroxytetraphenylmethane and benzenesulphonic acid, but neither II nor bis-triphenylmethyl peroxide are formed, suggesting that the reaction in the presence of SO2 and O2 is ionic. Also, the addition of iodine to the system (I-SO2-benzene or n-heptane) does not suppress the formation of II. This may be interpreted that iodine does not act as a scavenger, since iodine forms a complex with SO2 Moreover, phenylazotriphenylmethane and naphthylazotriphenylmethane derivatives when treated with SO2 in benzene give the corresponding sulphones. In these reactions, it was shown that σ-character radicals (p-methoxy, p-chloro, and m-nitrophenyl radicals, or α- and β-naphthyl radicals) react with SO2 to give sulphonyl radicals. In this case, the α-naphthyl radical reacts sluggishly owing to the steric effect of the peri-position of naphthalene ring.