The Transformation of the Triphenylmethyl Radical into the Triphenylmethyl Cation in the Sulfur Dioxide - Oxygen System

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The decomposition of phenylazotriphenylmethane (I) in the presence of SO2 and O2 in benzene at 60°C gives p-hydroxytetraphenylmethane (II) by the reaction of the trityl cation and the phenol formed in the reaction system. However, in the absence of O2 or SO2, the above-mentioned reaction produces trityl phenyl sulfone (III) or bistrityl peroxide (IV), without forming any II. Also, 1-diphenylmethylene-4-trityl-2,5-cyclohexadiene (Gomberg's trityl) (V) has been chosen as the trityl radical source, and reacted with phenol in the presence of SO2 and O2 to give II as the product. However, in the absence of SO2, IV and a trace of II are formed. Moreover, in the absence of O2 in the above system, p-benzhydryltetraphenylmethane (VI) and a small amount of II are formed. The benzene solution of VI is stable on exposure to air at 60°C. Further, the UV spectrum of V in the liquid SO2-O2 system shows λmax at 405 mμ (logε 4.1) and 434 mμ (logε 4.1) (trityl chloride in 98% H2SO4: λmax 430 mμ (logε 4.58)). However, the UV spectrum of VI in the liquid SO2-O2 system has no absorption in this range. The NMR spectrum in the liquid SO2-O2 system of V exhibits only aromatic protons (2.6–3.1 τ). These facts indicate that the trityl radical generated from V is transformed into the trityl cation in the SO2-O2 system at room temperature, whereas VI does not dissociate into the trityl radical even at 60°C in benzene.
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