PHOTOCHEMICAL NITRATION BY TETRANITROMETHANE .35. A POSSIBLE ADDITIONELIMINATION PATHWAY IN THE PHOTOCHEMICAL-REACTION OF 2,5-DI-TERTBUTYL-1,4-DIMETHOXYBENZENE AND TETRANITROMETHANE/

The photolysis of the charge transfer complex of 2,5-di-tert-butyl-1,4 -dimethoxybenzene (1) and tetranitromethane gives exclusively 4-tert-b utyl-2,5-dimethoxynitrobenzene (2) in both dichloromethane and acetoni trile at room temperature. Photolysis in dichloromethane in the presen ce of trifluoroacetic acid (0.10-1.0 mol dm(-3)), gives 2,5-di-tert-bu tyl-1,4-benzoquinone (3) (6-25%), 5-tert-butyl-4-methoxy-1,2-benzoquin one (4) (9-25%) and 5-tert-butyl-4-methoxy-1,2-dihydroxybenzene (5) (1 3-25%) together with 2 (25-71%). Nitration of 1 with HNO3/acetic anhyd ride or a solution of nitrogen dioxide in dichloromethane gives 2 as t he main product, together with products 3-5. It is suggested that 2 is formed in the photolysis by the decomposition of transient adducts, i n which trinitromethyl and NO2 have been added across the aromatic rin g. The protonation of trinitromethanide by trifluoroacetic acid elimin ates the nucleophile and thus inhibits the formation of adducts, and t he products are then formed mainly by coupling of nitrogen dioxide wit h the radical cation 1(.+) or 1.