PHOTOCHEMICAL NITRATION BY TETRANITROMETHANE .33. ADDUCT FORMATION INTHE PHOTOCHEMICAL-REACTIONS OF 1,2,4,5-TETRAMETHYLBENZENE AND 1,2,3,5-TETRAMETHYLBENZENE

The photolysis of the charge-transfer complex of tetranitromethane and 1,2,4,5-tetramethylbenzene in dichloromethane or acetonitrile gives t he epimeric ethyl-3-nitro-6-trinitromethylcyclohexa-1,4-dienes 8 and 9 , in addition to products of nuclear nitration 12 and side-chain modif ication 10, 11, and 13-18. Similar reactions of 1,2,3,5-tetramethylben zene gave methyl-6-nitro-3-trinitromethylcyclohexa-1,4-diene 30 and tw o isomeric 'double' adducts 31 and 32, in addition to products of nucl ear nitration 27 and side-chain modification 26, 28 and 29. The elimin ative rearrangements of adducts 8 and 30 to give re-aromatized product s in acetonitrile or [H-2(3)]acetonitrile and in [H-2]chloroform are r eported. The photolysis of the charge-transfer complexes of tetranitro methane with either 1,2,4,5-tetramethylbenzene or 1,2,3,5-tetramethylb enzene in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) gives a marked incre ase in the yields of ring-nitration products 12 or 27, respectively, r eactions presumed to proceed via a nitrosation-oxidation sequence. Rea ction of 1,2,4,5-tetramethylbenzene with excess nitrogen dioxide in HF P also results in extensive ring nitration to give 12 and 2,3,5,6-tetr amethyl-1,4-dinitrobenzene (25); the latter compound is seen as arisin g via the 2,3,5,6-tetramethyl- 1,4-dinitrosobenzene (34). Similar reac tion of 1,2,3,5-tetramethylbenzene gives ring-nitration product 27 as the major product. X-Ray crystal structures are reported for 2,4,6-tri methyl-1-(2',2',2'-trinitroethyl)benzene (26) and ethyl-6-nitro-3-trin itromethyl-cyclohexa-1,4-diene (30). (C) Acta Chemica Scandinavica 199 6.