Photochemical nitration by tetranitromethane. Part XXVI. Adduct formation in the photochemical reaction of 1,2,3-trimethylbenzene: The formation of 'double' adducts including nitronic esters

The photolysis of the charge-transfer complex of 1,2,3-trimethylbenzene and tetranitromethane gives a complex mixture of products, most of which arise by initial attack of trinitromethanide ion on the unsubstituted ring positions at C4(C6) and C5 of the radical cation of 1,2,3-trimethylbenzene. The products 7-19 are adducts resulting directly or indirectly from the addition of the elements of tetranitromethane to 1,2,3-trimethylbenzene, and the trinitromethyl aromatic compounds 22-25 are formed by eliminations from intermediate adducts. Six adducts are simple 'single' adducts, nitro-trinitromethyl adducts 7, 8, 10-12, while nitro cycloadduct 9 is formed by cycloaddition of nitro-trinitromethyl adduct 8. The remaining addition products are 'double' adducts, formed by secondary addition reactions initiated by attack of nitrogen dioxide on the buta-1,3-diene system of 'single' adducts, and include trinitro-trinitromethyl compounds 13 and 15, the hydroxy-dinitro-trinitromethyl compound 14, and a group of four nitronic esters 16-19 formed by nitro-denitrocyclization of initially formed hydroxy-trinitromethyl and nitro-trinitromethyl 'single' adducts. Minor amounts of other products are formed including two nitrodienones 21 and 22, and the rearrangement product, 4,5,6-trimethyl-2-nitrophenol (28), and the 2,3,4-trimethyl- and 3,4,5-trimethylnitrobenzenes 26 and 27. The modes of formation of the above products are discussed, and X-ray crystal structure determinations are reported for compounds 9, 13, 14, 18, 19, 22 and 29.