A new nitration process of N-methoxy-dinitroaniline and triarylhydrazine derivatives with sodium nitrite in the presence of crown ethers

We studied the reaction between solid sodium nitrite and derivatives of N-m ethoxy-4-R-1-2,6-dinitroaniline 1a-f (where: a, R-1 = H; b, R-1 = CH3; c, R -1 = CF3; d, R-1 = COOH; e, R-1 = COOCH3; f, R-1 = CN), of N-methoxy-6-R-2 2,4-dinitroaniline 1g-k (where: g, R-2 = H; h, R-2 = CF3; i, R-2 = CN; j, R -2 = COOH; k, R-2 = COOCH3) or of 2-(p-R-2-phenyl)-2-phenyl-1-(2,6-dioitro- 4-R-1-phenyl)-hydrazine 2a,b,d (where: a, R-1 =NO2, R-2 = H; b, R-1, = = R- 2 = NO2; d, R-1 = COOH, R-2 = H) in the presence of crown ethers. It was ob served that: compounds 1a-1e and 1g were nitrated leading to N-methoxy-2,4, 6-trinitroaniline 11 (compounds 1b - 1e being formed by ipso-substitution); compounds 2 were nitrated as follows: 2a --> 2b, 2b --> 2c [2,2-(bis-p-nit rophenyl)-1-picrylhydrazine] and 2d --> 2a (by ipso-substitution). The nitr ation is due to acid-base processes that occur in methylene chloride leadin g to the formation of nitrous acid and the corresponding anions of 1 and 2, followed by a redox homolytic process due to the NO2 free radical, formed by disproportionation of nitrous acid, which oxidizes the anions to the cor esponding free radicals, and finally by a radical + radical coupling yieldi ng the new nitroderivatives by selective nitration.