A general synthetic procedure for the synthesis of N dinitromethyl derivatives of nitrogen containing heterocycles has been developed. The procedure includes the destructive nitration of heterocyclic N acetonyl derivatives of tetrazoles, 1,2,4 and 1,2,3 triazoles, pyrazoles, imid azoles and their bicyclic analogs, as well as imides of carboxylic and sulfonic acids and substitut ed hydrazines with mixtures of sulfuric and nitric acids. The kinetic study of the reaction mechanism was performed using UV and NMR spectroscopy. It was found that the NO 2 groups were sequentially introduced into the methylene fragment by the addition of the nitronium ion to multiple bonds of intermediate enols followed by hydrolysis of the acetyl moiety. The rate and direction of the enolization (due to the CH 2 and CH 3 groups) of the N acetonyl com pounds in sulfuric acid solutions were determined by the study of the deuterium exchange kinetics. The synthesis of the N dinitromethyl compounds is complicated by side reactions, such as the decomposition of intermediate α nitroketone, the nitration of the methyl group in the acetonyl moiety, and the nitration of the dinitromethyl products to trinitromethyl derivatives.Nitration with acidic nitrating mixtures of the active methylene moiety of carbonyl structures (1) to form dini tromethyl compounds (destructive nitration) was studied. 1 It can be assumed that the process proceeds through the formation of dinitromethylene derivatives of carbonyl compounds (1´), whose hydrolysis affords dinitromethyl compounds (2) (Scheme 1).
Scheme 1In these works, the nitration conditions were selected empirically without revealing regularities of the reaction and its mechanism, which impedes the optimization of synthesis of dinitromethyl compounds.In the present work, in order to detail processes of destructive nitration of active methylene compounds, 2-9 we studied the mechanism, kinetics, and conditions of this reaction using easily accessible N acetonylazoles 10 as an example.
Results and DiscussionWe have earlier 11 studied by 13 С NMR spectroscopy the state of N acetonylazoles in an H 2 SO 4 solution for the lowest basicity tetrazole derivatives. It turned out that on going from solutions in neutral solvents to solutions in concentrated H 2 SO 4 the direct spin spin coupling (SSC) constants ( 1 J C,H ) for the N-CH 2 group and СH cycle increase by 4-5 and 16-18 Hz for 1 and 2 acetonyltet razoles and 5 methyltetrazole analogs, respectively. The same increase in 1 J C,H in neutral media is characteristic of N acetonyltetrazolium salts 4 compared to non quater nized N acetonyltetrazoles 3: these constants for the carbon atoms in the N-CH 2 , N-Me, and C-Me fragments in crease by 4-5 Hz, whereas for the С 5 cycle they increase by 15-20 Hz. 11 It follows from this that the N acetonyl derivatives of tetrazole and 5 methyltetrazole in concen trated H 2 SO 4 are protonated to the nitrogen atom of the cycle. 12 Even in the case of low basicity nitrotetrazole (pK BH + = -9.26), 13 the corresponding ketone is p...
