Novel energetic aminofurazans with a nitro-NNO-azoxy group

Novel energetic azoxy- and azofurazans bearing nitro-NNO- azoxy and amino groups were synthesized using the ammonolysis of some known (nitro-NNO-azoxy)furazans. 3-Amino-4-{[4′-(nitro-NNO-azoxy)f urazan-3′-yl]-NNO- azoxy}furazan displays the highest melting point (114 °C, decomp.) among the known (nitro-NNO-azoxy)furazans, optimal density (1.80 g cm⁻³), high experimental enthalpy of formation (639 kcal kg⁻¹) and mechanical sensitivity on the level of PETN. In terms of the specific impulse level, the model solid composite propellant formulations based on this compound outperform similar formulations based on RDX, HMX or CL-20 by 7–12 s.     

Synthesis of amino-substituted 1,3-bis(tert-butyl-NNO-azoxy)benzenes 2.* 2-amino and 2,4-diamino derivatives

Oxidation of one of the amino groups of 2-bromo-4,6-dichloro-1,3-phenylenediamine to the nitroso group followed by its conversion into thetert-butyl-NNO-azoxy group afforded a derivative ofm-(tert-butyl-NNO-azoxy)aniline,viz., 2-bromo-3-(tert-butyl-NNO-azoxyl)-4,6-dichloroaniline. Analogously, the second amino group was converted into thetert-butyl-NNO-azoxy group to form a derivative of 1,3-bis(tert-butyl-NNO-azoxy)benzene,viz., 3-bromo-2,4-bis(tert-butyl-NNO-azoxyl)-1,5-dichlorobenzene The reaction of the latter with ammonia yielded 2-amino- and 2,4-diamino-substituted 1,3-bis-(tert-butyl-NNO-azoxyl)benzenes. For Part 1, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2126–2130, November, 1999.     

Electrophilic substitution of thetert-butyl-NNO-azoxy group by the bromine atom

The electrophilic substitution of thetert-butyl-NNO-azoxy group by the bromine atom was observed for the first time when 6-bromo-2,4-bis(tert-butyl-NNO-azoxy)-5-chloro-1,3-phenylenediamine was treated with bromine in AcOH. The structural factors promoting this reaction are discussed. The direction of the replacement was confirmed by PM3 calculations of the heats of formation of intermediate cationic σ-adducts. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2131–2134, November, 1999.     

5,5-Bis(alkoxy-NNO-azoxy)-1,3,2-dioxathiane 2-oxides. Synthesis and X-ray diffraction study

2,2-Bis(alkoxy-NNO-azoxy)propane-1,3-diols reacted with thionyl chloride to give previously unknown 5,5-bis(methoxy-NNO-azoxy)- and 5,5-bis(ethoxy-NNO-azoxy)-1,3,2-dioxathiane 2-oxides. Replacement of the hydroxy groups by chlorine is a minor reaction path. According to the X-ray diffraction data, the heteroring in the molecule of 5,5-bis(methoxy-NNO-azoxy)-1,3,2-dioxathiane 2-oxide adopts a chair conformation with axial orientation of the S=O bond.     

The tert-butyl-NNO-azoxy group in the synthesis of 1,2,4-benzotriazin-3(4H)-one 1-oxides

Treatment of 2-(tert-butyl-NNO-azoxy)anilines with phosgene at 20 °C was proposed as a novel route to 1,2,4-benzotriazin-3(4H )-one 1-oxides. This method involves a new reaction, viz., an intramolecular interaction of the tert-butyl-NNO-azoxy group with a C-electrophile (leading to the formation of the N(2)—C(3) bond of the triazine ring) followed by elimination of the tert-butyl group. Complete assignment of the signals in the ¹H and ¹³C NMR spectra of the compounds obtained was performed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1507–1509, August, 2007.     

Synthesis of 1,1-bis(methoxy-NNO-azoxy)-3,3,3-trinitropropane from 1,1-bis(methoxy-NNO-azoxy)ethene and nitroform

A reaction of 1,1-bis(methoxy-NNO-azoxy)ethene with nitroform at ∼20 °C gave 1,1-bis-(methoxy-NNO-azoxy)-3,3,3-trinitropropane.     

Kinetics and possible mechanisms of alkaline hydrolysis of alkoxy-<Emphasis Type="Italic">NNO</Emphasis>-azoxy compounds

Hydrolysis rate of alkoxy-NNO-azoxy compounds like di(methoxy-NNO-azoxy)methane I, di-(methyl-NON-azoxy)formal II, di(methoxy-NNO-azoxy)methane III, and 2,2-di(methoxy-NNO-azoxy)propane IV in 5 M KOH solution was measured by manometric method at 80°C; rates relation is 1:40:540:10. Reversible deprotonation to form C-anions followed by their rapid decomposition is a presumable mechanism for compounds I–III. Nucleophilic attack of OH-anion on the carbon atom of CH₃ON=N(O) group is the most probable first stage of hydrolysis in the case of compound IV.     

Synthesis of 5-amino-6-nitro-1,2,3,4-tetrazine 1,3-dioxide

5-Amino-(tert-butyl-NNO-azoxy)-1,2,3,4-tetrazine 1,3-dioxide reacts with nitronium tetra-fluoroborate to give 5-amino-6-nitro-1,2,3,4-tetrazine 1,3-dioxide. This compound is of interest as a new energetic material. A plausible reaction mechanism involves electrophilic substitution of the tert-butyl-NNO-azoxy group by the nitro group.

     

Amino(tert-butyl-NNO-azoxy)furoxans: synthesis, isomerization, and rearrangement of N-acetyl derivatives

3-Amino-4-(tert-butyl-NNO-azoxy)furoxan (1a) and 4-amino-3-(tert-butyl-NNO-azoxy)-furoxan (1b) and their acetyl derivatives 6a,b were obtained. The equilibria 1a ai 1b and 6a ? 6b were studied. Furoxan 6b can undergo thermal rearrangement into 3-[(tert-butyl-NNO-azoxy)(nitro)methyl]-5-methyl-1,2,4-oxadiazole (7), prolonged heating of which gives N-(2-tert-butyl-5-nitro-1-oxido-2H-1,2,3-triazol-4-yl)acetamide (8). With the transformation 7 → 8 as an example, the possibility of participation of the azoxy group in the Boulton-Katritzky rearrangements was demonstrated for the first time.     

Synthesis of methoxy-NNO-azoxyethene

The first representative of the alkoxy-NNO-azoxy olefin series, viz., methoxy-NNO-azoxyethene, was synthesized by the pyrolysis of 1,1-bis(methoxy-NNO-azoxy)ethane.     

Generation of oxodiazonium ions 2. Synthesis of benzotetrazine-1,3-dioxides from 2-(tert-butyl-NNO-azoxy)-N-nitroanilines

A new method for the synthesis of benzotetrazine-1,3-dioxides was developed, which involves the reaction of 2-(tert-butyl-NNO-azoxy)-N-nitroanilines with the Ac₂O/H₂SO₄ system. This method was also used for the synthesis of [1,2,5]oxadiazolo[3,4-c]cinnoline-5-oxide from 3-nitramino-4-phenylfurazan. The suggested mechanism of these reactions involves the formation of the intermediate oxodiazonium ion, resulting from acetylation of the oxygen atom of the nitramine group, followed by protonation and ionic dissociation. Then the oxodiazonium ion enters the intramolecular reaction with the neighboring tert-butyl-NNO-azoxy or phenyl group to form the corresponding heterocyclic systems.     

Generation of oxodiazonium ions 4. Nitramine O-alkyl derivatives in the synthesis of benzotetrazine-1,3-dioxides

A new method for the synthesis of benzotetrazine-1,3-dioxides was developed from the 2-(tert-butyl-NNO-azoxy)-N-nitroaniline O-alkyl derivatives upon the action of strong acids (H₂SO₄, MeSO₃H, CF₃CO₂H) or BF₃·Et₂O. A mechanism suggested for these reactions includes transformation of the N=N(O)OR group (R = Me, Prⁱ) to the oxodiazonium ion (N=N=O)⁺, which intramolecularly reacts with the neighboring tert-butyl-NNO-azoxy group, furnishing the tetrazine-1,3-dioxide ring.     

2-Alkyl-4-amino-5-(tert-butyl-NNO-azoxy)-2H-1,2,3-triazole 1-oxides: synthesis and reduction

A new approach to the synthesis of 4-amino-5-(tert-butyl-NNO-azoxy)-2-R-2H-1,2,3-triazole 1-oxides 1 was developed. Compounds 1 were obtained by reactions of 3-amino-4-(tert-butyl-NNO-azoxy)furoxan with aliphatic amines RNH₂ (R = Me, Et, Prⁱ, Bu, and Bu^t). 4-Amino-5-(tert-butyl-NNO-azoxy)-2-tert-butyl-2H-1,2,3-triazole 1-oxide was transformed under the action of acids into 4-amino-5-(tert-butyl-NNO-azoxy)-1-hydroxy-1H-1,2,3-triazole. Methylation of the latter with diazomethane mainly involves the O atom of the triazole oxide ring. Reduction of compounds 1 gave 4-amino-5-(tert-butyl-NNO-azoxy)-2-R-2H-1,2,3-triazoles and 4-amino-5-(tert-butyldiazenyl)-2-R-2H-1,2,3-triazoles (R = Me, Prⁱ, and Bu^t). The structures of the compounds obtained were confirmed by ¹H, ¹³C, and ¹⁴N NMR spectroscopy.     

Reactivity of alkoxy-NNO-azoxy compounds toward hydrazine hydrate and inorganic reducing agents

The chemical stability of alkoxy-NNO-azoxy compounds to reduction with hydrazine hydrate has been studied. Methoxy-NNO-azoxymethane and bis(methyl-ONN-azoxy) formaldehyde acetal are more stable by orders of magnitude than bis(methoxy-NNO-azoxy)methane and 2,2-bis(methoxy-NNO-azoxy)propane. Methoxy-NNO-azoxymethane is also resistant to reduction with titanium(III) under acidic conditions and with iron(II) under basic conditions. Probable reaction mechanisms have been proposed on the basis of the substrate reactivity toward nucleophiles, acids, and alkalies.     

Syntheis of amino-substituted 1,3-bis(tert-butyl-NNO-azoxy)benzenes

Oxidation of 4,6-dichloro-1,3-phenylenediamine with Caro's acid yields the corresponding dinitrosobenzene, which reacts withN,N-dibromo-tert-butylamine to give 1,5-bis(tert-butyl-NNO-azoxy)-2,4-dichlorobenzene. Treatment of the latter with ammonia yields 4-amino-and 4,6-diamino-1,3-bis(tert-butyl-NNO-azoxy)benzenes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 7, pp. 1307–1310, July, 1999.     

Transformations of 3(4)-amino-4(3)-(<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">NNO</Emphasis>-azoxy)furoxans in the annulation reactions into 1,2,3,4-tetrazine 1,3-dioxides

Reactions of 3(4)-amino-4(3)-(tert-butyl-NNO-azoxy)furoxans with excess (NO₂)₂S₂O₇ or with a HNO₃—H₂SO₄—Ac₂O mixture unexpectedly produce [1,2,5]oxadiazolo[3,4-e]?[1,2,3,4]tetrazine 4,6-di-N-oxide (furazanotetrazine dioxide) and products of amino group oxidation (mainly to the corresponding azofuroxans) instead of the expected furoxanotetrazine dioxides. In some cases, individual (Z)-3,3´-((E)-diazene-1,2-diyl)-bis-((Z)-2-tert-butyl-1-oxidodiazenyl)-1,2,5-oxadiazole 2-oxide) was isolated. Formation of furazanotetrazine dioxides was observed in the reaction of 3-nitramino-4-(tert-butyl-NNO-azoxy)furoxan sodium salt with H₂SO₄ in Ac₂O. Quantum chemical calculation at the DFT/B3LYP/6-31G(d) level of theory was used to estimate several aspects of the reactivity of 3(4)-nitramino-4(3)-(tert-butyl-NNO-azoxy)furoxans in a comparison with 3(4)-nitramino-4(3)-phenylfuroxans and the possible causes of the observed transformations were revealed.     

Chlorination of geminal bis(alkoxy-NNO-azoxy) compounds with sodium hypochlorite

Chlorination of geminal bis(alkoxy-NNO-azoxy) compounds with sodium hypochlorite involves the central carbon atom and gives 1,1-bis(alkoxy-NNO-azoxy)-1-chloroalkanes with high yield. Dichlorobis-(methoxy-NNO-azoxy)methane oxidizes sodium iodide to elemental iodine. The signal from the central carbon atom in the ¹³C NMR spectra of bis(alkoxy-NNO-azoxy)dichloromethanes is broadened and displaced downfield relative to those of the initial compounds.     

Intramolecular interaction between ortho-azido and azoxy groups as a new way of forming a N—N bond. Synthesis of 2-alkylbenzotriazole 1-oxides

Heating of 2-(alkyl-NNO-azoxy)-1-azidobenzenes in boiling benzene gave 2-alkyl-benzotriazole 1-oxides (Alk = Me, Et, Prⁱ, and Bu^t). This first-order reaction involves an earlier unknown intramolecular interaction between the azido and azoxy groups with simultaneous release of molecular nitrogen. The cyclization rate increases in the following sequence of the alkyl groups: Me < Et < Prⁱ < Bu^t. Complete assignment of the signals in the ¹H, ¹³C, and ¹⁴N NMR spectra of 2-alkylbenzotriazole 1-oxides was performed. Dedicated to Corresponding Member of the Russian Academy of Sciences E. P. Serebryakov on the occasion of his 70th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 989–996, April, 2005.     

3-Ethoxy-2,2-bis(methoxy-<Emphasis Type="Italic">NNO</Emphasis>-azoxy)propan-1-ol. Synthesis and X-ray diffraction analysis

Reaction of bis(methoxy-NNO-azoxy)methane with formaldehyde in ethanol gives 3-ethoxy-2,2-bis(methoxy-NNO-azoxy)propan-1-ol as a minor product along with target 2,2-bis(methoxy-NNO-azoxy)ethanol. The structure of the former was confirmed by the counter synthesis and X-ray diffraction analysis.     

Aliphatic α-nitroalkyl-<Emphasis Type="Italic">ONN</Emphasis>-azoxy compounds and their derivatives

Interaction of primary amines and 2,2-dimethyl-5-nitro-5-nitroso-1,3-dioxane in the presence of dibromoisocyanurate generates 2,2-dimethyl-5-nitro-1,3-dioxan-5-yl-ONN-azoxyalkanes. Based on the reaction of the latter with AcCl/MeOH followed by further transformations, the first representatives of mononitro- and polynitroalkyl-ONN-azoxyalkanes, i.e., (methyl-NNO-azoxy)nitromethane and dinitro(methyl-NNO-azoxy)methane, as well as some their derivatives, were prepared.