Efficient Procedure for High-Yield Synthesis of 4-Substituted 3,5-Dinitropyrazoles Using 4-Chloro-3,5-dinitropyrazole

Abstract

The transformations of readily available 4-chloro-3,5-dinitropyrazole and its N-methylated derivative under the action of anionic S-/O-nucleophiles and neutral N-nucleophiles were studied. Independent of the substrate's charge (anionic, R = H, or neutral, R = Me), the nucleophilic substitution proceeds exclusively at position 4 replacing the chlorine nucleofuge. As a result of this study, the effective synthetic method for the preparation of 4-substituted 3,5-dinitropyrazoles via the nucleophilic substitution in 4-chloro-3,5-dinitropyrazole was elaborated.The current interest in the chemistry of pyrazoles is due to their wide practical applications. During last five years the number of publications on pyrazoles has doubled and is still continuing to grow. 1 Among pyrazoles, the polynitropyrazoles attract special attention because they belong to high-energy compounds and show some specific properties. 2,3 The effective synthetic approaches to 3,4-and 3,5-dinitropyrazoles through direct acid and nonacid nitration, as well as via C → N isomerization of N-nitropyrazoles, are well known. 4 In a series of papers, 5,6 we reported the nucleophilic substitution of NO 2 group in 3,4-and 3,5-dinitropyrazoles to be a quite powerful method for functionalization of C-3 and C-5 atoms of a pyrazole ring with formation of C(3/5)-X bonds (X = O, S, N).For example, it was found that in 3,4-dinitropyrazoles (pK a <6.5 7 ) under the action of heteroatom nucleophiles substitution proceeds selectively at position 3 (Scheme 1, route A). It should be stressed that such a process does not depend on the presence of the substituent at N-1. Even in the case of R = H, when the substrate reacts in its anionic form, only position 3 is functionalized. 5 3,5-Dinitropyrazoles (pK a <4.0 7 ) enter the substitution reaction with the same set of nucleophiles only in the case when a substituent R is present at N-1 (Scheme 1, route B). Otherwise, as a result of an acid-base reaction between NH acid and basic nucleophile, the reaction furnishes the respective salt (Scheme 1, route C). 6,8 All known methods of C-4 functionalization, particularly, in the case of N-unsubstituted pyrazoles, are based on the reactions with the electrophilic reagents. 4Quite recently as a result of our work, 9,10 as well as of Herve et al., 3 the first examples of fully carbon atomnitrated pyrazoles -3,4,5-trinitropyrazole (TNP) and its N-derivatives, 1-methyl-3,4,5-trinitro-1H-pyrazole 10a and 1-methoxymethyl-3,4,5-trinitro-1H-pyrazole 11 -became available for synthetic chemists. On the basis of systematic investigations, we found that the rules of nucleophilic substitution in these novel polynitropyrazoles are different compared to previously known ones. For instance, when TNP 12 in the form of its N-anion reacts with S-, O-, N-nucleophiles, the selective substitution of 4-NO 2 group occurs (Scheme 1, route

Trimerization of 4‐Amino‐3,5‐dinitropyrazole: Formation, Preparation, and Characterization of 4‐Diazo‐3,5‐bis(4‐amino‐3,5‐dinitropyrazol‐1‐yl) pyrazole (LLM‐226)

“…Compound 1 was prepared using a reported literature with slightly modifications . A mixture of 4‐chloro‐3,5‐dinitropyrazole (10.0 g, 51.9 mmol) and 100 mL of aqueous NH 4 OH (28–30%) was sealed in a high‐pressure vessel and heated for 16 h as described previously.…”

“…4‐Amino‐3,5‐dinitropyrazole (LLM‐116, 1 ) is an insensitive energetic material and a starting material for many new explosives and propellants . Several methods have been reported in the literature for the preparation of the material , but the amination of 4‐chloro‐3,5‐dinitropyrazole ( 3 ) via nitration of commercially available 4‐chloropyrazole has become the most popular approach . In 2001, we reported the first synthesis of 1 by direct amination of 3,5‐dinitropyrazole with 1,1,1‐trimethyl‐hydrazinun iodide, revealing that 1 is a thermally stable compound, exothermically decomposing at 183°C by differential scanning calorimetry (DSC) .…”

“…Recently, Shevelev et al . reported that the amination of 3 with 28% aqueous NH 4 OH solution gave 1 in high yield (Scheme ) .…”

Covalent and Ionic Insensitive High‐Explosives

“…(b) Nucleophilic substitution of the 4-positioned group in 3,4,5-trinitropyrazole [75] or 4-chloro-3,5-dinitro-pyrazole (ClDNP) [76];…”

Synthesis and Crystal Structure of 1-Methoxymethyl-3,4,5-trinitropyrazole

“…This title compound was prepared from 4-chloro pyrazole 1 by nitration, amination, oxidation and nucleophilic substitution reaction. Its structure was characterized by IR, 1 H NMR, 13 C NMR, MS and X-ray diffraction. Scheme 1.…”