# Patent

## Title
Synthesis of 3,4-Bis(4-nitro-1,2,5-oxadizaol-3-yl)-1,2,5-oxadizaole-N-oxide (DNTF) using 3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadizaole

## Abstract

A novel method for preparing 3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadiazole by reacting 4-amino-3-chlorocarbohydroxymoyl-1,2,5-oxadiazole with H2O2 and a tungsten based catalyst and use of the prepared 3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadiazole for synthesizing 3,4-Bis(4-nitro-1,2,5-oxadizaol-3-yl)-1,2,5-oxadiazole-N-oxide (DNTF).

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a non-provisional application that claims the benefit of the provisional patent application entitled “Synthesis Method for Preparation of 3,4-Bis(4-nitro-1,2,5-oxadizaol-3-yl)-1,2,5-oxadiazole-N-oxide (DNTF)” filed Mar. 12, 2015, as Ser. No. 62/131,972.


RIGHTS OF THE GOVERNMENT
The inventions described herein may be manufactured and used by or for the United States Government for government purposes without payment of any royalties.


FIELD OF INVENTION
A process for producing 3,4-Bis(4-nitro-1,2,5-oxadizaol-3-yl)-1,2,5-oxadiazole-N-oxide (DNTF), an energetic material, through a novel process for preparing its precursor 3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadiazole.
BACKGROUND OF THE INVENTION
There has been significant research on the synthesis and development of new energetic materials to meet the needs of U.S. Department of Defense. It is in this context that research has focused on a promising melt-castable energetic material 3,4-Bis(4-nitro-1,2,5-oxadizaol-3-yl)-1,2,5-oxadiazole-N-oxide (DNTF). Synthetic methods for preparing DNTF mainly involve treating 4-amino-3-chlorocarbohydroxymoyl-1,2,5-oxadiazole (chloro oxime) (1) with a base followed by extractive work-up to produce 3,4-bis (aminofurazano) furoxan (furoxofurazane) (2). The resulting furoxofurazane is further oxidized to produce DNTF (4).
Alternative methods have been explored to prepare a DNTF precursor by reacting 4-amino-3-chlorocarbohydroxymoyl-1,2,5-oxadiazole (chloro oxime)(1) with NaNO2 and an acid to convert the amino group in chloro oxime (1) into the corresponding nitro group in, 3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadiazole (3). These experiments, however, were unsuccessful. Thus, a need exists for preparing DNTF using alternative methods. Disclosed herein is a novel method for synthesizing 3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadiazole, an intermediate useful for the preparation of DNTF.
SUMMARY OF THE INVENTION
A novel process for preparing 3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadiazole, a precursor, using a tungsten catalyst and aqueous H2O2 and methods for synthesizing DNTF using such precursor.


DETAILED DESCRIPTION
A novel method for synthesis of 3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadiazole (3) is disclosed herein. This compound is further reacted with K2CO3 to produce an alternative method for preparing the energetic material DNTF as discussed in further detail below.




Preparation of 3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadiazole
3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadiazole, compound 3, a precursor to DNTF is prepared according to the process illustrated in schematic 1. The amino group of compound 1 was subjected to oxidation using aq. 70% H2O2 in presence of a tungsten based catalyst initially at room temperature, followed by heating at 52° C. for 4 h. An extractive work-up followed by removal of solvent afforded a pale yellow liquid. Carbon NMR analysis of this liquid showed a resonance at 158.71 ppm, a triplet due to coupling of the nitro group nitrogen with ring carbon, suggesting the formation of the desired nitro compound 3.
The identity of the liquid, an ethereal solution, was characterized by reacting it with an aq. potassium carbonate (K2CO3) solution. After stirring the reaction mixture at room temperature for 2 h followed by an extractive workup and removal of solvent yielded crude DNTF. The crude DNTF was purified by triturating the crude with diethyl ether, and separation of the solid via filtration. The spectral and thermal data of the white solid thus obtained matched with that of the literature reported values.
Preparation of 3,4-Bis(4-nitro-1,2,5-oxadizaol-3-yl)-1,2,5-oxadiazole-N-oxide, (DNTF)
A heterogeneous mixture of 3-chlorocarbohydroximoyl-4-amino-1,2,5-oxadiazole (400 mg) in 70% H2O2 (10 mL) and (Bmim)4W10O23 catalyst (200 mg) was stirred at room temperature for 16 h and then kept at 52° C. for 4 h. The reaction mixture was diluted with water (100 mL) and extracted with ethylacetate (3×30 mL). The combined organic layer was washed with water (2×50 mL), brine (1×50 mL), dried (Na2SO4) and filtered. The filtrate was evaporated on a rotary evaporator under vacuum at room temperature to dryness to obtain the product (320 mg, 67% yield) as a colorless liquid. 1H-NMR (acetone-d6): 13.03 (br S): 13C-NMR (acetone-d6): 123.74, 145.38 and 158.719 (t).
The product obtained above, i.e. 3-chlorocarbohydroxymoyl-4-nitro-1,2,5-oxadiazole, was used in the next step without any further purification. The nitro compound (320 mg) was dissolved in diethyl ether (5 ml). To this solution was added at room temperature drop-wise a solution of potassium carbonate (166 mg) in water (3 mL). The reaction mixture was then stirred at room temperature for 2 h. Ether layer was separated and the aqueous layer was extracted with diethylether (2×5 mL). The combined organic layer was then washed with water (1×5 mL), brine (1×5 mL), dried (Na2SO4) and filtered. The organic solution was evaporated under vacuum at room temperature on a rotary evaporator. The pale yellow crude solid residue thus obtained was triturated with ether (1 mL). The white solid was separated via filtration and air dried. Yield: 68 mg (27% from nitro derivative) m.p.: 107-108° C. (Lit m.p. 108-110° C.).1a 13C-NMR (acetone-d6): 104.45, 138.20, 140.55, 143.83, 160.82 (2 C).
While embodiments have been set forth as illustrated and described above, it is recognized that numerous variations may be made with respect to relative amounts of the constituents in the composition. Therefore, while the invention has been disclosed herein, it will be obvious to those skilled in the art that additions, deletions and modifications can be made without departing from the spirit and scope of this invention, and no undue limits should be imposed, except as to those set forth in the following claims.

## Claims

1. The process for preparing 3-chlorohydroximoyl-4-nitro-1,2,5-oxadiazole comprising the steps of:
(a) reacting 4-amino-3-chlorocarbohydroxymoyl-1,2,5-oxadiazole in the presence of a tungsten based catalyst and aqueous H2O2;
(b) heating the solution at greater than 30° C. to produce 3-amino-4-chlorohydroximoyl 1-2,4-oxadiazole in solution;
(c) isolating the 3-chlorohydroximoyl-4-nitro-1,2,5-oxadiazole from the solution.

2. The process of claim 1 wherein the tungsten based catalyst is (Bmim)4W10O23.

3. The compound, 3-chlorohydroximoyl-4-nitro-1,2,5-oxadiazole, prepared according to the process of claim 1.

4. A process for preparing 3,4-Bis(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole-N-oxide (DNTF) comprising:
(a) dissolving 3-chlorohydroximoyl-4-nitro-1,2,5-oxadiazole prepared according to the process of claim 1 in diethyl ether;
(b) adding drop-wise a solution of potassium carbonate;
(c) stirring the mixture;
(d) isolating the DNTF from the organic layer.