Production of hexanitrostilbene (HNS)

Details Production of hexanitrostilbene (HNS) Production of hexanitrostilbene (HNS)

1990-01-04

1991-06-11

Stoll, Robert L.

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

568928, C07C20506

Patent

active

050233866

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the production of 2,2',4.4',6,6'-hexanitrostilbene (HNS) (also known as 1,2bis(2,4,6-trinitrophenyl)ethane) from 2,4,6,trinitrotoluene (TNT).
HNS is a thermally-stable explosive which is especially useful as a crystal-modifying additive in melt-cast TNT. The first unequivocal synthesis of HNS is disclosed in U.S. Pat. No. 3,505,413 (Shipp). This document describes a process for HNS production which is based on the reaction of TNT with sodium hypochlorite in tetrahydrofuran/methanol solution at 15.degree. C. The crude HNS produced is washed in acetone to remove the bulk of coprecipitated impurities. The yield of HNS produced by this process is low, typically only about 30-35%, and the process also produces a large number of unwanted by-products, some of which are difficult to remove from the HNS product and from the recyclable tetrahydrofuran solvent. Later improvements to this process disclosed in the UK Patent Nos. 1513221 and 1570569 increased HNS yields to about 50%.
A further process for the production of HNS is disclosed in Hungarian Patent No. T/9639VE-719 (Kompolthy et al) which essentially consists of the oxidative coupling of TNT with free oxygen present in air. The reactions disclosed were carried out in the presence of methanolic potassium hydroxide solution, a polar aprotic solvent and optionally an oxidative catalyst consisting of anhydrous copper sulphate/pyridine or cobalt naphthenate, and were followed by the addition of a solution buffer and carboxylic acid to precipitate the production. Kompolthy et al also disclose that similar processes can be used for the production of the intermediate product DPE from TNT, and for the production of HNS from DPE (DPE=1,2dipicrylethane). Typically, they obtained crude yields of 30-55% HNS from TNT, indicating little if any improvement in yields over those disclosed in the above-mentioned UK Patents, though HNS yields of up to 90% from DPE were obtained using an anhydrous copper sulphate/pyridine catalyst. The yields were "crude" in the sense that the reported purification of the (precipitated) product did not generally extend beyond washing with water (to remove water-soluble impurities) followed by washing with methanol (to remove unreacted TNT); however this crude product was frequently found to be of sufficient purity (as measured by its melting point range) for use by the explosives industry. These yields were later generally confirmed by Golding and Hayes (Propellants and Explosives 4, 115-120 (1979)). However other workers have reportedly obtained yields of only 25-40% when repeating the DPE-to-HNS processes of Kompolthy et al.
In view of the poor yields and other difficulties outlined above which are associated with the processes of Shipp and Kompolthy et al for converting TNT directly to HNS, much recent research effort has been concentrated on the development of processes for converting the intermediate product 2,2',4,4',6,6'hexanitrobibenzyl (HNBB), also known as 1,2dipicrylethane (DPE), into HNS in high and reproducible yields. Such processes are described in the following U.S. Pat. Nos. 4,221,745 (reaction of HNBB with a copper salt and ammonium hydroxide in an aprotic solvent), 4,221,746 (reaction of HNBB with a halogen or organic halide in the presence of an aprotic solvent and a base), 4,243,614 (reaction of HNBB with a copper salt, especially copper sulphate, in an aprotic solvent with oxygen optionally added), 4,268,696 (reaction of HNBB with a quinone oxidant in an aprotic solvent, optionally in the presence of an organic amine base) and 4,270,012 (reaction of HNBB with oxygen in a aprotic solvent in the presence of a catalyst). Since HNBB can be produced in comparatively high yield by the process of Shipp (a yield of 79% is reported), using some of the above HNBB-to-HNS processes it it possible to obtain an overall TNT-to-HNS yield of some 70-75%. This is considerably better than the maximum yield of 55% mentioned above which could be obtained using the direct, one reaction-stage conversion of TNT to HNS disc

REFERENCES:
patent: 3505413 (1970-04-01), Shipp
patent: 4243614 (1981-01-01), Gilbert
patent: 4270012 (1981-05-01), Gilbert
patent: 4626606 (1986-12-01), Duffin et al.
Chemical Abstracts, vol. 84, No. 9, Mar. 1, 1976, Abstract No. 58886n.
Chemical Abstracts, vol. 92, No. 18, May 5, 1980, Abstract No. 149476s.

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