Method of preparing dinitramidic acid and salts thereof

Details Method of preparing dinitramidic acid and salts thereof Method of preparing dinitramidic acid and salts thereof

1998-01-13

1999-11-02

Langel, Wayne

Chemistry of inorganic compounds

Nitrogen or compound thereof

Oxygen containing

423387, C01B 2120

Patent

active

059764830

DESCRIPTION:

BRIEF SUMMARY
The invention relates to the preparation of dinitramidic acid and salts thereof. More specifically, the invention concerns a new method of preparing, by inexpensive nitration of suitable initial compounds, dinitramidic acid which constitutes an intermediate product in the preparing of dinitramide salts. The invention also relates to a method in the preparation of dinitramide salts by neutralisation of dinitramidic acid with suitable compounds. The invention particularly concerns a new method of recovering the dinitramide salt from the mixture of reaction products that is obtained in the neutralisation.
Dinitramide salts can be used as oxidisers in solid propellants.
In solid rocket propellants, use is made of mainly ammonium perchlorate or potassium perchlorate as oxidisers. The use of propellants containing chlorine, however, causes a number of problems, among other things from the viewpoint of air pollution. A serious drawback in military applications is that the chlorine content causes smoke that may be detected with radar and, in case of high humidity of the air, can also be seen as clear white smoke.
Oxidisers free from chlorine thus are desirable. The most suitable substance for replacing the perchlorate oxidisers is ammonium dinitramide (ADN) and other salts of dinitramidic acid. Dinitramide salts and methods for preparing the same are disclosed in WO 91/19669 and WO 91/19670. A further method of preparation is disclosed in WO 93/16002.
In the previously described syntheses of the dinitramidic acid, use is made of very strong oxidising systems of the type N.sub.2 O.sub.5 or NO.sub.2 BF.sub.4. These are very expensive and are not suitable for large-scale industrial preparation of oxidisers.
One object of the present invention is to provide a method of preparing dinitramide salts, which is suitable for large-scale production.
A further object is to prepare, from suitable initial substances, dinitramidic acid by a common nitration with nitrating acid, such as nitric acid/sulphuric acid, or a corresponding inexpensive nitration system.
One more object is to provide a simple method for separation of dinitramide salt from other inorganic salts in connection with the production of the salt by neutralisation of dinitramidic acid.
The invention relates to the preparation of dinitramidic acid, HN(NO.sub.2).sub.2 and salts thereof of the formula M.sup.+n (.sup.- N(NO.sub.2).sub.2).sub.n, wherein M is a metal cation or a nitrogen-containing cation and n=1-3, by neutralisation of the acid with a neutralising agent and recovery of the dinitramide salt from the resultant reaction mixture.
According to the invention, dinitramidic acid is prepared by nitration of a compound selected from a group consisting of NH.sub.2 NO.sub.2, NH.sub.4 NH.sub.2 CO.sub.2 ; NH.sub.2 SO.sub.3 H, NH(SO.sub.3 H).sub.2, N(SO.sub.3 H).sub.3, and its salts with metal cations or organic cations, for instance NH(SO.sub.3 NH.sub.4).sub.2, as well as other products that are formed when ammonia is reacted with sulphur trioxide, the nitration being carried out with a common nitrating acid. By common nitrating acid is meant nitrating acid mixtures such as nitric acid/sulphuric acid (HNO.sub.3 /H.sub.2 SO.sub.4), nitric acid/oleum (HNO.sub.3 /H.sub.2 SO.sub.4 /SO.sub.3), nitric acid/sulphur trioxide (HNO.sub.3 /SO.sub.3), nitric acid/perchloric acid (HNO.sub.3 HClO.sub.4), nitric acid/phosphoric acid (HNO.sub.3 /H.sub.3 PO.sub.4), nitric acid/diphosphorous pentoxide (HNO.sub.3 /P.sub.2 O.sub.5), nitric acid/acetic acid, nitric acid/acetic anhydride, nitric acid/trifluoroacetic acid and nitric acid/trifluoroacetic anhydride. HNO.sub.3 /H.sub.2 SO.sub.4 is especially preferred.
No aprotic solvent for the nitrating agent is required when nitrating with the nitrating acids according to the invention, which facilitates the subsequent processing.
It is preferred to use as initial substances salts which contain a cation of the same type as the cation of the neutralising agent which is later used for neutralising the formed dinitramidic acid to dinitramid

REFERENCES:
patent: 2752225 (1956-06-01), Revallier
patent: 5198204 (1993-03-01), Bottaro et al.
patent: 5254324 (1993-10-01), Bottaro et al.
patent: 5316749 (1994-05-01), Schmitt et al.
patent: 5415852 (1995-05-01), Schmitt et al.
Hatano et al., Europyro, 1995, New synthetic method and properties of ammonium dinitramide (AND), pp. 23-26.

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