Chemistry of inorganic compounds – Nitrogen or compound thereof – Oxygen containing
Reexamination Certificate
2002-03-13
2004-09-07
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Oxygen containing
C423S396000, C149S122000
Reexamination Certificate
active
06787119
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the preparation of dinitramidic acid and salts thereof. In particular the present invention relates to a process for the preparation of dinitramidic acid and salts ammonium dinitramide (ADN)/potassium dinitramide using solid acid catalysts such as metal ion exchanged clay catalysts and surface supported catalysts which finds use in making high-energy solid propellants. Ammonium dinitramide (hereafter referred to as ADN) is considered a suitable replacement for ammonium perchlorate (AP) in solid propellant formulations. It is a good halogen free oxidizer with better performance characteristics for use in solid propellant applications.
The present invention also relates to a novel and an ecofriendly process for the preparation of dinitramidic acid by nitration of ammonium sulfamate with fuming nitric acid as a nitrating agent using solid acid catalysts selected from the group consisting of a montmorillonite clay catalyst and metal ion exchanged K10 montmorillonite clay catalysts and surface supported catalysts and preparation of ammonium dinitramide by neutralization of the dinitramidic acid with ammonia and separation of ammonium dinitramide by a conventional work-up procedure. The same process is also used for making potassium dinitramide, which is prepared by taking potassium sulfamate as the starting material and KOH as the neutralising agent.
BACKGROUND OF THE INVENTION
Nitration is generally performed by the classical method employing the H
2
SO
4
—HNO
3
system and also with strong nitrating agents such as NO
2
BF
4
or N
2
O
5
.
Reference may be made to U.S. Pat. Nos. 5,316,749 and 5,316,749A, wherein ammonium salt of 1,1,3,3-tetraoxo-1,2,3-triazapropene anion (ADN) is prepared by the direct nitration of ammonia. Nitration is carried out at very low temperatures (−78° C.). The formation of the product can be explained by the following equations:
NH
3
+NO
2
BF
4
→NH
2
NO
2
+HBF
4
(1)
NH
2
NO
2
+NO
2
BF
4
→HN(NO
2
)
2
+HBF
4
(2)
HN(NO
2
)
2
+2 HBF
4
+3 NH
3
→H
4
N(NO
2
)
2
+2 N H
4
BF
4
(3)
The overall reaction is given in equation (4)
4NH
3
+2 NO
2
BF
4
→NH
4
N(NO
2
)
2
+2N H
4
BF
4
(4)
Reference may be made to U.S. Pat. Nos. 5,198,204 and 5,254,324, wherein the nitration of monoisocyanates of the type Z—CH
2
—CH
2
—NCO, where Z is an electron withdrawing group such as —CN, —COOR, or —COOH to the corresponding alkyl dinitramine is described. The nitration is carried out by using strong nitrating agents such as NO
2
BF
4
or N
2
O
5
. The alkyl dinitramine gives ADN on treatment with ammonia. The drawbacks are these strong nitrating agents are very expensive and are not suitable for large-scale industrial production of oxidizers.
Reference may be made to U.S. Pat. Nos. 5,145,852 and 5,659,080 wherein the nitration of deactivated amines such as NH
2
NO
2
, NH
2
CONH
2
or NH
2
COOC
2
H
5
to dinitramidic acid using the nitrating agents such as NO
2
BF
4
or N
2
O
5
is described. The drawbacks are these strong nitrating agents are very expensive and are not suitable for large-scale industrial production of oxidizers. Most of the reactions are highly exothermic and involves the use of highly reactive nitrating agents and hence are to be carried out at very low temperatures (−30° C. to −50° C.) in small batches.
Reference may be made a publication by Bottaro et al, J.Am.Chem. Soc, 9305, 1997 wherein ammonium dinitramide is prepared by the reaction of nitramide, nitronium tetrafluoroborate and ammonia or ammonia with N
2
O
5
or N
2
O
5
and ammonium nitromethane.
Reference may be made to U.S. Pat. No. 5,976,483 wherein the preparation of dinitramidic acid by nitration of a compound selected from a group consist of NH
2
SO
3
H, NH(SO
3
H)
2
, N(SO
3
H)
3
and its salts such as ammonium sulfamate using a common nitrating agent such as nitric acid/sulphuric acid or nitric acid/acetic anhydride is described. The invention also relates to a method of preparing dinitramide salt, comprising neutralization of the dinitramidic acid with ammonia, recovery and purification of the salt by passing through a column and then eluted by gradient elution.
2 HNO
3
+2 H
2
SO
4
+NH
2
SO
3
NH
4
→HN(NO
2
)
2
+2 H
2
SO
4
+NH
4
HSO
4
+H
2
O (5)
HN(NO
2
)
2
+2NH
3
+NH
4
HSO
4
→NH
4
N(NO
2
)
2
+(NH
4
)
2
SO
4
(6)
The drawbacks are the use of hazardous sulfuric acid and environmental pollution during disposal of spent acid.
Reference may be made a publication by Malesa and Skupinski in Propellants, Explosives, Pyrotechnics, 24, 83-89, 1999 wherein the ammonium dinitramide is prepared by the method described by Bottaro et al in acetonitrile and the product is separated by evaporation of the neutralised solution to dryness after filtration, followed by extraction with isopropanol and evaporation to dryness and finally by recrystallization from ethyl acetate.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide an ecofriendly method for preparing dinitramidic acid and its salts by nitration of ammonium sulfamate with fuming nitric acid as a nitrating agent using solid acid catalysts selected from the group consisting of a montmorillonite clay catalyst and metal ion exchanged K10 montmorillonite clay catalysts and surface supported catalysts and preparation of ammonium dinitramide by neutralization of the dinitramidic acid with ammonia and separation of ammonium dinitramide by a conventional work-up procedure which obviates the drawbacks as detailed above.
Another object of the present invention is the use of ecofriendly metal ion exchanged clays as solid acid catalysts in the nitration of ammonium sulfamate, dispensing the use of sulfuric acid which obviates the drawbacks as detailed above.
Another object of the present invention is to dispense the use of the nitrating agents such as NO
2
BF
4
or N
2
O
5
which obviates the drawbacks as detailed above.
SUMMARY OF THE INVENTION
The present invention provides an ecofriendly process for the preparation of dinitramidic acid by nitration of ammonium sulfamate with fuming nitric acid as a nitrating agent using solid acid catalysts selected from the group consisting of a montmorillonite clay catalyst and metal ion exchanged K10 montmorillonite clay catalysts and surface supported catalysts. Ammonium dinitramide is then prepared by the neutralization of the dinitramidic acid with ammonia and separation of ammonium dinitramide by a conventional work-up procedure.
Accordingly, the present invention relates to a process for the preparation of dinitramidic acid comprising nitrating ammonium sulfamate with fuming nitric acid as a nitrating agent using a solid acid catalyst selected from the group consisting of a montmorillonite clay catalysts, metal ion exchanged K10 montmorillonite clay catalysts and surface supported catalysts.
In one embodiment of the invention, the catalyst comprises a metal ion exchanged clay, with the metal ion preferably being selected from the group consisting of Fe
3+
, Al
3+
, La
3+
, Cu
2+
and Zn
2+
.
In another embodiment of the invention, the surface supported catalyst comprises titanium or molybdenum supported on silica-alumina.
In another embodiment of the invention, the reaction is carried out in the presence or absence of solvent.
In another embodiment of the invention, the solvent is selected from carbon tetrachloride and dichloroethane.
In another embodiment of the invention, the nitration is carried out in the absence of sulfuric acid.
In another embodiment of the invention, the solid acid catalyst used act as bifunctional catalysts, generating electrophile nitronium ion as well as instant adsorbent for water formed during the reaction to facilitate electrophilic substitution.
The invention also relates to a process for the preparation of ammonium dinitramide comprising nitrating ammonium sulfamate with fumin
Chidara Sridhar
Choudary Boyapati Manoranjan
Gopalakrishnan Santosh
Kantam Mannepalli Lakshmi
Karasala Vijayakumar
Council of Scientific and Industrial Research
Medina Maribel
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