DESC:FIELD OF INVENTION

The present invention relates to a process for the synthesis of 5, 5´-Bistetrazole-1, 1´-diol and its salts.

BACKGROUND OF INVENTION

5, 5´-Bistetrazole-1, 1´-diol and its salts have the potential to be used in modern, advanced propellant formulations.
Thomas M. Klapötke and coworkers have reported (J. Mater. Chem, 2012, 22, 20418-20422) methods of preparation of 5, 5´-Bistetrazole-1, 1´-diol. These methods of preparations suffer from various drawbacks. Some of these drawbacks pertain to the use of solvents like diethylether and dimethylforamide (DMF) in the preparation 5,5´-bistetrazole-1,1´-diol and its precursor, diazidoglyoxime, respectively. Dimethylforamide is a very high boiling solvent and water miscible; therefore, its recovery from aqueous reaction mixture poses serious challenge. Diethylethylether is a low boiling, highly volatile, flammable liquid; therefore, its use on an industrial scale poses serious safety hazards. The use of both the solvents in the synthesis renders the process totally un-scalable, thereby rendering unsuitable for adoption in industrial production of the product. Further, due to the problems associated with the recovery and recyclability of both the solvents the process not only creates environmental hazards but also renders it commercially unviable.
Therefore, there is a need to develop a process for preparing 5, 5´-bistetrazole-1,1´-diol that overcomes the aforesaid drawbacks.

SUMMARY OF THE INVENTION
The present invention relates to a process for preparing 5,5´-bistetrazole-1,1´-diol by treating diazidoglyoxime with an acid and an ether.
The present invention also relates to a process for preparing 5,5´-bistetrazole-1,1´-diol by treating dichloroglyoxime with an azide in the presence of an alcohol to obtain diazidoglyoxime, which on further treatment with an acid and ether forms 5,5´-bistetrazole-1,1´-diol.
Another aspect of the present invention relates to a process for preparing diazidoglyoxime by treating dichloroglyoxime with an azide in the presence of an alcohol.

DETAILED DESCRIPTION OF THE INVENTION
In an embodiment of the present invention, a process for preparing 5,5´-bistetrazole-1,1´-diol comprises of treating diazidoglyoxime with an acid in the presence of an ether to obtain 5, 5´-bistetrazole-1,1´-diol.
In a preferred embodiment of the present invention, a process for preparing 5, 5´-bistetrazole-1,1´-diol comprises of treating dichloroglyoxime with an azide in the presence of an alcohol to obtain diazidoglyoxime. Diazidoglyoxime is treated with an acid in the presence of an ether to obtain 5, 5´-bistetrazole-1, 1´-diol.
Another embodiment of the present invention relates to a process for preparing diazidoglyoxime by treating dichloroglyoxime with an azide in an alcohol or in water containing a small amount of a water miscible solvent. The water miscible solvents include alcohols such as methanol, ethanol, isopropanol or ethers such as tetrahydrofuran, 1,4-dioxane, monoglyme, diglyme or ketones such as acetone.
In an embodiment, dichloroglyoxime is treated with an azide in the presence of an alcohol.
Dichloroglyoxime is treated with an azide and alcohol at a temperature in the range of -30°C to 45°C.
The acid used here can be selected from a mineral acid or a Lewis acid, preferably hydrochloric acid.
The ether used in the process is selected from 1, 4-dioxane, monoglyme, diglyme, tetrahydrofuran, diisopropylether, methyl tert-butyl ether. Preferably, 1, 4-dioxane is used in the reaction. The volume of the ether used in the reaction can vary from 15 to 60 volumes of the amount of dichloroglyoxime used in the reaction.
Azide used in the process is selected from a group comprising of sodium azide, potassium azide, lithium azide; organic azides such as tetrabutylammonium azide, tetraethylammonium azide, trimethylsilyl azide, diphenylphosphoryl azide, tributyltin azide, preferably sodium azide.
The alcohol is selected from methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, tert-butanol, n-octanol. Preferably, methyl alcohol is used in the reaction. The volume of the alcohol used in the reaction can vary from 4 volumes to 20 volumes of the quantity of dichloroglyoxime used in the reaction, i.e. 8 ml to 40 ml if 2 g of dichloroglyoxime used.
An embodiment of the present invention relates to a process for converting 5, 5’- bistetrazole 1, 1- diol to dihydroxylammonium salt by treating 5, 5’ – bistetrazole 1, 1- diol with hydroxylamine hydrochloride.
In a preferred embodiment a process for preparing 5, 5’ – bistetrazole 1, 1 diol comprises of treating dichloroglyoxime with sodium azide in the presence of methanol to obtain diazidoglyoxime. The reaction is carried out at a temperature range of -30°C to 45°C. Diazidoglyoxime on further treatment with HCl and 1, 4- dioxane forms 5, 5’ – bistetrazole 1, 1- diol.

Another embodiment of the present invention relates to a process for preparing ammonium salt of 5, 5’ – bistetrazole 1, 1 diol by treating dichloroglyoxime with an azide in the presence of an alcohol to obtain diazidoglyoxime. The reaction is carried out at a temperature range of -30°C to 45°C. Diazidoglyoxime on treatment with an acid in the presence of ether forms 5, 5’ – bistetrazole 1, 1- diol, which on treatment with hydroxylamine hydrochloride results in dihydroxylammonium 5, 5’ – bistetrazole – 1, 1’- diolate.
The process steps can be carried out in a single pot, which obviates the need to isolate the intermediate products such as diazidoglyoxime.
The ethers used in the reaction can be easily recovered and reused in subsequent batches without any loss of yield or purity.
The process described herein is cost-effective, scalable and therefore can be adopted for large scale preparation of the product.

EXAMPLES
The examples described herein below illustrate the invention but are not limiting thereof.
Example 1: Preparation of Diazidoglyoxime
Sodium azide (1.8 g) was added to a cold solution of dichloroglyoxime (2 g) in methanol (10ml) at a temperature range -10 OC - 35 OC. . The reaction mixture was stirred at this temperature range until the reaction was complete as indicated by TLC. After the completion of the reaction, the reaction mixture was poured onto crushed ice and stirred for 0.5 h. The precipitated solid was filtered, washed with water and air-dried to give diazidoglyoxime; yield: 1.8 g. The material was carried over to the following step without further purification.
Example 2: Preparation of 5, 5´-Bistetrazole-1,1´-diol
Hydrogen chloride gas was bubbled into a cold solution of diazidoglyoxime (3 g) in 1,4-dioxane (150 ml) at a temperature range -10 OC to 30 OC for 3 h. The bubbling of hydrogen chloride gas was then stopped and the flask was sealed. The reaction mixture was allowed to warm to room temperature and stirred overnight at this temperature when the reaction was complete as indicated by TLC. The reaction mixture was concentrated under reduced pressure at 50 OC to dryness. The residue was slurred with diethylether for 10 minutes and filtered to give 5,5’-bistetrazole-1,1’-diol as a white solid; yield: 2.2 g.
Example 3: Preparation of Dihydroxylammonium 5,5´-bistetrazole-1,1´-diolate (TKX-50)
Water (10 ml) was added to 5,5’-bistetrazole-1.1’-diol (1 g) and the mixture was heated to 80° C when the reaction mixture became homogenous. The reaction mixture was then allowed to cool down to 70 OC, and a solution of hydroxylamine hydrochloride (0.9 g) in aqueous sodium hydroxide (0.52 g of sodium hydroxide dissolved in 3 ml of water) was added slowly to the reaction mixture at this temperature over. After the completion of addition, the reaction mixture was allowed to cool down to room temperature. The precipitated solid was filtered, washed with water and dried to give TKX-50; yield: 1.12 g.

CLAIMS:

1. A process for preparing 5, 5’- bistetrazole 1, 1-diol, the process comprises- treating diazidoglyoxime with an acid in the presence of an ether to obtain 5, 5’- bistetrazole 1, 1-diol.

2. A process for preparing 5, 5’- bistetrazole 1, 1-diol, the process comprising treating dichloroglyoxime with an azide in the presence of an alcohol to obtain diazidoglyoxime; and treating diazidoglyoxime with an acid in the presence of an ether to obtain 5, 5’- bistetrazole 1, 1-diol.

3. A process for preparing diazidoglyoxime, the process comprising treating dichloroglyoxime with an azide in the presence of an alcohol to obtain diazidoglyoxime.

4. The process as claimed in claim 1 or claim 2, wherein the acid is HCl.

5. The process as claimed in claim 1 or claim 2, wherein the ether is selected from 1, 4-dioxane, monoglyme, diglyme, tetrahydrofuran, diisopropylether, methyl tert-butyl ether.

6. The process as claimed in claim 2 or claim 3, wherein the azide is sodium azide, potassium azide, lithium azide; organic azides such as tetrabutylammonium azide, tetraethylammonium azide, trimethylsilyl azide, diphenylphosphoryl azide, tributyltin azide.

7. The process as claimed in claim 2 or claim 3, wherein the alcohol is selected from methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, tert-butanol, n-octanol.

8. The process as claimed in claim 2 or claim 3, wherein the step of treating dichloroglyoxime with an azide and alcohol is carried out in the presence of water.

9. The process as claimed in claim 2 or claim 3, wherein the step of treating dichloroglyoxime with an azide and alcohol is carried out at a temperature in the range of -30°C to 45°C.

10. The process as claimed in claim 1 or claim 2 comprising converting 5, 5’- bistetrazole 1, 1-diol to dihydroxylammonium salt by treating 5, 5’- bistetrazole 1, 1-diol with hydroxylamine hydrochloride.