Some impurities have been identified in the crude ambazone resulted from the chemical synthesis. These impurities are synthesis intermediates, synthesis secondary products and degradation products.

Impurities present in ambazone were isolated and characterized by current physical- chemical methods (RMN spectra, mass spectra, IR spectra, UV-VIS spectra).

The following impurities are presented in ambazone product: a) 1,4-benzoquinone guanylhydrazone (II); b) 1,4-benzoquinone bis-guanylhydrazone (III) ; c) 1, 4-benzoquinone guanylsemicarbazone (III); d) elementary sulfur.

The proposed technical solution is a purification method of crude ambazone resulted from chemical synthesis, in two steps.

In the first step, crude ambazone is macerated with a non-polar solvent (benzene, n-hexane, toluene or xylene) to remove the sulfur.

In the second step, ambazone is recrystallized from the mixture N, N-dimethylformamide and lower aliphatic alcohols (Cl-C4) at temperatures between 50-80°C, to remove the impurities (II), (Ill) and (IV).

The methods from literature indicate purifications of crude ambazone by dissolution in N, N-dimethylformamide and then precipitation with water [1], respectively dissolution of ambazone nitrate in N, N-dimethylformamide and water followed by neutralisation of salt with ammonia solution [2,3].

These purification methods have the disadvantage that they do not remove the sulfur from the product and the impurities (II), (III) (IV) are present in great concentrations. This makes problems in the utilisation of obtained ambazone in drug manufacturing.

The proposed method for sulfur removal from ambazone uses the maceration of ambazone in non-polar solvents (benzene, n-hexane, toluene or xylene). It is used a ratio ambazone: solvent = 1 : 1-5 (m/v) and temperatures between 20-60°C. It is preferably to use a ratio of 1: 3 and a temperature of 40°C.

In the phase of recrystallization of ambazone (1) it is used a ratio ambazone : N, N- dimethyformamide : lower alcohols (Cl-C4) = 1 : 1-3: 2-5 (m/v/v) and temperatures between 55-60°C. It is preferable to use a ratio of 1 : 2: 4 and temperatures of 55-60°C.

Analytical determination of sulfur content in ambazone has been accomplished by gravimetric method, by extraction of sulfur with n-hexane, followed by vaporisation of solvent on water bath.

Assay of ambazone (I) and of imp>ities from ambazone were determined by High Performance Liquid Chromatography (HPLC).

Some examples for the invention accomplishment are presented below: example 1.

22 g crude ambazone is macerated under stirring in 66 ml toluene for one hour at 40°C and is filtered. 20 g ambazone are isolated. The resulted ambazone is dissolved in 40 ml N, N-dimethylformamide, is again heated at 60°C and it is added 80 ml methanol. The temperature of solution must not be below 55°C during the addition of methanol. Ambazone solution in the mixture N, N-dimethylformamide : methanol is cooled and is maintained two hours at 5-10°C. 17 g pure ambazone are isolated with HPLC assay of minimum 99. 5 %.

Example 2.

22 g crude ambazone are macerated under stirring with 66 ml toluene for one hour at 45°C. Isolated ambazone by filtration (20.1 g) is dissolved at 60-65°C in 40 ml N, N-dimethylformamide and then 80 ml ethanol are slowly added. After cooling and perfection for two hours at 5-10°C it results 16.8 g ambazone with HPLC assay of minimum 99. 5 %.

Example 3.

30 g crude ambazone are macerated with 90 ml toluene for one hour at 40°C. 55 ml N, N-dimethylformamide and 110 ml methanol are added to ambazone isolated by filtration (27.75 g) and then heated, under stirring, at 60-65°C. After a perfection of approximately 15 minutes at this temperature, it is cooled and is perfected two hours at 5-10°C. It results 25 g ambazone with HPLC assay of minimum 99.5 %.

Bibliography 1. R081168 (1983), Appl. R019800103016, December 30,1980 2. GB 77494 (1957), Appl. DE 195300774794, June 16,1953 3. DE 965723 (1957), Appl. 195300010975, January 31,1953