Process for the preparation of bis-DMTD

Abstract

The present invention relates to a process for the preparation of bis(dimercaptothiadiazole) (or bis-DMTD), more particularly of 5,5-dithiobis(1,3,4-thiadiazole-2-thiol), said process being carried out in a single reactor and making possible a preparation with improved yields which is more respectful of the environment.

Claims

1. A process for the preparation of bis-DMTD solids, which comprises conducting, in a single reaction vessel without isolation of DMTD, at least the following stages: a) reaction of hydrazine (N.sub.2H.sub.4) with carbon disulfide (CS.sub.2) in a basic medium forming a DMTD salt containing reaction medium; b) acidification of the reaction medium containing the DMTD salt to result in DMTD in the reaction medium; and c) oxidation of the reaction medium containing the DMTD from step b) with an oxidizing agent and without isolating the DMTD from the reaction medium, and then; d) recovering the bis-DMTD solids from the single reaction vessel forming aqueous reaction effluents and optionally purifying the recovered bis-DMTD solids, and wherein the formed reaction effluents have a low organic matter load as measured by a Chemical Oxygen Demand (COD) value of less than 10 g/l and wherein the acidification stage is carried out under the action of sulfuric acid.

2. The process as claimed in claim 1, wherein the CS.sub.2/N.sub.2H.sub.4 molar ratio is between 1.8 and 4.0.

3. The process as claimed in claim 1, wherein stage a) is carried out in an aqueous phase.

4. The process as claimed in claim 1, wherein the basic medium has a base/hydrazine molar ratio is between 0.8 and 1.5.

5. The process as claimed in claim 1, wherein stage a) is carried out in the presence of a surfactant.

6. The process as claimed in claim 1, wherein the oxidation stage c) is carried out by addition of an oxidizing agent to the reaction medium, said oxidizing agent selected from the group consisting of peroxides, organic peracids, inorganic peracids, and mixtures thereof.

7. The process as claimed in claim 1, wherein the oxidizing agent/DMTD molar ratio is between 0.35:1 and 0.65:1.

8. The process as claimed in claim 1, wherein a processing aid is added to the reaction medium during stage d) to limit the pulverlent nature of bis-DMTD and facilitate recovery.

9. The process as claimed in claim 1, wherein the bis-DMTD solids recovered are washed with water and then advantageously dried at a temperature of between 50 C. and 150 C.

10. The process as claimed in claim 1, wherein the amount of organic matter dissolved in the reaction effluents is very low and results in a Chemical Oxygen Demand (COD) value of less than 5 g/l.

11. The process as claimed in claim 1, wherein the CS.sub.2/N.sub.2H.sub.4 molar ratio is between 2.0 and 3.0.

12. The process as claimed in claim 1, wherein stage a) is carried out in the presence of a strong base, an alkali metal, or alkaline earth metal hydroxide.

13. The process as claimed in claim 5, wherein the surfactant is a nonionic surfactant.

14. The process as claimed in claim 6, wherein the oxidizing agent is combined with one or more strong acids.

15. The process as claimed in claim 14, wherein the strong acid is sulfuric acid or hydrochloric acid and the oxidizing agent is hydrogen peroxide.

16. The process as claimed in claim 8, wherein the processing aid is an oil.

17. The process as claimed in claim 16, wherein the oil is a naphthenic oil, or a paraffinic oil.

18. A process for the preparation of bis-DMTD solids, which comprises conducting, in a single reaction vessel, at least the following stages: a) reaction of hydrazine (N.sub.2H.sub.4) with carbon disulfide (CS.sub.2) in a basic medium forming a DMTD salt containing reaction medium; b) acidification of the reaction medium containing the DMTD salt to result in DMTD in the reaction medium; and c) oxidation of the reaction medium containing the DMTD from step b) with an oxidizing agent and without isolating the DMTD from the reaction medium, and then; d) recovering the bis-DMTD solids from the single reaction vessel forming an aqueous reaction effluent and optionally purifying the recovered bis-DMTD solids, wherein stages a)-d) are carried out in the absence of mercaptans, and wherein the formed reaction effluents have a low organic load as measured by Chemical Oxygen Demand (COD) value of less than 10 g/l and wherein the acidification stage is carried out under the action of sulfuric acid.

19. The process of claim 1, wherein impurities generated in stage a) are not removed from the single reaction vessel.

20. The process of claim 18, wherein impurities generated in stage a) are not removed from the single reaction vessel.

21. The process of claim 10, wherein the amount of organic matter dissolved in the reaction effluents results in a Chemical Oxygen Demand (COD) value of less than 2 g/l.

22. The process as claimed in claim 1, wherein the oxidizing agent/DMTD molar ratio is between 0.45:1 and 0.55:1.

23. A process for the preparation of bis-DMTD solids, which comprises conducting, in a single reaction vessel without isolation of intermediate DMTD, at least the following stages: a) reaction of hydrazine (N.sub.2H.sub.4) with carbon disulfide (CS.sub.2) in a basic medium forming a DMTD salt containing reaction medium; b) acidification of the reaction medium containing the DMTD salt to result in DMTD in the reaction medium; and c) oxidation of the reaction medium containing the DMTD from step b) with an oxidizing agent and without isolating the DMTD from the reaction method medium, and then; d) recovering the bis-DMTD solids from the single reaction vessel forming aqueous reaction effluents and optionally purifying the recovered bis-DMTD solids, and wherein the formed reaction effluents have a low organic load as measured by a Chemical Oxygen Demand (COD) value of less than 10 g/l and wherein an oil processing aid is added to the reaction medium during stage d) to limit the pulverlent nature of bis-DMTD and facilitate recovery.

Description

(1) The present invention is now illustrated by means of the example which follows and which does not exhibit any limiting purpose from the viewpoint of the scope of the present invention, the scope furthermore defined by the appended claims.

(2) Example of the Synthesis of Bis-DMTD:

(3) Stage a)

(4) 4000 liters of water, 800 kg of hydrazine monohydrate and 1300 kg of a 50% by weight aqueous sodium hydroxide solution are added to a 16 m.sup.3 enameled reactor or a reactor made of stainless steel which has been rendered inert beforehand with nitrogen and which is provided with a stirring system. The temperature rises to approximately 30 C.

(5) 2900 kg of carbon disulfide are subsequently added over approximately 10 hours at a temperature of between 36 C. and 40 C. The hydrogen sulfide released during the reaction is trapped by absorption/reaction in an aqueous sodium hydroxide solution.

(6) The reaction medium is gradually heated to approximately 98 C. and stripping with nitrogen is carried out at this temperature for 5 hours. The reaction medium is subsequently cooled to 20 C. and then 2000 l of water are added.

(7) Stage b)

(8) 2200 kg of 42% sulfuric acid are added, still with stirring and under nitrogen, while maintaining the temperature at 20 C.

(9) Stage c)

(10) 770 kg of 35% aqueous hydrogen peroxide (H.sub.2O.sub.2) are then added while maintaining the temperature between 50 C. and 55 C., and then stirring is maintained at 50 C. for 2 hours.

(11) Stage d)

(12) 36 kg of 85 Neutral Solvent oil from Total are then added and then the product is filtered off on a centrifuge; the product is washed with water and then dried under vacuum at 70 C. 2240 kg of bis-DMTD are recovered, which product has a melting point of 162-164 C. and a purity of 98% (yield=92%).

(13) The COD (chemical oxygen demand) of the aqueous mother liquors is measured with a DR/5000 spectrophotometer (Hach-Lange), after filtration of the bis-DMTD. The COD measured is less than or equal to 5 g/l.

(14) The low toxicity of the effluents generated by the process of the present invention and the good yields observed render said process entirely appropriate for manufacture of bis-DMTD at the industrial level.