Process for the production of dithiazolyl disulfides

Details Process for the production of dithiazolyl disulfides Process for the production of dithiazolyl disulfides

2001-11-06

2003-08-26

Gerstl, Robert (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C548S186000

Reexamination Certificate

active

06610857

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a process for the production of 2,2′-dithiazolyl disulfides by oxidation of 2-mercaptothiazoles with peroxidic compounds in an aqueous suspension in a specific pH range.
BACKGROUND OF THE INVENTION
In the industrial production of dibenzothiazyl disulfides by oxidation of 2-mercaptobenzothiazoles, many different oxidizing agents have already been used (Ullmanns Encyclopedia of Industrial Chemistry, 5
th
ed. vol. A-26, p. 773-8, VCH, Weinheim, Basel, Cambridge, New York, Tokyo, 1995). Thus, oxidation with sodium chlorate and sodium nitrite solution in a hydrochloric acid medium at 30° C. is prior art. However, this process has a series of disadvantages. The consumption of mineral acid is very high (3 moles of HCl per mole of 2-mercaptobenzothiazole) and large quantities of co-products are formed. It is also known to perform the oxidation of 2-mercaptobenzothiazoles using nitrous acid. According to the process of U.S. Pat. No. 1,908,935, 2-mercaptobenzothiazole is suspended in water, a water-soluble nitrite is added and oxygen or an oxygen-containing gas, such as air, is passed through the reaction mixture. At the same time a mineral acid, which releases nitrous acid from the nitrite, is added. In the process according to U.S. Pat. No. 2,119,131 and U.S. Pat. No. 3,062,825, stoichiometric quantities of nitrite are used as the sole oxidizing agent. As a result, a more rapid and more complete reaction is achieved. These oxidation processes are also disadvantageous in so far as the consumption of mineral acid is again very high here, and salts and nitrogen oxides are formed in large quantities as by-products.
Chlorine has also been used as an oxidizing agent (Kirk-Othmer, Encyclopedia of Polymer Science and Technology (1970), vol. 12, p. 262). However, this is a complicated reaction with critical reaction conditions in which large quantities of superoxidized by-products are often formed. According to DE-A 23 09 584, to increase the product yield and reduce the quantity of excess chlorine required for adequate oxidation, separate streams of an aqueous solution of an alkali metal salt of mercaptobenzothiazole, an aqueous solution of an alkali metal hydroxide and gaseous chlorine are continuously reacted with one another under the surface of the liquid, with vigorous stirring, at 20 to 75° C., the pH and the redox potential of the aqueous mixture being kept at pH 7 to 10 and a redox potential of −150 to 250 mV by regulating the feed of the aqueous hydroxide solution and the gaseous chlorine. This process also requires very careful control in order to prevent the further oxidation of dibenzothiazyl disulfide to benzothiazyl-2-sulfinate and -sulfonate. The process is also disadvantageous because large quantities of alkali hydroxide are consumed and large quantities of common salt are formed as a co-product.
Hydroperoxides, such as hydrogen peroxide, alkyl hydroperoxides and aralkyl hydroperoxides, have also already been used as oxidizing agents in the production of dibenzothiazyl disulfide (cf. e.g. DE-A 23 49 314). However, the use of a low aliphatic alcohol as solvent is expressly required here. The use of organic solvents is disadvantageous for an industrial process, however, since they can represent both an environmental hazard and, owing to their high inflammability, a constant fire hazard. In addition, organic solvents have to be recycled, purified and disposed of after use, which is expensive.
The oxidation of heterocyclic thiols to disulfides with the aid of hydrogen peroxide or organic peracids in water or organic solvents or in mixtures thereof is described in EP-A 194 571 A1. However, no specific pH which must imperatively be adhered to during these reactions is disclosed therein. In the examples there is only a single reaction in an aqueous medium, in which, however, the thiol is reacted in great dilution (2% solution) and in a homogeneously dissolved form, with hydrogen peroxide. In this way, which is described herein, a very large quantity of water is required in the reaction and a correspondingly large quantity of wastewater is produced, which must be disposed of at great cost. No possibility of working heterogeneously in concentrated suspension, thus saving solvent or wastewater, is disclosed.
This possibility of reacting 2-mercaptothiazoles with hydroperoxides, especially with hydrogen peroxide, in concentrated aqueous suspension is described in U.S. Pat. No. 4,463,178. According to this publication, however, the use of an aqueous amine solution, such as e.g. ammonia or alkylamine solution, is explicitly required as a solubility promoter for the otherwise water-insoluble 2-mercaptothiazole. It is not disclosed that the oxidation reaction can take place without any problems and with quantitative yields even without any solubility-promoting auxiliary agent in pure water.
EP-A 008 548 describes the use of hydrogen peroxide as an oxidizing agent in combination with ethylenediaminetetraacetic acid or the salts thereof. The reaction times have to be very long here, over 24 hours in some cases, to achieve complete conversion. This is a great disadvantage for a large-scale process.
Common to all the above-mentioned oxidation processes is the disadvantage that comparatively expensive oxidizing agents, together with acids, bases, solvents or other auxiliary substances, are required and, in some cases, unusable co- or by-products are also formed.
A process for the electrolytic oxidation of 2-mercaptobenzothiazole to dibenzothiazyl disulfide should also be mentioned (cf. DE-A 27 43 629). This process is technically complex and therefore less economical.
SUMMARY OF THE INVENTION
There is still, therefore, a need to create an improved process for the oxidation of 2-mercaptothiazoles by means of peroxidic compounds.
Therefore, the present invention provides a process for the production of 2,2′-dithiazolyl disulfides of the general formula
wherein
R and R
1
can be the same or different and each denote hydrogen, halogen, nitro, hydroxyl or optionally substituted C
1
-C
12
alkyl or alkoxyl or C
6
-C
12
cycloalkyl or aryl or C
1
-C
12
heteroaryl, or jointly form the residue
wherein
R
2
to R
5
have the same meaning as R and R
1
, by oxidation of a corresponding substituted 2-mercaptothiazole with peroxidic compounds, characterized in that the oxidation is performed in an aqueous suspension at a pH in the range of 6.5 to 8.0.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a process for the production of 2,2′-dithiazolyl disulfides of the general formula
wherein
R and R
1
can be the same or different and each denote hydrogen, halogen, nitro, hydroxyl or optionally substituted C
1
-C
12
alkyl or alkoxyl or C
6
-C
12
cycloalkyl or aryl or C
1
-C
12
heteroaryl, or jointly form the residue
wherein
R
2
to R
5
have the same meaning as R and R
1
, by oxidation of a corresponding substituted 2-mercaptothiazole with peroxidic compounds, characterized in that the oxidation is performed in an aqueous suspension at a pH in the range of 6.5 to 8.0, preferably 6.8 to 7.5.
In the above formula, fluorine, chlorine, bromine or iodine, preferably chlorine or bromine, are suitable as halogen residues.
C
1
-C
12
alkyl is understood to mean all linear or branched alkyl residues with 1 to 12 C atoms known to the person skilled in the art, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, i-pentyl, neo-pentyl and hexyl, which, for their part, can, in turn, be substituted. Suitable substituents in this case are halogen, nitro, hydroxyl, or else C
1
-C
12
alkyl or alkoxy, and C
6
-C
12
cycloalkyl or aryl, such as benzoyl, trimethyl phenyl, ethyl phenyl, chloromethyl, chloroethyl and nitromethyl.
C
1
-C
12
alkoxyl is understood to mean all linear or branched alkoxyl residues with 1 to 12 C atoms known to the person skilled in the art, such as methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, t-butoxy, n-pentoxy, i-pentoxy, neo-pentoxy and hexoxy, which, for their

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