WO2007066844A1

WO2007066844A1 - Process for preparation of aromatic disulfide

Info

Publication number: WO2007066844A1
Application number: PCT/KR2005/004359
Authority: WO
Inventors: Je-Sung Jee; Jae-Geun Lee; Yong-Jin Cho; Do-Hee Lee
Original assignee: Jmc Corporation
Priority date: 2005-12-05
Filing date: 2005-12-16
Publication date: 2007-06-14
Also published as: KR100654208B1

Abstract

Provides is a process for preparing aromatic disulfide using aromatic sulfonyl chloride as a starting material and via aromatic sulfonate as an intermediate. The process of the present invention secures industrially advantageous reaction conditions via use of an iodine derivative as a catalyst, is economically advantageous due to use of inexpensive starting materials and reducing agents as compared to known methods and recovery of the catalyst, and can maximize the purity of the products via re-oxidation of thiophenol which is present as impurities in aromatic disulfide that is a final product of reduction reaction. The present invention can be widely applied to various fields of fine chemistry.

Description

PROCESS FOR PREPARATION OF AROMATIC DISULFIDE

FIELD OF THE INVENTION

The present invention relates to a process for preparation of aromatic disulfide. More specifically, the present invention relates to a process for preparation of aromatic disulfide comprising reducing aromatic sulfonyl chloride to obtain aromatic sulfinate as a first intermediate, reducing the resulting aromatic sulfinate without any separation process to obtain aromatic thiosulfonate as a secondary intermediate and reducing the resulting aromatic thiosulfonate to prepare aromatic disulfide represented by formula (I) below. Therefore, using industrially inexpensive aromatic sulfonyl chloride as a starting material, it is possible to prepare aromatic disulfide with high yield and high purity.

BACKGROUND OF THE INVENTION

Aromatic disulfide derivatives represented by formula (I) below can be economically used as a precursor of aromatic thiophenyl that is required in intermediates of agrochemical and medicinal raw materials. In addition, such compounds themselves can serve as intermediates of agrochemical and medicinal raw materials as well as intermediates of functional additives and/or auxiliary agents.

wherein each R is independently selected from the group consisting of hydrogen, C_1-4 alkyl, halogen, amine, nitro and C_1-4 alkoxy.

As known methods for preparing the aromatic disulfide derivatives of formula (I), there are generally methods involving oxidation or reduction of aromatic thiophenol or aromatic sulfonyl chloride as a raw material and methods involving substitution reaction of disulfur dichloride with an aromatic compound.

However, the method of preparing the aromatic disulfide via substitution of disulfur dichloride with the aromatic compound (Synth. Commun., 5 (3), 173 (1975)) suffers from a low purity of the desired product resulting from the production of large quantities of isomers.

Meanwhile, the methods of preparing the aromatic disulfide via oxidation of aromatic thiophenol commonly use various kinds of oxidizing agents, and Lewis acids and inorganic acids. As such oxidizing agents, it is known to use sulfur and sulfur- donating compounds, for example polysulfide and thiosulfate (US Patent No.

4,375,562), copper oxide, iodine, oxygen gas, antimony pentachloride, and Lewis acids and other inorganic acids (US Patent No. 4,931,542), aqueous hydrogen peroxide, potassium ferrocyanide, iron (III) chloride, dimethylsulfoxide (US Patent No.

5,986,143), hydrogen peroxide and aqueous bases or carbonates (US Patent No. 5,998,670, Japanese Patent No. 2001302616 and US Patent No. 5,932,731). Such synthetic methods using aromatic thiophenol as a starting material involves use of expensive raw material, aromatic thiophenol to which substituents such as amino, alkoxy and the like were introduced to thereby prepare the corresponding aromatic disulfide and therefore suffer from disadvantages such as unfeasibleness of mass production at competitive prices and problems associated with contamination resulting from the use of metal oxidizing agents and treatments of metal oxide wastes.

In addition, as methods of preparing aromatic disulfide via reduction of aromatic sulfonyl chloride, there are known methods involving direct reduction of aromatic sulfonyl chloride, and methods involving first reduction of aromatic sulfonyl chloride to obtain aromatic sulfϊnate which is then subjected to second reduction. Specifically, a method of preparing aromatic disulfide via direct reduction of aromatic sulfonyl chloride with trichlorosilane (TCS: SiCl₃H) and tertiary alkylamine is disclosed in US Patent No. 5,986,143, and a method of preparing aromatic disulfide by preparing aromatic sulfϊnate via use of a known method of reducing aromatic sulfonyl chloride with sodium sulfite and then reducing the resulting aromatic sulfϊnate into gaseous or liquid sulfur dioxide (SO₂) is disclosed in FIAT Final Report 949, pp. 23 - 24 and DE-A 3 302 647, Example 17 and US Patent No. 5,659,088.

However, where trichlorosilane and tertiary alkylamine are used as reducing agents, problems associated with silane-contamination in aromatic disulfide due to use of trichlorosilane may occur. In addition, where aromatic sulfonyl chloride is used as a starting material and sulfur dioxide (SO₂) is used as a reducing agent, this disadvantageous^ results in occurrence of impurities such as aromatic sulfide and sulfoxide and a decreased reaction rate, which in turn will require high-pressure conditions of 1 to 5 atm in order to enhance purity of the desired product and reduce the reaction time.

SUMMARY OF THE INVENTION

Therefore, the inventors of the present invention have made a great deal of efforts and attempts to improve industrial competitiveness of products by producing aromatic disulfide with high yield and high purity, using industrially inexpensive aromatic sulfonyl chloride as a starting material.

That is, as a result of a variety of extensive and intensive studies and experiments, the inventors of the present invention have discovered the facts that, when aromatic sulfinate obtained from reduction of sulfonyl chloride is first directly reduced, without any separation process, into aromatic thiosulfonate, using a catalyst such as iodine, iodic acid or metal iodide and sulfur dioxide (SO₂) as a reducing agent, and the resulting aromatic thiosulfonate, without any separation process thereof, is then reduced into aromatic disulfide to thereby a desired aromatic disulfide compound, this process leads to minimized production of impurities such as aromatic sulfide and sulfoxide, feasible industrial-scale production due to a shortened reaction time under atmospheric pressure conditions, in particularly improved purity of aromatic disulfide via re- oxidation of aromatic thiophenol, which occurs as a by-product during reduction reaction, with hydrogen peroxide and an alkali metal base and therefore it is possible to economically produce high-purity products. The present invention has been completed based on these findings. Therefore, an object of the present invention is to provide an economical process for preparing aromatic disulfide derivatives represented by formula (I) with high yield and high purity on industrial-scale production. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a process for preparing aromatic disulfide represented by formula (I):

wherein each R is independently selected from the group consisting of hydrogen, C_1-4 alkyl, halogen, amine, nitro and C_1-4 alkoxy,

using aromatic sulfonyl chloride as a starting material and via aromatic sulfinate as an intermediate, which comprises:

(a) reducing aromatic sulfonyl chloride with sodium bisulfite (NaHSO₃) and an aqueous base to obtain aromatic sulfinate, and removing aromatic sulfone impurities by extraction with a halogenated hydrocarbon solvent;

(b) adding an inorganic acid to the aqueous aromatic sulfinate solution such that the aromatic sulfinate is neutralized into aromatic sulfinic acid, and reducing the aromatic sulfinic acid with sulfur dioxide in the presence of an iodine derivative catalyst to obtain aromatic thiosulfonate; and (c) warming the aromatic thiosulfonate solution and reducing it with sulfur dioxide in the presence of an iodine derivative catalyst under high temperature and atmospheric pressure conditions to obtain aromatic disulfide, followed by extraction with a halogenated hydrocarbon solvent.

As described above, the most significant characteristics of the present invention reside in that an intermediate, i.e., aromatic thiosulfonate is first prepared using sulfur dioxide as a reducing agent in the presence of an iodine derivative catalyst, and the thus-prepared aromatic thiosulfonate is reduced again using the same catalyst and reducing agent under relatively high temperature conditions to prepare aromatic disulfide.

As shown in conventional arts, reduction reaction under atmospheric pressure using sulfur dioxide (SO₂) alone as a reducing agent exhibits a slow reaction rate and occurrence of impurities such as aromatic sulfide and sulfoxide. Therefore, in order to shorten the reaction time and inhibit occurrence of impurities, the reduction reaction is carried out at high pressure up to maximum of 10 atm.

Whereas, the present invention utilizes an iodine derivative having reducing power superior to sulfur dioxide as a reduction catalyst and thereby it is possible to carry out the reduction reaction at a fast rate under atmospheric pressure conditions, not under conventional high pressure conditions. In addition, it is also possible to inhibit production of impurities such as sulfide and sulfoxide by reduction of aromatic sulfonyl chloride into disulfide via an aromatic thiosulfonate intermediate.

In Step (a), aromatic sulfonyl chlorides containing isomers as impurities cannot be used as the starting material, but those containing aromatic sulfone as impurities are acceptable. This is because aromatic sulfone, which was contained in the starting material, can be easily removed by extraction with halogenated hydrocarbon, after carrying out the reduction reaction of Step (a).

Examples of the aqueous base that can be used in Step (a) include sodium hydroxide, sodium carbonate and the like.

The halogenated hydrocarbon solvent that can be used as an extraction solvent is not particularly limited and may include for example, dichloromethane and dichloroethane.

Where R in aromatic sulfonyl chloride of formula (I) is a strongly nucleophilic substituent, it is preferred to use R-blocked aromatic sulfonyl chloride as the starting material, in order to prevent reaction between R and sulfonyl chloride that is a strongly electrophilic substituent. For example, when R is an amine having strong nucleophilicity, a series of reactions are conducted using N-acetylsulfonilyl chloride that was blocked with a blocking agent such as acetic acid, acetic anhydride or acetylchloride, as the starting material, and thereafter deblocking of the blocked compound is carried out in the final step, thereby preparing a desired product.

The inorganic acid that can be used to neutralize aromatic sulfinate in Step (b) may include, for example sulfuric acid, hydrochloric acid and the like. When sulfuric acid is used as a neutralizing agent, it is preferably used in a mole ratio of 0.5 to 0.6 relative to aromatic sulfinate. Whereas, hydrochloric acid is preferably used in a mole ratio of 1 to 1.2 relative to aromatic sulfinate. Neutralization is preferably carried out at a temperature of 20 to 40 ^°C .

In Step (b), reduction of aromatic sulfinic acid may be carried out at a temperature of 55 to 85 ^°C under atmospheric pressure conditions, particularly preferably at a temperature of 60 to 70 ^°C . When the temperature is too low, the reaction rate is low. When the temperature is too high, this may undesirably result in production of large amounts of impurities such as aromatic sulfide.

In Step (b), an amount of the reducing agent sulfur dioxide (SO₂) used in reduction of aromatic sulfinic acid may be in a range of 0.5 to 1 mole ratio relative to aromatic sulfonyl chloride. Particularly preferred is a range of 0.6 to 0.8 mole ratio.

The iodine derivative used as the reduction catalyst may be selected from iodine, iodic acid, iodide of alkali metals (Group IA) and iodide of alkaline earth metals (Group 2A). As the iodides of alkali metals and alkaline earth metals, for example LiI, NaI, KI, RbI, MgI₂ and CaI₂ may be used.

The iodine derivative is used in a range of 0.01 to 0.1 mole ratio relative to aromatic sulfonyl chloride. Particularly, when iodic acid is used, it is preferably used in a range of 0.025 to 0.05 mole ratio.

In Step (c), sulfur dioxide (SO₂) as the reducing agent may be used in a range of 1 to 1.5 mole ratio relative to aromatic sulfonyl chloride. Particularly preferred is a range of 1 to 1.2 mole ratio.

In Step (c), reduction of aromatic thiosulfonate may be carried out at a temperature of 85 to 105 ^°C, particularly preferably at a temperature of 90 to 100^°C . When the temperature is too low, the reaction rate is low. When the temperature is too high, this may undesirably require high-pressure reaction.

The iodine derivative and halogenated hydrocarbon extraction solvent in Step (c) are the same as described hereinbefore.

In one preferred embodiment, the process in accordance with the present invention may further include, after Step (c), oxidation of aromatic thiophenol, which was contained as a by-product in a solution of aromatic disulfide in halogenated hydrocarbon, with aqueous hydrogen peroxide and an alkali metal base, thereby obtaining high-purity aromatic disulfide. Here, aqueous hydrogen peroxide may be used in a range of 0.02 to 0.05 mole ratio relative to the starting material aromatic sulfonyl chloride. Particularly preferred is a range of 0.015 to 0.03 mole ratio.

In this case, about 2% aromatic thiophenol impurities produced in the reduction reaction may be oxidized again into aromatic disulfide using proper amounts of aqueous hydrogen peroxide and alkali metal base, thereby being capable of obtaining high-purity aromatic disulfide.

If necessary, after Step (c), recovery of the iodine derivative catalyst may be further carried out. That is, from the aqueous solution which was separated from aromatic disulfide, the iodine derivative is oxidized into iodine using aqueous hydrogen peroxide, followed by extraction with the halogenated hydrocarbon solvent, and then the solvent was distilled to recover the iodine derivative catalyst in the form of iodine.

Alternatively, instead of recovering the iodine derivative catalyst in the form of iodine via distillation of the solvent, it is also possible to recover the iodine derivative catalyst as a metal iodide via reduction with sulfur dioxide or sodium bisulfite (NaHSO₃) and an aqueous base. Here, sulfur dioxide or sodium bisulfite (NaHSO₃) and aqueous base may be used in a range of 0.01 to 0.1 mole ratio relative to aromatic sulfonyl chloride, which is equal to the amount of the iodine derivative used as the reduction catalyst.

In the above recovery process, aqueous hydrogen peroxide may be used in a range of 0.11 to 0.6 mole ratio relative to aromatic sulfonyl chloride, which corresponds to equivalents that are capable of oxidizing the total of amounts of the catalyst used and excessive amounts of sulfur dioxide. Here, a recovery rate of iodine reaches a range of 91 to 97%.

Through the above-mentioned recovery process, it is possible to recover and recycle the iodine derivative catalyst used in the reduction reaction with a high yield.

In the foregoing, unless otherwise particularly indicated, ranges for various reaction parameters such as reactant ratios, temperatures, pressure and the like mean the optimal conditions for carrying out the reactions in accordance with the present invention. Hereinafter, one preferred embodiment in accordance with the present invention will be described in more detail with reference to Reaction Scheme 1 below.

[Reaction Scheme 1]

*'"•""<• '"•^•'^«

In Reaction Scheme 1, each R is independently hydrogen, Ci_-4 alkyl, halogen, amine, nitro or C_1-4 alkoxy, X is hydrogen, iodine, an alkali metal or alkaline earth metal, and M is Na or K.

For preparation of aromatic disulfide derivatives in accordance with the present invention, aromatic sulfonyl chloride which was substituted with R is reduced with sodium bisulfite (NaHSOs) and an aqueous base to obtain aromatic sulfonate. Here, aromatic sulfone, which is present as impurities in the aromatic sulfonyl chloride, can be removed from the aqueous aromatic sulfinate phase by extraction with a halogenated hydrocarbon solvent.

Next, an inorganic acid is added to the aqueous aromatic sulfinate solution to neutralize aromatic sulfinate, thereby obtaining an aromatic sulfinic acid, and the aromatic sulfinic acid is directly reduced at a temperature of 55 to 85 ^°C , without any separation process, using a reduction catalyst represented by formula (IX) and sulfur dioxide (SO₂) as a reducing agent thereby to obtain aromatic thiosulfonate.

Thereafter, the thus-obtained aromatic thiosulfonate is reduced again at a high temperature of 85 to 105 ^°C to prepare aromatic disulfide represented by formula (I). A small amount of aromatic thiophenol contained in aromatic disulfide may be oxidized again with aqueous hydrogen peroxide and an alkali metal base to further enhance the purity of desired product.

A flow diagram of oxidation-reduction reactions utilized in the present invention is shown in Fig. 1, and standard reduction potentials (Handbook of chemistry and physics 85th edition, David R. Lide) of catalysts and reducing agents used in reduction reactions are presented below.

Reduction potentials of catalysts and reducing agents

I₂ +2e 2r E⁰ = 0.620

SO₄ ^2' + 4H⁺ + 2e H₂SO₃ + H₂O E⁰ = 0.172

2ArSO₂H + 2H⁺ + 2e ArSSO₂Ar + 2H₂O E° > 0.62O =A

ArSSO₂Ar + 4H⁺ + 4e ArSSAr + 2H₂O E° > A H₂O₂ + 2H⁺ + 2e 2H₂O E⁰ = 1.776

In the above reduction potential table, Ar refers to a cyclic aromatic compound. As described above, the present invention is useful to produce high-purity aromatic disulfide containing substantially no impurities by preparing aromatic thiosulfonate at a suitable temperature using the iodine derivative catalyst and sulfur dioxide (SO₂) as reducing agents, preparing aromatic disulfide at a high temperature using the same reducing agents, and treating aromatic thiophenol impurities contained in aromatic disulfide with aqueous hydrogen peroxide as an oxidizing agent in the presence of the alkali metal base.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

Fig. 1 is a flow diagram of oxidation-reduction reactions utilized in the present invention.

EXAMPLES

Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only for illustrating the present invention and should not be construed as limiting the scope and spirit of the present invention. Example 1: Preparation of 4,4'-difluorophenyldisulfide

180 g of an aqueous 30% sodium hydroxide solution was added to 203.6 g of an aqueous 23% sodium bisulfite solution and the mixture was heated to 50 ^°C . 92.2 g of 95% pαrα-fluorobenzenesulfonylchloride (containing 0.05% bis(4- fluorophenyl)sulfone) was added dropwise thereto over 2 hours and the resulting solution was stirred at 50 "C for 4 hours. After cooling the reaction solution to 20 °C, 50 g of 99% dichloromethane was added, and bis(4-fluorophenyl)sulfone was then extracted, separated and removed.

53.0 g of 50% sulfuric acid was added dropwise at 30 ^°C for 1 hour to an aqueous 4-fluorobenzenesulfinate solution, from which bis(4-fluorophenyl)sulfone was removed, and 5.0 g of 57% iodic acid was then added dropwise thereto at that temperature in one portion. The reaction solution was elevated to 60 ^°C, then 90 ^°C over 2 hours while introducing 57.7 g of sulfur dioxide gas for 5 hours and reacted at that temperature for 4 hours. After cooling to 20^°C, the reaction solution was extracted with 38.2 g of 99% dichloromethane to separate 4,4'-difluorophenyldisulfide. 1.2 g of 50% sodium hydroxide and 1.5 g of 35% hydrogen peroxide (aqueous) were added to a solution of 4,4'-difluorophenyldisulfide in dichloromethane which was then stirred at room temperature for 1 hour, followed by separation of a dichloromethane layer. The separated dichloromethane layer was washed with 24.3 g of water and dichloromethane was removed by distillation under reduced pressure to afford 54.4 g (yield: 95%) of 4,4'-difluorophenyldisulfide with 99.9% purity. A content of isomers in the thus- obtained product was 0.064%. 24.1 g of 35% hydrogen peroxide (aqueous) was added dropwise to the aqueous solution separated from the solution of 4,4'-difluorophenyldisulfide in dichloromethane, and the resulting mixture was then stirred for 2 hours and separated by extraction with 50 g of 99% dichloromethane. Then, dichloromethane was removed by distillation under reduced pressure to recover 2.7 g (recovery rate: 95%) of iodine. It could be confirmed from analysis results of a final compound that the title compound was obtained as desired.

Example 2: Preparation of 4,4'-dichlorophenyldisulfϊde

271.3 g of an aqueous 25% sodium carbonate solution was added to 181.0 g of an aqueous 23% sodium bisulfite solution and the mixture was heated to 50 ^"C . 85.3 g of 99% /rørα-chlorobenzenesulfonylchloride (containing 0.1% bis(4-chlorophenyl)sulfone) was added dropwise thereto over 2 hours and the resulting solution was stirred at 50 ^°C for 4 hours. After cooling the reaction solution to 20 ^°C, 44.4 g of 99% dichloromethane was added and bis(4-chlorophenyl)sulfone was then extracted, separated and removed.

47.1 g of 50% sulfuric acid was added dropwise at 3 O⁰C for 1 hour to an aqueous 4-chlorobenzenesulfinate solution, from which bis(4-chlorophenyl)sulfone was removed, and 4.5 g of 57% iodic acid was then added dropwise thereto at that temperature in one portion. The reaction solution was elevated to 60⁰C, then 95 ^°C over 2 hours while introducing 51.2 g of sulfur dioxide gas for 5 hours and reacted at that temperature for 6 hours. After cooling to 20⁰C, the reaction solution was extracted with 34.3 g of 99% dichloromethane to separate 4,4'-dichlorphenyldisulfide. 1.1 g of 50% sodium hydroxide and 1.3 g of 35% hydrogen peroxide (aqueous) were added to a solution of 4,4'-dichlorophenyldisulfide in dichloromethane which was then stirred at room temperature for 1 hour, followed by separation of a dichloromethane layer. The separated dichloromethane layer was washed with 21.6 g of water and dichloromethane was removed by distillation under reduced pressure to afford 44.8 g (yield: 78%) of 4,4'-dichlorophenyldisulfide with 99.9% purity. A content of isomers in the thus- obtained product was 0.067%.

21.4 g of 35% hydrogen peroxide (aqueous) was added dropwise to the aqueous solution separated from the solution of 4,4'-dichlorophenyldisulfide in dichloromethane and the resulting mixture was then stirred for 2 hours and separated by extraction with 45 g of 99% dichloromethane. Then, 4.3 g of 23% sodium bisulfite and 2.3 g of 50% sodium hydroxide were added dropwise to a solution of iodine separated in dichloromethane, followed by separation to recover 9.0 g (recovery rate: 95%) of an aqueous 31.7% sodium iodide solution. From analysis results of a final compound, it could be confirmed that the title compound was obtained as desired. Example 3: Preparation of 4,4'-dibromophenyldisulfϊde

Using 85.3 g of 99% pαrα-bromobenzenesulfonylchloride (containing 0.1% bis(4-bromophenyl)sulfone), 41.6 g (yield: 67%) of 4,4'-dibromophenyldisulfide with 99.9% purity was obtained in the same manner as in Example 2. A content of isomers in the thus-obtained desired product was 0.064%. The reduction reaction with iodic acid and sulfur dioxide gas was carried out at 100 "C for 8 hours. From analysis results of a final compound, it could be confirmed that the title compound was obtained as desired.

Example 4: Preparation of 4,4'-diaminophenyldisulfide Using 93.6 g of 99.9% N-acetylsulfanilylchloride, 42.7 g (yield: 86%) of 4,4'- diaminophenyldisulfide with 99.9% purity was obtained in the same manner as in Example 2. Isomers were not detected in the thus-obtained product. The reduction reaction with iodic acid and sulfur dioxide gas was carried out at 100⁰C for 8 hours. From analysis results of a final compound, it could be confirmed that the title compound was obtained as desired.

Example 5: Preparation of pam-tolyldisulfide

Using 77.0 g of 99% /jαrα-toluenesulfonylchloride (containing 0.1% para- tolylsulfone), 46.8 g (yield: 95%) ofpαrα-tolyldisulfide with 99.9% purity was obtained in the same manner as in Example 2. Isomers were not detected in the thus-obtained product. The reduction reaction with iodic acid and sulfur dioxide gas was carried out at 90 ^°C for 4 hours. From analysis results of a final compound, it could be confirmed that the title compound was obtained as desired.

Example 6: Preparation of 4.4'-dimethoxyphenyldisulfide

Using 83.5 g of 99% /rørα-methoxybenzenesulfonylchloride (containing 0.1% /wα-methoxyphenylsulfone), 46.8 g (yield: 84%) of 4,4'-dimethoxyphenyldisulfide with 99.9% purity was obtained in the same manner as in Example 2. Isomers were not detected in the thus-obtained product. The reduction reaction with iodic acid and sulfur dioxide gas was carried out at 90 ^°C for 4 hours. From analysis results of a final compound, it could be confirmed that the title compound was obtained as desired.

Example 7: Preparation of diphenyldisulfide Using 77.0 g of 99% benzenesulfonylchloride (containing 0.2% diphenylsulfone), 44.8 g (yield: 95%) of diphenyldisulfide with 99.9% purity was obtained in the same manner as in Example 2. The reduction reaction with iodic acid and sulfur dioxide gas was carried out at 90 ^°C for 4 hours. From analysis results of a final compound, it could be confirmed that the title compound was obtained as desired.

Example 8: Preparation of 3.3'-dinitrophenyldisulfide

Using 89.5 g of 99% 3-nitrobenzenesulfonylchloride (containing 0.2% 3-bis(3- nitrophenylsulfone)sulfone)), 46.1 g (yield: 75%) of 4,4'-dinitrophenyldisulfide with 99.9% purity was obtained in the same manner as in Example 2. The reduction reaction with iodic acid and sulfur dioxide gas was carried out at 100°C for 8 hours. From analysis results of a final compound, it could be confirmed that the title compound was obtained as desired.

As confirmed above, the methods in accordance with Examples 1 through 8 of the present invention can prepare aromatic disulfide with a yield equal to or higher than conventional methods known in the art.

INDUSTRIAL APPLICABILITY

As apparent from the above description, a process for preparation of aromatic disulfide in accordance with the present invention secures industrially advantageous reaction conditions via use of an iodine derivative as a catalyst, is economically advantageous due to use of inexpensive starting materials and reducing agents as compared to known methods and recovery of the catalyst, and can maximize the purity of the products via re-oxidation of thiophenol which is present as an impurity in aromatic disulfide that is a final product of reduction reaction. Therefore, the present invention can be widely applied to various fields of fine chemistry.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS

1. A process for preparing aromatic disulfide represented by formula (I):

wherein each R is independently selected from the group consisting of hydrogen, CM alkyl, halogen, amine, nitro and C_1-4 alkoxy,

(a) reducing aromatic sulfonyl chloride with sodium bisulfite (NaHSθ₃) and an aqueous base to obtain aromatic sulfinate, and removing aromatic sulfone impurities by extraction with a halogenated hydrocarbon solvent;

(b) adding an inorganic acid to the aqueous aromatic sulfinate solution such that the aromatic sulfinate is neutralized into aromatic sulfinic acid, and reducing the aromatic sulfinic acid with sulfur dioxide in the presence of an iodine derivative catalyst to obtain aromatic thiosulfonate; and

(c) warming the aromatic thiosulfonate solution and reducing it with sulfur dioxide in the presence of an iodine derivative catalyst under high temperature and atmospheric pressure conditions to obtain aromatic disulfide, followed by extraction with a halogenated hydrocarbon solvent.

2. The process according to claim 1, further comprising, after Step (c), one or more steps selected from the group consisting of the following Steps:

(cl) oxidizing aromatic thiophenol contained in a solution of aromatic disulfide in halogenated hydrocarbon with aqueous hydrogen peroxide and an alkali metal base to obtain high-purity aromatic disulfide;

(c2) oxidizing the iodine derivative from the aqueous solution which was separated from aromatic disulfide into iodine using aqueous hydrogen peroxide, followed by extraction with the halogenated hydrocarbon solvent, and reducing the extract with sulfur dioxide or sodium bisulfite (NaHSO₃) and an aqueous base to recover the iodine derivative catalyst in the form of a metal iodide; and

(c3) oxidizing the iodine derivative from the aqueous solution which was separated from aromatic disulfide into iodine using aqueous hydrogen peroxide, followed by extraction with the halogenated hydrocarbon solvent, and distilling the solvent to recover the iodine derivative catalyst in the form of iodine.

3. The process according to claim 1 or 2, wherein the halogenated hydrocarbon solvent used as the extraction solvent is dichloromethane or dichloroethane.

4. The process according to claim 1, wherein the iodine derivative as the reduction catalyst is selected from iodine, iodic acid, iodide of an alkali metal and iodide of an alkaline earth metal.

5. The process according to claim 1, wherein the iodine derivative as the reduction catalyst is used in a range of 0.01 to 0.1 mole ratio relative to aromatic sulfonyl chloride, and when iodic acid is used as the reduction catalyst, iodic acid is used in a range of 0.025 to 0.05 mole ratio.

6. The process according to claim 1, wherein reduction of aromatic sulfinic acid in Step (b) is carried out at a temperature of 55 to 85 "C under atmospheric pressure.

7. The process according to claim 1 , wherein reduction of aromatic thiosulfonate in Step (c) is carried out at a temperature of 85 to 105⁰C .

8. The process according to claim 1, wherein the reducing agent sulfur dioxide

(SO₂) in Step (b) is used in a range of 0.5 to 1 mole ratio relative to aromatic sulfonyl chloride.

9. The process according to claim 1, wherein sulfur dioxide (SO₂) as the reducing agent in Step (c) is used in a range of 1 to 1.5 mole ratio relative to aromatic sulfonyl chloride.

10. The process according to claim 2, wherein aqueous hydrogen peroxide in Step (cl) is used in a range of 0.02 to 0.05 mole ratio relative to aromatic sulfonyl chloride.

11. The process according to claim 2, wherein aqueous hydrogen peroxide in Step (c2) or Step (c3) is used in a range of 0.11 to 0.6 mole ratio relative to aromatic sulfonyl chloride.

12. The process according to claim 2, wherein sulfur dioxide or sodium bisulfite (NaHSO₃) and aqueous base in Step (c2) are used in a range of 0.01 to 0.1 mole ratio which is equal to the amount of the iodine derivative used as the reduction catalyst, relative to aromatic sulfonyl chloride.