EP4237407A1

EP4237407A1 - Process for preparing 1,2-benzisothiazoline-3-one

Info

Publication number: EP4237407A1
Application number: EP21806645.4A
Authority: EP
Inventors: Rüdiger Baum; Holger Bittermann; Zhenghao YANG; Chaoqiang ZHANG; Changhua Zhang; Qinglin ZHENG
Original assignee: Thor GmbH
Current assignee: Thor GmbH
Priority date: 2020-10-30
Filing date: 2021-10-25
Publication date: 2023-09-06
Also published as: JP2023547235A; KR20230098155A; WO2022089774A8; CN116457337A; WO2022089774A1; US20240076276A1

Abstract

The invention relates to a process for preparing 1,2'-benzisothiazoline-3-one according to formula (I), comprising the following steps: (a) reacting a 2-halogenbenzonitrile compound of general formula (II) with a reaction mixture, containing: (i) alkaline sulphide and/or alkaline hydrogen sulphide and (ii) an alkyl halide compound, represented by general formula (III): R¹X (III) for producing an intermediate product of general formula (IV), and (b) reacting the intermediate product of general formula (V) obtained in step (a) with a halogenating agent or an oxidant and subsequent reaction of the 2-(alkylsulfoxy)benzonitrile with an acid to form 1,2-benzisothiazoline-3-one as well as a halide compound of general formula (V) R¹X (V).

Description

Process for preparing l,2-benzisothiazolin-3-one

The invention relates to a process for the preparation of 1,2-benzisothiazolin-3-one according to the formula (I), comprising the steps: (a) reaction of a 2-halobenzonitrile compound of the general formula (II) with a reaction mixture containing: (i ) alkali sulfide and/or alkali hydrosulfide and (ii) an alkyl halide compound represented by general formula (III): R'X (III) to form an intermediate of general formula (IV) and (b) reacting the obtained in step (a). Intermediate product of the general formula (IV) with a halogenating agent or an oxidizing agent, and subsequent reaction of the 2-(alkylsulfoxy)benzonitrile with an acid to give the 1,2-benzisothiazolin-3-one and a halide compound of the general formula (V) R' X(v).

1,2-Benzisothiazolin-3-one is a biocide used as a preservative in emulsion paints, lacquers, adhesives, detergents, fuels and in paper manufacture. Mixtures of 1,2-benzisothiazolin-3-one with 2-methyl-4-isothiazolin-3-one are used in particular for in-can preservation in paints.

Various processes for the preparation of 1,2-benzisothiazolin-3-one and its derivatives are known from the prior art.

For example, US 4,736,040 describes a process for preparing 1,2-benzisothiazolin-3-ones by reacting 2,2'-dithiobenzamides with an oxygenating agent in the presence of an aqueous alkaline medium. The 2,2'-dithiobenzamides are prepared by nitrosation of anthranilamides and subsequent reaction of the product thus obtained with sulfur dioxide in the presence of a catalyst. This process for preparing l,2-benzisothiazoline-3-

1

CONFIRMATION COPY ion is both time consuming and expensive as many reaction steps are required.

A simpler process for preparing 1,2-benzisothiazolin-3-ones is described in EP 2,687,519. In the process according to EP 2 687 519, a 2-halobenzonitrile is first reacted with an alkyl thiol having 1 to 4 carbon atoms

2-(alkylthio)benzonitrile. The 2-(alkylthio)benzonitrile is then reacted with a halogenating agent in the presence of water to obtain the 1,2-benzisothiazolin-3-one. In the course of this process, recycling of intermediate products, for example the resulting methyl chloride, which is obtained in the preparation of the 1,2-benzisothiazolin-3-one, is difficult because of its volatility.

Furthermore, European patent specification EP 2 949 650 B1 discloses a process for the preparation of BIT by reacting a 2-halobenzonitrile compound with a thiol compound having 5 to 15 carbon atoms to give a 2-(alkylthio)benzonitrile and subsequent reaction with a halogenating agent to convert the 1st ,2-benzisothiazoline

3-on to get. The process disclosed in this publication also has various disadvantages, for example large amounts of alkyl thioethers, which cannot be used further, are obtained in the described work-up of the halide compounds obtained as a by-product in the course of BIT production.

The object on which the present invention is based is therefore to provide an improved process for preparing a 1,2-benzisothiazolin-3-one. The process should not have the above-mentioned disadvantages of the prior art, or only to a significantly lesser extent. In addition, the method should be able to be carried out more simply, more safely and more cost-effectively than those described in the prior art.

This object is achieved by a process for preparing 1,2-benzisothiazolin-3-one of the formula (I), including the steps:

(a) Reaction of a 2-halobenzonitrile compound represented by general formula (II): where X is chlorine or bromine; with a reaction mixture containing:

(i) alkali sulfide and/or alkali hydrosulfide and

(ii) an alkyl halide compound represented by the following general formula (III): R*X (III), wherein

R ¹ is selected from the group consisting of unsubstituted or at least monosubstituted Ci-Cio-alkyl, unsubstituted or at least monosubstituted Cs-Cu-aryl and unsubstituted or at least monosubstituted C7-C18 aralkyl, wherein the substituents are selected from the group consisting from F, CI, Br, I, OH, NH ₂ , Ci-Cs-alkyl and OR ² , where

R ² is hydrogen or Ci-C4-alkyl; and X is chlorine or bromine to form an intermediate of general formula (IV)

(b) Reaction of the intermediate of general formula (IV) obtained in step (a) with a halogenating agent or an oxidizing agent and then Reaction of the 2-(alkylsulfoxy)benzonitrile with an acid to give the 1,2-benzisothiazolin-3-one and a halide compound of the general formula (V) R*X, where R ¹ is as defined above.

With the aid of the process according to the invention, the 1,2-benzisothiazolin-3-one, starting from the 2-halobenzonitrile compound, can be obtained in high yield in a particularly economical process using the alkyl halide compound.

Advantageously, the reaction of the one 2-halobenzonitrile compound of the general formula (II) with the reaction mixture containing (i) an alkali metal sulfide and/or alkali metal hydrogen sulfide and (ii) the alkyl halide compound of the general formula (III) is comparatively the process described in EP 2 949 650 B1 leads to a significant reduction in the amount of thioether obtained as a by-product. Compared to the processes described in the prior art, the process according to the invention is also distinguished by lower emissions of mercapto compounds.

A third advantage is that the alkyl halide compound, which occurs as a by-product in process step (b), can be reused directly and does not have to be first converted into an alkanethiol compound according to the prior art. The recycling of the alkyl halide compound is also more economical because the process according to the invention produces significantly smaller amounts of thioether as a by-product than the 10 to 25% known from the prior art.

In the first process step (a) of the process according to the invention for the preparation of l,2-benzisothiazolin-3-one, a 2-halobenzonitrile compound of the general formula (II), where X is chlorine or bromine, preferably chlorine, is reacted with a reaction mixture which:

(i) at least one alkali sulfide and/or alkali hydrosulfide and (ii) at least one alkyl halide compound represented by the following general formula (III): R'X, where R ¹ is selected from the group consisting of unsubstituted or at least monosubstituted Ci-Cio - Alkyl, unsubstituted or at least monosubstituted Cs-Cu-aryl and unsubstituted or at least monosubstituted C7-C18 aralkyl, and wherein the substituents are selected from the group consisting of F, Cl, Br, I,

OH, NH2, Ci-Cs-alkyl and OR ² , where R ² is hydrogen or Ci-C4-alkyl; and X is chlorine or bromine to obtain the intermediate of general formula (IV), wherein R ¹ is as defined above.

According to a preferred embodiment, 2-bromobenzonitrile and/or 2-chlorobenzonitrile, particularly preferably 2-chlorobenzonitrile, is used as the 2-halobenzonitrile compound.

The 2-halobenzonitrile compound of the general formula (II) is converted in process step (a) with (i) the at least one alkali metal sulfide and/or alkali metal hydrosulfide and (ii) the at least one alkyl halide compound of the general formula (III) to give the intermediate of the general formula ( IV) implemented. The alkali sulfide and/or alkali hydrosulfide is generally selected from the group consisting of sodium hydrosulfide, potassium hydrosulfide, sodium sulfide and potassium sulfide. According to a preferred embodiment of the invention, sodium sulfide is used in process step (a). According to a preferred embodiment of the invention, anhydrous sodium sulfide is used in process step (a). Anhydrous sodium sulfide means a product with a content of more than 90% by weight, preferably more than 95% by weight, of Na2S. The use of anhydrous/dry sodium sulfide leads to improved yields of 1,2-benzisothiazolin-3-one compared to hydrous sodium sulfide with, for example, 60% by weight NaiS content.

The alkyl halide compound according to the general formula (III): R'X is generally the compound(s) defined above, preferably it is a compound of the general formula (III), where R ¹ is selected from the group consisting of branched or unbranched Ci-Cio-alkyl and X is chlorine or bromine. Halide compounds selected from the group consisting of methyl chloride, methyl bromide, ethyl chloride, ethyl bromide, n-propyl chloride, n-propyl bromide, isopropyl chloride, isopropyl bromide, n-butyl chloride, n-butyl bromide, sec-butyl chloride, sec. -butyl bromide, isobutyl chloride, isobutyl bromide, tert. -butyl chloride, tert-butyl bromide, n-pentyl chloride, n-pentyl bromide, isopentyl chloride, isopentyl bromide, sec.-pentyl chloride, sec.-pentyl bromide, neo-pentyl chloride, neo-pentyl bromide, 1,2-dimethylpropyl chloride, 1 ,2-dimethylpropyl bromide, iso-amyl chloride, iso-amyl bromide, n-hexyl chloride, n-hexyl bromide, iso-hexyl chloride, iso-hexyl bromide, sec-hexyl chloride, sec-hexyl bromide, n-heptyl chloride, n-heptyl bromide, n-octyl chloride , n-octyl bromide, n-nonyl chloride, n-nonyl bromide, n-decyl chloride, n-decyl bromide. More preferably, the halide compounds are selected from the group consisting of n-propyl chloride, n-butyl chloride, n-pentyl chloride and n-hexyl chloride.

According to a preferred embodiment of the invention, the halide compound is selected from the group consisting of n-propyl chloride, n-butyl chloride, n-pentyl chloride and n-hexyl chloride. According to a particularly preferred embodiment of the invention, n-butyl chloride is employed or used as the alkyl halide compound in process step (a). The process according to the invention is preferably characterized in that the halide compound of the general formula (V) obtained in step (b) is at least partially separated off from the reaction mixture obtained and fed to process step (a). The recycling and reuse of the halide compound obtained as a by-product in the cyclization has already been described in the prior art, for example in EP 2 678 520 A1. Here, the 1,2-benzisothiazolin-3-one is prepared by cyclization of 2-methylthiobenzonitrile, with the readily volatile and difficult-to-handle methyl chloride being obtained as a by-product as the halide compound. Analysis of the currently commercially available batches of l,2-benzisothiazolin-3-one from various manufacturers provides evidence that at the time the application was filed, l,2-benzisothiazolin-3-one was produced on an industrial scale by cyclization of 2-methylthiobenzonitrile. As can be seen from the table below, the by-products methyl-1,2-benzisothiazolin-3-one (m-BIT) and methylthiobenzoic acid (MTBS) can be detected in all batches. There were no indications that 1,2-benzisothiazolin-3-one, for example, was also produced from 2-butylthiobenzonitrile, the by-product butylthiobenzoic acid was not detectable in any of the samples (nn), the detection limit was 10 ppm. nn: The BTBS content was below the detection limit of 10 ppm.

⁽¹⁾ Hikal Ltd., India; ⁽²⁾ Dafeng Yuelong, China; ⁽³⁾ GBT dealer, manufacturer Weifang Runan, China; ⁽⁴⁾ Hong Kong Hongtai distributors, manufacturers Shouguang Syntech Fine Chemical Cpo. Ltd, China; ⁽⁵⁾ Linva (Shanghai), manufacturer Shouguang Syntech Fine

Chemical Cpo. Ltd, China; ⁽⁶⁾ Scale Chemical Corporation, manufacturer Dalian Biochem, China; ⁽⁷⁾ Suzhou Guoxin Group Fengyuan, Lianyungang Sunlion Manufacturer, China.

As already described above, it is possible to use 2-methylthiobenzonitrile in the preparation of 1,2-benzisothiazolin-3-one; according to a particularly preferred embodiment of the invention, however, n-butyl chloride is employed or used as the alkyl halide compound in process step (a). Advantageously, the use of n-butyl chloride allows in the context of process according to the invention for the preparation of l,2-benzisothiazolin-3-one, the removal of the butyl chloride from the reaction mixture obtained in process step (b), which can be carried out easily in terms of process technology. Due to its boiling point of about 78° C., this can be removed and absorbed or recovered in a simple manner, for example by means of distillation, from the reaction mixture obtained in process step (b) and at least partially reused in process step (a).

In process step (a), the alkali metal sulfide and/or alkali metal hydrosulfide is generally used in an amount of 1 to 1.4 mol, preferably in an amount of 1 to 1.2 mol, per mol of 2-halobenzonitrile compound.

Process step (a) is preferably carried out in a suitable solvent, which leads to a smoother course of the reaction. The 2-halobenzonitrile compound and the alkali metal sulfide and/or alkali metal hydrogen sulfide are preferably placed in a reaction vessel in a solvent and the alkyl halide compound, optionally dissolved in a solvent, is added.

Any non-aqueous organic solvent can be used as the solvent as long as it is suitable for the reaction. The organic solvents that can be used are not particularly limited and include hydrocarbons such as n-hexane, n-heptane, cyclohexane, methylcyclohexane, benzene, toluene and xylene; and halogenated hydrocarbons such as methylene chloride, 1,2-dichloroethane, chlorobenzene and dichlorobenzene. The preferred solvent is chlorobenzene. The amount of the solvent used is usually 1 to 10 times, preferably 1 to 3 times the weight of the 2-halobenzonitrile.

According to a preferred embodiment of the invention, process step (a) is carried out under an inert gas atmosphere, preferably under a nitrogen atmosphere, in a low-water reaction solvent having a water content of less than 10% by weight, based on the reaction solvent. The low water content advantageously leads to a higher yield of the intermediate product according to general formula (IV). Reaction step (a) is preferably carried out in the presence of at least one

Phase transfer catalyst performed, which is added to the solvent system to promote the reaction. Phase transfer catalysts that can be used for this purpose are selected from the group consisting of quaternary ammonium salts, quaternary phosphonium salts and crown ethers. Preferred phase transfer catalysts include quaternary ammonium salts such as benzyltriethylammonium bromide, benzyltrimethylammonium chloride, hexadecyltriethylammonium bromide, hexadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, octyltriethylammonium bromide, tetra-n-butylammonium bromide, tetra-n-butylammonium chloride, tetra-n-butylammonium hydrogen sulfate, tetraethylammonium chloride and trioctylmethylammonium chloride; quaternary phosphonium salts such as hexadecyltriethylphosphonium bromide, hexadecyltributylphosphonium chloride, tetra-n-butylphosphonium bromide, tetra-n-butylphosphonium chloride,

trioctylethylphosphonium bromide and tetraphenylphosphonium bromide; and crown ethers such as 18-crown-6, dibenzo-18-crown-6 and dicyclohexyl-18-crown-6. From the economical point of view, quaternary ammonium salts such as tetra-n-butylammonium bromide, tetra-n-butylammonium hydrogen sulfate and tetra-n-butylammonium chloride are preferably usable.

According to a preferred embodiment of the invention, the phase transfer catalyst is selected from the group of quaternary ammonium salts such as tetra-n-butylammonium bromide, tetra-n-butylammonium hydrogen sulfate and tetra-n-butylammonium chloride.

In the case of using a phase transfer catalyst, the amount of the phase transfer catalyst used is usually 0.005 to 0.5 times, preferably 0.01 to 0.2 times the weight of 2-halobenzonitrile. If the amount of the phase transfer catalyst used is less than 0.005 times the weight of 2-halobenzonitrile, a satisfactory catalytic effect cannot be obtained.

The reaction temperature for the above reaction in process step (a) normally ranges from 60 to 80°C, preferably from 70 to 75°C. the Reaction time varies with the reaction temperature and types of phase transfer catalyst and solvent used, reactor geometry and agitation technique used, and cannot be generalized, but typically ranges from 1 to 40 hours.

The 2-halobenzonitrile compound of the general formula (II) is converted in process step (a) with (i) the at least one alkali metal sulfide and/or alkali metal hydrosulfide and (ii) the at least one alkyl halide compound of the general formula (III) to give the intermediate of the general formula ( IV) implemented. According to a preferred embodiment of the invention, the 2-halobenzonitrile compounds of the general formula (II) and the alkali metal sulfide and/or alkali metal hydrogen sulfide are initially introduced in a suitable solvent under an inert gas atmosphere, preferably under a nitrogen atmosphere, and the alkyl halide compound of the general formula (III) is optionally introduced dissolved in the same solvent, added. The addition of the alkyl halide compound of the general formula (III) takes place over a period of 10 to 40 hours, preferably over a period of 15 to 30 hours. The amount of alkyl halide compound added is either at a constant rate of addition or at a variable rate. In the case of adding the alkyl halide compound at a variable rate, a larger amount is added per unit time at the beginning of the reaction than at the end of the reaction.

The continuous addition of the alkyl halide compound according to the general formula (III) further minimizes the formation of by-products, in particular the formation of thioethers. The loss of alkyl halide compounds through the formation of thioether can thus be reduced to below 10%.

After the reaction has ended, the resulting intermediate product of the general formula (IV) can be isolated and purified in a customary manner. The reaction mixture can be washed with water, for example, and the organic phase can be subjected to fractional distillation after it has been separated off, in order to separate the organic solvent, any thioether formed, from the bottom product present intermediate, according to the general formula (IV) to separate in order to obtain this in the purest possible form.

The present invention also relates to a process for preparing a 2-(alkylthio)benzonitrile compound represented by the general formula (IV): wherein R ¹ is as defined above, comprising in a step (a), the reaction of a 2-halobenzonitrile compound of general formula (II): wherein R ¹ is as defined above, with a reaction mixture containing:

(i) alkali sulfide and/or alkali hydrosulfide and

(ii) an alkyl halide compound represented by the following general formula (III): R ^J X (III), wherein R ¹ is as defined above.

In the second process step (b) of the process according to the invention for the preparation of l,2-benzisothiazolin-3-one, the intermediate obtained in process step (a) according to the general formula (IV) is converted into the l,2-benzisothiazolin-3-one or .cyclized. Such methods are known to the person skilled in the art and are described, for example, in EP 2 687 519 A1 and WO 2015/055293 A1, the entire content of which is incorporated herein by reference. The reaction or cyclization of the intermediate obtained in process step (a) according to the general formula (IV) to give the 1,2-benzisothiazolin-3-one can take place in different ways:

(bl) with a halogenating agent in the presence of water, or

(b2) with an oxidizing agent and subsequent reaction of the 2-(alkylsulfoxy)benzonitrile with an acid to give the 1,2-benzisothiazolin-3-one, and a halide compound of the general formula R'X, where R ¹ is as defined above, and X is chlorine or bromine.

(bl) Cyclization of the intermediate of general formula (IV), the 2-(alkylthio)benzonitrile compound, with a halogenating agent to give 1,2-benzisothiazolin-3-one

In process step (bl), the intermediate product of the general formula (IV) obtained in process step (a), the 2-(alkylthio)benzonitrile compound, is reacted with a halogenating agent, preferably in the presence of water, if appropriate using a reaction solvent, to form a reaction mixture containing the 1,2-benzisothiazolin-3-one and a halide compound of the general formula (V). At this time, the halogenating agent is preferably used in an amount of about 0.8 to 3 moles, more preferably about 1 to 2 moles, per mole of the 2-(alkylthio)benzonitrile compound. Suitable halogenating agents include chlorine, bromine, sulfuryl chloride and sulfuryl bromide. Chlorine is preferably used as the halogenating agent in process step (bl).

Water is preferably used in an amount of about 0.8 to 5 moles, and preferably in an amount of about 1 to 3 moles, per mole of the 2-(alkylthio)benzonitrile compound. When the amount of water is out of this range, side reactions are easy to occur.

The water can be used in the form of an aqueous mineral acid solution by adding a mineral acid to water. Examples of mineral acids include hydrochloric acid, sulfuric acid and nitric acid. The concentration of the aqueous Mineral acid solution can be varied over a wide range. In the case of hydrochloric acid, the preferred range generally used is from 10% by weight to a saturated concentration. In the case of sulfuric acid or nitric acid, preferably 10 to 50% by weight is used. The addition of mineral acid to water improves the selectivity during the reaction and suppresses the formation of by-products.

In process step (bl) of the present invention, the use of a reaction solvent is not always necessary; However, if necessary, a reaction solvent can be used.

Any non-aqueous organic solvent can be used as the solvent as long as it is suitable for the reaction. The organic solvents that can be used are not particularly limited and include hydrocarbons such as n-hexane, n-heptane, cyclohexane, methylcyclohexane, benzene, toluene and xylene; and halogenated hydrocarbons such as methylene chloride, 1,2-dichloroethane, chlorobenzene and dichlorobenzene. The preferred solvent is chlorobenzene. The amount of the solvent used is usually 1 to 10 times, preferably 1 to 2 times the weight of the 2-(alkylthio)benzonitrile compound.

If appropriate, reaction step (bl) is carried out in the presence of at least one phase transfer catalyst, the suitable phase transfer catalysts corresponding to those which can be used in process step (a). In the case of using a phase transfer catalyst, the amount of the phase transfer catalyst used is usually 0.005 to 0.5 times, preferably 0.01 to 0.2 times the weight of the 2-(alkylthio)benzonitrile compound.

The reaction temperature for the cyclization reaction in process step (bl) is usually in the range of 20 to 80°C, preferably 40 to 50°C. The reaction time depends on the reaction temperature, the reaction solvent, etc.; generally it is about 1 to 40 hours. Isolation of the 1,2-benzisothiazolin-3-one from the reaction mixture obtained by the above process can be accomplished by conventional crystallization techniques, or by recrystallization after extraction. It can also be dissolved in and precipitated from aqueous alkaline solutions. According to a preferred embodiment of the invention, the I,2-benzisothiazolin-3-one is crystallized by cooling the reaction mixture, filtered off and optionally washed.

The halide compound of the general formula R*X obtained in the course of the cyclization, where R ¹ is as defined above and X is chlorine or bromine, is preferably worked up or purified and at least some of it is reused in process step (a).

(b2) Cyclization of the intermediate, of general formula (IV), the 2-(alkylthio)benzonitrile compound, with an oxidizing agent to give 1,2-benzisothiazolin-3-one

In process step (b2), the intermediate of general formula (IV) obtained in process step (a), the 2-(alkylthio)benzonitrile compound, is treated with an oxidizing agent and subsequent cyclization of the 2-(alkylsulfoxy)benzonitrile with an acid to give the 1,2 -Benzisothiazolin-3-one and a halide compound of the general formula R*X, where R ¹ is as defined above and X is chlorine or bromine.

In a first process step, starting from the 2-(alkylthio)benzonitrile, a 2-(alkylsulfoxy)benzonitrile is prepared using at least one peroxo compound.

Peroxo compounds are compounds in which an -O- group has been replaced by the -OO- group. The simplest and preferred representative of this group is hydrogen peroxide (H2O2). Further representatives of the peroxo compounds are the metal peroxides, in particular the alkali metal and alkaline earth metal peroxides, such as sodium peroxide and potassium peroxide; the peroxohydrates, ie the hydrogen peroxide addition compounds to borates, carbonates, urea and phosphates, such as sodium borate peroxohydrate (also known as known as sodium perborate), sodium carbonate peroxohydrate (also known as sodium percarbonate), urea peroxohydrate and phosphate peroxohydrate; peroxoacids such as peroxobenzoic acid, eta-chloroperoxobenzoic acid, peroxophosphoric acid and peroxosulfuric acid. The term "peroxo compounds" is also intended to include organic peracids such as peracetic acid, performic acid or perpropionic acid, which are usually referred to as peroxy compounds. Furthermore, alkyl hydroperoxides such as /-butyl hydroperoxide should also be understood as peroxo compounds.

In the preparation of the 2-(alkylsulfoxy)benzonitrile, preference is given to the 2-(alkylthio)benzonitrile, preferably before the addition of the oxidizing agent in a carboxylic acid such as, for example, acetic acid, formic acid, maleic acid, benzoic acid, meta-chlorobenzoic acid, adipic acid, oleic acid, butyric acid, citric acid and acrylic acid, particularly preferably dissolved in acetic acid, formic acid and maleic acid. In order to accelerate the establishment of equilibrium, sulfuric acid can be added in catalytic amounts. In addition to sulfuric acid, other suitable acids can also be used. Alternatively, peracids can also be used directly as oxidizing agents, but their in situ production is often easier.

According to a preferred embodiment of the invention, the peroxo compound is selected from the group consisting of peracetic acid, performic acid, sodium peroxide, potassium peroxide and hydrogen peroxide, with hydrogen peroxide being particularly preferred from an economical point of view.

The "one peroxo compound" can be either a peroxo compound in pure form or a mixture of several peroxo compounds according to the above definition. Peroxo compounds are preferably used in pure form.

If hydrogen peroxide is used as the preferred peroxo compound, it is generally used in the form of a hydrogen peroxide solution. Although the concentration of the peroxide solution is not critical, it is chosen to introduce as little water as possible into the reaction medium. Generally, an aqueous solution is used Hydrogen peroxide solution with at least 20% by weight H2O2, preferably one with 50% by weight.

According to one embodiment of the invention, as part of the preparation of the 2-(alkylsulfoxy)benzonitrile, starting from the 2-(alkylthio)benzonitrile, an oxidizing agent which is as anhydrous as possible, i.e. with the lowest possible water content, is used. The use of such an oxidizing agent makes it possible to add the amount of water that may be necessary for the further reaction of the 2-(alkylsulfoxy)benzonitrile to give the l,2-benzisothiazolin-3-one in such a way that the formation of by-products is further minimized, as a result of which the l, 2-Benzisothiazolin-3-one can be produced in even higher yields.

The peroxo compound is normally used in an amount of 0.8 to 1.6 moles, preferably 1.0 to 1.4 moles, per mole of 2-(alkylthio)benzonitrile. When the amount of the peroxo compound is less than 0.8 mol of the 2-(alkylthio)benzonitrile, the amount of the unreacted 2-(alkylthio)benzonitrile tends to increase. On the other hand, when the amount of the peroxo compound used exceeds 1.6 mol, side reactions occur and the yield of 2-(alkylsulfoxy)benzonitrile is remarkably reduced.

The process for preparing the 2-(alkylsulfoxy)benzonitrile is characterized in that the reaction is carried out in a heterogeneous solvent system in the presence of at least one peroxo compound. The reaction of the 2-alkylthiobenzonitrile used as starting material with the peroxo compound is preferably carried out in a two-phase solvent system since the 2-alkylthiobenzonitrile is insoluble in water. In this case, a phase transfer catalyst is preferably added to the solvent system to promote the reaction. Phase transfer catalysts that can be used for this purpose include quaternary ammonium salts such as benzyltriethylammonium bromide, benzyltrimethylammonium chloride, hexadecyltriethylammonium bromide, hexadecyltrimethylammonium chloride,

dodecyltrimethylammonium chloride, octyltriethylammonium bromide, tetra-n-butylammonium bromide, tetra-n-butylammonium chloride, tetra-n-butylammonium hydrogen sulfate, tetraethylammonium chloride and

trioctylmethylammonium chloride; quaternary phosphonium salts, such as Hexadecyltri ethylphosphonium bromide, Hexadecyltributylphosphonium chloride, T etra-n-butylphosphonium bromide, T etra-n-butylphosphonium chloride,

trioctylethylphosphonium bromide and tetraphenylphosphonium bromide; and crown ethers such as 18-crown-6, dibenzo-18-crown-6 and dicyclohexyl-18-crown-6.

The phase transfer catalyst selected from the group of quaternary ammonium salts such as tetra-n-butylammonium bromide, tetra-n-butylammonium hydrogen sulfate and tetra-n-butylammonium chloride is preferred. According to a particularly preferred embodiment of the invention, the phase transfer catalyst is tetra-n-butylammonium hydrogen sulfate.

In the case of using a phase transfer catalyst, the amount of the phase transfer catalyst used is usually 0.005 to 0.5 times, preferably 0.01 to 0.2 times the weight of the 2-alkylthiobenzonitrile. If the amount of the phase transfer catalyst used is less than 0.005 times the weight of the 2-alkylthiobenzonitrile, an appropriate catalytic effect cannot be obtained. Even if the amount of the phase transfer catalyst used exceeds 0.5 times the weight of the 2-alkylthiobenzonitrile used, no additional effect can be expected and therefore it is not advantageous from an economical point of view.

According to a preferred embodiment of the invention, the preparation of the 2-(alkylsulfoxy)benzonitrile can be carried out in a solvent. According to an alternative embodiment, however, the production can also take place without the addition of a solvent, using only the components necessary for the production (2-alkylthiobenzonitrile, water and oxidizing agent).

Solvents used in the process for producing the 2-(alkylsulfoxy)benzonitrile are not specifically limited as long as they are inert to the reaction. Examples of solvents usable in the reaction include hydrocarbons such as n-hexane, n-heptane, cyclohexane, methylcyclohexane, benzene, toluene and xylene, and halogenated hydrocarbons such as methylene chloride, 1,2-dichloroethane and chlorobenzene. It has proven to be particularly preferred within the scope of the invention the chlorobenzene proved. The amount of the solvent used is usually 1 to 30 times the weight of the 2-(alkylthio)benzonitrile.

The reaction temperature in the preparation of the 2-(alkylsulfoxy)benzonitrile is normally in the range from 0 to 90.degree. C., preferably at temperatures below 50.degree. The reaction time varies with the reaction temperature and the reaction solvent, and usually ranges between 1 and 40 hours.

The oxidation of the 2-(alkylthio)benzonitrile as described above is preferably carried out in the presence of a catalyst. Suitable catalysts here are all catalysts which are known to those skilled in the art and can be used in the oxidation of alkyl thioethers. The catalyst is preferably selected from the group consisting of phosphonic acids such as phenylphosphonic acid, tungsten and molybdenum catalysts such as Na2WO vanadium catalysts such as NaVCh, NH4VO3 and V2O5; H2SO4 and titanium complexes. A particularly preferred catalyst is a phosphonic acid or a mixture of two or more phosphonic acids. A very particularly preferred catalyst is a phenylphosphonic acid.

The amount of catalyst used is generally about 0.01 to 10 mol %, preferably about 0.05 to 5 mol %, particularly preferably about 0.1 to 0.5 mol %, based on one mole of 2 -(alkylthio)benzonitrile.

The 2-(alkylsulfoxy)benzonitrile produced in the first process step can be converted further into the 1,2-benzisothiazolin-3-one in the second process step, with or without prior treatment. According to a preferred embodiment, the 2-(alkylsulfoxy)benzonitrile is further converted into the 1,2-benzisothiazolin-3-one without further processing.

In the second process step following the preparation of the 2-(alkylsulfoxy)benzonitrile, the 1,2-benzisothiazolin-3-one is then prepared starting from a 2-(alkylsulfoxy)benzonitrile prepared as described above using at least one acid. Examples of acids that can be used in this process step include all strong acids known to those skilled in the art. The acids can be used both in pure form and in the form of their mixtures. The acids are preferably used in pure form.

Hydrochloric acid and/or hydrobromic acid are used as the acid. According to a preferred embodiment of the invention, hydrochloric acid is used as the acid.

The acid is normally used in an amount of 0.8 to 3.0 moles, preferably 1.0 to 2.0 moles, per mole of 2-(alkylsulfoxy)benzonitrile. The acid can be added in one or more stages. According to a preferred embodiment of the invention, 10% of the acid is added in a first stage and a further 100% of the acid is added in a second stage. For example, according to this embodiment, 0.1 molar equivalent (acid to benzonitrile) of acid is added at the beginning of the reaction, and an additional 1.0 molar equivalent is added later.

Solvents used in the process for preparing the 1,2-benzisothiazolin-3-one from the 2-(alkylsulfoxy)benzonitrile are not particularly limited as long as they are inert to the reaction. Examples of solvents usable in the reaction include hydrocarbons such as n-hexane, n-heptane, cyclohexane, methylcyclohexane, benzene, toluene and xylene, and halogenated hydrocarbons such as methylene chloride, 1,2-dichloroethane, chlorobenzene and dichlorobenzene. Chlorobenzene has proven to be particularly preferred. The amount of the solvent used is usually 1 to 30 times the weight of the 2-(alkylsulfoxy)benzonitrile.

The reaction temperature of the second process step, during which the 1,2-benzisothiazolin-3-one is prepared starting from 2-(alkylsulfoxy)benzonitrile, is usually in the range from 50 to 90° C., preferably at temperatures in the range from 70 to 80°C. The reaction time varies with the reaction temperature and the reaction solvent, and usually ranges between 1 and 40 hours.

Isolating the l,2-benzisothiazolin-3-one from the reaction mixture obtained by the above process can be accomplished by conventional crystallization techniques, or by Recrystallization done after extraction. It can also be dissolved in and precipitated from aqueous alkaline solutions. According to a preferred embodiment of the invention, the 1,2-benzisothiazolin-3-one is crystallized by cooling the reaction mixture, filtered off and optionally washed.

The halide compound of the general formula R'X obtained in the course of the cyclization, where R ¹ is as defined above and X is chlorine or bromine, is preferably worked up or purified and at least some of it is reused in process step (a).

The following example serves to further illustrate the present invention:

Process Step (a): Preparation of 2-(n-butylthio)benzonitrile (BTBN) from 2-chlorobenzonitrile (2-CBN), 1-chlorobutane and sodium sulfide

2-Chlorobenzonitrile (56.2 g, 0.40 mol), coarsely powdered anhydrous disodium sulfide (disodium sulfide content 93%, 40.3 g, 0.48 mol), tetrabutylammonium bromide (3.2 g, 0.01 mol) and chlorobenzene ( 60.0 g) were mixed in a 500 ml round bottom flask under a nitrogen atmosphere. The mixture was vigorously stirred at 70 to 75°C (internal temperature). A solution of butyl chloride (39.1 g, 0.42 mol) in chlorobenzene (55.0 g) was slowly added to the mixture at a continuous feed rate of 0.065 g/min, taking about 24 hours for complete addition. After the reaction had ended, the reaction mixture was washed with water (200 g), then with 5% NaCl (100 g) in water and the aqueous phases discarded. The organic phase was subjected to vacuum distillation to recover the chlorobenzene. The by-product dibutyl sulfide (2.2 g, 0.015 mol) was also removed by distillation to keep the bottom BTBN as pure as possible. Process step (b): Preparation of 1,2-benzisothiazolin-3-one (BIT) from 2-(n-butylthio)benzonitrile BTBN

The BTBN from process step (a) (calculated at most 0.39 mol) was transferred to a 500 ml round bottom flask. Chlorobenzene (133.0 g), hydrochloric acid (35 wt%, 19.9 g, hydrogen chloride 0.19 mol, water 0.71 mol) and tetrabutylammonium bromide (3.2 g, 0.01 mol) were added. The mixture was intensively stirred at 40 to 50°C while chlorine was introduced at a flow rate of 125 ml/min. Throughout the process, the BTBN content was monitored by HPLC and the chlorination continued until all the BTBN was consumed. Then, the reaction mixture was stirred at 70°C for one hour, followed by the addition of 150 g of water and heating to 90°C. Thereafter, 1-chlorobutane was recovered from the mixture by distillation. After complete distillation and stirring for 1 hour, the mixture was cooled to ambient temperature.

The obtained colorless crystals were separated by filtration, washed with chlorobenzene and water, and dried at 50°C to obtain 1,2-benzisothiazolin-3-one. Additional BIT could be obtained from the organic layer of the filtrate by extraction with dilute sodium hydroxide. The overall yield (including solid BIT and aqueous BIT sodium salt) based on 2-CBN is 90%.

Claims

Claims Process for the preparation of 1,2-benzisothiazolin-3-one according to the formula (I), including the steps:

(a) Reaction of a 2-halobenzonitrile compound represented by general formula (II): whereby

X is chlorine or bromine; with a reaction mixture containing:

(i) alkali sulfide and/or alkali hydrosulfide and

(ii) an alkyl halide compound represented by the following general formula (III): R'X (III), wherein

R ¹ is selected from the group consisting of unsubstituted or at least monosubstituted Ci-Cio-alkyl, unsubstituted or at least monosubstituted Cs-Cu-aryl and unsubstituted or at least monosubstituted C7-C18 aralkyl, wherein the substituents are selected from the group consisting of F, CI, Br, I, OH, NH ₂ , Ci-Cs-alkyl and OR ² , where

R ² is hydrogen or Ci-C4-alkyl; and X is chlorine or bromine to form an intermediate of general formula (IV) wherein R is ¹

23 as defined above,

(b) Reaction of the intermediate of general formula obtained in step (a).

(IV) with a halogenating agent or an oxidizing agent and subsequent reaction of the 2-(alkylsulfoxy)benzonitrile with an acid to form the l,2-benzisothiazolin-3-one and a halide compound of the general formula (V) R*X (V), whereby:

R ¹ is selected from the group consisting of unsubstituted or at least monosubstituted Ci-Cio-alkyl, unsubstituted or at least monosubstituted Cs-Cu-aryl and unsubstituted or at least monosubstituted C7-C18 aralkyl, wherein the substituents are selected from the group consisting from F, CI, Br, I, OH, NH ₂ , Ci-C ₈ alkyl and OR ² , wherein

R ² is hydrogen or C1-C4 alkyl; and X is chlorine or bromine.

2. Process according to Claim 1, characterized in that butyl chloride is used as the alkyl halide compound in step (a).

3. The method according to claim 1 or 2, characterized in that in step (a) sodium sulfide (Na ₂ S) is used as the alkali metal sulfide (i).

4. The method according to any one of claims 1 to 3, characterized in that in step (b) obtained in step (a) obtained intermediate of general formula (IV) with a halogenating agent to form a reaction mixture containing the l,2-benzisothiazoline 3-one of the general formula (I) and a halide compound of the general formula (V) is reacted.

5. The method according to any one of claims 1 to 4, characterized in that in step (b) the halogenating agent is selected from the group consisting of chlorine, bromine, sulfuryl chloride and sulfuryl bromide.

6. Process according to one of Claims 1 to 3, characterized in that in process step (b) the intermediate product of the general formula (IV) obtained in step (a) is treated with a peroxo compound to form 2-(alkylsulfoxy)benzonitrile of the general formula ( VI): wherein

R ¹ is as defined above, and then reacted with an acid to give the 1,2-benzisothiazolin-3-one of general formula (I) and a halide compound of general formula (V).

7. Process according to one of Claims 1 to 6, characterized in that the halide compound of the general formula (V) obtained in step (b) is at least partially separated off from the reaction mixture and fed to process step (a).

8. Process for preparing a 2-(alkylthio)benzonitrile compound represented by the general formula (IV): wherein R ¹ is as defined above, comprising in a step (a), the

Reaction of a 2-halobenzonitrile compound of general formula (II): wherein R ¹ is as defined above, with a reaction mixture containing:

(i) alkali sulfide and/or alkali hydrosulfide and

(ii) an alkyl halide compound represented by the following general formula (III): R'X (III), wherein R ¹ is as defined above.

9. The method according to any one of claims 1 to 8, characterized in that step (a) is carried out under an inert gas atmosphere.

10. The method according to any one of claims 1 to 7 and 9, characterized in that step (a) is carried out in the presence of at least one phase transfer catalyst which is selected from the group consisting of quaternary ammonium salts, quaternary phosphonium salts and crown ethers.

11. The method according to any one of claims 1 to 10, characterized in that in step (a) the 2-halobenzonitrile compound according to the general formula (II) and the alkali metal sulfide and / or alkali metal hydrogen sulfide are presented and the alkyl halide compound according to the general formula (III ) is added.

12. The method according to claim 11, characterized in that the alkyl halide compound according to the general formula (III) is added continuously over a period of 10 to 40 hours.

13. The method according to any one of claims 1 to 12, characterized in that step (a) is carried out at a temperature in the range from 60°C to 80°C.

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