Process for Preparing 1,2-Benzisothiazoline-3-One

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): R.sup.1X (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) R.sup.1X (V).

Claims

1. A process for preparing 1,2-benzisothiazolin-3-one according to formula (I), ##STR00008## comprising the steps: (a) reaction of a 2-halobenzonitrile compound of the general formula (II): ##STR00009## where X is chlorine or bromine; with a reaction mixture comprising: (i) alkali metal sulfide and/or alkali metal hydrogensulfide and (ii) an alkyl halide compound, represented by the following general formula (III): R.sup.1X (III), where R.sup.1 is selected from the group consisting of unsubstituted or at least monosubstituted C.sub.1-C.sub.10 alkyl, unsubstituted or at least monosubstituted C.sub.5-C.sub.14 aryl and unsubstituted or at least monosubstituted C.sub.7-C.sub.18 aralkyl, where the substituents are selected from the group consisting of F, Cl, Br, I, OH, NH.sub.2, C.sub.1-C.sub.8 alkyl and OR.sup.2, where R.sup.2 is hydrogen or C.sub.1-C.sub.4 alkyl; and X is a chlorine or bromine, to form an intermediate of the general formula (IV), where R.sup.1 is as defined above, ##STR00010## (b) reaction of the intermediate of the general formula (IV) obtained in step (a) with a halogenating agent or an oxidizing agent and subsequent reaction of the 2-(alkylsulfoxy)benzonitrile with an acid to form the 1,2-benzisothiazolin-3-one and a halide compound of the general formula (V) R.sup.1X (V), where: R.sup.1 is selected from the group consisting of unsubstituted or at least monosubstituted C.sub.1-C.sub.10 alkyl, unsubstituted or at least monosubstituted C.sub.5-C.sub.14 aryl and unsubstituted or at least monosubstituted C.sub.7-C.sub.18aralkyl, where the substituents are selected from the group consisting of F, Cl, Br, I, OH, NH.sub.2, C.sub.1-C.sub.8 alkyl and OR.sup.2, where R.sup.2 is hydrogen or C.sub.1-C.sub.4 alkyl; and X is chlorine or bromine.

2. The process as claimed in claim 1, characterized in that the alkyl halide compound used in step (a) is butyl chloride.

3. The process as claimed in claim 1, characterized in that the alkali metal sulfide (i) used in step (a) is sodium sulfide (Na.sub.2S).

4. The process as claimed in claim 1, characterized in that in process step (b) the intermediate of the general formula (IV) obtained in step (a) is reacted with a halogenating agent to form a reaction mixture comprising the 1,2-benzisothiazolin-3-one of the general formula (I) and a halide compound of the general formula (V).

5. The process as claimed in claim 1, characterized in that in step (b) the halogenating agent is selected from the group consisting of chlorine, bromine, sulfuryl chloride and sulfuryl bromide.

6. The process as claimed in claim 1, characterized in that in process step (b) the intermediate of the general formula (IV) obtained in step (a) is reacted with a peroxo compound to form 2-(alkylsulfoxy)benzonitrile of the general formula (VI): ##STR00011## in which R.sup.1 is as defined above, and is subsequently reacted with an acid to form the 1,2-benzisothiazolin-3-one according to the general formula (I) and a halide compound of the general formula (V).

7. The process as claimed in claim 1, characterized in that the halide compound of the general formula (V) obtained in step (b) is at least partially separated from the reaction mixture and fed to process step (a).

8. A process for preparing a 2-(alkylthio)benzonitrile compound according to the general formula (IV): ##STR00012## where R.sup.1 is as defined above, comprising, in a step (a), the reaction of a 2-halobenzonitrile compound of the general formula (II): ##STR00013## where R.sup.1 is as defined above, with a reaction mixture comprising: (i) alkali metal sulfide and/or alkali metal hydrogensulfide and (ii) an alkyl halide compound, represented by the following general formula (III): R.sup.1X (III), where R.sup.1 is as defined above.

9. The process as claimed in claim 1, characterized in that step (a) is performed under an inert gas atmosphere.

10. The process as claimed in claim 1, characterized in that step (a) is performed in the presence of at least one phase-transfer catalyst selected from the group consisting of quaternary ammonium salts, quaternary phosphonium salts and crown ethers.

11. The process as claimed in claim 1, 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 hydrogensulfide are initially charged and the alkyl halide compound according to the general formula (III) is added.

12. The process as claimed in 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 process as claimed in claim 1, characterized in that step (a) is performed at a temperature in the range from 60 C. to 80 C.

Description

[0089] 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

[0090] 2-Chlorobenzonitrile (56.2 g, 0.40 mol), coarsely pulverized anhydrous disodium sulfide (93% disodium sulfide content, 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 stirred vigorously at 70 C. 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 metering rate of 0.065 g/min, requiring about 24 hours for the complete addition. After the end of the reaction, the reaction mixture was washed with water (200 g) and then with 5% NaCl (100 g) in water and the aqueous phases were discarded. The organic phase was subjected to a distillation under reduced pressure in order to recover the chlorobenzene. The dibutyl sulfide formed as by-product (2.2 g, 0.015 mol) was also removed by distillation in order to obtain the BTBN as pure as possible at the bottom.

Process Step (b): Preparation of 1,2-Benzisothiazolin-3-One (BIT) from 2-(N-Butylthio)Benzonitrile BTBN

[0091] The BTBN from process step (a) (calculated maximum of 0.39 mol) was transferred into a 500 ml round-bottom flask. Chlorobenzene (133.0 g), hydrochloric acid (35% by weight, 19.9 g, 0.19 mol of hydrogen chloride, 0.71 mol of water) and tetrabutylammonium bromide (3.2 g, 0.01 mol) were added. The mixture was stirred intensely at 40 C. to 50 C. while chlorine was introduced at a flow rate of 125 ml/min. The content of BTBN was monitored by means of HPLC during the entire process and the chlorination was continued until all BTBN was consumed. The reaction mixture was subsequently stirred for one hour at 70 C., followed by the addition of 150 g of water and heating to 90 C. The 1-chlorobutane was then recovered from the mixture by distillation. After complete distillation and stirring for one hour, the mixture was cooled to ambient temperature.

[0092] The colorless crystals obtained were separated off by means of filtration, washed with chlorobezene and water and dried at 50 C. in order to obtain 1,2-benzisothiazolin-3-one. Additional BIT was recovered from the organic layer of the filtrate by extraction with dilute sodium hydroxide solution. The total yield (including solid BIT and aqueous BIT sodium salt), based on 2-CBN, is 90%.