PREPARATION OF ISOTHIAZOLONES

Abstract: Preparation of 3-isothiazolones may be carried out in a single reaction vessel synthesis from 3,3′-dithiodipropionic acid, 3-thiopropionic acid, or their related acid halide by reacting sequentially with a thionyl halide (if the (di)acid halide has not previously been formed), followed by reaction with halogenating agent, then reaction with primary amine in the presence of acid scavenger, and subsequently with halogenating agent.

Description: This invention is concerned with the preparation of 3-isothiazolones. 2-Substituted isothiazolones, 4-halo-, 5-halo-, and 4,5-dihaloisothiazolones are well-known as efficacious chemicals for the control of living organisms, especially as biocidal chemicals. See for example US-A-4,105,431 and 4,265,899. A conventional route to manufacture, as described inter alia in US-A-3,761,488 EP-A-95907 and J. Heterocyclic Chem., 8(4), (1971), involves the preparation of a 3-mercapto-N-substituted propionamide (or 3,3'-dithio-N,N'-substituted propionamide), followed by halogenation to produce the desired non-halogenated isothiazolone product. Preparation of the halogenated or dihalogenated isothiazolone can be accomplished by use of higher ratios of halogen/amide. Preparation of the mercaptopropionamide may require several preparative steps, involving costly or difficultly obtainable intermediates, especially when the amine functionality needed to form the amide is less reactive, such as when it is cycloalkyl or aryl. We have now found a process by which 3-isothiazolones can be prepared in a single reaction vessel, avoiding the preparation of (di)thiopropion-N,N'-diamide as a separate step. The term "halogen" when used alone or in the term "halogenating agent" herein, preferably means chlorine or bromine or a mixture thereof; chlorine being the most preferred halogen. Luttringhaus et al., [ Angew. Chem. Int. Ed. Eng., 3, 67 (1964); Liebigs Ann. Chem. 679 , 123 (1964)] reported low yields of saturated isothiazolidines by sequential, separate kettle reaction of dithiodiacid with thionyl chloride, then chlorine, and then amine with pyridine base but did not carry the reaction through to the active isothiazolones. In a similar manner, Kharasch et al. [ J.Org. Chem. , 28 , 1901 (1963)] produced a saturated six-membered ring from a 4-thiobutyric acid precursor. According to the invention there is provided a process for preparing a compound of the formula wherein R' is alkyl optionally substituted with one or more halo, cyano, carbalkoxy, alkoxy, aryloxy, isothiazolonyl, haloalkoxy or carbamoxy groups; aryl, optionally substituted with one or more halo, cyano, nitro, (C₁ to C₄)alkyl, (C₁ to C₄)alkoxy, (C₁ to C₄)alkyl-acylamino, (C₁ to C₄)carbalkoxy or sulfamyl groups; cycloalkyl; substituted cycloalkyl; or alkaryl; R² is hydrogen, halo or alkyl; and R³ is hydrogen or halo; wherein a compound of the formula: XOCCHR²CH₂SSCH₂CHR²COX IV wherein R² is as defined above and X is halo; is (a) reacted with a halogenating agent to form a compound of the formula XSCH₂C(R²) HCOX which is then (b) converted, by the addition, to the reaction product of halogenation (a), of acid scavenger and amine of the formula R′NH₂, wherein R′ is as defined above, to form a compound of the formula and (c) halogenating agent is added to the product of reaction (b) in such amount as to convert compound II to the desired compound(s) I. The invention provides a new path to the known biocidally active isothiazolones which have a variety of uses including uses in cooling towers, paper mills, metal working, oil fields, latex, cosmetics, house cleaners, laundry, textile, plastic and resins, wood, leather and hides, photography, fuel, paints, swimming pools, medical devices, pharmaceuticals, food and feed preservations, disinfectants and sanitizers. The process of the invention, together with a process for the formation of the starting material IV can be schematically exemplified and represented by the following reaction sequence: If the (di)acid is used as the starting material, isolation and handling of the hydrolytically sensitive (di)acid chloride can be avoided. Halogenation to the 5-halo- or 4,5-dihaloisothiazolone is also possible, either by addition of additional halogen or halogenating agent in the final stage, by further treatment of the isolated unhalogenated isothiazolone, or by co-feeding of the intermediate after reaction with amine, along with additional halogen or halogenating agent, to a second reaction vessel. Suitable as starting primary amines in the present reaction are alkyl amines, preferably C₁ to C₈ alkylamines, cycloalkyl amines, preferably cyclohexyl amine, aryl amines, such as phenyl amine and 4-chlorophenyl amine; alkaryl amines, such as benzyl amine, and other moieties which will not interfere with the halogenation/cyclization reaction. Particularly preferred is n -octylamine. (The amine must be a primary amine for the desired product to be obtained.) As suitable dithiodiacids (VI, supra), 3,3′-dithiodipropionic acid is most preferred, especially if it is desired to convert the resulting isothiazolone to chlorinated derivatives, such as 4,5-dichloroisothiazolone. Other starting acids may include 3,3′- dithio-2,2′-dialkyldipropionic acid and 3,3′-dithio-2,2′-dichlorodipropionic acid. Other groups may be substituted in the 2 and/or 2′ position if they do not interfere with the halogenation or ring closure reactions. Starting with dithiomethylpropionic acid and extending the final halogenation reaction will result in the formation of the desirable 4-methyl-5-halo-2-substituted isothiazolone. Such dithiodiacids are commercially available or readily prepared from published procedures. As suitable thioacids (V, supra), 3-thiopropionic acid is most preferred, especially if it is desired to convert the isothiazolone to chlorinated derivatives, such as the 4,5-dichloroisothiazolone. Other starting acids may include 3-thio-2-(lower alkyl)propionic acid and 3-thio-2- chloropropionic acid. Other groups may be substituted in the 2-position if they do not interfere with the halogenation/ring closure reactions. Starting with, 3-thio-2-methylpropionic acid and extending the final halogenation reaction will result in the formation of the desired 4-methyl-5-halo-2-substituted isothiazolone. Thioacids are commercially available or readily prepared from published procedures. The corresponding acid halides are also suitable starting materials. If thionyl halides are used either to prepare the (di)acid halide (IV, supra) in situ or separately, thionyl chloride and thionyl bromide are preferred; with thionyl chloride being most preferred. It is possible to prepare the (di)acid halide by other means, such as with phosphorus trichloride, phosphorus tribromide, or acetyl chloride, but the by-products of this conversion are less desirable when the one-kettle synthesis sequence is continued. The diacid halide (IV) is then treated with a halogenating agent to afford the halothio propionyl halide (III, supra). The halogenating agent is preferably chlorine or bromine; with chlorine being most preferred. Other halogenating agents include sulfuryl chloride, sulfuryl bromide, N-chlorosuccinimide and N-bromosuccinimide. It is necessary to use an acid scavenger to react with any excess acid. Any organic or inorganic base may be used as the scavenger; tertiary amines and nitrogenous cyclic compounds unaffected by the reaction conditions are preferred, with trialkyl amines being most preferred. The halothiopropionyl halide (III, supra) is treated with an amine of the formula R'NH₂, where R' is as defined above, to yield the ring closed isothiazidine (II, supra) which is halogenated to yield the desired, active isothiazolone (I, supra). The reaction sequence (halogenation - amidation - halogenation) may be conducted at a temperature of from about -20°C to about 35°C to minimize side reactions although temperatures outside that range may be used. Inert or substantially inert solvents may be used, such as halobenzenes for example chlorobenzene or halo aliphatic solvents. Reaction times for the sequence are usually from about one-half hour to about three hours per step, (the formation of the (di)acid halide in situ may be conducted over a longer time, such as from about one to about ten hours). The ratios of (di)acid or (di)acid halide to halogen are optionally kept at about 1:1 during the first addition of halogen. At least two moles of reactive amine and an equivalent amount of acid scavenger are then addition per mole of compound III. The use of 1 equivalent of halogen and 2 equivalents of amine are obviously the optimum amounts but deviation from these levels is permissible although the yield will be adversely affected. The final halogenation is best controlled by using, per mole of II, about two moles of halogen when the desired product is the non-halogenated isothiazolone. The non-halogenated isothiazolone may be isolated, stabilized, and purified by known methods, or may be used directly for further halogenation. If the 5-haloisothiazolone is desired, about four equivalents of halogenating agent may be added during the final reaction step. A preferred method would be to add the crude unhalogenated isothiazidine concurrently with about four equivalents of halogen to a second reaction vessel, in-line with the first, so that the overall reaction is conducted in one operation. If it is desired to prepare the 4,5-dihaloisothiazolone without isolation of any intermediate, the unhalogenated aminated intermediate may be added together with the necessary halogen (about six equivalents) into a second reaction vessel, as described above for the 5-halo compound. Experimental Example 1 . Preparation of 3- n -Octylisothiazolone from 3,3′-Dithiodipropionic acid To a 500 ml flask fitted with a mechanical stirrer, nitrogen inlet, and an outlet to a 10% sodium hydroxide trap was charged 20g(0.095M) of 3,3′-dithiodipropionic acid, 200 ml of chlorobenzene and 0.25 ml of pyridine. An addition funnel containing 24.9g (0.21M) of thionyl chloride was provided and the thionyl chloride was added dropwise. The mixture was warmed to 45°C and stirred for 2.5 hours. The mixture was not homogeneous and was stirred overnight. (The reaction was still not quite homogeneous but was carried on at this point.) The mixture was reheated to 45°C and sparged for 15 min with nitrogen. The remaining thionyl chloride was removed by stripping under house vaccuum for 1 hr and then 50 ml of chlorobenzene was charged. The mixture was cooled to -20°C and 6.8g(0.096M) of chlorine was added over 16 min. After stirring 0.5hr the mixture was warmed to 0-5°C and a solution of 24.6g (.188M) of n -octyl amine and 19.2g(.188M) of triethyl amine in 100 ml of chlorobenzene was added dropwise such that the reaction temperature remained below 5°C (addition time 1.75 hr). The solution was allowed to warm and then heated to 35°C. During this time the reaction thickened and then thinned out. Chlorine (13.5 g, 0.19M) was then fed over 40 min at 35°C and the mixture was stirred for an additional 1 hr. The reaction mixture was washed with 3x400 ml of water and then the solvent was removed under vaccuum to yield 36g of 3- n -octylisothiazolone as a dark oil. Analysis by capillary gas chromatography indicated a yield of 21.8g (53.7%) of 3- n -octylisothiazolone. Example 2 . Preparation of 3,3′-Dithiodipropionyl chloride To a 300 ml round bottom flask fitted with a mechanical stirrer, nitrogen inlet and an outlet to a 10% sodium hydroxide trap was charged 169g (1.42M) of thionyl chloride and 100g (0.48M) of 3,3′-dithiodipropionic acid. The slurry was stirred and 0.5 ml of pyridine was charged. The mixture was stirred overnight. Excess thionyl chloride was then removed under house vacuum at room temperature until bubbling ceased and then for an additional 1.5 h at 40°-50°C. The resulting orange liquid of 3,3′-dithiodipropionyl chloride was used in Example 3 without further purification. Example 3 . Preparation of 3- n -Octylisothiazolone The process of Example 1 was repeated, except that the product of Example 2 was diluted with chlorobenzene, cooled to -20°C and chlorinated. Analysis indicated a 59.6% yield of 3- n -octylisothiazolone. In a similar manner, cyclohexylamine may be substituted for n -octylamine to afford 3-cyclohexylisothiazolone. Example 4 . Preparation of 3- n -Octylisothiazolone from 3-thiopropionic acid By following substantially the procedure of Example 1 and by substituting 3-thiopropionic acid for the dithiodiacid described therein a white solid of 3- n -octylisothiazolone precipitated during the exothermic portion of the reaction. Analysis of the final reaction mixture by high pressure liquid chromatography indicates a 45.9% yield of the 3- n -octylisothiazolone.

Claims: A process for preparing a compound of the formula wherein R' is alkyl optionally substituted with one or more halo, cyano, carbalkoxy, alkoxy, aryloxy, isothiazolonyl, haloalkoxy or carbamoxy groups; aryl, optionally substituted with one or more halo, cyano, nitro, (C₁ to C₄)alkyl, (C₁ to C₄)alkoxy, (C₁ to C₄)alkyl-acylamino, (C₁ to C₄)carbalkoxy or sulfamyl groups; cycloalkyl; substituted cycloalkyl; or alkaryl; R² is hydrogen, halo or alkyl; and R³ is hydrogen or halo; wherein a compound of the formula: XOCCHR²CH₂SSCH₂CHR²COX IV wherein R² is as defined above and X is halo; is (a) reacted with a halogenating agent to form a compound of the formula XSCH₂C(R²)HCOX which is then (b) converted, by the addition, to the reaction product of halogenation (a), of acid scavenger and amine of the formula R′NH₂, wherein R′ is as defined above, to form a compound of the formula and (c) halogenating agent is added to the product of reaction (b) in such amount as to convert compound II to the desired compound(s) I. A process according to Claim 1 wherein X is chloro. A process according to Claim 1 or 2 wherein R² is H. A process according to Claim 1 or 2 wherein R² and/or R′ is/are (C₁-C₈)alkyl. A process according to any preceding Claim wherein R′ is n -octyl or cyclohexyl. A process according to any preceding Claim where the dithiodiacid halide is formed in situ by reacting thionyl halide with a compound of the formula HSCH₂CHR₂COOH. A process according to Claim 1, 2, 3, 5 or 6 in which, in step (c) about 2 equivalents of halogenating agent are used, to yield a product wherein R² and R³ are H; or about 4 equivalents of halogenating agent are used to yield a product in which R² is H and R³ is halo; or about 6 equivalents of halogenating agent are used to yield a product in which R² and R³ are halo. A process according to Claim 7 wherein halo is chloro. A process according to any preceding Claim wherein about 4 or about 6 equivalents of halogenating agent are used in step (c) which is carried out by cofeeding the reaction mixture from Step (b) with the halogenating agent into a further reaction vessel.

Inventors: LEIN, GEORGE MAX, JR.
Applicants: ROHM AND HAAS COMPANY
Application year: 1988
Main classification: C07D275
IPC codes: C07D275