An improved process for the preparation of benzonitrile compounds from the benzotrichloride compounds

Abstract

The present invention discloses an improved process for the preparation of benzonitrile compounds of formula (I) from the corresponding benzotrichloride compounds of formula (II).

Description

[0001] AN IMPROVED PROCESS FOR THE PREPARATION OF BENZONITRILE COMPOUNDS FROM THE BENZOTRICHLORIDE COMPOUNDS FIELD OF THE INVENTION: The present invention relates to an improved process for the preparation of benzonitrile compounds. More particularly, the present invention relates to an improved process for the preparation of benzonitrile compounds of formula (I) by nitrilation of the corresponding benzotrichloride compounds of formula (II). BACKGROUND OF THE INVENTION: The benzonitriles are products known in the art and used as intermediates particularly in the preparation of dyes, pharmaceuticals and agrochemicals. J. Am. Chem. Soc. 1930, 52, 7, 2951–2954 discloses a process for preparing ortho- chlorobenzonitrile from ortho-chlorobenzotrichloride using ammonium chloride. The drawback with this process is that it requires a closed tube and an elevated temperature of 210 to 220°C. Further, at least 60% excess of ortho- chlorobenzotrichloride is required if all the ammonium chloride needs to be consumed. Also, the process results in the polymerization of benzonitrile and tetraphenylmethane is obtained as a by-product. EP441004 discloses a process for preparing ortho-chlorobenzonitrile from ortho- chlorobenzotrichloride using copper (II) chloride or zinc chloride as a catalyst and ammonium chloride. The drawback associated with this process is that the reaction is carried out at an elevated temperature of more than 210°C and requires an expensive jacketed reactor. WO2022091014 discloses a process for the preparation of ortho-chloro benzonitrile, wherein the process comprises the reaction of 2- chlorobenzotrichloride with ammonium chloride in the presence of water, sulfuric acid and zinc acetate at room temperature. The reaction mixture was heated to 180 to 200°C for 16 hrs. The drawbacks associated with this process are low yield (85%- 90%) and less purity (96%) of ortho-chlorobenzonitrile. JP2652563 discloses a process for the preparation of ortho-chlorobenzonitrile and ortho-chlorobenzoyl chloride from ortho-chlorobenzotrichloride and ortho- chlorobenzamide using concentrated sulfuric acid as catalysts in the presence of ortho-chlorotoluene solvent. The reaction mixture was heated to 140°C. Further, the reaction solution was treated with ammonia gas to convert the acid chloride product into its corresponding acid amide. The typical reaction involves the conversion of ortho-chlorobenzotrichloride to ortho-chlorobenzoyl chloride and ortho-chlorobenzamide to ortho-chlorobenzonitrile. WO2024171098 discloses the synthesis of benzonitrile compounds from the corresponding benzotrichloride compounds. However, the process results in the lower yield ~90%. Thus, there is a need to develop an improved process for the preparation of benzonitrile compounds which obviates at least one problem of prior art processes, such as impure benzonitrile, specific reaction set-up, polymerization, less yield, and cost-ineffectiveness. The inventors of the present invention have found a simple, industrially feasible and advantageous process which obviates the use of expensive jacketed reactors, application of elevated temperature conditions, residue generation, formation of by- products such as benzonitrile polymer and tetraphenylmethane, and results in improved yield. OBJECTIVE OF THE INVENTION: Some of the objects of the present invention are described herein below: It is an object of the present invention to ameliorate one or more problems of the prior art or to at least provide a useful alternative. An object of the present invention is to provide an improved process for the preparation of benzonitrile compounds of formula (I) from the corresponding benzotrichloride compounds of formula (II). Another object of the present invention is to provide an improved process for the preparation of benzonitrile compounds of formula (I) from corresponding benzotrichloride compounds of formula (II) which obviates the use of expensive jacketed reactors or closed tubes. Yet another object of the present invention is to provide an improved process for the preparation of high purity benzonitrile compounds of formula (I) from corresponding benzotrichloride compounds of formula (II) which obviates or decreases the polymerization and the formation of undesired by-products and results in the improved yield. Yet another object of the present invention is to provide an improved process for the preparation of benzonitrile compounds of formula (I) from corresponding benzotrichloride compounds of formula (II) which obviates the solid waste generation and hence is environmentally friendly. Yet another object of the present invention is to provide an improved process for the preparation of benzonitrile compounds of formula (I) from corresponding benzotrichloride compounds of formula (II) which provides improved yield with less byproduct formation and therefore it is industrially feasible. Other objects and advantages of the present invention will be more apparent from the following description which is not intended to limit the scope of the present invention. SUMMARY OF THE INVENTION: In one aspect, the present invention provides an improved process for the preparation of benzonitrile compound of formula (I),

[0002] wherein, R1 and R2 are independently selected from the group consisting of hydrogen and cyano; when, R1and / or R2are / is hydrogen then said hydrogen may be substituted with X; n is an integer ranging from 0 to 3; comprising the step of nitrilation of a benzotrichloride compound of formula (II); wherein, R3and R4are independently selected from the group consisting of hydrogen and trichloromethyl; X is selected from the group consisting of fluoro and chloro; when, R3 and / or R4 are / is hydrogen then said hydrogen may be substituted with X; n is an integer ranging from 0 to 3; using suitable ammonium salt in the presence of a suitable catalyst and optionally in the presence of a suitable inert solvent at a temperature in the range of 150 to 210°C followed by treating the reaction mixture with a suitable reagent to afford the benzonitrile compound of formula (I). In accordance with the present invention the compound of formula (I) is obtained in the yield ranging from 98 to 99.5%. In accordance with the present invention the compound of formula (I) is having purity of more than 99.5%. In second aspect, the present invention provides an improved process for the preparation of benzonitrile compound of formula (I),

[0003] wherein, R1and R2are independently selected from the group consisting of hydrogen and cyano; when, R1 and / or R2 are / is hydrogen then said hydrogen may be substituted with X; n is an integer ranging from 0 to 3; comprising the step of nitrilation of a benzotrichloride compound of formula (II); wherein, R3 and R4 are independently selected from the group consisting of hydrogen and trichloromethyl; X is halogen selected from the group consisting of fluoro and chloro; when, R3 and / or R4 are / is hydrogen then said hydrogen may be substituted with X; n is an integer ranging from 0 to 3; using suitable ammonium salt in the presence of a suitable initiator, a suitable catalyst and optionally in the presence of a suitable inert solvent at a temperature in the range of 150 to 210°C followed by treating the reaction mixture with a suitable reagent to afford the benzonitrile compound of formula (I). In accordance with the present invention the compound of formula (I) is obtained in the yield ranging from 98 to 99.5%. In accordance with the present invention the compound of formula (I) has purity of more than 99.5%. It is unexpectedly surprising for the inventor that the amount of the initiator, the catalyst and the reagent plays an important role in obviating the use of expensive jacketed reactors, application of elevated temperature conditions and substantially reducing or obviating the formation of by-products such as benzonitrile polymer and at the same time results in the improved yield of the product. DESCRIPTION OF THE INVENTION: References in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. References in the specification to “preferred embodiment” means that a particular feature, structure, characteristic, or function described in detail thereby omitting known constructions and functions for clear description of the present invention. The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed and obviously many modifications and variations are possible in light of the above teaching. The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher / lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art. In case of conflict, the present document, including definitions will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present invention. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting. The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The term “halogen” includes fluorine or chlorine. The singular forms “a,” “an” and “the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments “comprising,” “consisting of’ and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not. In view of the above defined objectives, the present invention provides an improved process for the preparation of benzonitrile compounds of formula (I). In the first embodiment there is provided an improved process for the preparation of benzonitrile compounds of formula (I), wherein, R1 and R2 are independently selected from the group consisting of hydrogen and cyano; when, R1and / or R2are / is hydrogen then said hydrogen may be substituted with X; n is an integer ranging from 0 to 3; comprising the step of nitrilation of a benzotrichloride compound of formula (II); wherein, R3 and R4 are independently selected from the group consisting of hydrogen and trichloromethyl; X is halogen selected from the group consisting of fluoro and chloro; when, R3and / or R4are / is hydrogen then said hydrogen may be substituted with X; n is an integer ranging from 0 to 3; using suitable ammonium salt in the presence of a suitable catalyst and optionally in the presence of a suitable inert solvent at a temperature in the range of 150 to 210°C followed by treating the reaction mixture with a suitable reagent to afford the benzonitrile compound of formula (I). In accordance with the present invention the compound of formula (I) is obtained in the yield ranging from 98 to 99.5%. In accordance with the present invention the compound of formula (I) is having purity of more than 99.5%. Non limiting examples of the compound of formula (I) include but are not limited to ortho-chlorobenzonitrile, para-chlorobenzonitrile, meta-chlorobenzonitrile, ortho-fluorobenzonitrile, para-fluorobenzonitrile, meta-fluorobenzonitrile, 2,3- dichlorobenzonitrile, 2,4-dichlorobenzonitrile, 2,5-dichlorobenzonitrile, 2,6- dichlorobenzonitrile, 3,4-dichlorobenzonitrile, 3,5-dichlorobenzonitrile, 2,3- difluorobenzonitrile, 2,4-difluorobenzonitrile, 2,5-difluorobenzonitrile, 2,6- difluorobenzonitrile, 3,4-difluorobenzonitrile, 3,5-difluorobenzonitrile, 1,3- benzenedicarbonitrile and 1,4-benzenedicarbonitrile. Non limiting examples of the compound of formula (II) include but are not limited to ortho-chlorobenzotrichloride, para-chlorobenzotrichloride, meta- chlorobenzotrichloride, ortho-fluorobenzotrichloride, para-fluorobenzotrichloride, meta-fluorobenzotrichloride, 2,3-dichlorobenzotrichloride, 2,4- dichlorobenzotrichloride, 2,5-dichlorobenzotrichloride, 2,6- dichlorobenzotrichloride, 3,4-dichlorobenzotrichloride, 3,5- dichlorobenzotrichloride, 2,3-difluorobenzotrichloride, 2,4- difluorobenzotrichloride, 2,5-difluorobenzotrichloride, 2,6- difluorobenzotrichloride, 3,4-difluorobenzotrichloride, 3,5- difluorobenzotrichloride, 1,3-bis(trichloromethyl)benzene and 1,4- bis(trichloromethyl)benzene. Typically, the ammonium salt is selected from ammonium chloride or ammonium bromide. Non-limiting examples of the suitable catalyst include but are not limited to para- toluene sulfonic acid, methanesulfonic acid, phosphonic acid, amberlyst-15, indion resin, sulfuric acid, phosphoric acid, metal salts such as magnesium oxide (MgO), zinc chloride (ZnCl2), copper oxide (CuO), zinc acetate (Zn(OAc)2), iron chloride (FeCl3) or combinations thereof. By operating in accordance with the above specified conditions, the time required for completing or nearly completing the reaction is within the range from 8 to 25 hrs. More preferably, the time required for the completion of the reaction is in the range of 8 to 20 hrs. Non-limiting examples of the suitable inert solvent include but are not limited to benzonitrile, xylene, monochlorobenzene, dichlorobenzenes, sulfolane, ortho- chlorobenzonitrile, toluene or combination thereof. Non-limiting examples of the suitable reagents include but are not limited to thionyl chloride, phosphorous oxychloride, phosphorus trichloride, phosphorus pentachloride, cyanuric chloride, oxalyl chloride or combinations thereof. By operating in accordance with the above specified reagents for the process for the preparation of benzonitrile compound of formula (I) from benzotrichloride compound of formula (II), the reaction yield is surprisingly and unexpectedly enhanced. The process for the preparation of benzonitrile compound of formula (I) from benzotrichloride compound of formula (II) as disclosed in the present invention is as depicted in scheme 1 below: Scheme: 1 In an exemplary embodiment, the present invention provides an improved process for the preparation of ortho-chlorobenzonitrile comprising the step of nitrilation of a ortho-chlorobenzotrichloride using ammonium salt in the presence of a suitable catalyst and optionally in the presence of suitable inert solvent at a temperature in the range of 150 to 210°C followed by treating the reaction mixture with a suitable reagent to afford ortho-chlorobenzonitrile. In the second embodiment, the present invention provides an improved process for the preparation of benzonitrile compound of formula (I), wherein, R1 and R2 are independently selected from the group consisting of hydrogen and cyano; when, R1and / or R2are / is hydrogen then said hydrogen may be substituted with X; n is an integer ranging from 0 to 3; comprising the step of nitrilation of a benzotrichloride compound of formula (II); wherein, R3and R4are independently selected from the group consisting of hydrogen and trichloromethyl; X is halogen selected from the group consisting of fluoro and chloro; when, R3 and / or R4 are / is hydrogen then said hydrogen may be substituted with X; n is an integer ranging from 0 to 3; using suitable ammonium salt in the presence of a suitable initiator, a suitable catalyst and optionally in the presence of a suitable inert solvent at a temperature in the range of 150 to 210°C followed by treating the reaction mixture with a suitable reagent to afford the benzonitrile compound of formula (I). In accordance with the present invention the compound of formula (I) is obtained in the yield ranging from 98 to 99.5 %. In accordance with the present invention the compound of formula (I) is having purity of more than 99.5%. Non limiting examples of the compound of formula (I) include but are not limited to ortho-chlorobenzonitrile, para-chlorobenzonitrile, meta-chlorobenzonitrile, ortho-fluorobenzonitrile, para-fluorobenzonitrile, meta-fluorobenzonitrile, 2,3- dichlorobenzonitrile, 2,4-dichlorobenzonitrile, 2,5-dichlorobenzonitrile, 2,6- dichlorobenzonitrile, 3,4-dichlorobenzonitrile, 3,5-dichlorobenzonitrile, 2,3- difluorobenzonitrile, 2,4-difluorobenzonitrile, 2,5-difluorobenzonitrile, 2,6- difluorobenzonitrile, 3,4-difluorobenzonitrile, 3,5-difluorobenzonitrile, 1,3- benzenedicarbonitrile and 1,4-benzenedicarbonitrile. Non limiting examples of the compound of formula (II) include but are not limited to ortho-chlorobenzotrichloride, para-chlorobenzotrichloride, meta- chlorobenzotrichloride, ortho-fluorobenzotrichloride, para-fluorobenzotrichloride, meta-fluorobenzotrichloride, 2,3-dichlorobenzotrichloride, 2,4- dichlorobenzotrichloride, 2,5-dichlorobenzotrichloride, 2,6- dichlorobenzotrichloride, 3,4-dichlorobenzotrichloride, 3,5- dichlorobenzotrichloride, 2,3-difluorobenzotrichloride, 2,4- difluorobenzotrichloride, 2,5-difluorobenzotrichloride, 2,6- difluorobenzotrichloride, 3,4-difluorobenzotrichloride, 3,5- difluorobenzotrichloride, 1,3-bis(trichloromethyl)benzene and 1,4- bis(trichloromethyl)benzene. Non limiting examples of the initiator is selected from benzoic acids such as ortho- chlorobenzoic acid, para-chlorobenzoic acid, meta-chlorobenzoic acid, ortho- fluorobenzoic acid, para-fluorobenzoic acid, meta-fluorobenzoic acid, halogen substituted or unsubstituted 1,4-benzenedicarboxylic acid, halogen substituted or unsubstituted 1,3-benzenedicarboxylic acid; benzoyl such as ortho-chlorobenzoyl chloride, para-chlorobenzoyl chloride, meta-chlorobenzoyl chloride, ortho- fluorobenzoyl chloride, para-fluorobenzoyl chloride, meta-fluorobenzoyl chloride, halogen substituted or unsubstituted 1,4-benzenedicarbonyl dichloride, halogen substituted or unsubstituted 1,3-benzenedicarbonyl dichloride; benzamides such as ortho-chlorobenzamide, para-chlorobenzamide, meta-chlorobenzamide, ortho- fluorobenzamide, para-fluorobenzamide, meta-fluorobenzamide, halogen substituted or unsubstituted 1,4-benzenedicarboxamide, halogen substituted or unsubstituted 1,3-benzenedicarboxamide or combinations thereof. Typically, the ammonium salt is selected from ammonium chloride or ammonium bromide. Non-limiting examples of the suitable catalyst include but are not limited to para- toluene sulfonic acid, methanesulfonic acid, phosphonic acid, amberlyst-15, indion resin, sulfuric acid, phosphoric acid, metal salts such as magnesium oxide (MgO), zinc chloride (ZnCl2), copper oxide (CuO), zinc acetate (Zn(OAc)2), iron chloride (FeCl3) or combinations thereof. By operating in accordance with the above specified reagents for the process for the preparation of benzonitrile compound of formula (I) from benzotrichloride compound of formula (II), the reaction yield will improve. In an exemplary embodiment, the present invention provides an improved process for the preparation of ortho-chlorobenzonitrile comprising the step of nitrilation of a ortho-chlorobenzotrichloride using ammonium salt in the presence of ortho- chlorobenzoic acid as an initiator, a suitable catalyst and optionally in the presence of a suitable inert solvent at a temperature in the range of 150 to 210°C followed by treating the reaction mixture with a suitable reagent to afford ortho- chlorobenzonitrile. In another exemplary embodiment, the present invention provides an improved process for the preparation of ortho-chlorobenzonitrile comprising the step of nitrilation of a ortho-chlorobenzotrichloride using ammonium salt in the presence of ortho-chlorobenzoyl chloride as an initiator, a suitable catalyst and optionally in the presence of a suitable inert solvent at a temperature in the range of 150 to 210°C followed by treating the reaction mixture with a suitable reagent to afford ortho- chlorobenzonitrile. Typically, the amount of initiator ranges between 1 to 10 w / w% with respect to the compound of formula (II). Typically, the amount of the catalyst ranges between 0.1 to 0.5 w / w% with respect to the compound of formula (II). In one embodiment, the molar ratio of compound formula (II) and a suitable ammonium salt is in the range of 1:1 to 1:2. Non-limiting examples of the suitable inert solvent include but are not limited to xylene, monochlorobenzene, dichlorobenzenes, sulfolane, ortho- chlorobenzonitrile, benzonitrile, toluene or combination thereof. Non-limiting examples of the suitable reagents include but are not limited to thionyl chloride, phosphorous oxychloride, phosphorus trichloride, phosphorus pentachloride, cyanuric chloride, oxalyl chloride or combination thereof. By operating in accordance with the above specified conditions, the time required for completing or nearly completing the reaction is within the range from 8 to 20 hrs. By operating in accordance with the process of the present invention, practically complete conversion of compound of formula (II) is achieved with high selectivity thereby unexpectedly increasing the yield of the product. The benzonitrile obtained in accordance with the present invention can be easily separated from the reaction mixture, and in particular from the catalyst, reagent and the excess of the ammonium salt, by known techniques, such as distillation and solvent treatment. In particular, the benzonitrile can be directly distilled off from the reaction mixture, or it can be extracted by dissolution in a suitable organic solvent. In any case, the catalyst, initiator, reagent or the ammonium salt can be easily recovered and recycled to a subsequent reaction cycle, a feature of which is desirable and the intended outcome of the present invention. Examples: Example 1: To a reactor 400 g of ortho-chlorobenzotrichloride, 16 g of ortho-chlorobenzoic acid (OCBA), 0.8 g of sulfuric acid (98%) and 112 g of ammonium chloride were charged into the reactor. The reaction mass was heated to 180-195°C and the reaction mixture was maintained for 17 hrs. The reaction mass is cooled when the content of ortho-chlorobenzotrichloride <0.2%. Slowly add 40 g of oxalyl chloride. Maintain the temperature at 195-200°C for 1 hr. The crude ortho-chlorobenzonitrile thus obtained was purified by distillation. (Yield: 99.1%; Purity: >99.5 %). Example 2: To a reactor 400 g of ortho-chlorobenzotrichloride, 36 g of ortho-chlorobenzoyl chloride (OCBOC), 1 g of phosphoric acid, 0.01g copper oxide and 112 g of ammonium chloride were charged into the reactor. The reaction mass was heated to 180-195°C and the reaction mixture was maintained for 12 hrs. The reaction mass is cooled when the content of ortho-chlorobenzotrichloride <0.2%. Slowly add 21 g of cyanuric chloride. Maintain the temperature at 195-200°C for 2 hrs. The crude ortho-chlorobenzonitrile thus obtained was purified by distillation. (Yield: 99.05%; Purity: >99.5 %). Example 3: To a reactor 376 g of ortho-chlorobenzotrichloride, 36 g of ortho-chlorobenzoyl chloride (OCBOC), 0.8 g of para-toluene sulfonic acid, 0.01g zinc chloride and 112 g of ammonium chloride were charged into the reactor. The reaction mass was heated to 180-195°C and the reaction mixture was maintained for 18 hrs. The reaction mass is cooled when the content of ortho-chlorobenzotrichloride <0.2%. Slowly add 40 g of thionyl chloride. Maintain the temperature at 195-200°C for 1 hr. The crude ortho-chlorobenzonitrile thus obtained was purified by distillation. (Yield: 99.2%; Purity: >99.5 %). Example 4: To a reactor 200 g of ortho-chlorobenzotrichloride, 6 g of ortho-chlorobenzoic acid (OCBA), 0.010 g zinc chloride, 0.6 g of sulfuric acid (98%) and 57 g of ammonium chloride were charged into the reactor. The reaction mass was heated to 180-185°C and the reaction mixture was maintained for 20 hrs. The reaction mass is cooled when the content of ortho-chlorobenzotrichloride < 0.2%. Slowly add 20 g of thionyl chloride. Maintain the temperature at 195-200°C for 1 hr. The crude ortho- chlorobenzonitrile thus obtained was purified by distillation. (Yield: 99.12%; Purity: >99.5 %). Example 5: To a reactor 400 g of ortho-chlorobenzotrichloride, 16 g of ortho-chlorobenzamide (OCBAM), 1 g of amberlyst-15, and 112 g of ammonium chloride were charged into the reactor. The reaction mass was heated to 180-195°C and the reaction mixture was maintained for 15 hrs. The reaction mass is cooled when the content of ortho-chlorobenzotrichloride < 0.2%. Slowly add 40 g of thionyl chloride. Maintain the temperature at 195-200°C for 1 hr. The crude ortho-chlorobenzonitrile thus obtained was purified by distillation. (Yield: 99.23%; Purity: >99.5 %). Example 6: To a reactor charged 20g of ortho-chlorobenzotrichloride, 50g of ortho- chlorobenzonitrile (OCBN), 0.01g magnesium oxide at room temperature. The reaction mass was heated to 150-155°C. Added 1.4 g of 30.0% sulfuric acid solution into the reaction mass. Charge 55.8 g of ammonium chloride and the reaction mass was heated to 170-175°C. Add 190 g of ortho-chlorobenzotrichloride into the reactor for 10 hrs at 170-195°C and maintain for 6 hrs. After addition is completed, send the sample for the GC analysis. If the content of ortho-chlorobenzotrichloride < 0.2%, then cool the mass. Slowly add 20 g of thionyl chloride. Maintain the temperature at 195-200°C for 1 hr. The pure ortho-chlorobenzonitrile thus obtained by distillation. (Yield: 99.14%; Purity: >99.5 %). Example 7: To a reactor 400 g of 1,4-bis-trichloromethyl-benzene, 36 g of terephthaloyl chloride, 1.6 g of sulfuric acid (98%), 0.02 g zinc acetate and 224 g of ammonium chloride were charged into the reactor. The reaction mass was heated to 180-195°C and the reaction mixture was maintained for 21 hrs. The reaction mass is cooled when the content of 1,3-bis-trichloromethyl-benzene < 0.2%. Slowly add 42 g of cyanuric chloride. Maintain the temperature at 195-200°C for 2 hrs. The crude terephthalonitrile thus obtained was purified by distillation. (Yield: 99.03%; Purity: >99.0 %). Example 8: To a reactor 200 g of para-chlorobenzotrichloride, 6 g of para-chlorobenzoic acid (OCBA), 0.010 g zinc chloride, 0.6 g of sulfuric acid (98%) and 57 g of ammonium chloride were charged into the reactor. The reaction mass was heated to 180-185°C and the reaction mixture was maintained for 20 hrs. The reaction mass is cooled when the content of para-chlorobenzotrichloride < 0.2%. Slowly add 20 g of thionyl chloride. Maintain the temperature at 195-200°C for 1 hr. The crude para- chlorobenzonitrile thus obtained was purified by distillation. (Yield: 98.7%; Purity: >99.5 %). Comparative Example 1: To a reactor 400 g of ortho-chlorobenzotrichloride, 16 g of ortho-chlorobenzoic acid (OCBA), 0.8 g of sulfuric acid (98%) and 112 g of ammonium chloride were charged into the reactor. The reaction mass was heated to 180-195°C and the reaction mixture was maintained for 12 hrs. The reaction mass then cooled when the content of ortho-chlorobenzotrichloride was < 0.2%. The crude ortho- chlorobenzonitrile thus obtained was purified by distillation. (Yield: 90%; Purity: >99.5 %). Comparative Example 2: To a reactor 376 g of ortho-chlorobenzotrichloride, 36 g of ortho-chlorobenzoyl chloride (OCBOC), 0.8 g of sulfuric acid (98%) and 112 g of ammonium chloride were charged into the reactor. The reaction mass was heated to 180-195°C and the reaction mixture was maintained for 12 hrs. The reaction mass then cooled when the content of ortho-chlorobenzotrichloride was < 0.2%. The crude ortho- chlorobenzonitrile thus obtained was purified by distillation. (Yield: 89%; Purity: >99.5 %). Comparative Example 3: To a reactor 200 g of ortho-chlorobenzotrichloride, 0.4 g of sulfuric acid (98%) was added at room temperature and the reaction mass was heated to 150-155°C. To this reaction mixture 1.0 g water was added at 155-160oC for 20 minutes followed by the addition of 55.8 g of ammonium chloride. The reaction mass was heated to 180- 185°C. The resulting reaction mass was heated at 180-185oC for 25 hrs. After completion of the reaction when the content of ortho-chlorobenzotrichloride < 0.2%, the reaction mass was cooled to 110°C. The crude ortho-chlorobenzonitrile thus obtained was purified by distillation (Yield: 89.5 %; Purity: >99.5 %). The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to a person skilled in the art, the invention should be construed to include everything within the scope of the disclosure. The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein. The description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and / or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the invention herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. Various features and embodiments of the present invention are illustrated in the following representative examples, which are intended to be illustrative and non- limiting. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the scope of the present invention.

Claims

CLAIMS:

1. An improved process for the preparation of benzonitrile compounds of formula (I);wherein, R1 and R2 are independently selected from the group consisting of hydrogen and cyano; when, R1 and / or R2 are hydrogen then said hydrogen may be substituted with X; X is selected from the group consisting of fluoro and chloro; n is an integer ranging from 0 to 3; comprising the step of nitrilation of corresponding benzotrichloride compounds of formula (II);wherein, R3and R4are independently selected from the group consisting of hydrogen and trichloromethyl; provided that, R3 and R4 are not trichloromethyl at the same time; and when R3and / or R4are hydrogen then said hydrogen may be substituted with X; X is selected from the group consisting of fluoro and chloro; n is an integer ranging from 0 to 3; using suitable ammonium salt in the presence of a suitable catalyst and optionally in the presence of a suitable inert solvent and a suitable initiator at a temperature in the range of 150 to 210°C followed by treating the reaction mixture with a suitable reagent to afford the benzonitrile compound of formula (I).

2. The process as claimed in claim 1, wherein said suitable ammonium salt is selected from the group consisting of ammonium chloride or ammonium bromide or mixture thereof and the molar ratio of the benzotrichloride compound of Formula (II) to the suitable ammonium salt is in the range of 1:1 to 1:

2.

3. The process as claimed in claim 1, wherein said suitable catalyst is selected from the group consisting of para-toluene sulfonic acid, methanesulfonic acid, phosphonic acid, amberlyst-15, indion resin, sulfuric acid, phosphoric acid, metal salts such as magnesium oxide (MgO), zinc chloride (ZnCl2), copper oxide (CuO), zinc acetate (Zn(OAc)2), iron chloride (FeCl3) or mixture thereof and the amount of suitable catalyst is in the range of 0.5 w / w% of the benzotrichloride compound of Formula (II).

4. The process as claimed in claim 1, wherein said suitable reagents is selected from the group consisting of oxalyl chloride, thionyl chloride, phosphorous oxychloride, phosphorus trichloride, phosphorus pentachloride, cyanuric chloride, or mixture thereof.

5. The process as claimed in claim 1, wherein said suitable inert solvent is selected from the group consisting of benzonitrile, xylene, monochlorobenzene, dichlorobenzenes, sulfolane, ortho-chlorobenzonitrile, toluene or mixture thereof.

6. The process as claimed in claim 1, wherein said initiator is selected from the group consisting of benzoic acids such as ortho-chlorobenzoic acid, para- chlorobenzoic acid, meta-chlorobenzoic acid, ortho-fluorobenzoic acid, para- fluorobenzoic acid, meta-fluorobenzoic acid, halogen substituted or unsubstituted 1,4-benzenedicarboxylic acid, halogen substituted or unsubstituted 1,3-benzenedicarboxylic acid; benzoyl such as ortho- chlorobenzoyl chloride, para-chlorobenzoyl chloride, meta-chlorobenzoyl chloride, ortho-fluorobenzoyl chloride, para-fluorobenzoyl chloride, meta- fluorobenzoyl chloride, halogen substituted or unsubstituted 1,4- benzenedicarbonyl dichloride, halogen substituted or unsubstituted 1,3- benzenedicarbonyl dichloride; benzamides such as ortho-chlorobenzamide,para-chlorobenzamide, meta-chlorobenzamide, ortho-fluorobenzamide, para- fluorobenzamide, meta-fluorobenzamide, halogen substituted or unsubstituted 1,4-benzenedicarboxamide, halogen substituted or unsubstituted 1,3- benzenedicarboxamide or mixture thereof and the amount of suitable initiator is in the range of 1 to 10 w / w% of the benzotrichloride compound of Formula (II).

7. The process as claimed in claim 1, wherein the yield of benzonitrile compound of Formula (I) is in the range from 98 to 99.5%.

8. The process as claimed in claim 1, wherein the purity of benzonitrile compound of Formula (I) is more than 99.5%.

9. The process as claimed in claim 1, wherein said compound of formula (I) is selected from ortho-chlorobenzonitrile, para-chlorobenzonitrile, meta- chlorobenzonitrile, ortho-fluorobenzonitrile, para-fluorobenzonitrile, meta- fluorobenzonitrile, 2,3-dichlorobenzonitrile, 2,4-dichlorobenzonitrile, 2,5- dichlorobenzonitrile, 2,6-dichlorobenzonitrile, 3,4-dichlorobenzonitrile, 3,5- dichlorobenzonitrile, 2,3-difluorobenzonitrile, 2,4-difluorobenzonitrile, 2,5- difluorobenzonitrile, 2,6-difluorobenzonitrile, 3,4-difluorobenzonitrile, 3,5- difluorobenzonitrile, 1,3-benzenedicarbonitrile and 1,4-benzenedicarbonitrile.

10. The process as claimed in claim 1, wherein said compound of formula (II) is selected from ortho-chlorobenzotrichloride, para-chlorobenzotrichloride, meta-chlorobenzotrichloride, ortho-fluorobenzotrichloride, para- fluorobenzotrichloride, meta-fluorobenzotrichloride, 2,3- dichlorobenzotrichloride, 2,4-dichlorobenzotrichloride, 2,5- dichlorobenzotrichloride, 2,6-dichlorobenzotrichloride, 3,4- dichlorobenzotrichloride, 3,5-dichlorobenzotrichloride, 2,3- difluorobenzotrichloride, 2,4-difluorobenzotrichloride, 2,5- difluorobenzotrichloride, 2,6-difluorobenzotrichloride, 3,4- difluorobenzotrichloride, 3,5-difluorobenzotrichloride, 1,3- bis(trichloromethyl)benzene and 1,4-bis(trichloromethyl)benzene.

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