An improved process for the preparation of benzonitrile compounds

Abstract

The present invention provides 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).

Description

[0001] “AN IMPROVED PROCESS FOR THE PREPARATION OF BENZONITRILE 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 aromatic nitriles are products known in the art and used in particular as an intermediate in the pharmaceuticals, dyes, and plant medicines. At the present time, benzonitrile and halogenated benzonitriles are made on industrial scale by reacting benzotrichloride or a halogenated benzotrichloride, respectively, with ammonia gas, ammonium hydroxide, or ammonium chloride in the presence of catalyst selected from the group consisting of ferric chloride, zinc chloride, copper chloride, or copper oxide. While these reactions produce the desired product, they also produce unwanted byproducts, such as tar residues, resulting in a significant amount of solid waste. Several processes are known for producing organic nitriles. Exemplary thereof are a reaction of an aromatic halo-derivative with a metal cyanide, Sandmayer's reaction on anilines, Friedel-Craft's reaction with substitution of an aromatic ring by reaction with cyanogen chloride, ammonia oxidation of aromatic hydrocarbons bearing at least one methyl group, dehydration of benzoic amides and condensation of benzaldehydes with hydroxylamine and dehydration of the obtained oxime. The above processes known from the prior art suffer from the disadvantages like use of toxic reactants such as cyanides, with serious waste disposal problems, relatively low reaction yields, in particular in regards with Friedel-craft's reaction, high costs of raw materials, in particular in connection with the use of aldehydes and hydroxylamine, drastic reaction conditions imposed by the process of ammonia-oxidation, with consequent metal corrosion problems. Takikawa et al. (Fac. Eng., Iwate Univ., Morioka Japan, Nippon Kagaku Kaishi, 1976, 4, 637-41, Japan) discloses the process for the synthesis of benzonitrile by the reaction of α,α,α,-trichlorotoluene with liquid ammonia. The article also discloses the effect of additives such as water, ammonium chloride, ammonium bromide, sodium chloride, potassium iodide, metallic sodium, copper powder and copper acetate. The use of ammonia leads to the formation of benzamidine hydrochloride and ammonium chloride. Both of these by-products negatively affect the benzonitrile yield. Para-chlorobenzonitrile (PCBN) is used in the manufacturing of pigments, pharmaceuticals, and agrochemical products. It is made by reacting para- chlorobenzoic acid with para-chlorobenzotrichloride (PCBTC) and ammonium chloride. In the synthesis of PCBN, various side products and unreacted starting material remain as an impurity. Para-chlorobenzonitrile (PCBN) and 3,4-dichlorobenzonitrile (DCBN) can be prepared from para-chlorobenzotrichloride (PCBTC) and 3,4-dichlorobenzotrichloride (DCBTC), respectively, by reacting with ammonium chloride in the presence of a catalyst such as ferric chloride, titanium tetrachloride, molybdenum pentachloride, antimony pentachloride, or ferrous chloride. A major problem with this reaction is the formation of a trimer by-product believed to have the compound of formula (A) below:

[0002] Formula (A) The trimer which constitutes a waste of the benzotrichloride starting material, has little or no commercial value and creates a separation and disposal problem. The use of cupric chloride or cupric oxide suppresses the formation of the trimer when the starting benzotrichloride was 3,4-DCBTC but did not eliminate the trimer when the starting benzotrichloride was PCBTC. The formation of trimer compounds of formula (A) is particularly peculiar to compounds where halogen is para to the “trichloro” group in the benzene ring system. Therefore, it is not formed when halogen is “ortho” to “trichloro” group. US5760274 discloses a method of producing aromatic nitriles by the reaction of a benzotrichloride with a source of ammonia in the presence of catalyst such as oxides and halogen salts of group IIA metals, particularly magnesium chloride and magnesium oxide, which catalyze the production of the corresponding nitriles from various benzotrichloride. The process of US’ 274 appears to be demanding for reactors having material of construction (MOC) other than steel or iron. The reason being, if the reactors of steel or iron are used then iron released from such reactors may interfere with the reaction mass and lead to form trimer impurity thereby defeating its sole purpose of using catalyst such magnesium chloride or magnesium oxide. Thus, there exists an unmet need wherein the process that avoids use of expensive reactors having MOC other than steel or iron and still avoid formation of trimer impurities. US5866709 discloses the process for preparation of benzonitriles from benzotrichlorides using ammonium halide as reagent in the presence of an oxygen- donating initiator using iron based catalyst. The problem associated with the reaction processes reported in ‘274 & ‘709 is that an unwanted trimer by-product of the compound of formula (A) is formed thus resulting in the reduced yield of the desired product. In light of meeting the need, the inventors of the present invention envisaged an improved process for the preparation of benzonitrile compounds which obviates at least one problem of prior art processes such as polymerization and formation of trimer by- product. Accordingly, the inventors of the present invention have surprisingly and unexpectedly developed an improved, simple, industrially feasible and advantageous process that reduces the polymerization and the formation of the trimer by-product of the compound of formula (A) thereby improving the yield and purity. OBJECTIVE OF THE INVENTION: An object of the present invention is to ameliorate one or more problems of the prior art or to at least provide a useful alternative. One object of the present invention is to provide an improved, efficient and economical 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 the corresponding benzotrichloride compounds of Formula (II) which substantially obviates the polymerization and the formation of trimer by-product of formula (A). Another 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) which results in high yield & purity. 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: A first aspect of the present invention relates to an improved, efficient and economical process for the preparation of benzonitrile compounds of Formula (I) comprising the step of reacting benzotrichloride compounds of Formula (II) with a suitable ammonia source in the presence of a suitable catalyst, a suitable initiator, a suitable scavenger and optionally in the presence of a suitable inert solvent at a temperature in the range of 150°C to 210°C to afford benzonitrile compounds of Formula (I): wherein n is an integer ranging from 0 to 2; R is halogen selected from the group consisting of chlorine, bromine, iodine and fluorine; with the proviso that R is not substituted on ortho position of -CCl3or -CN. In another aspect, the present invention relates to an improved process for the preparation of benzonitrile compounds of Formula (I), comprising the step of reacting benzotrichloride compounds of Formula (II) with a suitable ammonia source in the presence of a suitable catalyst, a suitable initiator, a suitable scavenger and optionally in the presence of a suitable inert solvent at a temperature in the range of 150°C to 210°C to afford benzonitrile compounds of Formula (I); wherein, n is an integer ranging from 0 to 2; R is halogen selected from the group consisting of chlorine, bromine, iodine and fluorine; with the proviso that R is not substituted on ortho position of - CCl3 or -CN; the impurity of the trimer by-product compound of formula (A) in the benzonitrile compounds of Formula (I) is less than 2%.

[0003] Yet another aspect of the present invention relates to improved process for the preparation of benzonitrile compounds of Formula (I), comprising the step of reacting benzotrichloride compounds of Formula (II) with a suitable ammonia source in the presence of a suitable catalyst, a suitable initiator, a suitable scavenger and optionally in the presence of a suitable inert solvent at a temperature in the range of 150°C to 210°C to afford benzonitrile compounds of Formula (I); wherein, n is an integer ranging from 0 to 2; compounds of Formula (II) is selected from the group consisting of: X = Cl, Br, F or I; and compounds of Formula (I) is selected from the group consisting of:

[0004] R is halogen selected from the group consisting of chlorine, bromine, iodine and fluorine; with the proviso that R is not substituted on ortho position of - CCl3or -CN; the impurity of the trimer by-product compound of formula (A) in the benzonitrile compounds of Formula (I) is less than 2%. Formula (A) In yet another aspect, the present invention relates to an improved process for the preparation of benzonitrile compounds of Formula (I) from the corresponding benzotrichloride compounds of Formula (II), wherein benzonitrile compounds of Formula (I) are produced with high yield and purity using the conventional cheaper MOC reactors. DETAIL 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. 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 one embodiment, the present invention provides an improved process for the preparation of benzonitrile compounds of Formula (I) comprising the step of reacting benzotrichloride compounds of Formula (II) with a suitable ammonia source in the presence of a suitable catalyst, a suitable initiator, a suitable scavenger and optionally in the presence of a suitable inert solvent at a temperature in the range of 150°C to 210°C to afford benzonitrile compounds of Formula (I). Scheme: I wherein n is an integer ranging from 0 to 2; R is halogen selected from the group consisting of chlorine, bromine, iodine and fluorine; with the proviso that R is not substituted on ortho position of -CCl3 or -CN. In one embodiment, the present invention provides an improved process for the preparation of benzonitrile compounds of Formula (I), comprising the step of reacting benzotrichloride compounds of Formula (II) with a suitable ammonia source in the presence of suitable catalyst, a suitable initiator, a suitable scavenger and optionally in the presence of a suitable inert solvent at a temperature in the range of 150°C to 210°C to afford benzonitrile compounds of Formula (I); wherein, n is an integer ranging from 0 to 2; R is halogen selected from the group consisting of chlorine, bromine, iodine and fluorine; with the proviso that R is not substituted on ortho position of - CCl3 or -CN; the impurity of the trimer by-product compound of formula (A) in the benzonitrile compounds of Formula (I) is less than 2%. Formula (A) In another embodiment, the present invention provides improved process for the preparation of benzonitrile compounds of Formula (I), comprising the step of reacting benzotrichloride compounds of Formula (II) with a suitable ammonia source in the presence of suitable catalyst, a suitable initiator, a suitable scavenger and optionally in the presence of a suitable inert solvent at a temperature in the range of 150°C to 210°C to afford benzonitrile compounds of Formula (I); wherein, n is an integer ranging from 0 to 2; compounds of Formula (II) is selected from the group consisting of: , X = Cl, Br, F or I; and compounds of Formula (I) is selected from the group consisting of:

[0005] X = as defined above; R is halogen selected from the group consisting of chlorine, bromine, iodine and fluorine; with the proviso that R is not substituted on ortho position of - CCl3or -CN; the impurity of the trimer by-product compound of formula (A) in the benzonitrile compounds of Formula (I) is less than 2%. Formula (A) In yet another embodiment, the present invention provides an improved process for the preparation of benzonitrile compounds of Formula (I) from the corresponding benzotrichloride compounds of Formula (II) where in the process is carried out in the presence of scavengers which results in improved yield & purity. The benzonitrile compounds of Formula (I) is selected from benzonitrile (BN), para- chlorobenzonitrile (PCBN), meta-chlorobenzonitrile (MCBN), para- fluorobenzonitrile (PFBN), meta-fluorobenzonitrile (MFBN), para-iodobenzonitrile (PIBN), meta-iodobenzonitrile (MIBN), meta-bromobenzonitrile (MBBN), para- bromobenzonitrile (PBBN), 3,4-dichlorobenzonitrile (3,4-DCBN) and 3,5- dichlorobenzonitrile (3,5-DCBN). The benzotrichloride compounds of Formula (II) is selected from benzotrichloride (BTC), para-chlorobenzotrichloride (PCBTC), meta-chlorobenzotrichloride (MCBTC), para-fluorobenzotrichloride (PFBTC), meta-fluorobenzotrichloride (MFBTC), para-iodobenzotrichloride (PIBTC), meta-iodobenzotrichloride (MIBTC), meta-bromobenzotrichloride (MBBTC), para-bromobenzotrichloride (PBBTC), 3,4- dichlorobenzotrichloride (3,4-DCBTC) and 3,5-dichlorobenzotrichloride (3,5- DCBTC). The examples of ammonia includes but are not limited to dry ammonia, urea, ammonium chloride, ammonium bromide, ammonium iodine, ammonium fluoride, ammonium acetate, ammonium propionate, and the like. The examples of catalyst include but is not limited to para-toluene sulfonic acid, methanesulfonic acid, phosphonic acid, amberlyst-15, indion resin, concentrated sulfuric acid, aqueous sulfuric acid, phosphoric acid, metal salts selected from the group consisting of magnesium oxide (MgO), magnesium chloride (MgCl2), zinc chloride (ZnCl2), copper oxide (CuO), zinc acetate (Zn(OAc)2), aluminium chloride (AlCl3), lithium perchlorate (LiClO4), stannic chloride (SnCl4), and the like. In one aspect, when aqueous sulfuric acid is used as a catalyst, the concentration of sulfuric acid in an aqueous solution is in the range of 20 to 40 %. Preferably, the concentration of sulfuric acid in an aqueous solution is in the range of 25 to 35 %. The examples of initiator include but is not limited to benzoic acids selected from the group consisting of meta-chlorobenzoic acid (MCBA), meta-fluorobenzoic acid (MFBA), para-chlorobenzoic acid (PCBA), para-fluorobenzoic acid (PFBA); halogen substituted or unsubstituted 1,4-benzenedicarboxylic acid; benzoyl chlorides selected from the group consisting of para-chlorobenzoyl chloride (PCBOC), para- fluorobenzoyl chloride (PFBOC), meta-chlorobenzoyl chloride (MCBOC), meta- fluorobenzoyl chloride (MFBOC), 3,4-dichlorobenzoyl chloride (3,4-DCBOC), 3,5- dichlorobenzoyl chloride (3,5-DCBOC); halogen substituted or unsubstituted 1,4- benzenedicarbonyl dichloride; benzamides selected from the group consisting of meta- chlorobenzamide (MCBAM), meta-fluorobenzamide (MFBAM), para- chlorobenzamide (PCBAM), para-fluorobenzamide (PFBAM), halogen substituted or unsubstituted 1,4-benzenedicarboxamide, water, and the like. The examples of scavenger include but is not limited to N, N-dimethylformamide (DMF), P-donor ligands selected from the group consisting of phosphines selected from phosphine (Ph3), trimethylphosphine (PMe3), triphenylphosphine (PPh3), methyldiphenylphosphine (PPh2Me), trifluorophosphine (PF3), tricyclohexylphosphine (PCY)3, diphenylphosphino methane (DPPM), diphenylphosphino ethane (DPPE), triethanolamine, 1,2- bis(diphenylphosphino)propane (PROPHOS), dimethylphosphino methane (DMPM), dimethylphosphino ethane (DMPE), (2S,3S)-(-)-Bis(diphenylphosphino)butane, phenylanisylmethylphosphine (PAMP), (1S,2S)-(+)-Bis[(2- methoxyphenyl)phenylphosphino] ethane (DIPAMP), 2,3-O-isopropylidene-2,3- dihydroxy-1,4-bis(diphenylphosphino)butane (DIOP), phosphites selected from the group consisting of trimethylphosphite P(OMe)3, triphenylphosphite P(OPh)3,and the like. The time required for completing or nearly completing the reaction is within the range from 15 hrs. to 24 hrs. More preferably, the time required for the completion of the reaction is in the range of 15 hrs. to 20 hrs. Typically, the amount of the catalyst ranges between 0.05 to 0.2 wt % with respect to the compounds of Formula (II). The suitable initiator is in the range of 4 to 10 wt % with respect to the compounds of Formula (II). The suitable scavenger is in the range of 0.1 to 0.5 wt % with respect to the compounds of Formula (II). The molar ratio of Formula (II) and a suitable ammonia source is in the range of 1:1 to 1:1.5. In accordance with the present invention the compounds of Formula (I) is obtained in the yield ranging from 85% to 95%. In accordance with the process of the present invention, the benzonitrile compounds of Formula (I) is having a purity of more than 99%. In one exemplary embodiment, the present invention provides an improved process for the preparation of di-halobenzonitrile of Formula (iv) comprising the step of reacting di-halo benzotrichloride of Formula (iii) with a suitable ammonia source in the presence of a suitable catalyst, a suitable initiator, a suitable scavenger and optionally in the presence of a suitable inert solvent at a temperature in the range of 150°C to 210 °C to afford di-halobenzonitrile of Formula (iv). The process for the preparation of di-halobenzonitrile of Formula (iv) from di- halobenzotrichloride of Formula (iii) as disclosed in the present invention is as depicted in scheme II below:

[0006] Scheme: II The di-halobenzonitrile compound of Formula (iv) is selected from 3,4- dichlorobenzonitrile, 3,5-dichlorobenzonitrile, 3,4-difluorobenzonitrile, or 3,5- difluorobenzonitrile. The di-halobenzotrichloride compound of Formula (iii) is selected from 3,4- dichlorobenzotrichloride, 3,5-dichlorobenzotrichloride, 3,4-difluorobenzotrichloride or 3,5-difluorobenzotrichloride. The non-limiting examples of the suitable inert solvent include but are not limited to benzonitrile, xylene, monochlorobenzenes, dichlorobenzenes, sulfolane, ortho- chlorobenzonitrile, dimethyl sulfoxide, or combination thereof. The non-limiting examples of the suitable inert solvent include but are not limited to benzonitrile, xylene, monochlorobenzenes, dichlorobenzenes, sulfolane, ortho- chlorobenzonitrile, dimethyl sulfoxide, or combination thereof. The process for the preparation of para-halobenzonitrile of Formula (i) from para-halo benzotrichloride of Formula (ii) as disclosed in the present invention is as depicted in scheme III below:

[0007] Scheme: III In an exemplary embodiment, the para-halobenzonitrile compounds of Formula (i) is selected from para-chlorobenzonitrile or para-fluorobenzonitrile. In an exemplary embodiment, the para-halobenzotrichloride compounds of Formula (II) is selected from para-chlorobenzotrichloride or para-fluorobenzotrichloride. The process for the preparation of para-chlorobenzonitrile of Formula (i-a) from para- chloro benzotrichloride of Formula (ii-a) as disclosed in the present invention is as depicted in scheme IV below: Scheme-IV In yet another exemplary embodiment, the present invention provides an improved process for the preparation of meta-halobenzonitrile of Formula (i)’ comprising the step of reacting meta-halobenzotrichloride of Formula (ii)’ as disclosed in the present invention is as depicted in scheme V below: The non-limiting examples of the suitable inert solvent include but are not limited to benzonitrile, xylene, monochlorobenzenes, dichlorobenzenes, sulfolane, ortho- chlorobenzonitrile, dimethyl sulfoxide, or combination thereof. The meta-halo benzonitrile compounds of Formula (i)’ is selected from meta- chlorobenzonitrile or meta-fluorobenzonitrile. The meta-halo benzotrichloride compounds of Formula (II)’ is selected from meta- chlorobenzotrichloride or meta-fluorobenzotrichloride. The process for the preparation of meta-chlorobenzonitrile of Formula (i-b) from meta- chloro benzotrichloride of Formula (ii-b) as disclosed in the present invention is as depicted in scheme VI below:

[0008] Scheme: VI During piloting trials in metal reactors it was found that there was a formation of a trimer by-product of the compound of formula (A). After detailed investigation it was surprisingly observed that iron leaching out (1 to 100 ppm) from the reactor or the piping system was the cause for the formation of trimer by-product of the compound of formula (A). This observation was in stark contradiction to the teachings of US5866709 wherein iron is used as a catalyst for the preparation of benzonitriles from benzotrichlorides. The inventors of this invention tried various methods to mitigate the problem of formation of trimer by-product of the compound of formula (A) which adversely affected the yield of benzonitriles and iron leaching from metal reactors like changing the reactor with titanium, tantalum alloy or glass materials. However, these reactors are heavy on capital expenditure and therefore not preferred due to high cost. The use of a glass reactor is not favourable in high temperature conditions of the reaction (>150°C to 210°C). Considering these limitations inventors of the present invention contrary to the teachings of US’ 709 surprisingly after several experiments found that the use of scavengers is the most appropriate, cost effective solution to mitigate the problem of iron leaching during the preparation of benzonitriles from benzotrichlorides in metal reactors. During the synthesis of benzonitrile of Formula (I) from the corresponding benzotrichloride of Formula (II) the presence of iron metal impurities hinder the reaction and the resultant yield is low as shown in examples 1, 3, 5, 7, 9, 11, 13, 15, 17. However, the present invention provides an improved process for the synthesis of benzonitrile of Formula (I) wherein it is surprisingly observed that the addition of scavenger will significantly increase the yield as shown in the examples 2, 4, 6, 8, 10, 12, 14, 16, 18. By operating in accordance with the process of the present invention, practically complete conversion of the compounds of Formula (II) is achieved with high selectivity thereby surprisingly and 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 ammonia or suitable 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 ammonia or suitable 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. The preparation processes as disclosed in the present invention are preferably carried out batch-wise. However, semi-continuous or continuous reaction passages, for instance under flow reaction conditions, are also possible. Any person skilled in the art knows the best work-up of the reaction mixtures after the end of the respective reactions. In one embodiment, the work-up is usually carried out by isolation of the product by filtration, and optionally washing with a solvent, further optionally drying of the product if required. The isolation of the reaction product can also be carried out by a technique which includes but is not limited to decantation, centrifugation, evaporation, ultrafiltration, liquid-liquid extraction, distillation, recrystallization, chromatography, and the like. The process steps according to the invention are generally carried out under atmospheric pressure. The invention is further illustrated with reference to the following examples. It is apparent to those skilled in the art that many modifications, both to materials, methods and various reaction parameters, may be practiced without departing from the scope of the invention. The starting materials according to the present invention are known compounds that are commercially available or can be prepared in a known manner. Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention. To evaluate the impact of iron leaching from the reactor or reactor piping, iron is added externally in the following examples to mimic the reactor conditions at commercial scale. EXAMPLES General procedure for the examples which follow: Preparation of Benzonitrile (BN) of Formula (I) without using scavengers: To a reactor 400 g of benzotrichloride of formula (II), 24 g of initiator, 0.4 g of catalyst, 20 to 50 ppm of iron, and 97.70 g of ammonia source were charged at room temperature. The reaction mass was heated to 190-195°C and the reaction mixture was maintained for 15-20 hrs. The reaction mass is cooled to 110°C when the content of benzotrichloride of formula (II) reaches <0.2%. The crude benzonitrile of formula (I) thus obtained was purified by distillation. Preparation of Benzonitrile (BN) of Formula (I) using scavengers: To a reactor 400 g of benzotrichloride of formula (II), 24 g of initiator, 0.4 g of catalyst, 20 to 50 ppm of iron, 0.8 g of scavenger and 97.70 g of ammonia source were charged at room temperature. The reaction mass was heated to 190-195°C and the reaction mixture was maintained for 15-20 hrs. The reaction mass is cooled to 110°C when the content of benzotrichloride of formula (II) reaches <0.2%. The crude benzonitrile of formula (I) thus obtained was purified by distillation. The following table 1 depicts the examples with different catalysts, initiators, ammonia source and scavengers which are prepared by using the above mentioned process of the present invention. Table: 1 Exa Benz Benzo Initi Ammo Catalyst Scave Iron Yiel Purity Trimer mpl otric - ator nia nger (ppm) d (%) Formul e no. hlori source a (A) nitrile (%) de (%) (Prod (SM) uct) 1 PCB PCBN PCB NH4Cl p-toluene Nil 50 70 99 24 TC OC sulfonic acid 2 PCB PCBN PCB NH4Cl p-toluene Trietha 50 93 99 1.7 TC OC sulfonic nolami acid ne 3 PCB PCBN PCB NH4Cl amberlyst Nil 50 63 99 28 TC OC -15 PCB PCBN PCB NH4Cl amberlyst N, N- 50 90 99 2 TC OC -15 Dimet hyl forma mide PCB PCBN PCB NH4Cl phosphori Nil 50 70 99 25 TC OC c acid PCB PCBN PCB NH4Cl phosphori Trietha 50 94 99 1.5 TC OC c acid nolami ne PFB PFBN PFB NH4Cl Sulfuric Nil 50 68 99 26 TC OC acid PFB PFBN PFB NH4Cl Sulfuric Methyl 50 94 99 1.4 TC OC acid diphen yl phosph ine PFB PFBN PFB NH4Cl p-toluene Nil 20 75 99 19 TC OC sulfonic acid PFB PFBN PFB NH4Cl p-toluene Trietha 20 92 99 1.8 TC OC sulfonic nolami acid ne MCB MCB MC NH4Cl p-toluene Nil 50 65 99 29 TC N BOC sulfonic acid MCB MCB MC NH4Cl p-toluene N, N- 50 90 99 1.9 TC N BOC sulfonic Dimet acid hyl forma mide PCB PCBN PCB NH4Cl Sulfuric Nil 50 66 99 27 TC OC acid PCB PCBN PCB NH4Cl Sulfuric PPh3 50 94 99 0.8 TC OC acid 3,4- 3, 4 - 3, 4 - NH4Cl phosphori Nil 50 71 99 21 c acid DCB DCBN DCB TC OC 3,4- 3, 4 - 3, 4 - NH4Cl phosphori 50 92 99 1.5 c acid Methyl DCB DCBN DCB diphen TC OC yl phosph ine 3,5- 3,5 - 3,5 - NH4Cl Sulfuric Nil 50 69 24 acid DCB DCBN DCB TC OC 3,5- 3,5 - 3,5 - NH4Cl Sulfuric Trietha 50 90 1.8 acid nolami DCB DCBN DCB ne TC OC From table 1, it is clearly observed that the yield is affected by the presence of iron content. Further, it is observed that, upon the addition of scavenger the yield is significantly improved. 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 omission 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) comprising the step of reacting benzotrichloride compounds of Formula (II) with a suitable ammonia source in the presence of a suitable catalyst, a suitable initiator, a suitable scavenger and optionally in the presence of a suitable inert solvent at a temperature in the range of 150°C to 210°C to afford benzonitrile compounds of Formula (I);wherein n is an integer ranging from 0 to 2; R is halogen selected from the group consisting of chlorine, bromine, iodine and fluorine; with the proviso that R is not substituted on ortho position of - CCl3or -CN.

2. The process as claimed in claim 1, wherein the benzonitrile compounds of Formula (I) is selected from benzonitrile (BN), para-chlorobenzonitrile (PCBN), meta-chlorobenzonitrile (MCBN), para-fluorobenzonitrile (PFBN), meta-fluorobenzonitrile (MFBN), para-iodobenzonitrile (PIBN), meta- iodobenzonitrile (MIBN), meta-bromobenzonitrile (MBBN), para- bromobenzonitrile (PBBN), 3,4-dichlorobenzonitrile (3,4-DCBN) and 3,5- dichlorobenzonitrile (3,5-DCBN).

3. The process as claimed in claim 1, wherein the suitable ammonia source is selected from the group consisting of dry ammonia, urea, ammonium chloride, ammonium bromide, ammonium iodine, ammonium fluoride, ammonium acetate, ammonium propionate, and mixture thereof; and the molar ratio of benzotrichloride compounds of Formula (II) to the suitable ammonia source is in the range of 1:1 to 1:1.

5.

4. The process as claimed in claim 1, wherein the suitable catalyst is selected from the group consisting of para-toluene sulfonic acid, methanesulfonic acid, phosphonic acid, amberlyst-15, indion resin, concentrated sulfuric acid, aqueous sulfuric acid, phosphoric acid, metal salts selected from the group consisting of magnesium oxide (MgO), magnesium chloride (MgCl2), zinc chloride (ZnCl2), copper oxide (CuO), zinc acetate (Zn(OAc)2), aluminium chloride (AlCl3), lithium perchlorate (LiClO4), stannic chloride (SnCl4), and mixture thereof; and the amount of suitable catalyst is in the range of 0.05 to 0.2 wt % of the benzotrichloride compounds of Formula (II).

5. The process as claimed in claim 1, wherein the suitable initiator is selected from the group consisting of meta-chlorobenzoic acid (MCBA), meta-fluorobenzoic acid (MFBA), para-chlorobenzoic acid (PCBA), para-fluorobenzoic acid (PFBA); halogen substituted or unsubstituted 1,4-benzenedicarboxylic acid; benzoyl chlorides selected from the group consisting of para-chlorobenzoyl chloride (PCBOC), para-fluorobenzoyl chloride (PFBOC), meta- chlorobenzoyl chloride (MCBOC), meta-fluorobenzoyl chloride (MFBOC), 3,4-dichlorobenzoyl chloride (3,4-DCBOC), 3,5-dichlorobenzoyl chloride (3,5-DCBOC); halogen substituted or unsubstituted 1,4-benzenedicarbonyl dichloride; benzamides selected from the group consisting of meta- chlorobenzamide (MCBAM), meta-fluorobenzamide (MFBAM), para-chlorobenzamide (PCBAM), para-fluorobenzamide (PFBAM), halogen substituted or unsubstituted 1,4-benzenedicarboxamide, water, and mixture thereof; and the amount of suitable initiator is in the range of 4 to 10 wt % of the benzotrichloride compounds of Formula (II).

6. The process as claimed in claim 1, wherein the suitable scavenger is selected from the group consisting of N, N-dimethylformamide (DMF), P-donor ligands selected from the group consisting of phosphines selected from phosphine (Ph3), trimethylphosphine (PMe3), triphenylphosphine (PPh3), methyldiphenylphosphine (PPh2Me), trifluorophosphine (PF3), tricyclohexylphosphine (PCY)3, diphenylphosphino methane (DPPM), diphenylphosphino ethane (DPPE), triethanolamine, 1,2- bis(diphenylphosphino)propane (PROPHOS), dimethylphosphino methane (DMPM), dimethylphosphino ethane (DMPE), (2S,3S)-(-)- Bis(diphenylphosphino)butane, phenylanisylmethylphosphine (PAMP), (1S,2S)-(+)-Bis[(2-methoxyphenyl)phenylphosphino] ethane (DIPAMP), 2,3- O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane (DIOP), phosphites selected from the group consisting of trimethylphosphite P(OMe)3, triphenylphosphite P(OPh)3,and mixture thereof; and the amount of suitable scavenger is in the range of 0.1 to 0.5 wt % of the benzotrichloride compounds of Formula (II).

7. The process as claimed in claim 1, wherein the suitable inert solvent is selected from the group consisting of benzonitrile, xylene, monochlorobenzenes, dichlorobenzenes, sulfolane, ortho-chlorobenzonitrile, dimethyl sulfoxide, and mixture thereof.

8. The process as claimed in claim 1, wherein, the impurity of the trimer by- product compound of formula (A) in the benzonitrile compounds of Formula (I) is less than 2%.Formula (A) 9. An improved process for the preparation of benzonitrile compounds of Formula (I), comprising the step of reacting benzotrichloride compounds of Formula (II) with a suitable ammonia source in the presence of a suitable catalyst, a suitable initiator, a suitable scavenger and optionally in the presence of a suitable inert solvent at a temperature in the range of 150°C to 210°C to afford benzonitrile compounds of Formula (I);wherein, n is an integer ranging from 0 to 2; compounds of Formula (II) is selected from the group consisting of:,X = Cl, Br, F or I; and compounds of Formula (I) is selected from the group consisting of:X = as defined above; R is halogen selected from the group consisting of chlorine, bromine, iodine and fluorine; with the proviso that R is not substituted on ortho position of - CCl3 or -CN; the impurity of the trimer by-product compound of formula (A) in the benzonitrile compounds of Formula (I) is less than 2%.Formula (A) 10. The process as claimed in claim 9, wherein the suitable ammonia source is selected from the group consisting of dry ammonia, urea, ammonium chloride, ammonium bromide, ammonium iodine, ammonium fluoride, ammonium acetate, ammonium propionate, and mixture thereof; and the molar ratio of benzotrichloride compounds of Formula (II) to the suitable ammonia source is in the range of 1:1 to 1:1.

5.

11. The process as claimed in claim 9, wherein the suitable catalyst is selected from the group consisting of para-toluene sulfonic acid, methanesulfonic acid, phosphonic acid, amberlyst-15, indion resin, concentrated sulfuric acid, aqueous sulfuric acid, phosphoric acid, metal salts selected from the group consisting of magnesium oxide (MgO), magnesium chloride (MgCl2), zinc chloride (ZnCl2), copper oxide (CuO), zinc acetate (Zn(OAc)2), aluminium chloride (AlCl3), lithium perchlorate (LiClO4), stannic chloride (SnCl4), and mixture thereof; and the amount of suitable catalyst is in the range of 0.05 to 0.2 wt % of the benzotrichloride compounds of Formula (II).

12. The process as claimed in claim 9, wherein the suitable initiator is selected from the group consisting of meta-chlorobenzoic acid (MCBA), meta-fluorobenzoicacid (MFBA), para-chlorobenzoic acid (PCBA), para-fluorobenzoic acid (PFBA); halogen substituted or unsubstituted 1,4-benzenedicarboxylic acid; benzoyl chlorides selected from the group consisting of para-chlorobenzoyl chloride (PCBOC), para-fluorobenzoyl chloride (PFBOC), meta- chlorobenzoyl chloride (MCBOC), meta-fluorobenzoyl chloride (MFBOC), 3,4-dichlorobenzoyl chloride (3,4-DCBOC), 3,5-dichlorobenzoyl chloride (3,5-DCBOC); halogen substituted or unsubstituted 1,4-benzenedicarbonyl dichloride; benzamides selected from the group consisting of meta- chlorobenzamide (MCBAM), meta-fluorobenzamide (MFBAM), para- chlorobenzamide (PCBAM), para-fluorobenzamide (PFBAM), halogen substituted or unsubstituted 1,4-benzenedicarboxamide, water, and mixture thereof; and the amount of suitable initiator is in the range of 4 to 10 wt % of the benzotrichloride compounds of Formula (II).

13. The process as claimed in claim 9, wherein the suitable scavenger is selected from the group consisting of N, N-dimethylformamide (DMF), P-donor ligands selected from the group consisting of phosphines selected from phosphine (Ph3), trimethylphosphine (PMe3), triphenylphosphine (PPh3), methyldiphenylphosphine (PPh2Me), trifluorophosphine (PF3), tricyclohexylphosphine (PCY)3, diphenylphosphino methane (DPPM), diphenylphosphino ethane (DPPE), triethanolamine, 1,2- bis(diphenylphosphino)propane (PROPHOS), dimethylphosphino methane (DMPM), dimethylphosphino ethane (DMPE), (2S,3S)-(-)- Bis(diphenylphosphino)butane, phenylanisylmethylphosphine (PAMP), (1S,2S)-(+)-Bis[(2-methoxyphenyl)phenylphosphino] ethane (DIPAMP), 2,3- O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane (DIOP), phosphites selected from the group consisting of trimethylphosphite P(OMe)3, triphenylphosphite P(OPh)3,and mixture thereof; and the amount of suitablescavenger is in the range of 0.1 to 0.5 wt % of the benzotrichloride compounds of Formula (II).

14. The process as claimed in claim 9, wherein the suitable inert solvent is selected from the group consisting of benzonitrile, xylene, monochlorobenzenes, dichlorobenzenes, sulfolane, ortho-chlorobenzonitrile, dimethyl sulfoxide, and mixture thereof.

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