WO2009090669A2

WO2009090669A2 - A process for the preparation of 5-chloro-2(2,4-dichlorophenoxy) aniline

Info

Publication number: WO2009090669A2
Application number: PCT/IN2008/000659
Authority: WO
Inventors: Mahesh Subramaniyam; Abhay Bhalchandra Deshpande
Original assignee: Dorf Ketal Chemicals (I) Private Limited
Priority date: 2007-10-12
Filing date: 2008-10-10
Publication date: 2009-07-23
Also published as: WO2009090669A3; EP2209763A2

Abstract

A novel process for the selective reduction of halonitroarenes in general and halonitroaromatic arenes in particular, without the hydrogenolysis of the C-Cl (where, X represents F-, Cl-, Br- and I) and the C-O-C bonds, in the presence of platinum based catalysts and ammonium formate. The invention makes the use of duel function of ammonium formate, as a hydrogen source for partial reduction (catalytic transfer hydrogenation) and as an additive controlling the hydrogenolysis side reactions during the completion of the reduction by high pressure catalytic hydrogenation using external hydrogen gas source. Uniqueness of the invention lies in the fact that either the catalytic transfer hydrogenation with ammonium formal e or high pressure catalytic hydrogenation in the absence of ammonium formate, when used alone result in lower purity of the said amine. This invention -product is used to synthesize intermediates for making antibacterial compounds.

Description

A process for the preparation of 5-chloro-2-(2,4-dichlorophenoxy)aniline.

Field of Invention:

The invention relates to a process for the preparation of halogenated aromatic amines, optionally also containing an ether linkage, e.g., triclosan amine (5-chloro-2-(2,4- dichlorophenoxy)aniline), by catalytic hydrogenation of the corresponding halogenated aromatic nitro compounds with ammonium formate in the presence of noble metal catalysts, such as platinum supported on carbon.

Discussion of the Prior Art:

Chlorinated aromatic amines are important intermediates in the manufacture of dyestuffs and pigments. Halogenated amino diphenyl ethers form an important class of intermediates for the preparation of halogenated hydroxy diphenyl ethers useful as antimicrobial agents, e.g., triclosan.

Hydrogenation/reduction of aromatic nitro compounds to the corresponding aromatic amines is known to be one of the-most facile transformations. Several processes have been described in the literature for the said hydrogenation employing catalytic hydrogen transfer, that is, without using external hydrogen; as well as catalytic hydrogenations at elevated hydrogen pressures in the presence of noble metal catalysts, such as, platinum, palladium, ruthenium, rhodium iridium, etc. on various supports and Raney nickel catalysts.

However, when the aromatic nitro compound additionally contains one or several halogen atoms, substituted on the ring, the hydrogenation is accompanied by the hydrogenolysis of the C-Cl bonds, thereby generating undesirable dehalogenated products, which are difficult or sometimes impossible to be separated from the desired product after the reaction. The difficulty is further increased if an ether, e.g., diaryl ether linkage is present in the halonitro aromatic compound. Thus, halogen substituted aminoaryl ethers are extremely susceptible to two types of hydrogenolysis side reactions, one involving the C-X (where, X represents F-, Cl-, Br- and I-) bonds (dehalogenation) and the other involving the C-O-C bonds (ether cleavage). One such example of the halonitrodiarylether is 5-chloro-2-(2,4-dichlorophenoxy)nitrobenzene, which is hydrogenated to yield 5-chloro-2-(2,4-dichlorophenoxy)aniline, commonly known as TADE (trichloroaminodiphenylether), which is an intermediate in the production of a widely used antimicrobial agent, triclosan. The hydrogenolysis of the diaryl ether linkage gives rise to environmentally hazardous chlorophenols as byproducts.

Several strategies have been proposed for preventing the dehalogenation during the hydrogenation of halonitroarenes. Catalysts based on platinum metal have been extensively reported as best choice for the said hydrogenation. However, the problem of cleavage of ether linkage during hydrogenation of halonitroaromatic ethers has not been anticipated or addressed to by the earlier workers.

When the hydrogenation of halonitroarenes with prevention of dehalogenation is carried out using platinum based catalysts, US5041671 recommends the use of sulfited and sulfided platinum orr carbon as catalysts for the selective hydrogenation of 4-chloro-2,5-dimethoxynitrobenzene, in the presence of 1 °, 2° and 3° amines and compounds, which produce a pH of 8-10 in aqueous solutions, US4059627 recommends use of thioethers during the hydrogenation with platinum on carbon along with compounds giving pH of 7-9, US3073865 recommends magnesite (MgO) as an additive, US3149161 recommends sodium acetate as an additive, US3546297 recommends ammonia, morpholine derivatives (0.01 - 1.5 mole per mole of substrate) and Ni, Cr ions (5-500ppm based on the substrate) as additives, US4059627 recommends the use of thioethers and compounds giving a pH of 7-9, US4070401 recommends alkylamine, polyalkylene polyamines as additives, US4230637 recommends the use of 0.2 - 5% ammonia with platinum supported on carbon or barium/strontium carbonate or with rhodium on carbon or Raney nickel and EP0000805 recommends thiophene as an additive along with sodium carbonate for hydrogenation using plain or sulfided platinum on carbon.

Thus, the dehalogenation during the hydrogenation of halonitroarenes can be controlled either by;

1. Use of sulphur containing compounds, which can be used either to modify the catalyst prior to hydrogenation or can be added directly to trie reaction mass during the hydrogenation, or

2. Use of organic or inorganic compounds giving pH of about 7-10 that is, compounds that are basic in nature during the actual hydrogenation which act as neutralizing agents and scavenge the hydrohalic acid generated as a result of dehalogenation thereby preventing excessive dehalogenation, or

3. Both of them simultaneously.

The disadvantage of all these processes, however, is that the additives added need to be separated from the product after the reaction, thus adding one step to the overall process.

There are also several reporjs on the catalytic transfer hydrogenation of halonitroarenes. These methods use iron, zinc, magnesium, raney Ni and the like as the metal catalysts and ammonium formate, formic acid, isopropyl alcohol, hydrazine, hydrazinium monoformate and the like as hydrogen sources.

Problems with these methods are;

1. The metals are required to be employed in more than stoichiometric amounts,

2. The product, that is, the amine often has to be separated from the spent metal slurry using tedious separation procedures,

3. The hydrogen doner compound is needed in stiochiometric excess to achieve quantitative yields and the unconsumed donor compound also needs to be separated from the producl, 4. The throughput of the process is substantially low as a result of the inclusion of the hydrogen donor compound and the solvent in the reaction mass, and

5. Still another problem that needs to be considered is that the erosion of the reactors used for these reactions occurs due to the metal particles during agitation, giving rise to potentially unsafe conditions. The reactors thus need to be replaced frequently.

D. Channe Gowda et al. (Synthetic Communications, 30 (20), 2000, pp. 3639-3644) have reported a process for the catalytic transfer hydrogenation of various nitroarenes using 5% platinum on carbon as a catalyst and ammonium formate as the hydrogen source. Although it is claimed that the process gives around 90% yields of the desired haloamines without dechlorination, the process is not economically viable as the catalyst loading used is very high (0.2-0.3g for 5mmol of substrate). Also, the source of the 5% platinum on carbon catalyst used during the study and its state, that is, whether untreated, sulfided or sulfited has not been mentioned.

In spite of several reports on the selective hydrogenation of halonitroarenes using platinum based catalysts, howevsr, in industrial applications, iron/acetic acid system is still practiced as the method of choice for the hydrogenation of 5-chloro-2-(2,4- dichlorophenoxy)nitrobenzene.

During our study, we found that the hydrogenation of halonitrodiarylether resulted in poor selectivity towards the corresponding haloaminodiarylether, either by catalytic transfer hydrogenation as well as catalytic hydrogenation using external hydrogen, as a result of dehalogenation and/or ether cleavage. Moreover, the rate of catalytic transfer hydrogenation transfer at room temperature was found to be extremely sluggish. While the impurities generated as a result of ether cleavage, especially in the case of hydrogenation of NE are environmentally hazardous, the dehalogenation impurities are highly undesirable as they are very difficult to separate from the product, that is. TADE. These impurities tend to get carried forward till the final product, that is, trilcosan and are known to be very serious environmental hazards. In view of the above, there is a need for development of a new process for the preparation of 5-chloro-2-(2,4-dichlorophenoxy)aniline having high purity without introducing complicated separation steps, which process will overcome some of the abovementioned drawbacks and will be simple yet robust to practice.

Objects and advantages of the present invention:

Accordingly, the objects and advantages of the present invention are described below: An object of the present invention is to provide a process for the hydrogenation of halonitroarenes, specifically halonitroarenes also containing an ether linkage, more specifically, 5-chloro-2-(2,4-dichlorophenoxy)nitrobenzene, to yield 5-chloro-2-(2,4- dichlorophenoxy)aniline, using platinum on carbon as a catalyst.

Another object of the present invention is to provide a process, which combines the beneficial aspects of both catalytic hydrogen transfer and classical catalytic hydrogenation using gaseous hydrogen.

Yet another object of the present invention is to provide a process which minimizes the hydrogenolysis side reactions involving the C-Cl and Ar-O-Ar bonds, thereby increasing the first pass yield and purity of the product.

Still another object of the present invention is to provide a process, which utilizes catalytic transfer hydrogenation agents such as ammonium formate as an additive performing dual function, as a source of hydrogen during the initial catalytic transfer hydrogenation and as an additive controlling the formation of both, dehalogenation as well as ether cleavage impurities. Further object of the present invention is to provide a process, which minimizes the use of solvent or uses water as a solvent.

Still further object of the present invention is to provide a process, which is economically viable.

Summary of the invention:

Halonitroarenes are partially reduced by catalytic transfer hydrogenation "with ammonium formate (O.Olmole per mole to 2mole per mole of the substrate) as a^s hydrogen source in the presence.of 0.01% to 2% (based on the substrate) platinum based catalysts at ambient to 150⁰C and the hydrogenation is completed by introducing hydrogen to the autoclave from 0kg/cm2 to 50kg/cm2« Catalytic transfer hydrogenation with ammonium formate or high pressure catalytic hydrogenation in the absence of ammonium formate, when used alone with platinum based catalysts, result in lower purity of the corresponding amines as a result of hydrogenolysis of the C-CI (where, X represents F-, CI-, Br- and I) and the C-O-C bonds. The hydrogenation can be carried out either by using water as a solvent or lower quantity of solvent wherever required.

Detailed description of the invention:

According to the most preferred 'embodiment of the present invention is provided a process for the preparation of 5-chloro-2-(2,4-dichlorophenoxy)aniline, which process is completed by carrying out reduction of an aromatic halo nitro compound, such as 5-chloro-2-(2,4-dichlorophenoxy)nitrobenzene and the like, using a combination of hydrogenations, such as catalytic transfer hydrogenation , followed by gaseous hydrogenation, using an effective amount of an appropriate catalytic transfer hydrogenating agent, such as ammonium formate and the like, and an effective amount of an appropriate catalyst, such as platinum on carbon and the like. According to another embodiment of present invention is provided a process, wherein said catalytic transfer hydrogenation followed by gaseous hydrogenation, comprises the steps of: a. charging to an autoclave a predetermined amount of a nitroether, such as 5-chloro-2-(2,4-dichlorophenoxy)nitrobenzene, the effective amount of said ammonium formate being from 0.01 to 2 mol / mol of said nitroether, said appropriate catalyst being any one catalyst selected from the group consisting of an untreated platinum on carbon, a sulphiteα platinum on carbon and a sulphided platinum on carbon, wherein said effective amount of¹ said catalyst is from 0.01 % to 2 % w/w of said nitroether, with said catalyst having the amount of platinum content 0.1 % to 5% w/w of said catalyst, and an effective amount of any one solvent selected from the group consisting of alcohol and water, wherein ratio of said nitroether to said solvent is from 1 :0.1 to 1 :0.33w/w; b. completing the reaction of said catalytic transfer hydrogenation at autogenous pressure at a temperature from 50⁰C to 150°C, for period of 0.5 hour 15 hours; c. carrying out, after said period of reaction of step b is completed, the reaction of said gaseous hydrogenation, at a pressure between 1 to 50 kg/cm², by introducing in said autoclave external hydrogen gas, till hydrogen up - take ceases; d. isolating said 5-chloro-2-(2,4-dichlorophenoxy)aniline.

According to yet other embodiment of the present invention, is provided a process, wherein said catalyst is said sulphided platinum on carbon. According to still other embodiment of the present invention is provided a process, as claimed in claim 1 , wherein said catalyst is said untreated platinum on carbon.

According to further embodiment of the present invention, is provided a process, wherein said catalyst is said sulphited platinum on carbon.

The different embodiments of the present invention are illustrated in the examples from 9 to 18. The results of the experiments given in examples 1 to 20 are presented in TABLE. 1.

Distinguishing features of the present invention:

The present invention is a method of hydrogenating halonitro compounds using CTH agents, which function not only as a hydrogen source but also help in controlling the formation of impurities, such as, dehalogenation and ether cleavage impurities. The said agent can effectively be used with any type of platinum based catalysts. Unlike the prior arts, the current inventive process can be employed for the said reduction process using even untreated platinum on carbon catalyst, with high selectivity.

The process of the present invention does not use any additive, which is basic in nature.

EXAMPLE 1.

Catalytic hydrogen transfer using untreated 5% platinum on carbon with 5mol ammonium formate per mole of NE in butanol in open system: NE (25g, 78.5mmol), ammonium formate (25g, 396.5mmol), n-butanol (lOOgm) and 5% Pt/C catalyst (Monarch 203) (0.1 g, 0.4% w/w based on NE) were charged in a four necked round bottom flask equipped with thermometer pocket, reflux condensor and mechanical stirrer. The reaction mixture was heated to 85°C in a thermostated oil bath and maintained at that temperature and monitored by GC. The GC analysis surprisingly indicated only 7.77% conversion of NE even after 10 hours using monarch 203.

EXAMPLE 2.

Catalytic hydrogen transfer using sulfided 3% platinum on carbon with 5mol ammonium formate per mole of NE in butanol in open system: NE (25g,

78.5mmol), ammonium formate (25g, 396.5mmol), n-butanol (lOOgm) and 3% Pt/C catalyst (PMC 2020) (0.125g, 0.5% w/w based on NE) were charged in a four necked round bottom flask equipped with thermometer pocket, reflux condensor and mechanical stirrer. The reaction mixture was heated to 85°C in a thermostated oil bath and maintained at that temperature and monitored_^ by GC.

The conversion of NE reached 99.46% in 4 hours. However the hydrogenation also gave ether cleavage impurities as exemplified by the presence of 3.77% DCP in the^" final product. As a result, the selectivity towards the desired product, TADE, was only 90.03%.

EXAMPLE 3.

Catalytic hydrogen transfer using sulfided 3% platinum on carbon with 3mol ammonium formate per mole of NE in butanol in closed autoclave: NE (20Og, 628mmol), ammonium formate (12Og, 1.90mol), 3% Pt/C (PMC 2020) (0.8g, 0.4% w/w based on NE) and butanol (50g) were charged to the autoclave. The autoclave was closed, agitation was started and the air inside the autoclave was displaced by purging three times with nitrogen. Finally, the nitrogen pressure was released below 0.5kg/cm² and heating was started. The reaction was continued at autogenous pressure at 85°C for 3 hours. Finally the reaction mass was cooled to room temperature and the autoclave was purged with nitrogen. Unconverted NE could be seen as solids in the reaction mass. Therefore, the reaction mass was filtered using toluene and the organic layer was separated from the aqueous layer. The organic layer was distilled to remove the solvents and the product mixture was analysed by GC. The conversion of NE and percent selectivity towards TADE obtained was surprisingly found to be only 29.52% and 97.53%, respectively. The reaction also resulted in the formation of high levels of DCP, which was about 1.42%.

EXAMPLE 4.

Catalytic hydrogen transfer using sulfided 3% platinum on carbon with 3mol ammonium formate per mole of NE in water in closed autoclave: NE (20Og, 628mmol), ammonium formate (12Og, 1.90mol), 3% Pt/C (PMC 2020) (0.8g, 0.4% w/w based on NE) and water (20Og) were charged to the autoclave. The autoclave was closed, agitation was started and the air inside the autoclave was displaced Φy purging three times with nitrogen. Finally, the nitrogen pressure was released below 0.5kg/cm² and heating was stajted. The reaction was continued at autogenous pressure at 85°C for 3 hours. Finally the reaction mass was cooled to room temperature and the autoclave was purged with nitrogen. Unconverted NE could be seen as solids in the reaction mass. Therefore, the reaction mass was filtered using toluene and the organic layer was separated from the aqueous layer. The organic layer was distilled to remove the solvents and the product mixture was analysed by GC. The conversion of NE was found to be low even in this case (35.59%) and percent selectivity towards TADE obtained was found to be 98.93%. The formation of DCP was found to be 0.03% in the reaction mass and the dehalogenation amounted to 0.34%. EXAMPLE 5.

Catalytic hydrogen transfer using untreated 5% platinum on carbon with 0.5πiol ammonium formate per mole of NE in Butanol in closed autoclave: NE

(20Og, 628mmol), ammonium formate (2Og, 317mmol), 3% Pt/C (Monarch 203) (0.8g, 0.4% w/w based on NE) and butanol (50g) were charged to the autoclave. The autoclave was closed, agitation ^"was started and the air inside the autoclave was displaced by purging three times with nitrogen. Finally, the nitrogen pressure was released below 0.5kg/cm² and heating was started. The reaction was continued at autogenous pressure at 85°C for 3 hours. Finally the reaction mass was cooled to room temperature and the autoclave was purged with nitrogen. Unconverted NE could be seen as solids in the reaction mass. Therefore, the reaction mass was filtered using toluene and the organic layer was separated from the aqueous layer. The organic layer was distilled to remove the solvents and the product mixture was analysed by GC.

The conversion of NE and percent selectivity towards TADE obtained was found to be 18.70% and 90.93%, respectively. The formation of DCP was found to be 6.41% in the reaction mass and the dehalogenation amounted to 0.47%. It was surprisingly found in this case that the conversion of NE was stoichiometric with respect to the ammonium foπnate used. This was unexpected in view of example 1 and 4.

EXAMPLE 6.

Catalytic hydrogenation of NE using sulfided 3% platinum on carbon in but anolunder external hydrogen pressure: NE (20Og, 628mmol), 3% Pt/C (PMC 2020) (0.8g, 0.4% w/w based on NE) and butanol (50g) were charged to the autoclave. The autoclave was closed, agitation was started and the air inside the autoclave was displaced by purging three times with nitrogen followed by three times with hydrogen. Finally, the autoclave was pressurized to 25kG/cm2 and heating was started. The pressure was adjusted to 30kg/cm2 after hydrogen up-take started

I l indicated by the pressure drop. The reaction was continued at 30kg/cm2 pressure at 85°C till the hydrogen up-take ceased, which took 1 hour. Finally, the reaction mass was cooled to room temperature, hydrogen vented and the autoclave was purged with nitrogen. The reaction mass was filtered and the organic layer was separated from the^' aqueous layer. The organic layer was distilled to remove the solvent and the product mixture was analysed by GC.

The conversion of NE and percent selectivity towards TADE obtained was found to be 99.91% and 98.95%, respectively. The formation of DCP was found to be 0.17% in the reaction mass and the dehalogenation amounted to 0.58%.

EXAMPLE 7.

Catalytic hydrogenation of NE using untreated 5% platinum on carbon in butanol under external hydrogen pressure: Procedure of example 6 was repeated with Monarch 203 catalyst instead of PMC 2020. The total reaction time was 2 hours. The conversion of NE and percent selectivity towards TADE obtained was found to be 99.89% and 95.01%, respectively. The formation of DCP was found to be 1.41% in the reaction mass and the dehalpgenation amounted to 2.09%.

EXAMPLE 8.

Catalytic hydrogenation of NE using untreated 5% platinum on carbon in water under external hydrogen pressure: NE (20Og, 628mmol), 3% Pt/C (PMC Monarch 203) (0.8g, 0.4% w/w based on NE) and water (20Og) were charged to the autoclave. The autoclave was closed, agitation was started and the air inside the autoclave was displaced by purging three times with nitrogen followed by three times with hydrogen. Finally, the autoclave was pressurized to 25kG/cm2 and heating was started. The pressure was adjusted to 30kg/cm2 after hydrogen up-take started indicated by the pressure drop. The reaction was continued at 30kg/cm2 pressure at 85°C till the hydrogen up-take ce'ased, which took 2 hour. Finally, the reaction mass was cooled to room temperature, hydrogen vented and the autoclave was purged with nitrogen. The reaction mass was filtered and the organic layer was separated from the aqueous layer. The organic layer distilled to remove the solvent and the product mixture was analysed by GC.

The conversion of NE and percent selectivity towards TADE obtained was found to be 99.88% and 91.82%, respectively. The formation of DCP was found to be 2.88% in the reaction mass and the dehalpgenation amounted to 3.78%.

EXAMPLE 9.

Transfer hydrogenation of NE with O.Smol ammonium formate using untreated 5% platinum on carbon in butanol, followed by hydrogenation with external hydrogenation: NE (20Og, 628mmol), ammonium formate (2Og, 317mmol), 3% Pt/C (Monarch 203) (0.8g, 0.4% vv/w based on NE) and butanol (5Og) were charged to the autoclave. The autoclave was closed, agitation was started and the air inside the autoclave was displaced by purging three times with nitrogen. Finally, the nitrogen pressure was released below 0.5kg/cm² and heating was started. The reaction was continued at autogenous pressure at 85⁰C for 1 hour. After 1 hour, hydrogen was introduced in the autoclave upto"30kg/cm2 and the hydrogenation was continued at 30kg/cm2 pressure at 85°C till the hydrogen up-take ceased. The total reaction time was 3 hours. Finally, the reaction mass was cooled to room temperature, hydrogen vented and the autoclave was purged with nitrogen. The reaction mass was filtered and the organic layer was separated from the aqueous layer. The organic layer distilled to remove the solvent and the product mixture was analysed by GC. The conversion of NE and percent selectivity towards TADE obtained was found to be 99.76% and 99.67%, respectively. The formation of DCP was found to be 0.1 1% in the reaction mass and the dehalogenation amounted to 0.04%. Thus, there was substantial decrease in the formation of both, the dehalogenation and ether cleavage impurities by combining the catalytic transfer hydrogenation followed by hydrogenation under external hydrogen pressure.

EXAMPLE 10.

Transfer hydrogenation of NE with 0.5mol ammonium formate using untreated 5% platinum on carbon in water, followed by hydrogenation with external hydrogenation: NE (20Og, 628mmol), ammonium formate (2Og, 317mmol), 3% Pt/C (Monarch 203) (0.8g, 0.4% w/w based on NE) and water (20Og) were charged to the autoclave. The autoclave was closed, agitation was started and the air inside the autoclave was displaced by purging three times with nitrogen. Finally, the nitrogen pressure was released below 0.5kg/cm² and heating was started. The reaction was continued at autogenous pressure at 85°C for 1 hour. After 1 hour, hydrogen was introduced in the autoclave upto 30kg/cm2 and the hydrogenation was continue^'d at 30kg/cm2 pressure at 85°C till the hydrogen up-take ceased. The total reaction time was 4 hours. Finally, the reaction mass was cooled to room temperature, hydrogen vented and the autoclave was purged with nitrogen. The reaction mass was filtered and the organic layer was separated from the aqueous layer. The organic layer distilled to remove the solvent and the product mixture was analysed by GC. The conversion of NE and percent selectivity towards TADE obtained was found to be 99.96% and 98.40%, respectively. The formation of DCP was found to be 0.03% in the reaction mass and the dehalogenation amounted to 1.35%.

EXAMPLE 11.

Transfer hydrogenation of NE with lmol ammonium formate using untreated 5% platinum on carbon in butanol, followed by hydrogenation with external hydrogenation: the procedure in example 9 was repeated with the only difference that 4Og (634mmol) ammonium formate was used and the reaction temperature was maintained at 80°C. The total reaction time was 2.5 hours.

The conversion of NE and percent selectivity towards TADE obtained was found to be 99.33% and 99.77%, respectively. The formation of DCP was found to be 0.07% in the reaction mass and the dehalogenation amounted to 0.04%.

EXAMPLE 12.

Transfer hydrogenation of NE with lmol ammonium formate using untreated 5% platinum on carbon in water, followed by hydrogenation with external hydrogenation: the procedure in example 10 was repeated with the only difference that 4Og (634mmol) ammonium formate was used. The total reaction time was 4 hours.

The conversion of NE and percent selectivity towards TADE obtained was found to be 99.96% and 98.49%, respectively. The formation of DCP was found to be 0.01% in the reaction mass and the dehalogenation amounted to 1.21%.

EXAMPLE 13.

Transfer hydrogenation of NE with O.lmol ammonium formate using untreated 5% platinum on carbon in butanol, followed by hydrogenation with external hydrogenation: the procedure in example 9 was repeated with the only difference that 4g (63.4mmol) ammonium formate was used and the hydrogen was introduced after 30min. The total reaction time was 3 hours 15 minutes.

The conversion of NE and percent selectivity towards TADE obtained was found to be 99.93% and 99.68%, respectively. The formation of DCP was found to be 0.13% in the reaction mass and the dehalogenation amounted to 0.06%. EXAMPLE 14.

Transfer hydrogenation of NE with O.lmol ammonium formate using untreated 5% platinum on carbon in water, followed by hydrogenation with external hydrogenation: the procedure in example 10 was repeated with the only difference that 4g (63.4mmol) ammonium formate was used and the hydrogen was introduced after 30min. The total reaction time was 4 hours.

The conversion of NE and percent selectivity towards TADE obtained was found to be 99.87% and 97.03%, respectively. The formation of DCP was found to be 0.39% in the reaction mass and the dehalogenation amounted to 2.21%.

' EXAMPLE 15.

Transfer hydrogenation of NE with O.lmol ammonium formate using sulfided 3% platinum on carbon in butanol, followed by hydrogenation with external hydrogenation: the procedure in example 13 was repeated using PMC 2020 in stead of Monarch 203. The total reaction time was 2 hours.

The conversion of NE and percent selectivity towards TADE obtained was found to be 99.12% and 99.55%, respectively. The formation of DCP was found to be 0.15% in the reaction mass and the dehalogenation amounted to 0.06%.

EXAMPLE 16.

Transfer hydrogenation of NE with O.lmol ammonium formate using sulfided 3% platinum on carbon in butanol, followed by hydrogenation with external hydrogenation: the procedure in example 15 was repeated at 120°C. The total reaction time was 1 hour.

The conversion of NE and percent selectivity towards TADE obtained was found to be 99.71% and 99.59%, respectively. The formation of DCP was found to be 0.18% in the reaction mass and the dehalogenation amounted to 0.04%. . EXAMPLE 17.

Transfer hydrogenation of NE with O.lmol ammonium formate using sulfided 3% platinum on carbon in water, followed by hydrogenation with external hydrogenation: the procedure in example 14 was repeated with the only difference that PMC 2020 was used instead of Monarch 203. The total reaction time was 4 hours 30 minutes.

The conversion of NE and percent selectivity towards TADE obtained was found to be 99.72% and 99.6%, respectively. The formation of DCP was found to be 0.3% in the reaction mass and the dehalogenation amounted to 0.27%.

EXAMPLE 18.

«

Transfer hydrogenation of NE with O.lmol ammonium formate using sulfided 3% platinum on carbon in water, followed by hydrogenation with external hydrogenation: the procedure in example 17 was repeatedat 120⁰C. The total reaction time was 2 hours 20minutes.

The conversion of NE and percent selectivity towards TADE obtained was found to be 99.78% and 99.51%, respectively. The formation of DCP was found to be 0.02% in the reaction mass and the dehalogenation amounted to 0.4%.

EXAMPLE 19.

Catalytic hydrogen transfer using sulfided 3% platinum on carbon with 3mol ammonium formate per mole of NE in butanol in closed autoclave: NE (50g, 157mmol), ammonium formate (3Og, 476mol), 3% Pt/C (PMC 2020) (0.0.2g, 0.4% w/w based on NE) and butanol (20Og) were charged to the autoclave. The autoclave was closed, agitation was started and the air inside the autoclave was displaced by purging three times with nitrogen. Finally, the nitrogen pressure was released below 0.5kg/cm² and heating was started. The reaction was continued at autogenous pressure at 85°C for 5 hours. Finally the reaction mass was cooled to room temperature and the autoclave was purged with nitrogen. Unconverted NE could be seen as solids in the reaction mass. Therefore, he reaction mass was filtered using toluene and the organic layer was separated from the aqueous layer. The organic layer distilled to remove the solvents and the product mixture was analysed by GC. The conversion of NE and percent selectivity towards TADE obtained was found to be 53.70% and 97.20%, respectively. The formation of DCP was found to be 1.36% in the reaction mass and the dehalogenation amounted to 0.46%.

EXAMPLE 20.

Catalytic hydrogen transfer using untreated 5% platinum on carbon with 3mol ammonium formate per mole of NE in butanol in closed autoclave: Example 19 was repeated with the only difference that Monarch 203 was used instead of PMC 2020.

The conversion of NE and percent selectivity towards TADE obtained was found to be 45.73% and 97.96%, respectively. The formation of DCP was found to be 0.55% in the reaction mass and the dehalogenation amounted to 0.43%.

TABLE - 1

^♦Catalyst loading 0.5%

EXAMPLE 21.

Procedure for the preparation of nitroether [5-chloro-2-(2,4- dichlorophenoxy)nitrobenzene]: To molten 2,4,dichlorophenol in a reactor, potassium hydroxide flakes are added in lots taking care that the temperature does not increase above 1 10⁰C. First lot of water is then added and the resulting solution is maintained at 1 10⁰C for 30 minutes. 2,5 dichloronitrobenzene is then added in single installment and the reaction mass temperature is increased to 150°C, during which, water is distilled out. The reaction is continued for a period of 3-4 hours, during which, the 2,5 dichloronitrobenzene content in the reaction mass reaches below 0.1%. After the reaction is complete, the reaction mass is cooled to 130⁰C and second lot of water is added which is followed by 10% sodium hydroxide solution and the third' lot of water. The heterogeneous mass thus obtained is then cooled to room temperature and filtered to separate 5-chloro-2-(2,4-dichlorophenoxy)nitrobenzene from aqueous salt solution. The solid is then washed with water till the washings are free from sodium, potassium or chldride ions. The yield of 5-chloro-2-(2.4- dichlorophenoxy)nitrobenzene thus obtained is 95% based on the 2,5 dichloronitrobenzene charged and purity was 99.54%.

Although the invention has been described with reference to certain preferred embodiments, the invention is not meant to be limited to those preferred embodiments. Alterations to the preferred embodiments described are possible without departing from the spirit of the invention. However, the process described above is intended to be illustrative only, and the novel characteristics of the invention may be incorporated in other forms without departing from the scope of the invention.

Claims

CLAIMS:

1. A process for the preparation of 5-chloro-2-(2,4-dichlorophenoxy)aniline, by carrying out reduction of an aromatic halo nitro compound, such as 5-chloro-2-(2,4- dichlorophenoxy)nitrobenzene and the like, using a combination of hydrogenations, such as catalytic transfer hydrogenation , followed by gaseous hydrogenation, using an effective amount of an appropriate catalytic transfer hydrogenating agent, such as ammonium formate and the like, and an effective amount of an appropriate catalyst, such as platinum on carbon and the like.

2. A process, as claimed in claim 1, wherein said catalytic transfer hydrogenation followed by gaseous hydrogenation, comprises the steps of: a. charging to an autoclave a predetermined amount of a nitroether, such as 5-chloro-2-(2,4-dichlorophenoxy)nitrobenzene, the effective amount of said ammonium formate being from 0.01 to 2 mol / mol of said nitroether, said appropriate catalyst being any one catalyst selected from the group consisting of an untreated platinum on carbon, a sulphited platinum on carbon and a sulphided platinum on carbon, wherein said effective amount of said catalyst is from 0.01 % to 2 % w/w of said nitroether, with said catalyst having the amount of platinum content 0.1 % to 5% w/w of said catalyst, and an effective amount of any one solvent selected from the group consisting of alcohol and water, wherein ratio of said nitroether to said solvent is from 1 :0.1 to 1 :0.33 w/w; b. completing the reaction of said catalytic transfer hydrogenation at autogenous pressure at a temperature from 50°C to 150⁰C, for period of 0.5 hour 15 hours; c. carrying out, after said period of reaction of step b is completed, the reaction of said gaseous hydrogenation, at a pressure between 1 to 50 kg/cm", by introducing in said autoclave external hydrogen gas, till hydrogen up - take ceases; d. isolating said 5-chloro-2-(2,4-dichlorophenoxy)aniline.

3. A process, as claimed in claim 1,- wherein said catalyst is said sulphided platinum on carbon.

4. A process, as claimed irj claim 1, wherein said catalyst is said untreated platinum on carbon.

5. A process, as claimed in claim 1 , wherein said catalyst is said sulphited platinum in carbon.

6. A process for the preparation of 5-chloro-2-(2,4-dichlorophenoxy)aniline substantially as herein described and illustrated in examples.