Indian Patents. 268523:A PROCESS FOR PREPARATION OF DIBENZYLAMINE (DBA) & TRIBENZYLAMINE (TBA)

Title of Invention	A PROCESS FOR PREPARATION OF DIBENZYLAMINE (DBA) & TRIBENZYLAMINE (TBA)
Abstract	The invention provides an improve process for the amination of alcohols by reacting benzylamine and benzyl alcohol in presence of an additive, base and Cu/AI hydrotalcite. Dibenzylamine so obtained is further reacted with benzyl alcohol in the presence of potassium carbonate and Cu/AI hydrotalcite, at elevated temperature to obtain Tribenzylamine.

Full Text	Background of the invention The present invention relates to an improved process for the preparation of Di/Tribenzylamine. More particularly, the present invention relates to an improved process for the amination of benzylalcohol in presence of base, hydrotalcite-like compound, as catalysts with an additive. The role of additive is to prevent the formation of benzyl ether, a by-product and facilitates to the formation of Dibenzylamine (DBA) selectively. The Dibenzylamine (DBA) is further subjected to benzylation with benzyl alcohol in the presence of a base and hydrotalcite catalyst for the preparation of Tribenzylamine (TBA). Background of the invention Dibenzylamine and tribenzylamine are important industrial organic compounds. Dibenzylamine is a secondary amine, which finds the use in the production of synthetic pencillins and in the vulcanization of rubber. Dibenzylamine acts as a novel blocker of the voltage -dependent K+ current in myocardial mouse cells. It also exhibits anti-convulasant actions in-vivo. DBA derivatives are used for elevating HDL cholesterol level. DBA is used as a starting compound for manufacturing vulcanization accelerator, tetrabenzylthiuram disulfide, which remains in the rubber as non-carcinogenic nitrosamines on decomposition. DBA occupies a special position in the manufacture of tire treads with increased tread life; tire treads provides substantial wear reduction. In addition to the wear resistance (particularly weathering and aging), the presence of DBA derivatives enhances the vulcanization properties such as, resistance, elongation at failure, tear propagation resistance, and particularly the property of elasticity when heat built-up. Therefore the use of this inventive intermediate cross-linking reagent is therefore particularly effective. Dialkyl and dibenzyl amines are used in the modification of polyvinyl chloride resin composition. Thus after improving the PVC resin composition, it shows excellent corrosion resistance, weather ability and exhibits excellent characteristic as a resin coating. Numerous procedures for the production of the benzylamine and dibenzylamine are described in the literature and include: the reductive amination of benzaldehyde by hydrogen and ammonia in the presence of a catalyst; the catalytic reduction of benzonitrile, benzylhydroxylamine; the condensation of benzaldehyde and benzylamine followed by catalytic hydrogenation of the intermediate Schiffs base. Generally, benzylamine and dibenzylamine are obtained in poor yields and each amine must be carefully separated from mixtures containing primary, secondary or tertiary amines, imines, aldehydes, alcohols or amides to obtain a high purity product. For example, it is known that nitriles can be catalytically reduced to the primary amine through the intermediate imine by a wide variety of catalysts. The intermediate imine further reacts with the primary amine to produce a Schiffs base with the liberation of ammonia, In the presence of a catalyst and hydrogen, the Schiffs base is further reduced to the secondary amine, in a batch process, the above reactions compete for reactants and a variety of reaction products are formed. Many optimizations have been exercised to minimize the extent of these reactions including reduction in different solvent systems and catalyst selection. Reference may be made to patents, such as US 5430187 (1995); WO-A-931304, US 5616804 (1997) wherein dibenzylamine is prepared by reacting benzaldehyde and ammonia in the presence of hydrogen and a hydrogenation catalyst in an inert organic solvent. Although high conversion and selectivity is attained in the transformation of benzaldehyde to dibenzylamine, the drawback in the above-described processes is the formation of number of by-products, monobenzylamine, tribenzylamine and benzyl alcohol, which require efficient separation to obtain dibenzylamine. Reference may be made to a patent, such as U.S. Pat. No. 4163025 (1979) wherein high conversion is attained in the transformation of benzonitrile to benzylamine and dibenzylamine by passing benzonitrile and hydrogen counter-current through catalyst bed under suitable temperature and pressure conditions. The drawback in the above-described process is the formation of number of by-products which require efficient separation to obtain selectively primary amine and secondary amine. Reference may be made to patents, such as U.S. Pat. No. 3,117,162(1964) and Annals N. Y. Acad. Sci. 214:100-109 (1973); U.S. Pat. No 3923891(1975) to a batch process for the reduction of benzonitrile in dilute hydrocarbon and alcohol solvent by hydrogenation over rhodium, palladium, platinum, or ruthenium catalysts (all are 5 wt.% on carbon). The drawback in the above-described process is poor selectivity in formation of benzylamine and dibenzylamine (63% and 34% respectively). The formation of dibenzylamine is favored in this process by the selective use of rhodium on carbon or platinum on carbon catalysts, but in all other cases it is obtained as a mixture containing large amounts of the primary amine. In addition, long reaction times, 2 to 21 hours, are required to reduce the benzonitrile. As a result, these prior art techniques are time consuming, requires efficient separation and costly. Catalytic processes for the amination of aliphatic alcohols to form amines are known. One of the most widely practiced routes is the reaction of ammonia with alcohols at relatively high operating temperatures (about 250 to 500.degree. C.) and low to moderate pressures (atmospheric to about 200 atm) in the presence of dehydration catalysts such as aluminum oxide, silica, aluminum phosphate, or chromium oxide. Alkylation of ammonia with alcohols has also been carried out in the presence of hydrogen and hydrogenation catalyst such as copper, nickel, cobalt and platinum. Below are described representative publications illustrating catalysts used in the amination of alcohols to produce amines. Dibenzylamine is specifically manufactured by hydrogenation of benzonitrile with Pt catalysts (U.S. Pat. No.3,923,891, 1975). Other reports suggest synthesis of dibenzylamine starting with benzylamine (Synthesis (1), 70 (1979); J. Organomet. Chem. 208 (2), 249 (1981); Chem. Lett. (6), 889 (1984); Ind. J. Technol. 23 (7), 266 (1985). In addition to the above processes, dibenzylamine forms as a by-product in the industrial synthesis of benzylamine from benzaldehyde by the reaction with ammonia and catalytic hydrogenation with Raney nickel (Ullmanns Encyclopadie der technischen Chemie, 4 th edition.Vol. 8, 440). Dibenzylamine is therefore formed via the monobenzylamine and N-benzylidenimine and can be separated from the intermediate reaction mixture by fractionation. The reaction mixture can also contain tribenzylamine as a secondary product, and benzyl alcohol and toluene as reduction products of benzaldehyde. Objectives of the invention The main object of the present invention is to provide an improved process for the synthesis of di/tribenzylamine. Another object of the present invention is to utilize non-corrosive and low cost heterogenous catalyst such as hydrotalcite-like compound, as catalyst for the synthesis of di/tribenzylamine. Yet another object of the present invention is to utilize the copper aluminum hydrotalcite (Cu-AI-HT) with a Cu/AI atomic ratio of 3, 2.5 and 2 (CuAl 3.0-HT; CuAl 2.5-HT; CuAl 2.0-HT). Yet another object of the present invention is the use of an additive for selective formation of dibenzylamine. Yet another object of the present invention is the use of anhydrous base with particle size ranges from 20-50 u and vacuum dried for 8 h at 100°C. Yet another object of the present invention is the use of reusable catalyst. Summary of invention Accordingly, the present invention provides an improved process for the preparation of di/tribenzylamine, which comprises coupling benzyl alcohol and benzylamine in the presence of anhydrous base, an additive and Cu/AI-HT hydrotalcite , as catalyst, optionally in water immiscible organic solvent, at a temperature in the range of 120-160°C, under vigorous stirring, for a period of 7-16 hrs, followed by the separation of dibenzylamine from the crude mixture and further subjecting the resultant dibenzylamine to benzylation with benzyl alcohol in the presence of Cu/AI-HT hydrotalcite , as catalyst and base to obtain the desired product of tribenzylamine. In an embodiment of the present invnetion the ratio of alcohol to amine is in the range of 1:1-1:2.5, preferably 1:2. In yet another embodiment the base used is alkali metal carbonate. In yet another embodiment the base used is potassium carbonate. In yet another embodiment the concentration of base used is in the range of 0.01-0.02M, preferably 0.015M. In yet another embodiment the concentration of additive used is in the range of 0.003-0.005M, preferably 0.004 moles. In yet another embodiment the additive used is hydroquinone. In yet another embodiment the Cu to Al ratio used in heterogeneous catalyst, Cu/AI-HT, is in the range of 2:1-3:1, preferably 2.5:1. In yet another embodiment the concentration of the catalyst used is in the range of 6-10 weight % of benzyl alcohol. In yet another embodiment the organic solvent used is selected from toluene and xylene. In still another embodiment the catalyst used is recyclable. In still another embodiment the particle size of the catalyst used is in the range of 30-40um. Detailed description of the invention The present invention describes a batch process, which comprises a novel approach to the desired synthesis of dibenzylamine from benzylamine and benzyl alcohol in presence of base, hydrotalcite-like compounds as catalysts and an additive. In this invention aliphatic and aromatic alcohols, R'-OH react with aliphatic amines, R"-NH2 in presence of catalytic amount of hydrotalcite like compound as a catalyst to afford secondary amine in excellent yields and selectivities, where R' is selected from aryl alkyl and open chain alkyl groups consisting of benzyl, 4-methoxy benzyl, 2,4-methoxy benzyl, 2-amino benzyl, 2-chloro benzyl, in open chain aliphatic alcohols, alkyl group is ranging from C7 to C12, etc., R" is selected from aliphatic, benzyl amines and substituted benzyl amines, 4-methyl benzyl, 2-methoxy benzyl, etc. The base is selected from mainly carbonate, hydroxide and alkoxide of alkali metals, and heterogeneous catalyst, Cu-AI-hydrotalcite where the ratio of Cu:AI varies from 3:1, 2.5:1, 2:1, etc., additives are selected from the hydroxy-substituted aromatic compounds, preferably dihydroxy compounds. The reaction is carried out in the presence of 6-10 weight % of catalyst at a temperature ranging from 120 to 160 degree C for 7-16 h. with continuous stirring using benzyl amine as self-solvent or toluene or xylene under air atmosphere. The process of the invention overcomes the disadvantage of the prior art enumerated above since inter alia, the work up is simple, and the catalyst is recoverable and recyclable with consistent activity for several cycles. The synthesis of secondary amines, particularly DBA at high temperature and the products can be used further for the benzylation to prepare tertiary amines, tribenzylamine without adding the additive in excellent yield and selectivities. The use of cheap inorganic base, cheap catalyst and different aliphatic/ aromatic alcohols as well as benzyl amines provides secondary amines as products in good to excellent yields in a single step. Generally the ratio of Cu to Al in the catalyst is 2.5:1 and the quantity used in the reactions is 6-10 weight % with respect to benzyl alcohol. The catalyst used in the reactions can be recovered by simple filtration and reused for number of cycles with consistent activity. The novelty of present invention lies in the use of cheap heterogeneous catalyst for the first time for the amination of benzyl alcohol. The present invention provides a process for the production of dibenzylamine, which includes reacting aromatic aliphatic amines with aromatic/ aliphatic alcohols in the presence of a base, additive and catalyst, wherein the base is alkali metal hydroxide/ carbonate/ alkoxide. The additive used in this coupling reaction is nitrogen based aromatic heterocycle. The solid base catalyst of general formula, [M(ll)1-x M(lll)x (OH)2]n- An-x/n-yH20, where M(ll) and M(lll) are divalent and trivalent cations such as Cu2+, Mg2+ and Al3+ respectively, An- is the interlayer anion such as CI", N03-, C032- etc., and x = 0.1-0.33. The goal of the present invention is to provide a simple method in which, in particular, a higher selectivity for dibenzylamine, using a cheaper heterogeneous catalyst in a single step without using a pressure reactor. The reaction is preferably carried out in the presence of catalyst, base and an additive at a temperature ranging from 120-160 degree C, equipped with Dean-Stark apparatus to remove the water from the reaction mixture. The process comprises the unique activation of alcohol to facilitate simultaneous C-N bond formation with amine in presence of base and additive in a single pot. Post benzylation of the DBA to TBA is not occurred in the same reaction. The process for the TBA comprises benzylation of DBA to TBA with fresh stoichiometric amount of benzyl alcohol in presence of catalyst and a base only. Incidentally this forms the first report of formation of DBA and TBA obtained in higher yields in single pot using a cheap heterogeneous catalyst. The consistent activity obtained for several cycle makes the process economical and possible for the commercial realization. The process of the invention comprises the activation of -CH2-OH bond to facilitate simultaneous attack by nucleophile to obtain secondary amine (DBA) in excellent yield in a single pot. The catalytic cycle of coupling reaction of benzyl amine and benzyl alcohol involves first generation of bezylamine anion in presence of base and basic catalyst at high temperature. Thus the base abstracts the proton from the benzylamine under basic catalytic condition producing bezylamine anion act as a nucleophile. Thus the nucleophilic attacked by benzylamine anion at benzylic -CH2+ of benzyl alcohol further proceeded to coupling reaction to produce dibenzylamine. Further, the invention ascertains the optimum use of the additive, which requires achieving the selective formation of benzylamine and suppressed the formation byproduct (dibenzyl ether) with maximum conversion of benzyl alcohol. Thus, the catalyst can be recovered by simple filtration and reuse for the next cycle. Thus the invented strategy offers an environmentally acceptable and extremely convenient heterogeneous catalytic process for the synthesis dibenzylamine from the coupling reaction of benzyl alcohol and benzyl amine in batch processes. A] Dibenzylamine (DBA) Preparation: (Formula Removed) B] Tribenzylamine (TBA) Preparation (Formula Removed) The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention EXAMPLE 1 Catalyst preparation A: Catalyst A: Cu-AI hydrotalcite (3:1) Cu: Al hydrotalcite (3:1) is prepared as follows: About 200 ml of deionised water was taken into a 1 litre four necked round bottomed flask and stirred at 25°C with a overhead mechanical stirrer. A mixture of solution of Cu(N03)2.3H20 (32.92g, 0.1404 moles) and AI(N03)3.9H20 (16.88g, 0.045 moles) in deionised water (140 ml) and the aqueous solutions of NaOH (13.124g, 0.328 moles) and Na2C03 (8.9252g, 0.0842 moles) in deionised water were added simultaneously into the round bottom flask. The pH of the reaction mixture was maintained constantly (7-8) by continuous addition of the base solution. The resulting slurry was aged at 70°C for two hours. The solid product was isolated by filtration, washed thoroughly with deionised water (to make base free) and dried under 70°C for 15h. B: Catalyst B: Cu-AI hydrotalcite (2.5 : 1) Cu: Al hydrotalcite (2.5:1) is prepared as follows : About 200 ml of deionised water was taken into a 1 litre four necked round bottomed flask and stirred at 25°C with a overhead mechanical stirrer. A mixture of solution of Cu(N03)2.3H20 (90.57g, 0.375 moles) and AI(N03)3.9H20 (56.27g, 0.0.15 moles) in deionised water (140 ml) and the aqueous solutions of NaOH (42.97g, 2.09 moles) and Na2C03 (33.12g, 0.312 moles) in deionised water were added simultaneously into the round bottom flask. The pH of the reaction mixture was maintained constantly (7-8) by continuous addition of the base solution. The resulting slurry was aged at 70°C for two hours. The solid product was isolated by filtration, washed thoroughly with deionised water (to make base free) and dried under 70°C for 15h. C: Catalyst C: Cu-AI Hydrotalcite ( 2: 1) Cu: Al hydrotalcite (3:1) is prepared as follows: About 200 ml of deionised water was taken into a 1 litre four necked round bottomed flask and stirred at 25°C with a overhead mechanical stirrer. A mixture of solution of Cu(N03)2.3H20 (24.16g, 0.1 mole) and AI(N03)3.9H20 (18.76g, 0.0499 moles) in deionised water (140 ml) and the aqueous solutions of NaOH (17.5g, 0.44moles) and Na2C03 (11.91g, 0.112moles) in deionised water were added simultaneously into the round bottomed flask. The pH of the reaction mixture was maintained constantly (7-8) by continuous addition of the base solution. The resulting slurry was aged at 70°C for two hours. The solid product was isolated by filtration, washed thoroughly with deionised water (to make base free) and dried under 70°C for 15h. EXAMPLE 2: Preparation of dibenzylamine catalysed by Cu-hydrotalcite (2.5:1) 5.045g (0.046 moles) benzyl alcohol, 2.04g(0.015 moles) potassium carbonate, and 7.85g (0.074 moles) of benzylamine, 0.3g (6 wt% w. r. t. benzyl alcohol) Cu-HT catalyst, 0.050g (0.00046 moles) of hydroquinone (additive) and 8.56g (0.08 moles) of xylene were initially introduced, while stirring, into a two-necked round-bottomed flask with a teflon magnetic bead, fitted with a Dean-Stark apparatus filled with 2.56g xylene. Red-brown suspension formed was heated up to the reflux temperature (with vigorous stirring). The temperature of the reaction mixture was gradually raised to 120-160°C over a period of 1h. Thereafter, only a slight evolution of water initially occurred, but this increases in the course of the reaction and then remained constant at a low level. Unfiltered samples were collected after every 1 h and the samples were analyzed by means of GC. After 7 h.the reaction was stopped and the crude reaction mixture was subjected to GC analysis. A residual benzylalcohol value of (2.2%), a DBA content of 90.1 %, a 1.7%, of benzaldehyde resulted here. The total conversion based on benzylalcohol (0.0146 mole %) is 97.8% and the yield of DBA is 92.12%. (Note: Approx. 6% unaccounted materials are observed as tar and unidentified compounds when DBA is distilled out.) The following table depicts the various GC selectivities of different products obtained using selected catalysts. It can be observed from the below table, the best selectivity obtained using Cu-HT (2.5:1) as a catalyst under identical reaction condition. Cuh I DBA I DBE I Benzaldehy I Benzyl I Tribenzyl (Table Removed) - * Un-accounted (unidentified) materials are not eluted in GC column EXAMPLE 3: Preparation of dibenzylamine catalysed by Cu-hydrotalcite (2.5:1) 5.045g (0.046 moles) benzylalcohol, (0.015 moles) inorganic base, and 7.85g (0.074 moles) of benzylamine, 0.3g (6 wt% w. r. t benzyl alcohol) Cu-HT catalyst, 0.050g (0.004 moles) of additive (hydroquinone) and 8.56g (0.08 moles) of xylene were initially introduced, while stirring, into a two-necked round-bottomed flask with a teflon magnetic bead, fitted with a Dean-Stark apparatus filled with 2.56g xylene. Red-brown suspension formed was heated up to the reflux temperature (with vigorous stirring). The temperature of the reaction mixture was gradually raised to 120-160°C over a period of 1h. Thereafter, only a slight evolution of water initially occurred, but this increasees in the course of the reaction and then remained constant at a low level. Unfiltered samples were collected after every 1h and the samples were analysed by means of GC. After 7 h, the reaction was stopped and the crude reaction mixture was subjected to GC analysis. The following table depicts the various GC selectivities of different products obtained using selected bases. The best selectivity obtained using K2C03 as base under identical reaction conditions (entry 6). (Table Removed) EXAMPLE 4: Preparation of Tribenzylamine catalysed by Cu/AI-hydrotalcite (2.5:1) 5.0 g (0.046 moles) benzyl alcohol, 3.0 g (0.22 moles) potassium carbonate, and 10.7g (0.53 moles) of dibenzylamine and 0.5g (10wt% w. r. t benzylalcohol) Cu-HT catalyst were initially introduced, while stirring, into a two-necked round-bottomed flask with a teflon magnetic bead. Red-brown suspension formed was heated up to the reflux temperature (with vigorous stirring). The temperature of the reaction mixture was gradually raised to 120-160°C over a period of 1h. The temperature of the reaction mixture was therefore maintained at 160°C for nearly 5-7 hours after which the reaction was completed as observed through GC in which no benzyl alcohol was noticed in the reaction mixture after 5-7 hours. No residual benzylalcohol was observed, a TBA content of 99 % (w. r. t. benzyl alcohol), a DBA (unreacted) value of 0.048% resulted here. The total conversion based on benzylalcohol is 100% and selectivity of TBA is 99%, 13.06g, (0.0045 moles) (w. r. t. benzyl alcohol). No additive was required for the formation of TBA. In presence of additive, only 10-20 % formation of TBA was observed after 10-16 hours. The main advantages of the present invention are: 1. The present invention comprises a novel approach to the desired synthesis of DBA from the simple condensation reaction of benzylamine and benzyl alcohol in excellent yield without any operational difficulty experienced during the course of the reaction. 2. The solid base, hydrotalcite-like compounds as a catalyst used for amination of alcohol which is recyclable and reusable for at least next four consecutive cycles without loss of catalytic activity 3. The present process envisages optimal use of additive to ensure highest conversion and selectivity. 4. An eco-friendly and very simple synthetic protocol is developed using cheap and non-corrosive hydrotalcite like compound as catalysts. 5. The selectivity, yield and purity of DBA and TBA produced in this process are quite high. 6. The reaction conditions are relatively mild. 7. monitoring of the reaction and subsequent work-up procedures are easy. 8. Isolation of the product from the crude reaction mixture is straightforward due to negligible quantity of organic by-products, which are considerably less volatile. 9. The overall process is economical. We claim 1. An improved process for the preparation of di/tribenzylamine, which comprises coupling benzyl alcohol and benzylamine in the presence of a base, an additive and Cu/AI-HT hydrotalcite , as catalyst, optionally in water immiscible organic solvent, at a temperature in the range of 120-160°C, under vigorous stirring, for a period of 7-16 hrs, followed by the separation of dibenzylamine from the crude mixture and further subjecting the resultant dibenzylamine to benzylation with benzyl alcohol in the presence of Cu/AI-HT hydrotalcite , as catalyst and base to obtain the desired product of tribenzylamine. 2. An improved process as claimed in claim 1, wherein the ratio of alcohol to amine is in the range of 1:1-1:2.5, preferably 1:2. 3. An improved process as claimed in claims 1&2, wherein the base used is alkali metal carbonate. 4. An improved process as claimed in claims 1-3, wherein the base used is potassium carbonate. 5. An improved process as claimed in claims 1-4, wherein the concentration of base used is in the range of 0.01-0.02M, preferably 0.015M. 6. An improved process as claimed in claims 1-5, wherein the concentration of additive used is in the range of 0.003-0.005M, preferably 0.004 moles. 7. An improved process as claimed in claims 1-6, wherein the additive used is hydroquinone. 8. An improved process as claimed in claims 1-7, wherein the Cu to Al ratio used in heterogeneous catalyst, Cu/AI-HT, is in the range of 2:1-3:1, preferably 2.5:1. 9. An improved process as claimed in claims 1-8, wherein the concentration of the catalyst used is in the range of 6-10 weight % of benzyl alcohol. 10. A process as claimed in claims 1-9, wherein the organic solvent used is selected from toluene and xylene. 11. An improved process as claimed in claims 1-10, wherein the catalyst used is recyclable. 12. An improved process as claimed in claim 1 to 11 wherein there is absolutely no leaching of the metal content during the reaction as well as during the workup.

Full Text

Background of the invention
The present invention relates to an improved process for the preparation of Di/Tribenzylamine. More particularly, the present invention relates to an improved process for the amination of benzylalcohol in presence of base, hydrotalcite-like compound, as catalysts with an additive. The role of additive is to prevent the formation of benzyl ether, a by-product and facilitates to the formation of Dibenzylamine (DBA) selectively. The Dibenzylamine (DBA) is further subjected to benzylation with benzyl alcohol in the presence of a base and hydrotalcite catalyst for the preparation of Tribenzylamine (TBA).
Background of the invention
Dibenzylamine and tribenzylamine are important industrial organic compounds. Dibenzylamine is a secondary amine, which finds the use in the production of synthetic pencillins and in the vulcanization of rubber. Dibenzylamine acts as a novel blocker of the voltage -dependent K+ current in myocardial mouse cells. It also exhibits anti-convulasant actions in-vivo. DBA derivatives are used for elevating HDL cholesterol level.
DBA is used as a starting compound for manufacturing vulcanization accelerator, tetrabenzylthiuram disulfide, which remains in the rubber as non-carcinogenic nitrosamines on decomposition. DBA occupies a special position in the manufacture of tire treads with increased tread life; tire treads provides substantial wear reduction. In addition to the wear resistance (particularly weathering and aging), the presence of DBA derivatives enhances the vulcanization properties such as, resistance, elongation at failure, tear propagation resistance, and particularly the property of elasticity when heat built-up. Therefore the use of this inventive intermediate cross-linking reagent is therefore particularly effective.
Dialkyl and dibenzyl amines are used in the modification of polyvinyl chloride resin composition. Thus after improving the PVC resin composition, it shows excellent corrosion resistance, weather ability and exhibits excellent characteristic as a resin coating.

Numerous procedures for the production of the benzylamine and dibenzylamine are described in the literature and include: the reductive amination of benzaldehyde by hydrogen and ammonia in the presence of a catalyst; the catalytic reduction of benzonitrile, benzylhydroxylamine; the condensation of benzaldehyde and benzylamine followed by catalytic hydrogenation of the intermediate Schiffs base. Generally, benzylamine and dibenzylamine are obtained in poor yields and each amine must be carefully separated from mixtures containing primary, secondary or tertiary amines, imines, aldehydes, alcohols or amides to obtain a high purity product. For example, it is known that nitriles can be catalytically reduced to the primary amine through the intermediate imine by a wide variety of catalysts. The intermediate imine further reacts with the primary amine to produce a Schiffs base with the liberation of ammonia, In the presence of a catalyst and hydrogen, the Schiffs base is further reduced to the secondary amine, in a batch process, the above reactions compete for reactants and a variety of reaction products are formed. Many optimizations have been exercised to minimize the extent of these reactions including reduction in different solvent systems and catalyst selection.
Reference may be made to patents, such as US 5430187 (1995); WO-A-931304, US 5616804 (1997) wherein dibenzylamine is prepared by reacting benzaldehyde and ammonia in the presence of hydrogen and a hydrogenation catalyst in an inert organic solvent. Although high conversion and selectivity is attained in the transformation of benzaldehyde to dibenzylamine, the drawback in the above-described processes is the formation of number of by-products, monobenzylamine, tribenzylamine and benzyl alcohol, which require efficient separation to obtain dibenzylamine.
Reference may be made to a patent, such as U.S. Pat. No. 4163025 (1979) wherein high conversion is attained in the transformation of benzonitrile to benzylamine and dibenzylamine by passing benzonitrile and hydrogen counter-current through catalyst bed under suitable temperature and pressure conditions. The drawback in the above-described process is the formation of number of by-products which require efficient separation to obtain selectively primary amine and secondary amine.

Reference may be made to patents, such as U.S. Pat. No. 3,117,162(1964) and Annals N. Y. Acad. Sci. 214:100-109 (1973); U.S. Pat. No 3923891(1975) to a batch process for the reduction of benzonitrile in dilute hydrocarbon and alcohol solvent by hydrogenation over rhodium, palladium, platinum, or ruthenium catalysts (all are 5 wt.% on carbon). The drawback in the above-described process is poor selectivity in formation of benzylamine and dibenzylamine (63% and 34% respectively). The formation of dibenzylamine is favored in this process by the selective use of rhodium on carbon or platinum on carbon catalysts, but in all other cases it is obtained as a mixture containing large amounts of the primary amine. In addition, long reaction times, 2 to 21 hours, are required to reduce the benzonitrile. As a result, these prior art techniques are time consuming, requires efficient separation and costly.
Catalytic processes for the amination of aliphatic alcohols to form amines are known. One of the most widely practiced routes is the reaction of ammonia with alcohols at relatively high operating temperatures (about 250 to 500.degree. C.) and low to moderate pressures (atmospheric to about 200 atm) in the presence of dehydration catalysts such as aluminum oxide, silica, aluminum phosphate, or chromium oxide. Alkylation of ammonia with alcohols has also been carried out in the presence of hydrogen and hydrogenation catalyst such as copper, nickel, cobalt and platinum. Below are described representative publications illustrating catalysts used in the amination of alcohols to produce amines.
Dibenzylamine is specifically manufactured by hydrogenation of benzonitrile with Pt catalysts (U.S. Pat. No.3,923,891, 1975). Other reports suggest synthesis of dibenzylamine starting with benzylamine (Synthesis (1), 70 (1979); J. Organomet. Chem. 208 (2), 249 (1981); Chem. Lett. (6), 889 (1984); Ind. J. Technol. 23 (7), 266 (1985). In addition to the above processes, dibenzylamine forms as a by-product in the industrial synthesis of benzylamine from benzaldehyde by the reaction with ammonia and catalytic hydrogenation with Raney nickel (Ullmanns Encyclopadie der technischen Chemie, 4 th edition.Vol. 8, 440).
Dibenzylamine is therefore formed via the monobenzylamine and N-benzylidenimine and can be separated from the intermediate reaction mixture by

fractionation. The reaction mixture can also contain tribenzylamine as a secondary product, and benzyl alcohol and toluene as reduction products of benzaldehyde.
Objectives of the invention
The main object of the present invention is to provide an improved process for the synthesis of di/tribenzylamine.
Another object of the present invention is to utilize non-corrosive and low cost heterogenous catalyst such as hydrotalcite-like compound, as catalyst for the synthesis of di/tribenzylamine.
Yet another object of the present invention is to utilize the copper aluminum hydrotalcite (Cu-AI-HT) with a Cu/AI atomic ratio of 3, 2.5 and 2 (CuAl 3.0-HT; CuAl 2.5-HT; CuAl 2.0-HT).
Yet another object of the present invention is the use of an additive for selective formation of dibenzylamine.
Yet another object of the present invention is the use of anhydrous base with particle size ranges from 20-50 u and vacuum dried for 8 h at 100°C.
Yet another object of the present invention is the use of reusable catalyst.
Summary of invention
Accordingly, the present invention provides an improved process for the preparation of di/tribenzylamine, which comprises coupling benzyl alcohol and benzylamine in the presence of anhydrous base, an additive and Cu/AI-HT hydrotalcite , as catalyst, optionally in water immiscible organic solvent, at a temperature in the range of 120-160°C, under vigorous stirring, for a period of 7-16 hrs, followed by the separation of dibenzylamine from the crude mixture and further subjecting the resultant dibenzylamine to benzylation with benzyl alcohol in the presence of Cu/AI-HT hydrotalcite , as catalyst and base to obtain the desired product of tribenzylamine.
In an embodiment of the present invnetion the ratio of alcohol to amine is in the range of 1:1-1:2.5, preferably 1:2.
In yet another embodiment the base used is alkali metal carbonate.

In yet another embodiment the base used is potassium carbonate.
In yet another embodiment the concentration of base used is in the range of
0.01-0.02M, preferably 0.015M.
In yet another embodiment the concentration of additive used is in the range of 0.003-0.005M, preferably 0.004 moles.
In yet another embodiment the additive used is hydroquinone.
In yet another embodiment the Cu to Al ratio used in heterogeneous catalyst, Cu/AI-HT, is in the range of 2:1-3:1, preferably 2.5:1.
In yet another embodiment the concentration of the catalyst used is in the range of 6-10 weight % of benzyl alcohol.
In yet another embodiment the organic solvent used is selected from toluene and xylene.
In still another embodiment the catalyst used is recyclable.
In still another embodiment the particle size of the catalyst used is in the range of 30-40um.
Detailed description of the invention
The present invention describes a batch process, which comprises a novel approach to the desired synthesis of dibenzylamine from benzylamine and benzyl alcohol in presence of base, hydrotalcite-like compounds as catalysts and an additive. In this invention aliphatic and aromatic alcohols, R'-OH react with aliphatic amines, R"-NH2 in presence of catalytic amount of hydrotalcite like compound as a catalyst to afford secondary amine in excellent yields and selectivities, where R' is selected from aryl alkyl and open chain alkyl groups consisting of benzyl, 4-methoxy benzyl, 2,4-methoxy benzyl, 2-amino benzyl, 2-chloro benzyl, in open chain aliphatic alcohols, alkyl group is ranging from C7 to C12, etc., R" is selected from aliphatic, benzyl amines and substituted benzyl amines, 4-methyl benzyl, 2-methoxy benzyl, etc. The base is selected from mainly carbonate, hydroxide and alkoxide of alkali metals, and heterogeneous catalyst, Cu-AI-hydrotalcite where the ratio of Cu:AI varies from 3:1, 2.5:1, 2:1, etc., additives are selected from the hydroxy-substituted aromatic compounds, preferably dihydroxy compounds. The reaction is carried out in

the presence of 6-10 weight % of catalyst at a temperature ranging from 120 to 160 degree C for 7-16 h. with continuous stirring using benzyl amine as self-solvent or toluene or xylene under air atmosphere. The process of the invention overcomes the disadvantage of the prior art enumerated above since inter alia, the work up is simple, and the catalyst is recoverable and recyclable with consistent activity for several cycles. The synthesis of secondary amines, particularly DBA at high temperature and the products can be used further for the benzylation to prepare tertiary amines, tribenzylamine without adding the additive in excellent yield and selectivities. The use of cheap inorganic base, cheap catalyst and different aliphatic/ aromatic alcohols as well as benzyl amines provides secondary amines as products in good to excellent yields in a single step.
Generally the ratio of Cu to Al in the catalyst is 2.5:1 and the quantity used in the reactions is 6-10 weight % with respect to benzyl alcohol. The catalyst used in the reactions can be recovered by simple filtration and reused for number of cycles with consistent activity.
The novelty of present invention lies in the use of cheap heterogeneous catalyst for the first time for the amination of benzyl alcohol. The present invention provides a process for the production of dibenzylamine, which includes reacting aromatic aliphatic amines with aromatic/ aliphatic alcohols in the presence of a base, additive and catalyst, wherein the base is alkali metal hydroxide/ carbonate/ alkoxide. The additive used in this coupling reaction is nitrogen based aromatic heterocycle. The solid base catalyst of general formula, [M(ll)1-x M(lll)x (OH)2]n- An-x/n-yH20, where M(ll) and M(lll) are divalent and trivalent cations such as Cu2+, Mg2+ and Al3+ respectively, An- is the interlayer anion such as CI", N03-, C032- etc., and x = 0.1-0.33.
The goal of the present invention is to provide a simple method in which, in particular, a higher selectivity for dibenzylamine, using a cheaper heterogeneous catalyst in a single step without using a pressure reactor.
The reaction is preferably carried out in the presence of catalyst, base and an additive at a temperature ranging from 120-160 degree C, equipped with Dean-Stark apparatus to remove the water from the reaction mixture. The process comprises the unique activation of alcohol to facilitate simultaneous C-N bond formation with amine

in presence of base and additive in a single pot. Post benzylation of the DBA to TBA is not occurred in the same reaction. The process for the TBA comprises benzylation of DBA to TBA with fresh stoichiometric amount of benzyl alcohol in presence of catalyst and a base only.
Incidentally this forms the first report of formation of DBA and TBA obtained in higher yields in single pot using a cheap heterogeneous catalyst. The consistent activity obtained for several cycle makes the process economical and possible for the commercial realization.
The process of the invention comprises the activation of -CH2-OH bond to facilitate simultaneous attack by nucleophile to obtain secondary amine (DBA) in excellent yield in a single pot. The catalytic cycle of coupling reaction of benzyl amine and benzyl alcohol involves first generation of bezylamine anion in presence of base and basic catalyst at high temperature. Thus the base abstracts the proton from the benzylamine under basic catalytic condition producing bezylamine anion act as a nucleophile. Thus the nucleophilic attacked by benzylamine anion at benzylic -CH2+ of benzyl alcohol further proceeded to coupling reaction to produce dibenzylamine. Further, the invention ascertains the optimum use of the additive, which requires achieving the selective formation of benzylamine and suppressed the formation byproduct (dibenzyl ether) with maximum conversion of benzyl alcohol. Thus, the catalyst can be recovered by simple filtration and reuse for the next cycle. Thus the invented strategy offers an environmentally acceptable and extremely convenient heterogeneous catalytic process for the synthesis dibenzylamine from the coupling reaction of benzyl alcohol and benzyl amine in batch processes.

A] Dibenzylamine (DBA) Preparation:
(Formula Removed)
B] Tribenzylamine (TBA) Preparation
(Formula Removed)

The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention
EXAMPLE 1 Catalyst preparation A: Catalyst A: Cu-AI hydrotalcite (3:1)
Cu: Al hydrotalcite (3:1) is prepared as follows: About 200 ml of deionised water was taken into a 1 litre four necked round bottomed flask and stirred at 25°C with a overhead mechanical stirrer. A mixture of solution of Cu(N03)2.3H20 (32.92g, 0.1404 moles) and AI(N03)3.9H20 (16.88g, 0.045 moles) in deionised water (140 ml) and the aqueous solutions of NaOH (13.124g, 0.328 moles) and Na2C03 (8.9252g, 0.0842 moles) in deionised water were added simultaneously into the round bottom flask. The pH of the reaction mixture was maintained constantly (7-8) by continuous addition of the base solution. The resulting slurry was aged at 70°C for two hours.

The solid product was isolated by filtration, washed thoroughly with deionised water (to make base free) and dried under 70°C for 15h.
B: Catalyst B: Cu-AI hydrotalcite (2.5 : 1)
Cu: Al hydrotalcite (2.5:1) is prepared as follows : About 200 ml of deionised water was taken into a 1 litre four necked round bottomed flask and stirred at 25°C with a overhead mechanical stirrer. A mixture of solution of Cu(N03)2.3H20 (90.57g, 0.375 moles) and AI(N03)3.9H20 (56.27g, 0.0.15 moles) in deionised water (140 ml) and the aqueous solutions of NaOH (42.97g, 2.09 moles) and Na2C03 (33.12g, 0.312 moles) in deionised water were added simultaneously into the round bottom flask. The pH of the reaction mixture was maintained constantly (7-8) by continuous addition of the base solution. The resulting slurry was aged at 70°C for two hours. The solid product was isolated by filtration, washed thoroughly with deionised water (to make base free) and dried under 70°C for 15h.
C: Catalyst C: Cu-AI Hydrotalcite ( 2: 1)
Cu: Al hydrotalcite (3:1) is prepared as follows: About 200 ml of deionised water was taken into a 1 litre four necked round bottomed flask and stirred at 25°C with a overhead mechanical stirrer. A mixture of solution of Cu(N03)2.3H20 (24.16g, 0.1 mole) and AI(N03)3.9H20 (18.76g, 0.0499 moles) in deionised water (140 ml) and the aqueous solutions of NaOH (17.5g, 0.44moles) and Na2C03 (11.91g, 0.112moles) in deionised water were added simultaneously into the round bottomed flask. The pH of the reaction mixture was maintained constantly (7-8) by continuous addition of the base solution. The resulting slurry was aged at 70°C for two hours. The solid product was isolated by filtration, washed thoroughly with deionised water (to make base free) and dried under 70°C for 15h.
EXAMPLE 2: Preparation of dibenzylamine catalysed by Cu-hydrotalcite (2.5:1) 5.045g (0.046 moles) benzyl alcohol, 2.04g(0.015 moles) potassium carbonate, and 7.85g (0.074 moles) of benzylamine, 0.3g (6 wt% w. r. t. benzyl alcohol) Cu-HT catalyst, 0.050g (0.00046 moles) of hydroquinone (additive) and 8.56g (0.08 moles)

of xylene were initially introduced, while stirring, into a two-necked round-bottomed flask with a teflon magnetic bead, fitted with a Dean-Stark apparatus filled with 2.56g xylene. Red-brown suspension formed was heated up to the reflux temperature (with vigorous stirring). The temperature of the reaction mixture was gradually raised to 120-160°C over a period of 1h. Thereafter, only a slight evolution of water initially occurred, but this increases in the course of the reaction and then remained constant at a low level. Unfiltered samples were collected after every 1 h and the samples were analyzed by means of GC. After 7 h.the reaction was stopped and the crude reaction mixture was subjected to GC analysis. A residual benzylalcohol value of (2.2%), a DBA content of 90.1 %, a 1.7%, of benzaldehyde resulted here. The total conversion based on benzylalcohol (0.0146 mole %) is 97.8% and the yield of DBA is 92.12%. (Note: Approx. 6% unaccounted materials are observed as tar and unidentified compounds when DBA is distilled out.) The following table depicts the various GC selectivities of different products obtained using selected catalysts. It can be observed from the below table, the best selectivity obtained using Cu-HT (2.5:1) as a catalyst under identical reaction condition. Cuh I DBA I DBE I Benzaldehy I Benzyl I Tribenzyl
(Table Removed) -

* Un-accounted (unidentified) materials are not eluted in GC column

EXAMPLE 3:
Preparation of dibenzylamine catalysed by Cu-hydrotalcite (2.5:1) 5.045g (0.046 moles) benzylalcohol, (0.015 moles) inorganic base, and 7.85g (0.074 moles) of benzylamine, 0.3g (6 wt% w. r. t benzyl alcohol) Cu-HT catalyst, 0.050g (0.004 moles) of additive (hydroquinone) and 8.56g (0.08 moles) of xylene were initially introduced, while stirring, into a two-necked round-bottomed flask with a teflon magnetic bead, fitted with a Dean-Stark apparatus filled with 2.56g xylene. Red-brown suspension formed was heated up to the reflux temperature (with vigorous stirring). The temperature of the reaction mixture was gradually raised to 120-160°C over a period of 1h. Thereafter, only a slight evolution of water initially occurred, but this increasees in the course of the reaction and then remained constant at a low level. Unfiltered samples were collected after every 1h and the samples were analysed by means of GC. After 7 h, the reaction was stopped and the crude reaction mixture was subjected to GC analysis. The following table depicts the various GC selectivities of different products obtained using selected bases. The best selectivity obtained using K2C03 as base under identical reaction conditions (entry 6).

(Table Removed)
EXAMPLE 4: Preparation of Tribenzylamine catalysed by Cu/AI-hydrotalcite (2.5:1) 5.0 g (0.046 moles) benzyl alcohol, 3.0 g (0.22 moles) potassium carbonate, and 10.7g (0.53 moles) of dibenzylamine and 0.5g (10wt% w. r. t benzylalcohol) Cu-HT catalyst were initially introduced, while stirring, into a two-necked round-bottomed

flask with a teflon magnetic bead. Red-brown suspension formed was heated up to the reflux temperature (with vigorous stirring). The temperature of the reaction mixture was gradually raised to 120-160°C over a period of 1h. The temperature of the reaction mixture was therefore maintained at 160°C for nearly 5-7 hours after which the reaction was completed as observed through GC in which no benzyl alcohol was noticed in the reaction mixture after 5-7 hours. No residual benzylalcohol was observed, a TBA content of 99 % (w. r. t. benzyl alcohol), a DBA (unreacted) value of 0.048% resulted here. The total conversion based on benzylalcohol is 100% and selectivity of TBA is 99%, 13.06g, (0.0045 moles) (w. r. t. benzyl alcohol). No additive was required for the formation of TBA. In presence of additive, only 10-20 % formation of TBA was observed after 10-16 hours.
The main advantages of the present invention are:
1. The present invention comprises a novel approach to the desired synthesis of
DBA from the simple condensation reaction of benzylamine and benzyl alcohol in excellent yield without any operational difficulty experienced during the course of the reaction.
2. The solid base, hydrotalcite-like compounds as a catalyst used for amination of alcohol which is recyclable and reusable for at least next four consecutive cycles without loss of catalytic activity
3. The present process envisages optimal use of additive to ensure highest conversion and selectivity.
4. An eco-friendly and very simple synthetic protocol is developed using cheap and non-corrosive hydrotalcite like compound as catalysts.
5. The selectivity, yield and purity of DBA and TBA produced in this process are quite high.
6. The reaction conditions are relatively mild.
7. monitoring of the reaction and subsequent work-up procedures are easy.
8. Isolation of the product from the crude reaction mixture is straightforward due to negligible quantity of organic by-products, which are considerably less volatile.
9. The overall process is economical.

We claim
1. An improved process for the preparation of di/tribenzylamine, which comprises coupling benzyl alcohol and benzylamine in the presence of a base, an additive and Cu/AI-HT hydrotalcite , as catalyst, optionally in water immiscible organic solvent, at a temperature in the range of 120-160°C, under vigorous stirring, for a period of 7-16 hrs, followed by the separation of dibenzylamine from the crude mixture and further subjecting the resultant dibenzylamine to benzylation with benzyl alcohol in the presence of Cu/AI-HT hydrotalcite , as catalyst and base to obtain the desired product of tribenzylamine.
2. An improved process as claimed in claim 1, wherein the ratio of alcohol to amine is in the range of 1:1-1:2.5, preferably 1:2.
3. An improved process as claimed in claims 1&2, wherein the base used is alkali metal carbonate.
4. An improved process as claimed in claims 1-3, wherein the base used is potassium carbonate.
5. An improved process as claimed in claims 1-4, wherein the concentration of base used is in the range of 0.01-0.02M, preferably 0.015M.
6. An improved process as claimed in claims 1-5, wherein the concentration of additive used is in the range of 0.003-0.005M, preferably 0.004 moles.
7. An improved process as claimed in claims 1-6, wherein the additive used is hydroquinone.
8. An improved process as claimed in claims 1-7, wherein the Cu to Al ratio used in heterogeneous catalyst, Cu/AI-HT, is in the range of 2:1-3:1, preferably 2.5:1.
9. An improved process as claimed in claims 1-8, wherein the concentration of the catalyst used is in the range of 6-10 weight % of benzyl alcohol.
10. A process as claimed in claims 1-9, wherein the organic solvent used is selected from toluene and xylene.
11. An improved process as claimed in claims 1-10, wherein the catalyst used is recyclable.
12. An improved process as claimed in claim 1 to 11 wherein there is absolutely no leaching of the metal content during the reaction as well as during the workup.

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Patent Number

268523

Indian Patent Application Number

669/DEL/2008

PG Journal Number

36/2015

Publication Date

04-Sep-2015

Grant Date

01-Sep-2015

Date of Filing

17-Mar-2008

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI-110 001,INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	DR.PRAVIN R. LIKHAR	DR.PRAVIN R. LIKHAR, INORGANIC & PHYSICAL CHEM.DIVISION, INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, UPPAL ROAD TARNAKA, HYDERABAD-500007,INDIA
2	R.ARUNDHATHI	DR.PRAVIN R. LIKHAR, INORGANIC & PHYSICAL CHEM.DIVISION, INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, UPPAL ROAD TARNAKA, HYDERABAD-500007,INDIA
3	DR.B.SREEDHAR	DR.PRAVIN R. LIKHAR, INORGANIC & PHYSICAL CHEM.DIVISION, INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, UPPAL ROAD TARNAKA, HYDERABAD-500007,INDIA
4	DR.M.LAKSHMI KANTAM	DR.PRAVIN R. LIKHAR, INORGANIC & PHYSICAL CHEM.DIVISION, INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, UPPAL ROAD TARNAKA, HYDERABAD-500007,INDIA

PCT International Classification Number

C07C 68/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA