EP0623109A1

EP0623109A1 - Method of preparing dibenzylamine

Info

Publication number: EP0623109A1
Application number: EP93901030A
Authority: EP
Inventors: Burkhard Weuste; Manfred Bergfeld
Original assignee: Akzo Nobel NV
Current assignee: Akzo Nobel NV
Priority date: 1991-12-21
Filing date: 1992-12-16
Publication date: 1994-11-09
Also published as: WO1993013047A1; BR9206800A; US5430187A

Abstract

Procédé de fabrication de dibenzylamine par réaction de benzaldéhyde et d'ammoniac, en présence d'hydrogène et d'un catalyseur d'hydrogénation dans un solvant organique inerte, caractérisé en ce que la réaction est effectuée avec une proportion d'ammoniac supérieure à 0,5 mole par mole de benzaldéhyde, et avec un catalyseur d'hydrogénation sur un support au platine métallique et/ou au fer métallique. Le procédé est mis en oeuvre à des températures peu élevées, de préférence de 40 à 90 °C. On obtient en particulier une sélectivité élevée pour la dibenzylamine, jusqu'à plus de 90 %, et une réaction pratiquement complète.Process for the manufacture of dibenzylamine by reaction of benzaldehyde and ammonia, in the presence of hydrogen and of a hydrogenation catalyst in an inert organic solvent, characterized in that the reaction is carried out with a proportion of ammonia greater than 0 , 5 mole per mole of benzaldehyde, and with a hydrogenation catalyst on a metallic platinum and / or metallic iron support. The process is carried out at low temperatures, preferably 40 to 90 ° C. In particular, a high selectivity for dibenzylamine, up to more than 90%, and a substantially complete reaction is obtained.

Description

Process for the preparation of dibenzylamine

* * *

Description:

The present invention relates to a process for the preparation of dibenzylamine from benzaldehyde and ammonia with catalytic hydrogenation.

Dibenzylamine does not form a carcinogenic nitrosamine and can be used as a starting compound for the production of the vulcanization accelerator tetrabenzylthiuram disulfide, which also forms only non-volatile nitrosamines remaining in the rubber. The manufacture and use of this vulcanization accelerator is therefore largely harmless to health.

Dibenzylamine is specifically produced by hydrogenating benzonitrile with Pt catalysts (US Pat. No. 3,923,891). Further synthesis proposals for dibenzylamine start from benzylamine (Synthesis (1), 70 (1979); J. Organomet. Che. 208 (2), 249 (1981); Chem. Lett. (6), 889 (1984); Ind. J. Technol. 23 (7), 266 (1985)). Furthermore, dibenzylamine is obtained as a by-product in the technical synthesis of benzylamine starting from benzaldehyde by reaction with ammonia with catalytic hydrogenation with Raney nickel (Ullmanns Encyclopedia of Industrial Chemistry, 4th edition, Vol. 8, 440):

C ₆ H ₅ -CHO + NH + H- ^C 6 ^H 5 ^-CH 2 ^NH 2 ^{+ H} 2 °

C ₆ H ₅ -CH ₂ H2 ^' + C ₆ H ₅ -CH0 -> CgH ₅ -CH ₂ N = CH-CgH ₅ + H ₂ 0

C ₆ H ₅ -CH ₂ N = CH-CgH ₅ + H ₂ -----> CgH ₅ -CH ₂ NHCH ₂ -CgH ₅

Dibenzylamine is thus formed via the stage of monobenzylamine and N-benzylbenzylidenimine and can be separated from the reaction mixture by fractionation. The reaction mixture may also have tribenzylamine as the secondary product and benzyl alcohol and toluene as the reduction products of the benzaldehyde. According to information in Ullmann's Encyclopedia, Vol. 8, page 440, 500 kg of benzaldehyde (4.72 mol) and 110 kg of ammonia (6.47 mol), i.e. with a stoichiometric excess of ammonia, become a mixture of 470 kg at 100 ° C. in the reaction Monobenzylamine, 2 kg of benzylbenzylidenimine, 1 kg of dibenzylamine and 1 kg of benzyl alcohol were obtained.

J. A er. Chem. Soc. 61 (1939), page 3566 describes the preparation of monobenzylamine with dibenzylamine as a by-product by reacting benzaldehyde with a stoichiometric excess of ammonia under catalytically hydrogenating conditions using Raney nickel as a catalyst, specifically According to the test example given there, 3 mol of benzaldehyde and 3 mol of ammonia, ie stoichiometric amounts in relation to the formation of monobenzylamine, but stoichiometric excess of ammonia in relation to the formation of dibenzylamine, become a mixture with 287 at 70 ° C. g of monobenzylamine and 21.7 g of dibenzylamine. On the other hand, according to Table I of this literature citation with stoichiometric amounts of benzaldehyde and ammonia (1/2 equivalent) with respect to the formation of dibenzylamine, the proportion of dibenzylamine can predominate (80.8% in addition to 11.8% monobenzylamine).

There was therefore still a need for an economical process for the preparation of dibenzylamine from benzaldehyde and ammonia by catalytic hydrogenation; and it was an object of the present invention to provide such a process in which, in particular, a higher selectivity for the dibenzylamine is achieved and a more manageable catalyst can be used or smaller amounts of catalyst metal are required.

This object is achieved by a process for the preparation of dibenzylamine by reacting benzaldehyde and ammonia in the presence of hydrogen and a hydrogenation catalyst in an inert organic solvent, characterized in that the reaction with an ammonia content> 0.5 mol per mol of benzaldehyde and with a hydrogenation catalyst containing a platinum metal and / or an iron metal is carried out.

The advantageous result according to the invention, in particular the high selectivity for dibenzylamine up to over 90% with practically complete conversion, is very surprising, because the prior art cited at the beginning teaches about Molar ratio of benzaldehyde and ammonia from the ammonia excess to be used according to the invention (> 0.5 or 0.8 or 1.0 mol of ammonia per mol of benzaldehyde corresponds to a stoichiometric excess of> 0 or 60 or 100% in relation to the formation of dibenzylamine) away: the excess of ammonia used in accordance with this prior art in relation to the formation of dibenzylamine (according to Ullmanns Encyclopedia, vol. 8, page 440, or J. Amer. Chem. Soc. 62, page 3567, 1.37 mol or 1 mole of ammonia per mole of benzaldehyde) leads to monobenzylamine and not dibenzylamine as the main product. In addition, the test results in J. Amer. Chem. Soc. 61, p. 3567, rather to increase the dibenzyl a in yield even close to an ammonia deficit. An excess of ammonia was therefore not only not suggested by the prior art, but was even advised against.

A more distant prior art according to DE-A-21 18 283, which relates to the production of secondary or tertiary aliphatic amines by reacting aliphatic carbonyl compounds and an amine or ammonia with catalytic hydrogenation, does indeed describe excess ammonia. However, since this document specifies process conditions and also start connections which differ significantly from the present invention, the content of DE-A 21 18 283 in no way suggested the latter.

Thus, the reaction according to DE-A-21 18 283 takes place at very high temperatures of at least 130 ° C. (180 to 200 ° C. in the case of the only experimental example 15 relating to the use of ammonia; in contrast, according to the invention, preferably below 100 ° C. ) in the absence of a solvent with very high excess ammonia (up to 8 moles of amine per mole of carbonyl compound; according to Example 15 4 moles of ammonia per mole of cyclohexanone) and in the presence of a special catalyst ("a mixture of sintered on a support sintered by heating and known per se as a catalyst Silver and palladium "), where no special aromatic carbonyl compound such as benzaldehyde, but a (cyclo) - aliphatic carbonyl compound (according to Example 15 cyclohexanone) is used, the reactivity of which cannot be easily compared. Under these conditions, only a relatively low yield of secondary amine is achieved (according to experimental example 15: 73% dicyclohexylamine in addition to 18% monocyclohexylamine, 1 - 2% corresponding imine and 2% cyclohexanol).

Accordingly, the prejudice against the use of ammonia in excess or in equimolecular amounts still existed in the professional world due to the closer prior art described at the outset. This is also confirmed by the recent textbook "Organic Chemistry" by A. Streitwieser and C.H. Heathcook, Verlag Chemie 1990, pages 927 and 928, because it is found there that the reaction from monobenzylamine to dibenzylamine can be suppressed by excess ammonia, that is to say it is not promoted, but is even impeded.

The ammonia excess is essential to the invention. With increasing ammonia excess, the selectivities for the dibenzylamine continue to increase, accompanied by a surprisingly strong suppression of the known, very easy direct hydrogenation of the benzaldehyde to benzyl alcohol and by a suppression of the formation of tribenzylamine with a slightly increased formation of monobenzylamine, in fact especially when using non-sulfided catalysts. Compared to these, the sulfided catalysts advantageously suppress the formation of benzyl alcohol and toluene much more anyway, but this is associated with an increase in the amounts of tribenzylamine. When using sulfided catalysts, an increase in the amount of ammonia essentially only leads to a shift in the amount of tribenzylamine: monobenzylamine towards the latter. If relatively large amounts of ammonia are used, a decrease in the selectivity for the dibenzylamine is finally found again.

The process according to the invention is therefore preferably carried out with an ammonia content in the range from 0.8 to 4 mol and particularly preferably from 1 to 3 mol per mol of benzaldehyde.

The process according to the invention is advantageously carried out at low temperatures of at most 100 ° C., preferably in the range from 40 to 90 ° C. and particularly preferably from 60 to 90 ° C. The dibenzylamine selectivity drops at higher temperatures, apparently as a result of U alkylation. The formation of benzyl alcohol increases sharply with lower temperatures.

The platinum metals contained in the hydrogenation catalyst according to the invention are the elements of atomic numbers 44 to 46 and 76 to 78 of the periodic table, preferably ruthenium, palladium and platinum, and the elements of atomic numbers 26 to 28, preferably cobalt and nickel, are to be understood as iron metals. The platinum metals in their sulfided form can be used particularly advantageously. The amount of catalyst required for the process according to the invention is surprisingly small: at most 0.5% by weight and preferably at most 0.2% by weight of platinum metal or iron metal, based on the amount of benzaldehyde used, is required.

According to the invention, the known coarse-surface substances, such as substances containing activated carbon, aluminum oxide and aluminum oxide, and substances containing silica, silicates and silicates, such as silica gel, kieselguhr, kaolin, talc and clays, preferably activated carbon, aluminum oxide, silica gel and kieselguhr, are suitable as supports for the hydrogenation catalyst.

The process according to the invention is preferably carried out with a palladium on a hydrogenation catalyst containing carbon support.

By adding cocatalysts, e.g. catalytic amounts of methanesulfonic acid, the dibenzylamine selectivity can be increased in the process according to the invention.

Suitable inert organic solvents according to the invention are, in particular, those liquids which are customary in the catalytic hydrogenation of carbonyl compounds and in which the ammonia can be dissolved and a homogeneous liquid phase of the reaction mixture is formed. Such liquids can be water, water-miscible alcohols, preferably methanol, and water-miscible ethers such as dioxane, tetrahydrofuran, ethylene glycol methyl ether or ethylene glycol diethyl ether.

The execution of the method according to the invention is very simple. For example, in a simple Metal autoclaves are worked, which is equipped with a gas turbine, floor drain, heating device and stirrer. The latter is filled with the benzaldehyde, very small amounts of supported catalyst and a solution with ammonia, and hydrogen is applied until no more hydrogen is taken up at the reaction temperature, the reaction times advantageously being only 10 to 45 minutes. After draining the reaction mixture and filtering off the catalyst, it can then be separated in a simple manner by stripping off the solvent and subsequent fractional distillation (cf. Ullmanns Encyclopedia of Industrial Chemistry, 4th edition, vol. 8, p. 440). Depending on the intended use of the dibenzylamine, it is generally sufficient to distill off the solvent and the majority of the lower-boiling constituents of the reaction mixture, after which no further purification step is then required.

A particular advantage lies in the ease with which the catalyst used according to the invention is supported and can be regenerated compared to the prior art using Raney nickel.

The process according to the invention thus provides an economical process for the preparation of dibenzylamine with high selectivity. It can also be carried out continuously.

The present invention is explained in more detail by the following experimental examples. Examples 1 to 4

A 500 ml Büchi steel autoclave with a hollow-shaft gassing turbine filled with protective gas was charged with 21.2 g benzaldehyde (0.2 mol) and with 2.72 g (example 1), 6.8 g (example 2), 10.2 g (example 3) and 13.6 g ammonia (example 4) charged in methanol. Then 0.85 g of palladium catalyst, type ElOl R / W from Degussa (5% Pd on carbon; approx. 50% H ₂ 0) was added and was rinsed with enough methanol that the reaction mixture contains approx. 10% benzaldehyde . It was pressed twice with hydrogen and heated to 70 ° C. under 5 »10 ^J Pa hydrogen pressure. Then 20 »10 ^J Pa were pressed until no more hydrogen was taken up. After cooling and decompression, the solution for separating off the solid catalyst was drained off via a frit and used directly for gas chromatographic analysis. Finally, the solvent was evaporated on a rotary vacuum evaporator and the resulting oily products were weighed out (approx. 20 g).

As in the other test examples, the composition of this crude product was determined by means of gas chromatography.

The following compositions were determined (in addition to small amounts of other by-products):

BA = benzaldehyde MBA = monobenzylamine DBA = dibenzylamine TBA = tribenzylamine BOH = benzyl alcohol

Examples 5 to 7

The procedure was as in Example 1, but instead of the catalyst used there, a sulfided palladium catalyst, type ElOl RS / W from Degussa (5% Pd on carbon) (Examples 5 and 7) or type Escat (reduced) Engelhardt (5% Pd on coal) (Example 6) used. Furthermore, the amount of ammonia in Example 6 was 3.4 g (1.0 mol of NH ₃ per mol of BA) and in Example 7 5.1 g (1.5 mol of NH ₃ per mol of BA).

This resulted in products of the composition (area%)

0.1 monobenzylamine - 83.9 dibenzylamine - 10.2 tribenzylamine - 2.9 benzyl alcohol (Example 5), 1.7 monobenzylamine - 84.3 dibenzylamine - 7.1 tribenzylamine - 1.6 benzyl alcohol (Example 6) and 2.8 monobenzylamine - 93.3 dibenzylamine - 1.0 tribenzylamine - 1.0 benzyl alcohol (Example 7).

Examples 8 and 9

The procedure was as in Example 7, but not at a reaction temperature of 70 ° C, but at 50 ° C (Example 8) and at 90 ° C (Example 9). The results were products with a composition (area%) of 70.0 DBA - 0.2 TBA - 29.5 BOH (Example 8) and 11.6 MBA - 84.7 DBA - 1.7 TBA (Example 9).

Examples 10 to 12

The procedure was as in Example 1, but with 5.1 g of ammonia and instead of the catalyst used there, a platinum catalyst (not sulfided), type F101B from Degussa (5% Pt on carbon) (Example 10), a sulfided Platinum catalyst, type F101RSH from Degussa (5% Pt on carbon) (example 11) and a ruthenium catalyst (not sulfided), type H 101 BW from Degussa (5% Ru on carbon) (example 12) used. The results were products with the composition (area%) 2.6 MBA - 80.1 DBA - 0.6 TBA - 6.1 BOH (Example 10), 6.6 MBA - 76.5 DBA - 0.6 TBA - 1.9 BOH (Example 11) and 82.0 DBA - 1.7 TBA - 1.5 BOH (example 12).

Example 13

This example describes the use of a unsupported catalyst.

The procedure was as in Example 1, but with 6.8 g of ammonia, and instead of the catalyst used there, 1 g of Raney nickel from Merck, article no. 820875 (50% water). The result was a product with the composition (area%) 1.3 MBA - 5.6 DBA - 89.2 BOH. Mostly only benzyl alcohol is formed here.

Claims

* * * Claims:

1. Process for the preparation of dibenzylamine by reacting benzaldehyde and ammonia in the presence of hydrogen and a hydrogenation catalyst in an inert organic solvent, characterized in that the reaction with an ammonia content> 0.5 mol per mol of benzaldehyde and with a a platinum metal and / or an iron metal on a carrier-containing hydrogenation catalyst is carried out.

2. The method according to claim 1, characterized in that the reaction is carried out with an ammonia content in the range from 0.8 to 4 mol and preferably from 1 to 3 mol per mol of benzaldehyde.

3. The method according to claim 1 or 2, characterized gekenn¬ characterized in that the reaction is carried out at a temperature of at most 100 ° C and preferably in the range of 40 to 90 ° C and particularly preferably from 60 to 90 ° C.

4. The method according to one or more of claims 1 to 3, characterized in that the reaction is carried out with a hydrogenation catalyst containing a sulfided platinum metal on a support.

5. The method according to one or more of claims 1 to 4, characterized in that the hydrogenation catalyst is used in an amount of at most 0.5 wt.% And preferably at most 0.2 wt.% Platinum metal or iron metal, based on the amount of benzaldehyde used .

6. The method according to one or more of claims 1 to 5, characterized in that activated carbon, aluminum oxide, silica gel and diatomaceous earth is used as the carrier for the hydrogenation catalyst.

7. The method according to one or more of claims 1 to 6, characterized in that the reaction is carried out with a palladium on a carbon carrier-containing hydrogenation catalyst.