GB2149790A - Process for producing aminobenzylamines - Google Patents

Abstract

A process for producing m-aminobenzylamine or p-aminobenzylamine, which comprises reacting m-nitrobenzaldehyde or p-nitrobenzaldehyde with ammonia, in the presence of a reducing catalyst, in an organic solvent.

Description

SPECIFICATION Process for producing aminobenzylamines This invention relates to a new process for the production of aminobenzylamines; the compounds are important as curing agents for epoxy resins, as starting materials for polyamides and polyimides, and as intermediates for agricultural chemicals.

Aminobenzylamines have been prepared in various ways from nitrobenzaldehyde or nitrobenzonitrile.

None is particularly suitable for industrial practice.

Kornblum eta!, J.A.C.S. 71(1949) 2137, disclose the conversion of m-nitrobenzaldehyde to m-nitrobenzyl bromide which is then reacted with potassium phthalimide to obtain N-(m-nitrobenzyl) phthalimide; m-aminobenzylamine is produced in about 20% yield, by a two-step reduction reaction. Potassium phthalimide is expensive, the reactions are complex, and recovery is uneconomic.

Siddiqui metal, Synth. Comm. 7(1977) 71-78, disclose reacting m-nitrobenzaldehyde with phenylhydrazine, and subjecting the resulting hydrazone compound to catalytic reduction; m-aminobenzylamine is obtained in 60% yield. Phenylhydrazine is expensive, the reactions are complex, and recovery is uneconomic.

Griffith etna!, NRL Report 6439, disclose two processes for preparing m-aminobenzylamine, respectively in 52% and 49% yield. The first process comprises converting m-nitrobenzaldehyde to m-nitrobenzaldoxime which is then catalytically reduced under high pressure, using Raney nickel catalyst. This procedure is long and hydroxylamine (a necessary starting material for the aldoxime) is expensive. The second process comprises catalytically reducing m-nitrobenzonitrile, using Raney nickel, under high pressure. The apparatus is expensive and the volume efficiency low, in both cases.

Brown metal, J. Med. Chem. 20(177)1189, disclose deriving p-aminobenzonitrile from p-nitrobenzonitrile, followed by reduction with lithium aluminium hydride; p-aminobenzylamine is obtained in 37% yield. The reducing agent is expensive and difficult to handle.

British Patent Application No 8422642 discloses preparing aminobenzylamines by reducing a benzaldoxime in an organic solvent in the presence of boric acid, phosphoric acid or an anhydride of either, CO2 gas or an organic acid.

According to the present invention, m-aminobenzylamine or p-aminobenzylamine is prepared by the process of reacting m-nitrobenzaldehyde or p-nitrobenzaldehyde with ammonia, in the presence of a reducing catalyst, in an organic solvent.

The catalytic reduction process of the present invention may be carried out using at least 1, and preferably 3 to 10, mols ammonia per mol of the nitrobenzaldehyde. If the amount of ammonia is less than the preferred range, the amount of undesirable by-products such as secondary amines increases; if greater, there is little or no increase in effect. Gaseous ammonia may be used, but liquid ammonia is preferred.

The organic solvent may be any solvent conventionally employed for catalytic hydrogenation. Aliphatic (usually anhydrous) lower alcohols in which ammonia is highly soluble, such as methanol and ethanol, are preferred. The amount of the solvent is not critical, but 1 to 15 times the weight of the raw material is usually sufficient.

Examples of the reducing catalyst used in the present invention are those of noble metals such as platinum, palladium and rhodium, and Raney catalysts. Noble metal catalysts may be used as such, but are usually supported on the surface of a carrier such as carbon, silica gel or alumina. Raney nickel or raney cobalt, etc. are commercially advantageous. The amount of the catalysts used is in the range of 0.01 to 30% by weight in terms of metal based on raw material nitrobenzaldehyde. Usually a range of 2 to 20% by weight is preferred in the case where Raney catalysts are used, while a range of 0.1 to 5% by weight, in the case where noble metals supported on a carrier are used.

Further, the reaction temperature is preferably in the range of 30 to 1 500C, particularly 60 to 1 200C.

As for the reaction pressure employed, higher ones are better, but usually a range of 10 to 150kg/cm2 G is suitable. If the reaction pressure is so low that the reaction does not proceed rapidly, there is a tendency of reduction in the yield.

In a general embodiment of the process of the present invention, a catalyst may be added to the raw material in a state where it is dissolved or suspended in a solvent, followed by introducing ammonia and sucessively introducing hydrogen to carry out reaction till its absorption ceases, but in a preferable embodiment, the raw material and ammonia (liquid ammonia) are dissolved in a solvent, and while the resulting mixed solution is introduced in divided manner into a reactor having hydrogen, a solvent and a catalyst bed therein in advance, catalytic reduction is carried out at a desired pressure and temperature. At thattime, its amount fed per once somewhat varies depending on reaction conditions, but usually the amount is preferred to be adjusted so that the hydrogen absorption may cease within about 30 minutes per once.

In the above process of introducing the mixed solution in divided manner, if the reaction pressure is low, it is necessary to reduce its divided amount introduced; this is uneconomical since the reaction time is prolonged as much.

In the process of the present invention, when the mixed solution is introduced in divided manner.

The product is obtained with a higher yield than that in the case where it is introduced all at once and also deterioration of the catalyst is small; hence such a process is very advantageous even in view of its reuse.

Further, the quantity of heat generated at the time of the reaction is easily controlled. After completion of the reaction, the catalyst is filtered off and the filtrate is distilled in conventional manner to obtain the objective product.

The present invention will be described in more detail by way of Examples.

Example I Into a 1 è capacity stainless autoclave were fed methanol (100 me) and Raney nickel (made by Toyo CCI) (4.6 g in terms of nickel), followed by purging with nitrogen, successively purging with hydrogen to make the hydrogen pressure 40 kg/cm2G and raising the temperature up to 90 C.

Into a raw material vessel were fed p-nitrobenzaldehyde (60.4 g, 0.4 mol), methanol (400 mC) ) and liquid ammonia (ca. 80g), which were then agitated at 0 to 5 C for about 30 minutes to prepare a mixed solution.

This solution was divided into 8 portions (each about 58 g), and introduced into the autoclave while the reaction temperature was kept at 90"C. Hydrogenation reaction for each amount of about 58 g was 5 to 15 minutes, and the total reaction time required was 80 minutes, during which 33 Nt in total of hydrogen were absorbed. After aging for 30 minutes, the reaction solution was allowed to cool down to room temperature, followed by taking out the reaction mass, filtering and subjecting the filtrate to vacuum distillation under a pressure of 5-6 mm Hg to obtain a fraction (distillation temperature: 129.5"C-130"C) (47.8g, yield 97.7%). This fraction was found to have a purity of 99.9% according to gas chromatography, and it was confirmed to be p-aminobenzylamine.Further the values of elemental analysis were as follows: Elemental analysis (C7H70N2) C H N Calculated value (%) 68.8 8.25 22.9 Observed value (%) 68.8 8.29 22.8 Example 2 Reaction was carried out in the same manner as in Example 1 except that p-nitrobenzaldehyde was replaced by m-nitrobenzaldehyde. Reaction was complete in 115 minutes, during which hydrogen (32 Ne) was absorbed. Post-treatment as in Example 1 was successively carried out to obtain m-aminobenzylamine having a purity of 99.91% (46.79, yield 95.5%, b.p. 131-132'C!6 mm Hg).

Example 3 Into a 500 me capacity stainless autoclave were fed p-nitrobenzaldehyde (30.29, 0.2 mol), methanol (200 m4) and Raney nickel (made by Toyo CCI) 4.69 in terms of nickel), followed by purging with nitrogen gas, stirring for a while, introducing ammonia (about 409) while cooling the autoclave with ice water, successively pressurizing hydrogen to make the gage pressure 40 kg/cm2 G, thereafter raising the temperature up to 70"C, and carrying out reaction at this temperature for 60 minutes. As a result, hydrogen (16.3 Ne) was absorbed and the reaction was complete. The reaction solution was ailowed to cool down to room temperature, followed by taking out the reaction mass, filtering and subjecting the filtrate to vacuum distillation under a pressure of 6 mm Hg to obtain a fraction (distillation temperature: 129.5-130"C) (22.0 g, yield 90.0%), corresponding to p-aminobenzylamine. Its purity according to gas chromatography was 99.91%.

Example 4 Reaction was carried out as in Example 3 except that p-nitrobenzaldehyde was replaced by mnitrobenzaldehyde. Reaction was complete in 55 minutes, during which hydrogen (15.8 Ne) was abosrbed.

Post-treatment as in Example 3 was carried out to obtain m-aminobenzylamine having a purity of 99.94% (21.5 g, yield 88.0%, b.p. 131-132"C/6 mm Hg).

Claims (8)

1. A process for producing m-aminobenzylamine or p-aminobenzylamine, which comprises reacting m-nitrobenzaldehyde or p-nitrobenzaldehyde with ammonia, in the presence of a reducing catalyst, in an organic solvent.

2. A process according to claim 1, wherein the nitrobenzaldehyde and ammonia are in the form of a solution which is introduced portionwise.

3. A process according to claim 1 or claim 2, wherein 3 to 10 mols ammonia are used per mol nitrobenzaldehyde.

4. A process according to any preceding claim, wherein the organic solvent is an aliphatic lower alcohol.

5. A process according to any preceding claim, wherein the reducing catalyst is Raney nickel or Raney cobalt.

6. A process according to any preceding claim, wherein the ammonia is used in the form of liquid ammonia.

7. A process according to any preceding claim, which is carried out at from 60 to 120 C.

8. A process according to claim 1, substantially as described in any of the Examples.