GB2084146A

GB2084146A - Process for preparing 4-aminomethylbenzoic acid

Info

Publication number: GB2084146A
Application number: GB8128015A
Authority: GB
Original assignee: Kureha Corp
Current assignee: Kureha Corp
Priority date: 1980-09-17
Filing date: 1981-09-16
Publication date: 1982-04-07
Also published as: FR2490220A1; JPS6017780B2; DE3137091C2; JPS5753441A; FR2490220B1; GB2084146B; DE3137091A1; CA1180723A

Abstract

Known processes for preparing 4-aminomethylbenzoic acid suffer from a variety of disadvantages, such as low yields and the use of starting materials which are not readily available. These problems are now overcome by preparing 4-aminomethylbenzoic acid or a salt thereof by catalytically hydrogenating 4-hydroxyiminomethyl- benzoic acid dispersed in an aqueous acidic or neutral medium in the presence of a catalyst of at least one of palladium and rhodium, and if desired converting a resulting salt to the free acid.

Description

SPECIFICATION Process for preparing 4-aminomethylbenzoic acid The present invention relates to a process for preparing 4-aminomethylbenzoic acid from 4-hydroxyiminomethylbenzoic acid. More particularly, the present invention relates to a process in which 4-hydroxyiminomethylbenzoic acid is reduced to 4-aminomethylbenzoic acid by using a catalyst containing at least a palladium compound or a rhodium compound within an aqueous medium of pH of not higher than 7.

Concerning the process for preparing 4-aminomethylbenzoic acid (hereinafter referred to as AM), the following methods have been hitherto known: (1) Amination of 4-chloromethylbenzoic acid by aqua ammoniae, (2) Reduction of 4-carboxybenzaldehyde in the presence of Raney Nickel in methanol containing aqua ammoniae (refer to Japanese Patent Publication No. 34-421), (3) Reduction of methyl 4-cyanobenzoate in the presence of Raney Nickel in an aqueous alkali solution (refer to Japanese Patent Application Laying Open No. 48-57951) and (4) Reduction of 4-cyanobenzoic acid in the presence of a ruthenium catalyst in an aqueous alkali solution (refer to Japanese Patent Application Laying Open No. 51-32536).

However, although method (1) is carried out under an ordinary pressure, a large amount of by-products such as secondary amine and tertiary amine is formed and accordingly, the yield of AM if not favorable; in order to improve the yield of method (2), it is necessary to carry out the reaction under a high pressure; and starting material of (3) and (4), 4-cyanobenzoic acid, is not easily prepared in an industrial scale.

Accordingly, every one of the publicly known methods cannot be said to be the sufficiently satisfactory method for preparing 4-aminomethylbenzoic acid.

It is an object of the present invention to provide a process for preparing 4-aminomethylbenzoic acid, comprising catalytically hydrogenating 4-hydroxyiminomethylbenzoic acid dispersed in an aqueous acidic- or neutral medium in the presence of a catalyst containing at least one palladium compound or one rhodium compound. Other objects will appear hereinafter.

The present invention will be explained more in detail as follows: The starting substance of the present invention,i.e., 4-hydroxyiminomethylbenzoic acid is an oxime compound which may be obtained by the reaction of 4-carboxybenzaldehyde and hydroxylamine hydrochloride. 4-Carboxybenzaldehyde is obtained by oxidation of mono- or dichloromethylbenzoic acid as the object compound. However, industrially, the 4-carboxybenzaldehyde obtained as a by-product in the production of terephthalic acid which is the raw material for synthetic fibers, is utilized.

The catalyst used in the process of the present invention (hereinafter referred to as the present process) is a catalyst containing at least one member selected from the group consisting of palladium compounds and rhodium compounds, and preferably, a metallic catalyst comprising palladium and/or rhodium or a mixed catalyst comprising one or two members of palladium and rhodium and one or more members of other metals of platinum group, particularly, platinum and ruthenium. However, mixed catalysts containing palladium, rhodium and platinum are excluded in cases where the reduction is carried out in an aqueous acidic medium. Specifically preferable is an unitary catalyst comprising palladium or rhodium.

The form of the active metallic element contained in the catalyst of the present process is metal, compound of the metal, for instance, oxide, or alloy of the metals. These metals and metal compounds are used while being carried on a carrier such as activated carbon and diatomaceous earth, the preferable carrier being activated carbon. The specifically preferable catalyst is the catalyst comprising palladium metal carried on activated carbon. In the ordinarily used catalyst, the content of the metallic element carried on the carrier is about 2 to 10 % by weight of the total weight of the catalyst. The amount of catalyst used is so that the total sum of the weight of palladium or rhodium becomes to about 0.25 to 10 % by weight, preferably, about 0.5 to 5 % by weight of 4-hydroxyiminomethylbenzoic acid.

The reaction medium used in the present process is the medium of pH of lower than 7, that is, an acidic medium or a neutral medium.

In the reduction of an oxime compound, an organic solvent is generally used as the reaction medium, aqueous medium not being used because of the extremely small solubility and the presumable hydrolysis of the oxime compound in an aqueous medium.

However, in the present process, it is characteristic that the hydrogenation of the oxime compound dispersed in an aqueous medium is possibly carried out at a relatively low temperature and under a relatively low pressure. Namely, the starting substance, the oxime compound, is reduced in an emulsified state in an acidic medium containing a mineral acid, and the thus formed AM by reduction of the oxime becomes to the salt of the mineral acid. The reason why the mineral acid salt of AM is easily obtained in a high yield is considered to be the protection of the aminomethyl group by the mineral acid resulting in the prevention of side reactions such as deamination and formation of secondary amine.

On the other hand, in the case where the reaction medium is an aqueous neutral medium, the reduction of the oxime compound proceeds in a nearly emulsified state of the oxime, and after the reaction is over, AM is obtained as crystallites. Under the neutral condition, it is characteristic that the reaction proceeds in a heterogeneous state.

In the case where the reaction is carried out in an aqueous basic medium, although the reaction proceeds in a homogeneous system, it has been found that by-production of secondary amine is inevitable resulting in a poor yield of AM.

As an aqueous acidic medium, an aqueous solution of a mineral acid such as hydrochloric acid, sulfuric acid and nitric acid which forms a water-soluble salt with AM, is used at an ordinary concentration of 3 to 5 %. The amount of the mineral acid used in the reaction is at least more than the equivalent amount of 4-hydroxyiminomethylbenzoic acid, preferably, about 1 to 3 times of the equivalent amount. The amount of the reaction medium is 10 to 50 times by weight of 4-hydroxyiminomethylbenzoic acid, preferably, 10 to 20 times in both cases of acidic- and neutral conditions.

The reaction of the present process is ordinarily carried out at a temperature of about 10 to about 80"C, and in the case of using a palladium catalyst, the reaction proceeds smoothly enough at about 10 to about 50"C, however, in the case of using rhodium catalyst, a little higher temperature is necessary.

The reaction of the present process can be carried out under a pressure of hydrogen of higher than 1 atm, and the reaction easily proceeds under a pressure of hydrogen of 1 to 10 atm in usual cases.

The time period of the reaction of the present process depends on the reaction conditions such as the kind of the catalyst and the amount thereof, the temperature, the pressure of hydrogen, etc., however, the absorption of hydrogen completes usually within about 2 to 7 hours.

After the reaction is over, in the case of using an aqueous acidic medium, the catalyst is removed by filtering the reaction mixture and the crystals of AM is sedimented by neutralizing the filtrate, and after collecting the crystals by filtration, the filtrate is condensed to further obtain the crystals of AM. On the other hand, in the case of using an aqueous neutral medium, concentrated aqua ammoniae or concentrated hydrochloric acid is added to the reaction mixture to dissolve the product, and after removing the catalyst by filtration, the filtrate is neutralized to obtain the crystals of AM.

The present invention will be further explained more in detail while referring to the nonlimitative examples as follows: EXAMPLE 1 In an autoclave of a capacity of 500 ml made of pressure-resistant glass, 16.5 g (0.1 mol) of 4-hydroxyiminomethylbenzoic acid was dispersed into 200 ml of aqueous 3.5 % hydrochloric acid solution, and 1.6 g of 5 % palladium on activated carbon (hereinafter abbreviated to as 5 % Pd-C) was added to the dispersion. The catalytic hydrogenation of 4-hydroxyiminomethylbenzoic acid was carried out under the initial pressure of hydrogen of 5 kg/cm2 at a temperature of from ordinary temperature to 45"C. The absorption of hydrogen came to an end after 3 hours.

After removing the catalyst by filtering the reaction mixture, the filtrate was condensed and the thus sedimented crystals were collected by filtration, washed with acetone and dried to obtain 16.0 g of white powdery crystals melting at 284-288"C. The crystalline product thus obtained was identified as 4-aminomethylbenzoic acid hydrochloride by comparing its infrared absorption spectrum with that of the authentic specimen of 4-aminomethylbenzoic acid hydrochloride, the yield being 85.0 %.

A saturated aqueous solution of the product, 4-aminomethylbenzoic acid hydrochloride (hereinafter abbreviated to as AM-HCL) was neutralized with aqueous 20 % sodium hydroxide solution, and after collecting the thus sedimented crystals by filtration, the filtrate was condensed to obtain a further amount of the crystals. After drying the thus obtained crystals, the combined crystals amounted to 12.5 g.

EXAMPLE 2 In the same manner as in Example 1 except for using distilled water as the reaction medium and at a temperature of from room temperature to 40"C, the catalytic hydrogenation of 4-hydroxyiminomethylbenzoic acid was carried out. The absorption of hydrogen came to an end after 3 hours. After adding 20 g of concentrated hydrochloric acid into the reaction mixture to dissolve the product, the mixture was filtered to remove the catalyst and the filtrate was condensed under a reduced pressure. The thus sedimented crystals were collected by filtration, washed with acetone and dried to obtain 14.5 g of white powdery crystals which were identified as 4-aminomethylbenzoic acid by comparing its infrared absorption with that of the authentic specimen of 4-aminomethylbenzoic acid hydrochloride. The yield was 77.3 %.

By treating the thus obtained product with alkali in the same manner as in Example 1, to obtain 8.2 g of crystals in the first step and 2.6 g of crystals in the second step. These crystals were identified as AM by comparing their infrared absorption spectrum with that of the authentic specimen of 4-aminomethylbenzoic acid.

EXAMPLE 3 In the same manner as in Example 1, except for using as the catalyst 5 % rhodium carried on activated carbon (hereinafter abbreviated to as 5 % Rh-C), catalytic hydrogenation of 4-hydroxyiminomethylbenzoic acid was carried out a temperature from room temperature to 60"C.

Absorption of hydrogen came to an end after 5 hours. By treating the reaction mixture as in Example 2, 14.0 g of white powdery product melting at 282 to 285"C was obtained, and identified as AM HCI by comparing its infrared absorption spectrum with that of the authentic specimen of AMHCI, the yield being 74.6 %.

By treating the thus obtained product with neutralization with alkali, 10.2 g of white powdery substance was prepared, which was identified as AM by infrared spectral analysis.

EXAMPLES 4 to 6 A series of catalytic hydrogenation experiments were carried out in the same manner as in Example 1, however, using each one of the mixed catalysts shown in Table at a temperature of from room temperature to 50"C. In these experiments, the reactions of hydrogenation of the oxime moiety and of the benzene ring could be traced by observing the consumed amount of hydrogen corresponding to the reduced pressure of hydrogen in the autoclave.

After the reaction was over, the catalyst was removed by filtering the reaction mixture, and after confirming that the filtrate contained solely AM HCI by the presence of ultraviolet absorption at 228 nm, the filtrate was condensed. The thus sedimented crystals were collected by filtration and dried. The product was identified by infrared analysis to be AMHCI.

Table EXAMPLE Composition of Period for Product No catalyst H2 absorption (g) (hours) weight (g) Identification 4 5 % pd-C 1.6 2.5 13.7 AMHCI 5 % Pt-C" 1.6 5 % pt-C 1.6 50 13.1 the same 5 5 % Rh-C 1.6 as above 6 5% Pd-C 1.6 25 13.5 the same 5 5 % Ru-C"" 1.6 as above Note: "5 % Pt-C means a catalyst containing 5 % by weight of platinum on activated carbon.

""5 % Ru-C means a catalyst containing 5 % by weight of ruthenium on activated carbon.

EXAMPLE 7 In the same manner as in Example 1, except for using distilled water as the reaction medium and using a mixed catalyst consisting of 1.6 g of 5 % Pd-C, 1.6 g of 5 % Pt-C and 1.6 g of 5 % Rh-C, catalytic hydrogenation of 4-hydroxyiminomethylbenzoic acid was carried out at a temperature of from room temperature to 50"C. The absorption of hydrogen came to an end after about 4 hours.

Since some crystals appeared in the reaction mixture, 20 ml of concentrated hydrochloric acid was added to the mixture to dissolve the crystals, and the solution was filtered to remove the catalyst by filtration. After condensing the filtrate and adding acetone to the condensate to sediment the crystals, they were collected by filtration and dried to obtain white powdery crystals melting at 284 to 286"C in amount of 14.5 g, which were identified as AM HCI by infrared analysis, the yield being 77 %.

Claims

1. A process for preparing 4-aminomethylbenzoic acid or a salt thereof, which process comprises catalytically hydrogenating 4-hydroxyiminomethylbenzoic acid dispersed in an aqueous acidic or neutral medium in the presence of a catalyst of at least one of palladium and rhodium, and if desired converting a resulting salt to the free acid.

2. A process according to claim 1, wherein the catalyst comprises a carrier.

3. A process according to claim 2, wherein the carrier is activated carbon.

4. A process according to any one of the preceding claims, wherein the catalyst comprises palladium metal and/or rhodium metal.

5. A process according to claim 4 wherein the catalyst comprises palladium metal on activated carbon.

6. A process according to claim 4, wherein the catalyst comprises rhodium metal on activated carbon.

7. A process according to any one of the preceding claims, wherein the catalyst comprises a palladium compound and/or a rhodium compound.

8. A process according to any one of the preceding claims, wherein the catalyst is a catalyst of an element of the platinum metal group selected from ruthenium, osmium, iridium and platinum, either in the form of the metal ora compound thereof, and palladium and/or rhodium, with the proviso that the catalyst is not a catalyst of palladium, rhodium and platinum in the case where the aqueous medium contains a mineral acid.

9. A process according to claim 8, wherein the element of the platinum metal group is platinum or ruthenium.

1 0. A process according to any one of the preceding claims, wherein 4-hydroxyiminome- thylbenzoic acid is catalytically hydrogenated at a temperature of 10 to 80"C.

11. A process according to any one of the preceding claims, wherein 4-hydroxyiminomethylbenzoic acid is catalytically hydrogenated under an initial pressure of hydrogen of 1 to 10 atmospheres.

1 2. A process according to any one of the preceding claims, wherein 4-hydroxyiminomethylbenzoic acid is catalytically hydrogenated for 2 to 7 hours.

1 3. A process for preparing 4-aminomethylbenzoic acid or a salt thereof substantially, as hereinbefore described in any one of the Examples.