Secondary amines are conventionally prepared by hydrogenation of alkyl- or alkenylnitriles either directly to secondary amines or via primary amines which are sub¬ sequently reacted to secondary amines. For hydrogenation to primary amines Raney nickel is most often used as catalyst. At direct hydrogenation to secondary amines nickel has primarily been used as ^' catalyst and it has in some cases been used on a support such as aluminium oxide, silica or active carbon. Both when the preparation of secondary amines is carried out via primary amines and at direct hydrogenation the reaction has to be very carefully controlled to get selectivity and to avoid undesired formation of tertiary amine. Zeolite supported metal catalysts are per se known and their use, among other things, for hydrogenation of olefins has been suggested.

According to the present invention it has been found that secondary amines, dialkylamines, dinitriledialkylene amines, di(arylalkyl)amines and di(alkylarylalkyl)amines, can be prepared with a very high selectivity by hydrogena¬ tion or reduction of nitriles in the presence of a zeolite supported metal catalyst. The high selectivity is obtained without demands on special control steps in the process by the fact that the reaction takes place in the cavities of the zeolite.

The present invention thus relates to a process for the preparation of dialkylamines, dinitriledialkylene amines, di(arylalkyl)amines and di(alkylarylalkyl)amines as defined in the patent claims.

The starting material for the preparation of the dialkylamines and the dinitriledialkylene amines are alkyl-

or alkenylnitriles, whereby the alkyl and alkenyl groups may be straight or branched and may be, or contain, cyclo- alkyl- or cycloalkenyl groups, and the corresponding dinitriles containing from 3 to 24 carbon atoms per mole- cule, containing one and two nitrile groups respectively. The starting material for the preparation of di(arylalkyl)- amines and di(alkylarylalkyl)amines are aryl nitriles containing from 7 to 24 carbon atoms per molecule, contain¬ ing one nitrile group. The term aryl nitriles used herein includes monocyclic and polycyclic compounds, with and without aliphatic substituents on the nucleus. The aryl nitriles with aliphatic substituents can be arylalkyl- nitriles, arylalkenylnitriles, alkyl- or alkenylarylnitril- es, alkyl- or alkenylarylalkylnitriles, alkyl- or alkenyl- arylalkenylnitriles. It is preferred that the aryl nitriles are mono- or dicyclic and especially preferred are mono- cyclic aryl nitriles. The present process is particularly suitable for the preparation of dialkylamines starting from alkyl- or alkenylnitriles having 3 to 24 carbon atoms, and particularly from such containing from 8 to 20 carbon atoms. According to the present invention secondary alkyl- and arylamines are thus prepared according to the schematic reaction R-CN > (R-CI^^NH and secondary dinitrile alkylene amines according to the schematic reaction NC-R-CN > NC-R-CH2-NH-CH -R-CN. The in the latter case obtained dinitriledialkylene amine can be further hydrogenated to the corresponding triamine, H2N-<^2 ^~ * ^R-CH 2 ^~NH~CH 2~ ^R ~ ^CH 2~ ^NH 2- It is of course within the scope of the invention that the nitriles which are the starting material may contain substituents, which do not have a negative effect on the hydrogenation/reduction reaction, in the aliphatic group or on the aryl nucleus. As an example of such a substituent can be mentioned a hydroxyl group.

As some examples of suitable nitriles for the prepa- ration of the corresponding secondary amines according to the process of the invention can be mentioned butyro- nitrile, 3-pentenonitrile, caprylonitrile, lauronitrile, myristylnitrile, palmitoylnitrile, stearonitrile, benzo-

nitrile, phenylacetonitrile, phenethylnitrile, succino- nitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile and sebaconitrile.

The hydrogenation is carried out by means of hydrogen gas and reduction by means of reducing agents or reducing agent systems which under the conditions used in the process form hydrogen gas or hydride. As examples of such reducing agents and reducing agent systems can be mentioned hydrazine, zinc in combination with acetic acid, hypo-, meta-, ortho- or pyrophosphoric acid and formic acid in combination with formiate. It is preferred to produce the amines through hydrogenation.

The present process is advantageous in that it can be carried out in the absence of solvent. If solvents are used it is suitable to use lower aliphatic alcohols, which can be mono-, di- or polyhydric, or hydrocarbons. Particularly suitable solvents are saturated aliphatic monohydric alcohols with from 1 to 8 carbon atoms or saturated alipha¬ tic hydrocarbons with from 5 to 12 carbon atoms. Preferred solvents are methanol, ethanol, isopropanol, pentane, hexane and petroleum ether.

According to the present invention a zeolite support¬ ed metal catalyst is used in the hydrogenation or reduc¬ tion. The metal catalyst is present in the pores or cavi- ties of the zeolite and the reaction takes place within the pores or cavities. The metal of the catalyst is one of the elements of group VIII and is preferably rhodium, nickel, iridium or iron. The metals can also, in addition to combinations with each other, be used in combination with titanium as metal catalyst. Zeolite supported metal catalysts are previously known and can be prepared for example by incorporation of metal at the production of zeolite, by impregnation of zeolite with metal salt follow¬ ed by reduction or by ion exchange in a finished zeolite. Particularly suitable zeolite supported metal catalysts for the preparation of amines according to the present inven¬ tion are such which have been prepared starting from zeolite and an alkyl- or alkene complex of the metal in

question in the principle manner disclosed in the US patent 4,444,898, which is hereby incorporated herein as refer¬ ence. The reaction between zeolite and .metal complex can be illustrated according to the following where OH stands for the reactive hydroxyl groups in a cavity of the zeolite, M stands for any metal and R for an alkyl or alkene group in the metal complex and n corresponds to the oxidation state of the metal: (Zeolite)-OH + M-R _n > (ZeoliteJ-O-M-Rn.i + R-H (Zeolite)-0-M-R _n _*]_ + H ₂ > (Zeolite)-0-M-R _n _ ₂ (H)

(Zeolite)-0-M-R _n _ ₂ (H) + H ₂ > (Zeolite)-0-M-R _n _ ₃ (H) ₂

For rhodium(allyl)3 especially, the sequence would be as follows:

(Zeolite)-OH+Rh(allyl)3 >(Zeolite)-0-Rh(allyl) ₂ +propene (Zeolite)-0-Rh(allyl) ₂ + H ₂ > (Zeolite)-0-Rh(allyl) (H)

(Zeolite)-0-Rh(allyl) (H) + H ₂ > (Zeolite)-0-Rh(H) ₂

These zeolite supported metal catalysts do, in comparison with other ones, contain the metal bonded in the cavities of the zeolite to a larger extent and hereby give a higher structure selectivity. To obtain improved re- producability it is further suitable to modify the process for the production of the catalyst as disclosed in the US patent by using n-pentane as a solvent and by using fairly long reaction times, suitably at least 5 days and nights. The zeolite base material can be naturally occurring zeolites or synthetically prepared zeolites. As examples of suitable zeolites can be mentioned zeolites of the types Faujasite, Erlonite, Mordenite, Chabasite, Philipsite, Gmelinite, Silikalite, Zeolite X, Zeolite Y, Zeolite T, Zeolite ZK-5, zeolites of the ZSM-5 family, zeolites of the Linde family, ZSM-11, ZSM 12, ZSM 23, ZSM 35, ZSM-38. It has been found that the best results are obtained with a zeolite support which has a molar ratio Siθ2:Al2θ3 greater than 4 and particularly with zeolites which have a hydro- phobic character and have a molar ratio Siθ2 Al2θ3 > 40. Particularly suitable types of zeolites are Zeolite Y and Faujasite. At the production of the zeolite supported metal catalyst according to the above discussed preferred manner

it is especially suitable to start from the H-form of the zeolite, and particularly from such a zeolite where the Na residual value does not exceed 2%. In zeolite supported metal catalyst prepared by reaction between zeolite and metal complex the metal catalyst is bonded in the cavities of zeolites. The metal catalyst can hereby be present in pure metallic form, bonded by van der Waals forces, or in the form of oxide or hydride inside the pores or cavities of the zeolite. It is particularly preferred that the metal is present as hydride which is obtained when the alkyl metal or alkenyl metal complexes reacted into the zeolite are activated or reacted with hydrogen gas. The metal can hereby be present as metal hydride, alkyl metal hydride or alkenyl metal hydride. The alkyl and alkenyl groups should suitably not contain more than 4 to 5 carbon atoms and are preferably allyl groups. The amount of metal in the zeolite supported catalyst is suitably within the range of from 0.04 to 10 mole per cent, calculated on the nitrile which is to be hydrogenated or reduced, preferably within the range of from 0.1 to 2 mole per cent. The amount of metal with regard to zeolite is not critical in itself. As large amount of metal as possible is of course desirable for increased activity. The upper limit is primarily set to avoid that metal is present on the outer surface of the zeolite and as an example of a suitable amount can be mentioned from about 5 to about 10 mg of metal per g of zeolite.

The process of the invention is advantageous in that it can be carried out at low pressures, and for short chain nitriles, at low temperatures. The process can be carried out at temperatures of from about 10 to about 250 ^β C and is suitably carried out at room temperature or moderately elevated temperatures, up to about 150°C. The temperature is of course also dependent on the melting point of the starting material and of the product, and, generally, higher temperatures also give a faster process. The press¬ ure is normally within the range of from about 100 kPa up to about 20000 kPa and suitably within the range of from

about 400 to about 15000 kPa. As stated above, the process gives good selectivity for secondary amines, which can be used directly in industrial uses or as intermediates in organic synthesis. The invention is further illustrated in the following examples which, however, are not intended to limit the same. Example 1 -8

Hydrogenation of nitriles with zeolite based rhodium catalyst was carried out at temperatures between 25 and 60°C using 0.4 to 1 mole per cent, calculated on the nitrile, of zeolite based rhodium catalyst. The catalyst was prepared according to the following method, based on the method disclosed in US patent 4,444,898: ^" 10 g of H-Faujasite with a Siθ2:Al2θ3 ratio greater than 40 were dried at 50 to 75°C in vacuum for 10 hours and then, at room temperature and under stirring, added to a solution containing 100 mg Rh(allyl) ₃ in 100 ml of n-pentane. The obtained slurry was allowed to stand for 5 days and nights under stirring and the product was then filtered off and washed with methanol 2x20 ml and acetone 2x20 ml. The metal catalyst was activated and for this the zeolite with the bonded metal was added to 30 ml methanol in a reactor at room temperature and under stirring. The reactor was flushed with hydrogen gas and the pressure was then set at 500 kPa. The slurry was then allowed to stand under stirr¬ ing for 3 days and nights whereafter the catalyst was filtered off. A hydrogen gas pressure of between 1 and 5 bars was used at the hydrogenation. Methanol, ethanol or isopropanol was used as solvent. In a typical process 1 g of zeolite (5mg, 0,05 mmoles Rh/g zeolite) was added at room temperature to 2 g(ll mmoles) of undecylcyanide in 10 ml methanol under stirring. The reactor was flushed 3 times with hydrogen gas and the hydrogen gas pressure was set at 500 kPa. After completed reaction (22 hours), which was followed by GC, the reaction mixture was vacuum filtered and the catalyst was washed with warm methanol 2x10 ml, whereafter the solvent was evaporated to give 2.10 g of raw

product. Bulb-to-bulb distillation gave 61 mg (3%) dodecyl- amine and 1.95 g (95%) didodecylamine. In Table l below the results of hydrogenation of some other, nitriles are given:

TABLE 1

a. In examples 1 to 8 zeolite supported rhodium was used as catalyst (0.4-0.5 mole per cent); b. GC yield; c. Isolated yield. Example 9

3 g of zeolite based rhodium catalyst (5 mg, 0.05 mmoles Rh/g zeolite) were added to 15 g (185 mmoles) 2-butenecyanide in 550 ml of ethanol at room temperature. The reactor was flushed with hydrogen gas 3 times and the pressure was then set to 61 bar and the temperature raised to 70°C. After 24 hours the reaction was stopped and analyzed on GC. The yield at the reaction was 47% of dipentylamine, 0.3% tripentylamine and unreacted starting material. Example 10

4 g of zeolite based rhodium catalyst (5 mg, 0.05 mmoles Rh/g zeolite) were added to 25 g (94 mmoles) hep- tadecylcyanide in 550 ml of isopropanol at room tempera¬ ture. The reactor was flushed with hydrogen gas 3 times and the pressure was then set to 61 bar and the temperature raised to 75°C. The reaction was stopped after 24 hours. The yield at the reaction was 60% dioctadecylamine and unreacted starting material.

Example 11

10 g of zeolite based rhodium catalyst (5 mg, 0.05 mmoles Rh/g zeolite) were added to 395 g (1.49 moles) heptadecylcyanide at room temperature. The reactor was flushed with hydrogen gas 3 times and the pressure was then set at 61 bar and the temperature raised to 150°C. Every 24th hour the reactor was flushed and the pressure again set to the original value. The reaction was stopped after 84 hours. The yield at the reaction was 73% dioctadecyl- amine (NMR) corresponding to a N^ (tot) value of 51, and unreacted starting material. Example 12

1 g of zeolite based rhodium catalyst (5 mg, 0.05 mmoles Rh/g zeolite) was added to 1 g (10.6 mmoles) glu- taronitrile in 10 ml of methanol at room temperature. The reactor was flushed with hydrogen gas 3 times and the hydrogen gas pressure was then set to 5 bar. After complet¬ ed reaction (22 hours), which was followed by GC, the reaction mixture was vacuum filtered and the catalyst was washed with warm methanol 2x10 ml and the solvent was then evaporated to give 1.1 g of raw product. Bulb-to-bulb distillation gave 780 mg (82%) 4,4'-dicyanodibutylamine.