DE1768321B2 - Process for the production of SchifF bases by incomplete catalytic hydrogenation of nitriles - Google Patents

Description

Schiff bases are often used as intermediates in organic chemistry. They are produced in generally by reacting aldehydes and ketones with primary amines. To get good yields as to obtain, must be carried out at low temperature (J. Am. Chem. Soc. 66, p. 93 [1944]). While the production of the lower members in this way does not present any difficulty, must in the synthesis higher compounds that are solid at room temperature are worked in the presence of solvents, in order to be able to maintain the required low temperature during the reaction. Side reactions such as trimerization and aldol condensation (Ber. 82, p. 316 [1949]) or the formation of higher unsaturation Schiff bases (J. Am. Chem. Soc. 63, S 872 [1941]; USA. Patent 2,498,419; Chem. Abstr. 44, p. 7865 [1950]), reduce the yield.

Schiff bases also occur in the catalytic production of secondary amines from primary amines Amines as intermediates. For example, if a primary amine is heated with Raney nickel, it is observed in addition to the elimination of ammonia, there is a considerable evolution of hydrogen; next to the secondary The Schiff base is formed in amine (K. K i η α i e r u Mitarb. Ann. 644, pp. 23 to 30, 1961). Analogue the Schiff base would have to be formed during the hydrogenation of the nitriles to amines. So far, however, it has been successful not to direct the reaction in such a way that it leads to an economical production of Schiff bases could be exploited.

The invention now relates to a process for the preparation of Schiff bases by incomplete catalytic hydrogenation of nitriles in the presence of Raney nickel, which is characterized in that saturated and unsaturated, straight-chain and branched nitriles with 1 to 20 carbon atoms in a reaction vessel under vigorous stirring hydrogenated at 100 to 200 ⁰ C, preferably at 150 to 180 ° C, treated with hydrogen so long until 1,5MoI of hydrogen per mole of nitrile are added.

The following reaction mechanism can be assumed:

T. R • C = N + H ₂ -> R • CH = NH

H-RC = N + 2H ₂ - ^ R-CH ₂ NH ₂

III. R · CH = NH + R · CH ₂ NH ₂ - ^ - R · CH ₂ NHCH · R

NH ₂ - R • CH ₂ N = CH • R + NH ₃

This results in summary
2R ■ C s N + 3H ₂ - * R • CH ₂ N = CH • R + NH ₃

The ammonia formed can be removed by taking off the exhaust gas. With higher moiekular Nitriles are worked under normal pressure; short-chain nitriles, such as. B. propionitrile, require in the hydrogenation slight excess pressure, optionally in the presence of an inert gas such as nitrogen, to the to reach the required reaction temperature.

In unsaturated nitriles, such as day fat nitrile, the olefinic double bond is practically retained during the hydrogenation.

The reaction was surprising in that the nitrile group was not expected to be selective can be hydrogenated without the double bond of the Schiff base formed, as well as the olefinic Double bond, which is noticeably attacked.

After the hydrogenation, the contact, which can be used for several batches, is separated off and the reaction mixture obtained is distilled. Unreacted nitrile and primary amine are used as The preliminary run has been removed and can be used again in the next approach. Then the distilled Schiff base in high purity over; Any secondary amine present can be removed by recrystallization removed. Higher molecular compounds are only formed in subordinate quantities and remain in the residue of the distillation.

The Schiff bases obtained in this way are valuable interconnections.

E.g. 1 1

550 g of propionitrile (= 10 mol) together with 30 g of propionitrile-moist Raney nickel are placed in an autoclave. Then 15 mol of hydrogen are injected and heated to 165 ° C. for 1 hour 80 parts of di-C ₃ -Schiffscher base consists; the remaining 20 parts are propionitrile and dipropylamine. 8% higher molecular weight compounds remain in the residue. The pure N-propylidene-propylamine, which boils from 100 to 102 ° C. at a boiling point of _{760, can be separated from the nitrile-amine azeotrope by fine fractionation of the main fraction.}

65

Example 2

543 g of lauryl nitrile (= 3 mol) together with 27 g of moist cyclohexane are placed in a glass flask

Submitted Raney nickel and hydrogenated at 165 ° C while passing in about 341 hydrogen per hour. In about 4 _^3/4 hour 99.0 normal liters of hydrogen are added (theory for 4.5 mol = 100.8 1) and 19.5 g of ammonia (theory 25.5 g) with the exhaust gas discharged. After the contact has been separated off, the distillation through a Claisen attachment gives 28% first runnings, consisting of about 42 parts of unreacted nitrile and 58 parts of laurylamine and 66 "; main run, the 90% Schiff base (N-laurylidene-laurylamine) and 10 % Contains dilaurylamine

Residue remain

fertilize

6% higher molecular weight compounds

Example 3

540 ρ, stearyl nitrile (= 2.04 mol) are placed in a glass flask together with 27 g of Raney nickel cyclohexane and treated with vigorous stirring ir-t about 301 hydrogen at normal pressure and lföC. In about 5 hours you will get 64.8 norir; ! liter of hydrogen absorbed (theory for 3.0o mol = 68.4 l) and 132 g of ammonia discharged with the exhaust gas (theory: 17.3 g). One nitrates from; The catalyst is removed and the filtrate is distilled in a pump vacuum through a Claisen attachment. After a preliminary run of about 25%, consisting of 40% unreacted stearyl nitrile and 60% stearylamine, 70% pass at 267 to 330 ° C / 0.3 to 0.4 mm, 90% of which consists of Schiff base (N-stearylidene- stearylam in). The rest is distearylamine, which can be removed by urocrystallization. At a pot temperature of 36O ⁰ C 5% higher molecular weight substances, remain as residue.

Example 4

700 g of a pure C ₁₈ fraction of tallow fatty nitrile (= 2.65 mol) (iodine number: 74) are placed in a flask together with 35 g of Raney nickel moistened with cyclohexane and at 165 ^° C. with about 40 liters of hydrogen per hour with vigorous stirring treated. In 4 _^3/4 hours 93.7 normal liters of hydrogen was added (3.98 mol theory = 89.11) and 18.1 g of ammonia with the exhaust gas discharged (theory: 22.5 g). After the contact has been separated off, the Claisen distillation yields 26% first run, consisting of 35% unreacted nitrile and 65% primary amine and 66% main run, consisting of 90% Schiff base with an iodine number of 64 and 8% residue.

Example 5

704 g of a mixture of

a) 322 g of fresh stearyl nitrile and

b) 269 g of stearylamine and
113 grams of stearyl nitrile

(both from the forerunner of the previous hydrogenation)

are cyclohexane moist together with 35 g of Raney nickel presented in a flask and with the introduction of sthr. 16.5 liters of hydrogen per hour at 165 ° C hydrogenated. In 4 hours 45.0 normal liters of hydrogen were absorbed and 15.9 g of ammonia with the Exhaust gas discharged. After the contact has been removed, the Claisen distillation gives 32% forerunners, consisting of from 28% unreacted stearyl nitrile and 72% stearylamine, as well as 63% main run, the 90% Schiff base and 10% distearylamine. The distillation residue is 5%.

Claims (2)

Patent claims: 1. A process for the preparation of Schiff's bases by incomplete catalytic hydrogenation of nitriles in the presence of Raney nickel, characterized in that saturated and unsaturated, straight-chain and branched nitriles with 1 to 20 carbon atoms in a reaction vessel with vigorous stirring at 100 to 200 ⁰ C treated with hydrogen until 1.5 moles of hydrogen per mole of nitrile used are absorbed. 2. The method according to claim 1, characterized in that hydrogenation is carried out at 150 to 180 ⁰ C.