NO121908B - - Google Patents

Description

Process for the production of aldehydes by hydrolysis of aldimides obtained by reduction of nitriles.

It is known that nitriles can be reduced

to aldimines, which can be converted to the corresponding nitriles by hydrolysis. Various reducing agents can be used for this reduction. For the production of unsaturated aldehydes, attention has been drawn to lithium aluminum hydride as a reducing agent. This has the advantage that it does not attack the unsaturated bonds. In the aforementioned case, however, it has some disadvantages, so that there has been less interest in producing aldehydes from nitriles in this way. In some cases, the yields were less than expected.

The inventors have found that it is achieved

good yields of aldehydes, which belong to the mixed aliphatic-aromatic, mixed aliphatic-alicyclic or mixed aliphatic-heterocyclic series, if the corresponding nitriles are reduced with a dialkyl aluminum hydride and the resulting aldimine complex is then hydrolyzed in an aqueous environment.

As examples of compounds such as in;

according to the invention can be converted into; aldehydes can be mentioned benzonitrile, cinnamon-; acid nitrile, (3-ionylidene acetonitrile and vita-<1 >min A-acid nitrile.

It is beneficial to perform the reduction

in the absence of oxygen, which is why it is preferably carried out in a nitrogen atmosphere. Furthermore, it is important that the temperature is kept low during the reduction. Between -=- 50° and + 50° C, the reaction takes place well. Furthermore, it is recommended that no greater amount of reducing agent be used than that required

is allowed to reduce the nitrile group so that the aldimine complex is formed. Preferably, it is used for the reduction of 1 mol of nitrile approx. 1 mole of dialkyl aluminum hydride. At other ratios, results are certainly obtained, but the yield of aldehyde after the hydrolysis of the aldimine complex is then less.

Very good results are obtained by reduction with dialkyl aluminum hydride in which the number of carbon atoms in each individual alkyl group is between 1 and 6, e.g. diethyl aluminum hydride, or diisobutyl aluminum hydride. The reduction should be carried out in an inert solvent, e.g. in n-hexane, cyclohexane, benzene, toluene or petroleum ether. The reaction can also be carried out in aliphatic or cyclic ethers, e.g. in diethyl-methylethyl-, diisopropyl- or dipropyl ether, in dioxane or tetrahydrofuran.

The reduction is particularly important for the production of (3-jonylidene-acetaldehyde or vitamin A-aldehyde from |3-jonylidene-acetonitrile or vitamin A-acid nitrile, where the aldimine complex formed in the intermediate step is hydrolysed.

The reaction product between the nitrile and the reducing agent can be cleaved to the aldimine complex by the addition of moist ether. The aldimine complex can be cleaved by the addition of dilute, aqueous acid.

Execution examples:

1. Under the exclusion of moisture, in a nitrogen atmosphere and with constant stirring, a solution of 21.5 g (0.1 mol) of [3-ionylidene acetonitrile in 150 ml of cyclohexane, which has been cooled to approx. 5° C, added a similarly cooled solution of 14.2 g (0.1 mol) of diisobutyl aluminum hydride in cyclohexane. After everything had been added, it was stirred further for y2 hours at an elevated temperature (approx. 35° C). The reaction mixture was then cooled (0° C) and cleaved very carefully by adding moist diethyl ether dropwise. The gel formed was dissolved by acidifying with dilute H 2 SO + . The solution of the reaction product was separated, washed with water, and dried over Na 2 SO 1 . The solvent was distilled off, and the crude (3-ionylidene acetaldehyde was distilled in vacuum. Kp. at 0.01 mm Hg was 101-104° C. The absorption spectrum of the distilled product in ethanol had two maxima, namely at 275 and 325 mjx. The extinction was 12,200 and 14,600 respectively. With semicarbacid acetate a solid was obtained, which after recrystallization from benzene melted at 193-196° C. 2. 14.05 g (0.05 mol) vitamin A -acid nitrile was reduced with 7.1 g (0.05 mol) of diisobutyl aluminum hydride in the manner described in example 1. After the reaction mixture had been split and acidified with H2SO4, the organic matter was extracted and the solution dried over Na2SO4. the solvent was distilled off in vacuo. The crude, orange-brown vitamin A aldehyde was dissolved in ethanol, and the absorption spectrum had a maximum at 382 mji e = 32,000. A portion reacted with semicarbacid acetate gave the corresponding semicarbazone After two recrystallizations this was pure and melted at 197° C. Absorption The ns spectrum in chloroform had a maximum at 385 m\ in e = 60,600. 3. 14.2 g (0.1 mol) of diisobutylaluminum hydride was added to a solution of 10.3 g (0.1 mol) of benzonitrile in petroleum ether. The reaction temperature was 20° C. The mixture was then stirred for 15 min. at + 10° C. After cooling to -=- 20° C, the reaction mixture was carefully cleaved by the addition of a solution of methanol in petroleum ether, followed by the addition of water. After acidification with dilute sulfuric acid, the petroleum ether solution was separated, washed with water and dried over Na2SOi. When the solvent was evaporated, 9.9 g of benzaldehyde with b.p. 176-180° C. 4. In the same way as described in example 3, a solution of 6.45 g (0.05 mol) cinnamic nitrile in ether was reduced at -f- 30° C with a solution of 4.3 g (0.05 mol) of diethyl aluminum hydride in ether.

The cinnamic aldehyde was isolated in the form of its phenylhydrazone (8.7 g). Temp. 163— 166° C. 5. In the same way as described in example 3, a solution of 11.9 g (0.1 mol) of furfurylidene acetonitrile in benzene was reduced at 10° C with a solution of 14.2 g (0.1 mole) of diisobutyl aluminum hydride in benzene.

The aldehyde was obtained in the form of a yellowish oil which solidified after distillation (bp.ir, = 118-120° C). The solid's m.p. was 48-50° C. The yield was 10.4 g.

Patent claims:

Claims (2)

1. Process for the production of aldehydes in that a nitrile with the general formula R-A-CN, in which formula R means an aromatic, aliphatic or heterocyclic radical and A means a saturated or unsaturated aliphatic carbon chain containing 0-12 carbon atoms, is reduced and the formed aldimine complex is hydrolysed in an aqueous environment, characterized in that a dialkyl aluminum hydride is used as reducing agent. 2. Process according to claim 1, characterized in that the reduction is carried out with equimolar amounts of nitrile and reducing agent, the latter containing alkyl groups each having 1-6 carbon atoms, and that the reduction is carried out at a temperature between -f- 50 and + 50° C, preferably in an oxygen-free environment, as well as in the presence of an inert solvent, e.g. n-hexane, cyclohexane, benzene, toluene, petroleum ether, or in an ether such as e.g. diethyl, methyl ethyl, diisopropyl, dipropyl ether, dioxane or tetrahydrofuran.