NO137194B - PROCEDURES FOR THE PREPARATION OF DIFENYLAMINE AND DERIVATIVES THEREOF - Google Patents

Description

The present invention relates to a method for production

of diphenylamine and substituted derivatives thereof, where an imine of the general formula

in which R and R' are substituents selected from the group comprising alkyl, hydrogen, phenyl, amino, alkoxy and hydroxy at a temperature between 300 and 500°C is passed over a dehydrogenation catalyst, and the distinctive feature of the method according to the invention is that the dehydrogenation catalyst is used a catalyst based on Ni, Pt, Pd or Cu-Cr, the reaction preferably being carried out in the presence of a diluent selected from pure hydrogen, pure inert gas or a mixture of hydrogen and an inert gas, with a molar ratio between diluent and imine fed in of from 0:1 to 100:1 and preferably from 20:1 to 50:1.

Such imines can be easily synthesized by methods described in the literature, e.g. from aromatic amines (aniline and derivatives thereof containing substituents in the benzene nucleus) and cyclohexanone and derivatives thereof.

It is known that diphenylamine is synthesized industrially by reacting

aniline in the presence of suitable autocondensation catalysts (BF^,

FeC^, ammonium halides and mineral acids) in liquid phase at 300-

400°C. The indicated conversion of aniline is 50% at selectivities up to 90%.

An alternative method consists of adding aniline

temperatures above 400°C over alumina or titanium dioxide-based catalysts. The conversion is lower than 20% at selectivities of approx. 90%.

British patent document 989,257 describes a method for synthesizing aromatic amines by reacting alicyclic ketones and amines in the presence of a dehydrogenation catalyst. The reaction is carried out in the liquid phase at temperatures lower than 350°C

according to a discontinuous method at high contact times.

According to the present invention, it is possible to achieve good yields by simply starting from previously synthesized imines.

Typical examples of the method according to the invention can be the production of diphenylamine from N-cyclohexylideneaniline, 4-methyldiphenylamine from N-4-methyl-cyclohexylideneaniline, 2-ethyldiphenylamine from N-cyclohexylidene ortho-ethylaniline, 4-methoxydiphenylamine from N-cyclohexylidene-para- anisidine and 3-dimethylamino-diphenylamine from N-cyclohexylidene-3-dimethylaminoaniline.

As mentioned, the imines are reacted at temperatures varying from 300°C

to 500°C on one of the aforementioned catalysts.

The reaction is preferably carried out in the presence of inert diluents, the use of which is advantageous in terms of increasing the selectivity of the reaction and the lifetime of the catalyst.

The ratio between diluent and introduced imine is varied as mentioned from 0:1 to 100:1, preferably from 20:1 to 50:1.

Pure hydrogen or a pure inert gas, or a mixture of hydrogen and inert gas, is advantageously used as a diluent.

The pressure can vary from a few mm Hg to 20 atmospheres.

The apparent contact time between the reagents and the catalyst can be selected from the range of 0.01 to 20 seconds, especially 0.05 to 5 seconds.

Contact time means the ratio between the reactor volume in which the reaction takes place and the flow of the reagents in gas form under the reaction conditions.

The following examples show some of the possible applications of the method according to the invention in the production of diphenylamine and derivatives thereof with industrial interest.

In the examples, the terms conversion, selectivity <p>g yield shall be understood as follows:

Example 1

225 cm<3> nickel catalyst (14% Ni) on aluminum oxide as carrier was introduced into a reactor which had an internal diameter of approx. 38 mm. N-cyclohexylidene aniline, hydrogen and nitrogen were added to the reactor in a molar ratio of 1:7.5:45 with a contact time of 0.5 second at 370°C. Diphenylamine was obtained at 90% selectivity and 100% conversion.

Example 2

Cyclohexylidene aniline and hydrogen were introduced into the same reactor using the same catalyst in a molar ratio of 1:7 and with a contact time of 6 seconds at 425°C. A was achieved

selectivity to diphenylamine of 55% at 100% conversion.

By comparing examples 1 and 2 it will be possible to see

the positive influence on the selectivity caused by the diluent and the reduction of the contact time.

Example 3

N-4-methylcyclohexylideneaniline, hydrogen and nitrogen in a molar ratio of 1:7:30 were introduced into the same reactor and using the same catalyst with a contact time of 0.7 seconds at 390°C. 4-methyl-diphenylamine was obtained at 81% selectivity and 100% conversion.

Example 4

To the same reactor and using the same catalyst, N-cyclohexylidene-2-ethylaniline, hydrogen and nitrogen were introduced in a molar ratio of 1:7:40 with a contact time of 0.6 seconds at 360°C. 2-ethyldiphenylamine was obtained at 79% selectivity and 100% conversion.

Example 5

N-cyclohexylidene-p-anisidine, hydrogen and nitrogen were added to the same reactor and catalyst in a molar ratio of 1:7:40 with a contact time of 0.5 seconds. 4-Methoxydiphenylamine was obtained at 80% selectivity and 100% conversion.

Example 6

N-cyclohexylidene-3-dimethylaminoaniline, hydrogen and nitrogen were added to the same reactor and catalyst in a molar ratio of 1:7:40 with a contact time of 0.5 seconds. 3-Dimethylaminodiphenylamine was obtained at 78% selectivity and 100% conversion.

Example 7

To the same reactor containing a CuO-C^O^ catalyst on a support of SiC^ was added N-cyclohexylidenaniline, hydrogen and nitrogen in a molar ratio of 1:10:8 at 410°C and a contact time of 3.6 seconds.

Diphenylamine was obtained at 40% selectivity and 75% conversion.

Claims (1)

Process for the preparation of diphenylamine and substituted derivatives thereof, where an imine of the general formula in which R and R' are substituents selected from the group comprising alkyl, hydrogen, phenyl, amino, alkoxy and hydroxy at a temperature between 300 and 500°C is passed over a dehydrogenation catalyst, characterized in that a catalyst based on Ni, Pt, Pd is used as the dehydrogenation catalyst or Cu-Cr, the reaction preferably being carried out in the presence of a diluent selected from pure hydrogen, pure inert gas or a mixture of hydrogen and an inert gas, with a molar ratio between diluent and imine fed from 0:1 to 100:1 and preferably from 20:1 to 50:1.