The invention relates to a process for the preparation of a ketoxime by reaction of an aminoalkane with a peroxide under the influence of a catalyst on the basis of a transition metal.

Such a process is known from US-A-3960954, which describes the preparation of a cycloalkanone oxime with utilization of an organic hydroperoxide. The catalyst used in that process is a dissolved metal compound, the metal being chosen from the group comprising Ti, V, Cr, Se, Zr, Nb, Mo, Te, Ta, W, Re and U. By the formation of the ketoxime the organic hydroperoxide is reduced to the corresponding alcohol. It has appeared, however, that such a process has a number of drawbacks which have an adverse effect on the process operation and the selectivity. Thus it has appeared that there is a steady increase in side reactions of the peroxide during the process, as a result of which only a moderate selectivity in terms of hydroperoxide conversion is achieved. Side reactions are due to the use of secondary hydroperoxides, for instance, giving rise to oxidation reactions with the alcohols released.

Consequently there is a need for a process in which said drawback is eliminated. According to the invention this is achieved due to the preparation of the ketoxime being effected with a catalyst containing a metal-peroxo complex. Metal-peroxo complexes are known per se. Reference can be made to the publication by H. Mimoun in 'The Chemistry of Functional Groups, Peroxides', 1983, pages 464- 82, issued by John Wiley & Sons, Ltd. (Edt. S. Patai). In this overview articles the properties and syntheses of such peroxo complexes are described.

The use of such complexes in a process according to the present invention is not described, nor suggested. This is even more evident in the article by H. Mimoun in

'Catalysis Today', 281-95, 1987, where said complexes are only used in the heterolytic epoxidation of olefines and the homolytic oxidation of hydrocarbons.

Surprisingly, the applicant has found that such peroxo complexes are eminently suitable for preparation of a ketoxime starting from an aminoalkane.

The peroxo complexes that are suitable for the invention can be described in general as:

0 a) L - M I , or

0 b) L - M - ( - O - O - R), where M represents: a transition metal, L: one or more ligands, and R: hydrogen or an organic radical group.

As said above, a transition metal in the complex is started from. Vanadium, cobalt, platinum, palladium, molybdenum, chromium, titanium, zirconium, tungsten, osmium and iridium in particular have been found to be suitable transition metals for the invention. In general, it is possible to use more than one metal in such a catalyst. The following radical groups can be used as ligand L at the complex (for a more detailed description, reference can be made to for instance DE-A-3.135.008, in particular pp. 10- 15): a) anionic groups, such as halides, carboxylates, phenolates or alcoholates, b) non-ionic, electron-yielding groups, such as amides, tertiary amines, imines or ethers.

As indicated above, the peroxo part of the complex can

be applied in the M | configuration or in the M-O-O-R

0 configuration, in which latter case the term 'μ-peroxo complex' is used. In a μ-peroxo complex the substituent may be either R or H (which means that the peroxo part may

originate from hydrogenperoxide (H ₂ 0 ₂ ) ) or an organic radical group with 1-30 carbon atoms, such as alkyl, aralkyl, cycloalkyl and the like, which group may be either substituted or not. R is preferably alkyl or cycloalkyl. By preference, a catalyst is used with the peroxo part originating from the hydroperoxide which is formed in the oxidation of the alkane corresponding to the aminoalkane. The process is in particular very suitable for application of primary, but preferably secondary hydroperoxides, because in the reaction according to the state of the art, these relatively easily cause side reactions leading to low selectivity. By preference a cycloalkylhydroperoxide is applied, such as for instance cyclohexylhydroperoxide, cyclooctylhydroperoxide or cyclododecylhydroperoxide. The hydroperoxides can already be used in low concentrations. It is possible for instance to apply alkylhydroperoxide-containing mixtures which are formed in the preparation of an alkylhydroperoxide by oxidation of an alkane with oxygen.

For further information on suitable peroxo complexes, reference is made to Mimoun's publications mentioned in the foregoing. The process according to the invention can be applied for the reaction with any aminoalkane, giving the corresponding ketoxime. For this purpose substituted or non- substituted aliphatic as well as cycloaliphatic aminoalkanes, preferably with 3-30 carbon atoms, can be used. Thus the process according to the invention can well be applied for the preparation of 2-butane oxime, the oxime derived from 2-amino butane. Other examples of suitable amines are cyclooctyl amine and cyclododecyl amine. Preferably, the aminoalkane started from is cyclohexylamine, because the reaction product, cyclohexanone oxime, is a very suitable starting material for the preparation, via a Beckmann rearrangement, of caprolactam, the starting material for nylon 6.

It is advantageous to immobilize the metal-peroxo

complex on a carrier material so that the catalyst becomes heterogeneous and, for instance, is easily separated from the reaction mixture. For this purpose can be used any method for anchoring of catalysts on a carrier which is known in the art and has appeared to be suitable. Thus, one of the ligands chosen for the metal-peroxo complex can be of a type that will form a bond with the carrier material applied. As an example of this can be mentioned the use of a ligand containing an amine or amide group which reacts with a carrier with hydroxyl groups, such as γ-alumina or anatase (Ti0 ₂ ).

During the preparation of the ketoxime ^' the peroxo part of the complex is converted into the corresponding alkanolate. Surprisingly, it has been found that the alkanolate thus formed does not affect the activity and selectivity of the reaction, which is in contrast to the known state-of-the-art processes, in which alcohols appear to have a negative effect. This is the case in particular if the reaction is carried in the virtual absence of water. The alkanolate probably remains bonded to the metal complex then.

By preference, every reaction step is carried out in the virtual absence of water. By preference, water- extracting agents are added to the reaction mixture, such as for instance raol sieves.

In order to recover the active, metal-peroxo complex containing catalyst, the metal complex is separated out after the preparation of the ketoxime, and the complex is reacted with the desired peroxide compound so that the catalyst is oxidized to the metal-peroxo complex. The alcohol thereby released can be removed. Preferably, the formation of the peroxo complex is carried out at a temperature of 0-50°C, in any case at a temperature which is so low that no significant thermal or catalytic decomposition of the peroxide or of the complex occurs.

The preparation of the ketoxime may or may not take place in a solvent. For suitable solvents, reference can be

made to US-A-3960954, except for alcohols which the applicant has found to have a decelerating effect on the catalytic activity of the complex or not to be chemically inert. The temperature at which the preparation takes place is between 0 and 200°C, preferably between 40 and 160°C, more in particular between 60 and 120°C. The pressure applied is generally between 0.1 and 10 MPa. By preference, a catalyst concentration, calculated as moles of transition metal in the peroxo complex per mole of aminoalkane, of 5:1 to 1:10 is applied.

The reaction may be carried out for instance in a plug flow reactor as well as in a stirred tank reactor, depending on parameters such as type of catalyst, the nature of side reactions occurring, etc. A person skilled in the art is very well capable of making a responsible choice here.

Upon completion of the preparation the ketoxime obtained can be removed from the reaction product by processes known per se and be recovered as such or be used as starting material for a subsequent process, the cyclohexanone oxime for instance for production of caprolactam. Due to the process according to the present invention it is achieved in that case that the traditional formation of cyclohexanone oxime, i.e. from cyclohexanone and hydroxylamine, is not necessary any more. The principal advantage of this lies in the option to do without a complicated hydroxylamine preparation, which in some cases will result in a substantial reduction of the amount of ammoniumsulphate obtained as side product in the preparation of hydroxylamine.

The invention will now be elucidated with the following example.

Example

Ligand preparation

^H 2°

A solution of salicylaldehyde (0.1 mole; 12.2 g) in toluene was added to a solution of 2-aminophenol (0.1 mole; 10.9 g) in a 1:1 (vol/vol) mixture of toluene and ethanol (100 ml). The resulting mixture was boiled for three minutes at 80°C, causing its colour to shift from bright colourless to bright orange. Upon cooling in an ice-and-salt bath, orange-coloured crystals were formed. The solution was filtered off and the crystals were washed with methanol. The crystals [N-(2-oxidophenyl)salicylidenamine] were dried in vacuum.

Preparation of peroxide complex OxorN-(2-oxidophenyl)- salicylidenaminato1vanadium cyclohexylperoxide

VO(OiPr) ₃ (0.7 mmole; 1.7 g) (iPr = iso-propyl) was added to C ₂ H ₄ C1 ₂ (50 ml) simultaneously with the ligand (7 mmole; 1.5 g) and stirred for one hour at room temperature. An excess of cyclohexylhydroperoxide (CHHP) was added dropwise at 0°C with vigorous stirring. This caused the colour of the solution to shift from red-brown to deep- brown.

Concentrating of the solution at 20°C and addition of n- hexane resulted in precipitation. The solution was filtered and the solid substance was washed with n-hexane. The yield was 80%.

Oxidation of cyclohexanone and ammonia to oxime

2 mmole cyclohexylamine and 4 mmole of the above peroxo complex were added to a suspension of 1 g 3A

Mol.sieve in 50 ml dichloroethane stirred under nitrogen at room temperature. The reaction was monitored by means of gas chromatography until no increase in product was observed any more. The solvent was partly removed at 20°C under lowered pressure; addition of n-hexane enabled the product to be separated from the precipitated vanadium compounds. The oxime yield was 72%. The peroxo complex was regenerated by adding cyclohexylhydroperoxide to the precipitate.