CATALYTIC PROCESS FOR THE PREPARATION OF OXIMES

Abstract: Described is a catalytic process for the preparation of oximes by reaction, in the liquid phase, of the corres­ ponding carbonyl compounds with NH₃ and H₂O₂, wherein the catalyst is selected from solid compositions substantially consisting of titanium and oxygen, chemically combined with each other.

Description: EP-A-208,311 describes the preparation of cyclohexanone-oxime in the liquid phase from cyclohexanone, ammonia and hydrogen peroxide in the presence of a catalyst consisting of a crystalline compound having a zeolitic structure. The obtainment of said zeolitic structure, however, necessitates the treatment of silicon compounds and titanium compounds with organic compounds known as templating agents, in particular tetraalkylammonium hydroxides or salts thereof, which can be synthesized only with extreme difficulty. EP-A-299,430 and 311,983 suggest to use, as the source of silicon and/or titanium, solid amorphous materials but nevertheless, in order to obtain from said amorphous materials a crystalline structure which is catalytically active, the presence of templating agents cannot be dispensed with. The preparation of said crystalline structure requires very long residence times and the use of high temperatures and pressures. Furthermore, it is necessary to subject the catalyst to complex post-treatments. Subsequently it was found (see IT-A-21076 A/88) that the synthesis of the oximes may also be promoted by titanium- and silicon-based catalysts which do not exhibit the above zeolitic structure. It has now, surprisingly, been found that the synthesis of oximes, starting from carbonyl compounds, may also be promoted by catalysts based on titanium only, or containing silicon at the most in very low concentrations (traces), which catalysts may be prepared without the use of templating agents in a very simple way and within a very short time. In its broadest aspect the present invention relates to a catalytic process for the preparation of oximes by reaction, in the liquid phase, of the corresponding carbonyl compounds with NH₃ and H₂O₂ (ammoximation). Said process is characterized in that the catalyst is selected from solid compositions substantially consisting of titanium and oxygen, chemically combined with each other, said compositions being preferably selected from: a) crystalline compositions, particularly rutile, anatase and brookite; b) amorphous compositions, i.e. compositions characterized by an XR-diffractogram, obtained by X-ray diffraction using the K α radiation of copper, which shows, in the (2ϑ) range from 10° to 65°, a smooth-trend line (halo), typical for amorphous solids; c) mixed compositions, i.e. compositions characterized by an XR-diffractogram which, in addition to said halo, also shows the reflections of rutile and/or anatase and/or brookite (a typical example thereof is represented by the diffractogram of figure 1); d) mixtures of compositions according to a), b) and c) above. In said compositions, as already mentioned, silicon is absent or present at the most in trace amounts. The surface area of said compositions preferably ranges from 10 to 1000 m²/g, most preferred from 100 to 800 m²/g. The present catalysts have also been employed in a continuous process for many hours without any sign of exhaustion, with yields equal to and sometimes higher than the ones obtained in the discontinuous tests, and they proved to be very active not only in the case of the ammoximation of aldehydes and ketones, but also in the case of other organic syntheses such as, e.g., the synthesis of N,N-dialkylhydroxylamines described in EP-A-314,147. Aldehydes that may catalytically be converted into oximes in general are aldehydes of formula R₁CHO, wherein R₁ is selected from alkyl, cycloalkyl, aryl or heterocyclic groups (containing one or more of O, N and S atoms in the ring) having from 1 to 18 carbon atoms. The term "alkyl group" also includes arylalkyl and cycloalkyl-alkyl groups as well as alkyl groups substituted with heterocyclic groups. "Cycloalkyl group" also covers alkyl-cycloalkyl and aryl-cycloalkyl groups as well as cycloalkyl groups substituted with heterocyclic groups. "Heterocyclic groups" includes alkyl-, cycloalkyl- or aryl-substituted heterocyclic groups. Specific examples of the (basic) groups mentioned above are C₁₋₁₂-, particularly C₁₋₆-alkyl such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl and tert.-butyl and pentyl; C₄₋₁₂-cycloalkyl, such as cyclopentyl and cyclohexyl; C₆₋₁₂-aryl, such as phenyl, naphthyl and biphenylyl; C₅₋₁₀-heterocyclic groups such as pyrrolyl, pyridinyl, pyrimidinyl, furanyl, pyranyl, thienyl and the completely or partially saturated equivalents thereof. The ketones that can catalytically be converted into oximes generally are ketones of formula R₂-CO-R₃, wherein R₂ and R₃, the same or different from each other, have the same meaning as R₁ and can be linked at their ends, thus forming a carbocyclic or heterocyclic ring. Particularly preferred carbonyl compounds are acetone, cyclohexanone, methyl-ethyl-ketone, acetophenone, benzophenone, tert-butyl-cyclohexanone, cyclo-dodecanone, enanthic aldehyde (1-heptanal) and benzaldehyde. The catalyst can be prepared starting from various titanium and silicon sources, according to methods which are known for the preparation of heterogeneous catalysts or, more generally, of oxides. Without being limitative in any way of the scope of the invention, a few possible procedures are given below: a) The catalyst of the present invention can be prepared by hydrolysis of alcoholic solutions containing titanium alcoholates, and, optionally, small amounts of tetraalkylsilicate (see, for example: Journal of Catalysis 102, pages 249-251 (1986)). The hydrolysis may be carried out by blowing an inert gas, saturated with water vapor (steam), into the alcoholic solution, possibly heated at a temperature lower than or equal to the boiling temperature. b) Alternatively, the catalyst may be obtained from aqueous solutions of hydrosoluble titanium compounds by precipitation with a base (for example ammonium hydroxide); see, for instance, Journal of Catalysis 105 (1987), pages 511-520. c) The method according to b) may also be applied in the case of aqueous solutions of soluble trivalent titanium compounds. In this case, after precipitation, the product is subjected to oxidation, for example by blowing air into the suspension or by calcination after filtration and washing; see, for instance, Journal of Colloid and Interface Science; Vol. 101(2), October 1984, page 369. d) A volatile titanium compound may be subjected to combustion (see, for example, Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd edition, vol.23, page 145). After the preparation the dried catalyst can be used directly for the ammoximation or it may be calcined in a stream of air or of another gas, or under vacuum, at a temperature ranging from 50° to 800°C. As exemplary sources of titanium the following may be mentioned: alkyl titanates and, particularly, tetraisopropyl titanate and/or di-isopropyl-bis(triethanolamine)titanate; titanium halides and, particularly, titanium tetrachloride (TiCl₄) and/or titanium trichloride (TiCl₃); combinations thereof and their equivalents. Generally, the conversion of the carbonyl compound into the oxime is carried out in the liquid phase at temperatures from 25° to 100°C, preferably of from 40° to 90°C, and even more preferred of from 60° to 90°C. Tests carried out at 15°C generally did not result in satisfactory results. The reaction may be conducted at atmospheric pressure or at slightly higher than atmospheric pressure, in order to keep dissolved in the reaction medium an amount of NH₃ which is at least commensurate with the requirements of the synthesis. The catalyst may be provided on a fixed bed, in particular a trickle-bed, or may be finely dispersed in the reaction medium, provided the reactor surfaces can withstand hydrogen peroxide. If the reaction is performed discontinuously it is advisable to use from 0.1 to 50 parts by weight, preferably from 1 to 20 parts, of catalyst per 100 parts of carbonyl compound. If the reaction is performed continuously, it is recommended to operate at a space velocity of from 0.1 to 200 kg/hour of carbonyl compound per kg of catalyst. The molar ratio H₂O₂/carbonyl compound in general ranges from 0.3 to 2.5, preferably from 0.5 to 1.3, H₂O₂ being calculated as 100% pure hydrogen peroxide, dilution water being excluded. The molar ratio NH₃/H₂O₂ generally is equal to or greater than 1, preferably greater than 1.5, since otherwise parallel reactions might occur. The reaction medium may consist of water and/or organic solvents. Particularly good results may be obtained by using as solvent tert-butanol and/or cyclohexanol, optionally in admixture with dioxane or toluene. The molar ratio of tert-butanol (and/or cyclohexanol) to carbonyl compound preferably ranges from 0.1 to 100. At the end of the reaction the oxime may be separated in different ways, for example by means of extraction with suitable solvents such as, for instance, benzene, toluene or the ketone (or aldehyde) employed as starting material, whereby a hydrophobic organic phase and an aqueous phase are formed. Oxime and unreacted carbonyl compound are present in the organic layer. The aqueous layer, containing the excess NH₃ as well as traces or carbonyl compound and oxime, may suitably be recycled to the reaction. Alternatively, the extraction may be conducted simultaneously with the synthesis by operating in a two-phase system. A suitable system may be prepared by using a couple of solvents of different characteristics, for example tert-butanol (hydrophilic) and toluene (hydrophobic). In case the ammoximation is to be conducted continuously, it is recommended to maintain the space velocity in the range of from 0.1 to 200 kg/h of carbonyl compound (preferably from 2 to 200 kg/h) per kg of pure catalyst, binders excluded, and to feed the carbonyl compound in admixture with the organic solvent, for instance tert-butanol (and/or cyclohexanol). For the ammoximation the technique of percolation on a catalytic bed, also called "trickle-bed" technology,may conveniently be used. In this case the catalyst preferably is in the form of pellets, rings, optionally polylobated extrudates etc. One of the alternatives to percolation is the continuous reaction in a suspended bed and under stirring. In this case it is convenient to feed the reactants through dipping pipes, immersed beneath the level of the liquid. Obviously, one or more reactants may be introduced portionwise during the reaction, for instance through a series of inlet or feeding points, thus achieving a better control of the reaction. The following examples are given in order to illustrate the present invention without, however, being a limitation of possible embodiments thereof. EXAMPLE 1 A solution of 300 g of tetraisopropyl-orthotitanate in 300 ml of anhydrous isopropanol was mixed, at room temperature under vigorous stirring and by dripping (dripping rate: 5 ml/minute), with 300 ml of H₂O. Stirring was continued for 4 hours, whereafter the product was filtered, washed with distilled H₂O and finally dried for 16 hours at 120°C. Thereupon the product was calcined for 2 hours at 200°C (heating rate of 1°C/minute). Thereby a catalyst with a surface area of 185 m²/g was obtained. The corresponding XR-diffractogram, shown in figure 1, is marked by the letter 'A' and shows the presence of the more intensive reflection of anatase (d = 0.352 nm; 2ϑ= 25.3°); see card JCPDS-21-1272. EXAMPLE 2 A glass reactor, equipped with stirrer and heating jacket, was previously pressurized with an inert gas (nitrogen). Into the reactor were then introduced 15.06 g of the catalyst powder obtained according to example 1. Thereupon there were added 21 g of water (1.17 mol), 25 g of tert-butanol (0.34 mol) and 4 g of ammonia (0.24 mol). The resulting mixture was subjected to stirring and then there were added 10.34 g of cyclohexanone (0.105 mol), thus forming a bi-phasic (solid/liquid) system which was kept homogeneous by means of vigorous stirring. The temperature was raised to 80°C by feeding into the heating jacket of the reactor a thermostatic liquid. Thereupon an aqueous 33% b.w. solution of hydrogen peroxide was introduced into the reactor by means of a metering pump. During the heating, the pressure rose slightly above atmospheric pressure. The addition of H₂O₂was continued for 5 hours, the total amount of added H₂O₂ being 11.33 g (0.096 mol). During the addition the pressure inside the autoclave dropped. To the suspension thus obtained there was added, after cooling, diethyl ether and the resulting mixture was stirred for a few minutes. The aqueous and ethereal phases were then separated from the catalyst by means of filtration whereafter the liquid phases were separated in a separatory funnel. Gas-chromatographic analysis revealed a cyclohexanone conversion of 72.8% and a selectivity to oxime of 88.4%. The oxime yield (with respect to H₂O₂) was 61.4%. All data and results are recorded in Table 1. EXAMPLE 3 200 g of tetraisopropyl-orthotitanate were placed in a flask provided with reflux cooler, thermometer, magnetic stirrer and a dipping pipe for bubbling in a hydrous inert gas (nitrogen). Then there were added 150 ml of anhydrous isopropanol and into the resulting solution, heated to 60°C, there was injected a stream of an inert gas, previously passed through a scrubber, said gas containing H₂O heated up to 60°C. A total of 50 ml of water was thus introduced into the reactor in the form of steam during a period of 20 hours. The product obtained at the end of the hydrolysis was filtered, washed with anhydrous isopropanol and dried for 15 hours at 120°C. The product was finally calcined at 200°C for 2 hours. There was obtained a catalytic powder with a surface area of 478 m²/g. The corresponding XR-diffractogram, shown in figure 1, is marked by the letter "B". EXAMPLE 4 To a solution of 754 g of TiCl₃ (in the form of a 15% b.w. aqueous solution) in 3.5 litres of distilled H₂O were added, under vigorous stirring and at room temperature, 560 ml of a 15% b.w. aqueous solution of ammonia, until reaching neutrality (pH=7.1). The black precipitate of the thus formed titanous hydrate was then oxidized to the white (titanic) form by bubbling air through the suspension. The white titanium hydroxide was then filtered, washed until complete disappearance of the Cl⁻ions from the washing water, and finally dried for 48 hours at a temperature of 120°C. One portion of the thus obtained solid was calcined for 6 hours at 300°C. Thereby a catalytic powder having a surface area of 244 m²/g was obtained. The corresponding XR-diffractogram, shown in figure 1, is indicated by the letter "C". EXAMPLES 5 AND 6 Example 2 was repeated, varying the catalyst as indicated in Table 1 which also shows the results of the corresponding ammoximation.

Claims: Catalytic process for the preparation of oximes by reaction, in the liquid phase, of the corresponding carbonyl compounds with NH₃ and H₂O₂ (ammoximation), wherein the catalyst is selected from solid compositions substantially consisting of titanium and oxygen chemically combined with each other. Process according to claim 1, wherein said solid compositions are selected from: a) crystalline compositions, particularly rutile, anatase and brookite; b) amorphous compositions, i.e. compositions characterized by an XR-diffractogram, obtained by means of X-ray diffraction using the K α radiation of copper, which shows, in the (2ϑ) range from 10° to 65°, a smooth-trend line (halo) typical for amorphous solids; c) mixed compositions, i.e. compositions characterized by an XR-diffractogram which, in addition to said halo, also shows the reflections of rutile and/or anatase and/or brookite; d) mixtures of compositions according to a), b) and c). Process according to anyone of claims 1 and 2, wherein said compositions have a surface area from 10 to 1000 m²/g, particularly from 100 to 800 m²/g. Process according to anyone of the preceding claims, wherein said compositions are obtained by using, as source of titanium, compounds selected from: alkyl titanates, in particular tetraisopropyl titanate and/or di-isopropyl-bis(triethanolamine)titanate; titanium halides, in particular titanium tetrachloride and titanium trichloride; combinations and equivalents thereof. Process according to anyone of the preceding claims, wherein said compositions are obtained by using, as source of titanium, a compound selected from TiCl₄, tetraisopropyltitanate and/or di(isopropyl)-bis(triethanolamine)-titanate. Process according to anyone of the preceding claims, wherein the catalytic compositions are obtained by hydrolysis of alcoholic solutions of a titanium alcoholate or from aqueous solutions of hydrosoluble titanium compounds by precipitation with a base, in particular ammonium hydroxide (NH₄OH). Process according to anyone of the preceding claims, wherein the catalytic compositions, before being used, are calcined at a temperature of from 50° to 800°C. Process according to anyone of the preceding claims, wherein the carbonyl compound is an aldehyde of formula R₁CHO, wherein R₁ is selected from alkyl, cycloalkyl, aryl or heterocyclic groups having from 1 to 18 carbon atoms, or is a ketone of formula R₂-CO-R₃, wherein R₂ and R₃, the same or different from each other, have the same meaning as R₁ and, additionally, may be combined to form a carbocyclic or heterocyclic ring. Process according to anyone of the preceding claims, wherein the carbonyl compound is selected from acetone, cyclohexanone, methylethyl-ketone, acetophenone, benzophenone, tert.-butyl-cyclohexanone, cyclo-dodecanone, enanthic aldehyde and benzaldehyde. A solid catalytic composition, particularly suitable for the preparation of oximes by ammoximation of the corresponding carbonyl compounds, substantially consisting of titanium and oxygen, chemically combined with each other, and being characterized by an XR-diffractogram, obtained by means of X-ray diffraction using the K α radiation of copper, which, in the (2ϑ) range from 10° to 65°, shows a smooth-trend line (halo) typical for amorphous solids and, optionally, the reflections of rutile and/or anatase and/or brookite.

Inventors: CESANA, ALBERTO, GENONI, FAUSTO, LEOFANTI, GIUSEPPE, PADOVAN, MARIO, PETRINI, GUIDO, ROFFIA, PAOLO
Applicants: MONTEDIPE S.R.L.
Application year: 1990
Main classification: C07C249
IPC codes: C07C249, B01J21