DE4447231A1 - Selective epoxidation of alkene(s) for use in e.g. glycol prodn. - Google Patents

Abstract

A process for the selective epoxidation of alkenes of formula (i) with atmos. oxygen in the presence of a catalyst of formula MxOy(L)z (1) is new, where R<1>-R<4> = H, 1-20C alkyl, 1-12C alkoxy or 6-10C aryl; or R<1> + R<2> may form a 5-30C ring; M = Mo, Ru or V; L = donor ligand; x = 1-3; z = 2-2x; y = 1-(2x + 1), and y is selected so that the sum of x + z gives a metal oxidn. state of +6 (Mo or Ru) or +5 (V). Pref. olefin starting materials are opt. branched aliphatic 2-30C olefins and 5-12C alicyclic olefins. Pref. oxidising agent is pure oxygen and oxygen diluted with inert gas. The process may be carried out in pure olefin without solvent, or in a solvent selected from halogenated aromatics, opt. halogenated hydrocarbons, 1-12C alcohols or water. The reaction temp. is 30-300 deg C for oxidn. of 6-12C alkenes and 120-230 deg C for 2-5C alkenes, and the pressure is such that reaction proceeds in the liq. phase. An activator or radical starter may be added, pref. in stoichiometric amts. based on the catalyst. The selectivity of the reaction is more than 40% with Mo complexes and more than 30% with Ru and V complexes.

Description

Epoxies (oxiranes) are compounds of considerable industrial importance. she find use in the production of a variety of economically important He Testimonies.

For example, epoxides can be hydrolyzed to glycols, which as Deicing agents or as reactive monomers for the production of Find condensation polymers application.

Are polyether polyols made by ring opening polymerization of epoxides commonly used as an intermediate in the manufacture of polyurethane foam fabrics, elastomers, coatings, sealants or similar items.

The reaction of epoxides with alcohols leads to glycol ethers, e.g. B. as polar Find solvents.

Many different processes have been developed for the production of epoxides, which should allow selective epoxidation of alkenes.

For example, Huybrecht (J. Mol. Catal. 71, 129 (1992); EP-A-311 983) the epoxidation of olefins with hydrogen peroxide in the presence of titanium silicate compounds as a catalyst. The range of products at However, oxidation of alkenes with titanium silicate catalysts is only obtained insufficiently controllable, so that even minimal changes in the Reaction conditions or the reactants used to drastic  Changes in the proportions of end products.

The epoxidation of propylene with atmospheric oxygen in the presence of tungsten or Catalysts containing molybdenum are described in DE-C-22 35 229. The ep oxidation reaction is carried out in a solvent that coexists with Oxygen can be oxidized to form hydroperoxides. The educated However, hydroperoxides lead to oxygen-containing ones in subsequent reactions By-products, usually alcohols, are used as reaction coupling products attack.

A process for the epoxidation of ethylene with t-butyl hydroperoxide (TBHP) in The presence of molybdenum complexes as a catalyst is described by Kelly et al. (Polyhedron, Vol. 5, 271-275, (1986)). As connections with high Complexes such as e.g. B. MoO₂ (8-hydroxyquinoline) ₂, MoO₂ (phenylene-bis-salicylimine) (= MoO₂ (salphen)), MoO₂ (salicylaldoxime) ₂ and MoO₂ (5-nitroso-8-hydroxyquinoline) ₂ called. The actual active catalyst is a molybdenum complex that has already added TBHP and one equivalent of epoxy. The process proceeds with high selectivity, but it becomes expensive Oxidation agent used. There are also problems with the Reproducibility on what prevents a technical use of the process.

The processes described in the prior art for the epoxidation of alkenes have the disadvantage that in addition to the desired epoxy end product also Series of undesirable by-products is obtained, d. that is, the reaction is not can be controlled selectively. Furthermore, in addition to that used Another oxidation agent is often used as a catalyst (generally a Hydroperoxide), the final reduction product after the reaction has been carried out must be disposed of.

The oxidation of olefins with air or oxygen as an oxidizing agent would be tech  nisch of great advantage, since the oxidizing agent is available inexpensively and the reaction could proceed without the formation of reduced by-products.

A process for the production of epoxides in the catalyzed Liquid phase oxidation of olefins with molecular oxygen or air is described in DD-B-1 59 075. Epoxidation active as catalysts Transition metal salts or complexes of molybdenum used, for. B. chlorine, Carbonyl or chloronitrosyl complexes that still donor ligands like Hexamethylphosphoric triamide (HMPT), triphenylphosphite or acetonitrile contain. The most active compounds here are those that use HMPT as donor ligands included, with HMPT known as a carcinogen.

In the case of the epoxidation of oct-1-ene in the presence of Molybdenum acetylacetonate 34% epoxy selectivity, in the presence of MoO₃ 28% found [J. Prod. Chem. 334 (1992) 165-75, Table 1, 7th column]. The so far best epoxy selectivity of 43.8% is for the complex MoCl₂ (NO) ₂ (HMPT) ₂ given [J. Practical Chemistry, 1984, 326, 1025-1026].

These catalysts all have the disadvantage only of epoxy selectivities of less than 45% (molybdenum (VI) only leads to selectivities 35%) and thus generate over 55% by-products.

In the scientific journal of the TH Leuna-Merseburg, (1985, 27, 282-294), is a measure of the influence of the catalyst in the liquid phase oxidation introduced by Oct-1-en, which catalyzes the epoxide selectivities obtained from uncatalyzed reaction. A number greater than 1 describes one catalytic effect. This table shows that the best value so far for MoO₂ (acac) ₂ is obtained with 1.91.

The aim of the present invention is to provide a method which allows olefins with oxygen or air with high selectivities to the  to oxidize corresponding epoxides.

The invention thus relates to a process for the selective epoxidation of alkenes of the formula

with atmospheric oxygen in the presence of a catalyst. As catalysts Compounds of the general formula (1) are used.

M _xO y (L) (1)

The symbols R¹, R², R³, R⁴, M, L, x, y and z have the following meaning:
R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₂₀-alkyl, C₁-C₁₂-alkoxy or C₆-C₁₀-aryl or R¹ and R² together form a ring with 5 to 30, preferably 5 to 8 carbon atoms.

The indices x, y and z have the following meaning:
x is an integer from 1 to 3, preferably 1 to 2, y is an integer from 1 to 2x + 1, preferably y = 1 or 2, where y is chosen so that the sum of x + z is a metal oxidation state of +6 (molybdenum, ruthenium) or +5 (vanadium); the index z is an integer in the range from 2 to 2x, preferably x = 2.
M means molybdenum, ruthenium or vanadium and
L stands for a donor ligand.

Particularly suitable donor ligands are compounds which differ from all  derived general formulas (2), (3) and (4).

X is oxygen (O), nitrogen (N) or sulfur (S) and R⁵ and R⁶ are un depending on each other for hydrogen, a branched or un branched, optionally halogenated C₁-C₁₂ alkyl radical or an optionally substituted C₆-C₁₄ aryl or heteroaryl or both together for one Group C = O or C = S. Optionally, the ring can be alkyl, aryl or Alkoxy groups can be substituted.

Preferred ligands are, for example, 1,1- (C₁-C₆) alkyl-1- (2-pyridyl) methanol, 1- (2-pyridyl) cyclohexan-1-ol, 1,1- (C₁-C₆) perfluoroalkyl-1- (2-pyridyl) methanol, 1,1- (C₁- C₆) alkyl-1- (2-thiophenyl) methanol, 1,1- (C₁-C₆) perfluoroalkyl-1- (2- thiophenyl) methanol, 1,1- (C₁-C₆) -alkyl-1- (2-pyrrolyl) methanol, 1,1- (C₁-C₆) -alkyl-1- (2-imidazole) methanol, 1,1- (C₁-C₆) perfluoroalkyl-1- (2-imidazole) methanol.

A process for the preparation of transition metal complexes of the formula (1) is described in the priority German applications P. . . . . . . . . . . (HOE 94 / F 401 and HOE 94 / F 402).

With a high selectivity are ins special aliphatic, optionally branched C₂-C₃₀ olefins and alicyclic C₅-C₁₂ olefins, preferably linear olefins having 2 to 12 carbon atoms and cycli olefins with 5 to 12 carbon atoms epoxidized.  

Oxygen serves as the oxidizing agent, in pure form or with an inert gas such as CO₂, N₂, noble gases or methane can be diluted.

The oxidation conditions are chosen so that even without the addition of Noticeable oxidation occurs, in which case the selectivity the epoxy formation is low.

The temperature at which the reaction can be carried out is in the range from 30 to 500 ° C, the pressure range can be varied from normal pressure to 200 bar and is preferably not more than 100 bar.

In general, the temperature / pressure range should be selected so that neither temperature pressure still assume extremely high values because the reaction under these conditions gene will be more difficult to handle.

For example, there is a temperature range of 30 to 300 ° C and a pressure in the range from normal pressure to 30 bar in the oxidation of C₆-C₁₂ alkenes proven advantageous during the epoxidation of alkenes with less than 6 Carbon atoms preferably at lower temperatures in the range of 120 to 230 ° C and pressures in the range of 30 to 100 bar is carried out. It will be so worked that the oxidation always takes place in the liquid phase.

The liquid phase oxidation takes place either in pure olefin or diluted in an oxidation stable solvent. Suitable solvents are, for. B. the following groups in question: halogenated aromatics, such as chlorobenzene, 1-chloro-4-bromobenzene, bromobenzene, halogenated and non-halogenated Hydrocarbons such as B. chloroform, chloropropanol, dichloromethane, 1,2- Dichloroethane, trichlorethylene, also alcohols, especially C₁-C₁₂ alcohols, such as Ethanol, methanol or propanol as well as higher alcohols and water.

The oxidation can be carried out continuously or in a batch process. The catalyst can be added in bulk. The catalyst can too  are generated in situ during catalysis, e.g. B. from precursor and ligands. Furthermore, the reaction can be carried out by adding stoichiometric amounts, based on the catalyst, an activator such as hydroperoxides, hydrogen peroxides or Peracids and / or by adding a radical initiator such as azobisisobutyronitrile be accelerated.

In the case of a continuous procedure, the addition of oxygen is metered in such a way that a residence time in the reactor of less than 60 minutes, preferably less than 1 minute, results. In the batch process, the oxygen uptake can be achieved until the conversion of the Alkene take place, but preference is given to an oxygen up to one Alkene turnover <50%. An oxygen uptake <50% leads to a Increased sales but also a reduction in selectivity as the Further oxidation of the epoxide increases. The reaction product is worked up and e.g. B. purified by distillation. This also applies to the continuous procedure.

With the help of the method according to the invention, the epoxy yields in Significantly improved compared to the prior art. For example, at achieved the oxidation of oct-1-ene epoxy yields of <50%, while in the previously known processes the highest yields were 43.8%. This means, that with the method according to the invention measures for the influence of the catalyst (Ratio of epoxy selectivity from catalyzed and uncatalyzed Response) of <2 can be achieved.

In general, it can be said that the selectivity of the reaction of the present Process when using molybdenum complexes <40%, in particular < Is 49% and when using vanadium and ruthenium complexes < 30%, in particular <35%.

The one used as an oxidizing agent in the process according to the invention Oxygen is available inexpensively and the formation of reduced ones  By-products that are disposed of after the epoxidation reaction must be dropped.

The invention is illustrated by the following examples.

Example 1 (comparative example) Autoxidation of oct-1-ene

2.0 ml (12.6 mmol) are placed in a 10 ml reactor heated to 100 ° C. Given oct-1-en. The apparatus is rinsed with O₂ and with a clean one O₂ atmosphere (1 bar) filled. After 6 hours the O₂ intake is 10 ml (0.45 mmol). It is then cooled, 1 ml of the reaction solution with exactly 50 µl Heptane (external GC standard) added and analyzed by gas chromatography. The Selectivity for 1,2-epoxyoctane is 21%.

Example 2 (comparative example) Oxidation of oct-1-ene, cat: MoO₂ (acac) ₂

2.0 ml (12.6 mmol) oct-1-ene and 54 mg MoO₂ (acac) ₂ (120 µmol) are placed in a 10 ml reactor heated to 100 ° C. The apparatus is rinsed with O₂ and filled with a pure O₂ atmosphere (1 bar). After 150 minutes and an O₂ uptake of 10 ml, the reaction is stopped by cooling, 1 ml of the reaction solution is mixed with exactly 50 μl of heptane (external GC standard) and analyzed by gas chromatography.
Selectivity for 1,2-epoxyoctane: 7%
Catalyst index: 0.30.

The catalyst index is defined as the ratio of the epoxide selectivity of the  catalyzed reaction from this example to the uncatalyzed reaction Example 1.

Examples 3-15 Oxidation of oct-1-enes (Table 1)

2.0 ml (12.6 mmol) of - are placed in a 10 ml reactor heated to 100 ° C. Oct-1-en and 120 µmol each of the catalyst. The apparatus comes with O₂ rinsed and filled with a pure O₂ atmosphere (1 bar). The time to one O₂ recording of 10 ml is measured, the reaction is stopped by cooling, 1 ml of Reaction solution with exactly 50 µl heptane (external GC standard) and analyzed by gas chromatography. Table 1 shows the ones used Catalysts assigned to the examples and the time to take 10 ml O₂, the epoxy selectivity and the measure of the influence of the catalyst, as in Example 2 defined, listed.

Example 16 Oxidation of oct-1-ene, longer O₂ uptake

2.0 ml (12.6 mmol) of oct-1-ene and 45 mg of MoO 2 (L2) 2 (120 μmol) are placed in a 10 ml reactor heated to 100 ° C. The apparatus is rinsed with O₂ and filled with a pure O₂ atmosphere (1 bar). After 360 minutes and an O₂ uptake of 35 ml, the reaction is stopped by cooling, 1 ml of the reaction solution is mixed with exactly 50 μl of heptane (external GC standard) and analyzed by gas chromatography.
Selectivity for 1,2-epoxyoctane: 55%
Catalyst number 2.63.

From this example it can be seen that the epoxide selectivity is independent of the conversion (oxygen uptake) (see Example 4).

Example 17 Oxidation of oct-1-ene, activation with tert-butyl hydroperoxide

2.0 ml (12.6 mmol) oct-1-ene and 45 mg MoO₂ (L2) ₂ (120 µmol) and 10 ml (105 mmol) 70% are placed in a 10 ml reactor heated to 100 ° C. in tert-butyl hydroperoxide solution in water. The apparatus is rinsed with O₂ and filled with a pure O₂ atmosphere (1 bar). After 120 minutes and an O₂ uptake of 10 ml, the reaction is stopped by cooling, 1 ml of the reaction solution is mixed with exactly 50 μl of heptane (external GC standard) and analyzed by gas chromatography.
Selectivity for 1,2-epoxyoctane: 53%
Catalyst number 2.53.

This makes it clear that by adding approximately stoichiometric amounts (based on catalyst) hydroperoxide the reaction can be accelerated (see Example 4).

Example 18 Oxidation of propene

In a 200 ml autoclave, 18 mg MoO₂ (L1) ₂ are dissolved in 20 ml chlorobenzene and condensed 15 g of propene at -20 ° C. The reaction mixture is on Brought 180 ° C, at this temperature 15 bar air and 10 minutes touched. The reaction is then stopped by cooling, one at 20 ° C. Gas and liquid samples taken and both by gas chromatography analyzed. The selectivity for propene oxide is 21% with an O₂ conversion of 85%.  

Table 1

Claims (11)

1. Process for the selective epoxidation of alkenes of the formula with atmospheric oxygen in the presence of a catalyst of the general formula (1) M _x O _y (L) _z (1) where the symbols R¹, R², R³, R⁴, M, L, x, y and z have the following meaning:
R¹, R², R³ and R⁴ independently represent hydrogen, C₁-C₂₀-alkyl, C₁-C₁₂-alkoxy or C₆-C₁₀-aryl or R¹ and R² together form a ring with 5 to 30 carbon atoms;
the indices x, y and z have the following meaning:
x is an integer from 1 to 3, y is an integer from 1 to 2x + 1, where y is chosen so that the sum of x + z is a metal oxidation state of +6 (molybdenum, ruthenium) or +5 (vanadium ) results; the index z is an integer in the range from 2 to 2x;
M means molybdenum, ruthenium or vanadium and
L stands for a donor ligand. 2. The method according to claim 1, characterized in that compounds derived from the general formulas (2), (3) and (4) are used as donor ligands where X is oxygen (O), nitrogen (N) or sulfur (S) and R⁵ and R⁶ independently represent hydrogen, a branched or unbranched C₁-C₁₂ alkyl radical or an optionally substituted C₆- C₁₄ aryl radical or both together for one Group C = O stand. 3. The method according to claim 2, characterized in that as donor ligands Compounds are used, which are from 1,1- (C₁-C₆) alkyl-1- (2-pyri dyl) methanol, 1- (2-pyridyl) cyclohexan-1-ol, 1-phenyl-1- (2-pyridyl) methanol, 1,1- (C₁-C₆) alkyl-1- (2-thiophenyl) methanol, 1,1- (C₁-C₆) perfluoro-alkyl-1- (2-  thiophenyl) methanol, 1,1- (C₁-C₆) -alkyl-1- (2-pyrrolyl) methanol, 1,1- (C₁-C₆) - alkyl-1- (2-imidazole) methanol, 1,1- (C₁-C₆) perfluoroalkyl-1- (2-imidazole) derive methanol. 4. The method according to claim 1, characterized in that aliphatic, optionally branched C₂-C₃₀ olefins and alicyclic C₅-C₁₂ olefins be epoxidized. 5. The method according to claim 1, characterized in that as the oxidation medium oxygen is used in pure form or with a Inert gas is diluted. 6. The method according to claim 1, characterized in that the reaction temperature temperature in the oxidation of C₆-C₁₂ alkenes in the range of 30 to 300 ° C. and in the oxidation of C₂-C₅ alkenes in the range of 120 to 230 ° C. and the pressure is chosen so that the reaction takes place in the liquid phase. 7. The method according to claim 1, characterized in that the oxidation without solvent, in pure olefin. 8. The method according to claim 1, characterized in that the oxidation in a solvent selected from the group of halogenated aromatics, the halogenated or non-halogenated hydrocarbons, the C₁-C₁₂- Alcohols or in water.   9. The method according to claim 1, characterized in that the reaction medium an activator and / or a radical initiator is added. 10. The method according to claim 9, characterized in that the activator in stoichiometric amounts based on the catalyst is added. 11. The method according to claim 1, characterized in that the selectivity of the Reaction when using molybdenum complexes <40% and when using formation of vanadium or ruthenium complexes is <30%.