MXPA99010971A - A process for the epoxidation of alkenes - Google Patents

Abstract

The invention provides a process for the catalytic epoxidation of alkene comprising contacting a transition metal substituted polyoxometalate and molecular oxygen with alkene.

Description

PROCEDURE FOR THE EPOXIDATION OF ALKENS TECHNICAL FIELD The present invention relates to the catalytic activation of molecular oxygen for epoxidation of alkene using polyoxometalates substituted by transition metal as catalysts.

TECHNICAL BACKGROUND The epoxidation of alkenes is an important chemical transformation in which an oxygen atom is added to a carbon-carbon double bond to form an epoxide. Epoxides are often used as intermediates that can then be transformed into final products. Examples include but are not limited to ethylene glycol and polyethylene glycol from ethylene oxide, propylene glycol from propylene oxide, phenylacetaldehyde from styrene oxide and propanolol from 2R-glycolid. The epoxidation of alkenes can be carried out using numerous techniques. The oldest and probably the most common method is to react the alkene with an organic peracid, according to the reaction described in equation (1).

Typical peracids used in the art include perbenzoic acid, peracetic acid, performic acid, perphthalic acid and substituted perbenzoic acids such as 3-chloroperbenzoic acid. Salts of such acids can also be effective oxidants as in the case of magnesium monoperoxophthalate. The acids can be used as pure compounds or as in situ preparations in the reaction mixture by, for example, adding hydrogen peroxide to acetic anhydride to form peracetic acid. Although the reaction-based methods as described in equation (1) are known, there are certain disadvantages that are associated with such reactions. Among these are the propensity for the formation of by-products such as glycols and glycolic esters by reaction of the epoxide with water and / or acid in the reaction medium, (b) the need to recover and / or recycle the co-product. -acid product and (c) the need for strict reaction control due to the safety hazard involved in the use of organic peracids (acyl hydroperoxides). In order to minimize the hazard by using peroxides as oxidants, the use of alkyl and alkylaryl hydroperoxides instead of acyl hydroperoxides has been suggested and applied. These oxidants do not react normally with alkenes and the addition of a catalyst is required as shown in the reaction illustrated in equation (2).

R = alkylo, Some hydroperoxides commonly used in such reactions are fe / t-butylhydroperoxide, eumenohydroperoxide and ethylbenzene hydroperoxide. The catalysts used are more commonly based on compounds containing Ti (IV), V (V), Mo (VI) or W (VI) although many compounds based on other metals have been described as effective catalysts. These reactions are safer due to the lower reactivity of alkyl and alkyl aryl hydroperoxides compared to the organic peracids, however, the other disadvantages associated with the use of acyl hydroperoxides remain. In this way, the reactions are not necessarily more selective, because the presence of catalysts often leads to additional side reactions, for example, substitution and oxidation in the allylic carbon of the alkene instead of the addition of oxygen to the double bond. . Similar to the problems encountered with the use of acyl hydroperoxides, the alcohol co-product must be recovered, recycled and / or used in another way.

An additional method to epoxidize alkenes is to use aqueous hydrogen peroxide as the oxidant as shown in the reaction illustrated in equation (3).

Such reaction represents a conceptual improvement compared to the use of organic hydroperoxides in which the co-product is water and therefore is benign with the environment and does not need to be recovered or recycled. As in the use of alkyl and alkylaryl hydroperoxides the presence of a catalyst is necessary, whose catalyst are again frequently compounds containing Ti (IV), V (V), Mo (VI) or W (VI), among others. In only certain cases, a high selectivity for alkene epoxidation has been reported. Some effective and selective catalysts include titanium silicate-1 and other substituted titanium zeolites, and polyoxometalates such as [WZnMn2 (ZnW9? 34) 2] '12"and { PO4 [WO (2) 2] 4.}. 3". In many cases, the use of hydrogen peroxide represents an ideal oxidant with the proviso that the reactions are selective. An exception is in cases where the low price of the epoxide makes the use of hydrogen peroxide prohibitively expensive. An additional important method for the synthesis of epoxides from alkenes is via the formation of a halohydrin, preferably a hydrochloride, using hypochlorous acid in the first step, followed by the use of base, for example NaOH to close the ring in the second step. step, as shown in the reaction illustrated in equation (4).

This is a very simple procedure which has, however, two problems. First, normally the presence of molecular chlorine in hypochlorous acid leads to the formation of dichlorinated organics which are undesirable by-products and must be discarded. Second, the process also forms large quantities of salts as co-products which must also be treated or recycled. The ideal oxidant for alkene epoxidation both from an ecological and economic point of view would be molecular oxygen (dioxygen) as it is found in the air. The addition of dioxygen to an alkene is disadvantaged kinetically, therefore the catalytic processes need to be applied. In cases where there is no allylic carbon to the double bond, oxygen can be added to the double bond using a silver catalyst at elevated temperatures. In this way, ethylene oxide is manufactured from ethylene. For similar procedures with other alkenes, such as 1-butene, propene, etc., this reaction fails to give epoxide in significant amounts. The basic problem in the use of dioxygen for epoxidization of alkene lies in the radical nature of the molecule of molecular oxygen. In homogeneous reactions, this radical nature always leads to a preferred radical reaction via the substitution of hydrogen at an allylic carbon atom. Therefore, the common mode of use of dioxygen in catalyzed reactions of liquid phase does not yield epoxide as a main product. The situation in gas phase reactions is similar in which the activation of alkenes leads to allylic type carbocations, carbanions of carbon radicals that again prevent the formation of epoxides as a significant product. Conceptually, in order to use dioxygen for alkene epoxidation, the activation of dioxygen must be through the formation of a high valence oxo metal compound formed after cutting the oxygen-oxygen bond. These high valence metal-oxo intermediates are effective epoxidation agents. More commonly this is carried out in nature by the use of monoxigenase-like enzyme such as cytochrome P-450 or methane monoxigenase. Such enzymes can be simulated, for example, using manganese and iron porphyrins as catalysts. The mechanism of monooxygenase, however, requires two electrons of a reducing agent in order to cut the oxygen-oxygen bond that leads to the formation of the active high-valence metal-oxo intermediate in alkene epoxidation. From a process point of view the reducing agent becomes the limiting reagent instead of the dioxygen and negates the attractiveness of such a process.

The alternative is the activation of dioxygen in a dioxygenase type mechanism. In such a reaction, the dioxygen is cut using two metal centers that lead to the formation of two high valence oxo-metal species. This type of reaction has only been carried out using a ruthenium-substituted tetramesitylpyridine (RuTMP). The epoxide conversion rates are very low and the catalyst has limited stability. The limited stability of the porphyrin ligands has led to the suggestion that transition metal-substituted polyoxometalates may be important alternating catalysts to metalloporphyrins as described and discussed in Hill, U.S. Pat. No. 4,864,041. These catalysts would retain the high activity of their metalloporphyrin counterparts, however, they are significantly more stable thermally and oxidatively, thus allowing their use as long-lasting catalysts. This previous work 'describes the application of transition metal-substituted polyoxometalates for the epoxidation of alkenes using oxygen donors such as iodocylbenzene. Other reported academic research has evolved from this report and has described the epoxidation of alkene using other oxygen donors such as tert-butylhydroperoxide, hydrogen peroxide and p-cyano-N, N-dimethylaniline-N-oxide. The use of transition metal-substituted polyoxometalates as catalysts for alkene epoxidation with molecular oxygen has never been described.

BRIEF DESCRIPTION OF THE INVENTION According to this, is u? object of this invention is to provide a new process for the epoxidation of alkenes using molecular oxygen as an oxidant. It is also an object of this invention to provide a method for carrying out this epoxidation of alkenes with molecular oxygen using a transition metal catalyst. Additionally, it is an object of this invention to carry out said epoxidation using polyoxometalate substituted by transition metal as a catalyst. In accordance with the present invention, a process using transition metal-substituted polyoxometalates as catalysts for the epoxidation of alkenes with molecular oxygen has now been discovered. More in particular the present invention provides a process for the catalytic epoxidation of alkene which comprises contacting a polyoxometalate substituted by transition metal and molecular oxygen with alkene. The process described in this invention relates to the use of transition metal-substituted polyoxometalates (TMSP) to catalyze the epoxidation of alkenes with molecular oxygen according to the following equation (5).

Polyoxometalates are oligomeric oxides of defined structure based on the addition of tungsten, molybdenum, niobium or vanadium or a combination thereof. More specifically, the polyoxometalates substituted by transition metal are compounds of the general formula Xx (TM) andMmOzq "wherein the heteroatom, X, if present (x_0) can be metals of the main or transition group, the added atoms , M, are molybdenum, tungsten, niobium or vanadium or a combination thereof, and TM is one or several different transition metals, The specific classes of polyoxometalates substituted by transition metals, [WZnTM2 (XW9? 34) 2] ", used in the process described by the present invention are characterized as a dimer of a truncated Keggin structure having a" band "of W, Zn and other transition metal (TM) cations" sandwiched "between the two fragments [ RU2ZnW (ZnW9? 34) 2] 11"Keggin trivacant the structure of which is shown in Figure 1 which is attached.The transition metal cations are assumed to be placed in terminal positions and are hexacoordinated with at least It's a labile ligand like water. The TM atom can be any transition metal of the first, second or third row. More preferably the TM atom is a noble metal selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium and platinum. More preferably the TM atom is ruthenium. The heteroatom atom, X, of the trivalent Keggin fragments can be any hetero atom known for Keggin compounds as is well known in the art. For example, X may be a non-metal such as phosphorus, silicon, germanium, boron or arsenic. Alternatively X can be a metal such as zinc, cobalt, iron, etc. The polyoxometalate substituted by transition metal preferred for this process is [WZnRu2 (ZnW9? 34) 2] 11. "None of the polyoxometalates substituted by transition metal or those of the general structure described and shown above have been used as catalysts for the epoxidation of alkenes with molecular oxygen The counter cation of the above transition metal-substituted polyoxometalates can be any cation including for example alkali metal, alkaline earth metal cations, transition metal cations or organic cations such as quaternary ammonium salts. described in equation (5), it is carried out by contacting the catalyst with molecular oxygen and alkene, in a catalytic process, molecular oxygen is contacted, followed by contact with the alkene, in another procedure the catalyst is contacted simultaneously with the catalyst. molecular oxygen and alkene, the reaction or contac The catalyst and the reactants (alkene and molecular oxygen) can take place in a solvent in which the reactants are added to the catalyst dissolved in a liquid phase. Some typical solvents are aliphatic hydrocarbons, aromatic, or halogenated. Illustrative solvents of these classes are 1,2-dichloroethane, heptane, toluene, xylene, chlorobenzene or mixtures thereof. Alternatively, the catalyst may be placed on a support or used as a simple solid followed by the addition of the reagents. The support used for the catalyst can be any support used in heterogeneous catalysis including among others silica, alumina and other oxides. The alkenes applicable as reagents in this process can be any type of known alkenes. These include simple terminal and linear alkenes such as ethene, propene, 1-butene, 1-ketene, etc. The alkene can be a branched or linear internal alkene such as 2-butene, 2-octene, 2-methyl-2-heptene, 2,3-dimethyl-2-butene, etc. The alkene can also be cyclic, for example cyclohexene, cyclooctene, norbornene, etc. Molecular oxygen can be used pure, as air, as air enriched with oxygen, or as air devoid of oxygen. Inert gases can be added. The suggested temperature scale of the reaction is between 0 and 350 ° C. More preferably between 25 and 250 ° C and more preferably between 60 and 180 ° C. The reaction can be operated at atmospheric, subatmospheric or superatmospheric pressures. More preferably the reaction is run at superatmospheric pressures. Although the invention will now be described in connection with certain preferred embodiments in the following examples and with reference to the appended figures so that aspects thereof can be more fully understood and appreciated, it is not intended to limit the invention to these embodiments. particular. On the contrary, it is designed to cover all alternatives, modifications and equivalents as they may be included within the scope of the invention as defined by the appended claims. Therefore, the following examples which include preferred embodiments will serve to illustrate the practice of this invention, it being understood that the features shown are by way of example and for illustrative discussion objects of preferred embodiments of the present invention only and present with the intention of providing what is believed to be the most useful and easily understandable description of formulation procedures as well as the principles and conceptual aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates the molecular structure of a polyoxometalate substituted by illustrative transition metal, [WZnRu2 (ZnW9? 34) 2] 11", active in the catalysis of the addition of molecular oxygen to alkenes to form epoxides.

EXAMPLE 1 A 5 ml solution of degassed 1,2-dichloroethane containing 100 μmol of QnWZnRu2 (ZnW9? 34) 2, in which Q is tricaprilmethyl ammonium was maintained under 1 atm of molecular oxygen at 90 ° C for 9 hours in a vessel closed. The oxygen solution was cooled to room temperature and 1.2 mg of cyclooctene was added. After 2 hours the solution was analyzed by GLC. The analysis showed a conversion of 67.5% to cyclooctene oxide.

EXAMPLE 2 A 5 ml solution of degassed 1,2-dichloroethane containing 100 μmol of QnWZnRu2 (ZnWg? 34) 2, in which Q is tricaprylmethyl ammonium was maintained under 1 atm of molecular oxygen at 120 ° C for 6 hours in a vessel closed. The oxygen solution was cooled to room temperature and 11.2 mg of cyclooctene were added. After 2 hours the solution was analyzed by GLC. The analysis showed a conversion of 72.1% to cyclooctene oxide.

EXAMPLE 3 A 5 ml solution of degassed 1,2-dichloroethane containing 100 μmol of QnWZnRu2 (ZnW9 34 34) 2, in which Q is tricamycinium ammonium was maintained under 1 atm of molecular oxygen at 90 ° C for 9 hours. hours in a closed container. The oxygen solution was cooled to room temperature and 9.4 mg of norbornene were added. After 2 hours the solution was analyzed by GLC. The analysis showed a conversion of 82.1% to norbonene oxide.

EXAMPLE 4 A 5 ml solution of degassed toluene containing 100 μmol of QnWZnRu2 (ZnW9 34 34) 2, in which Q is tricaprilmethyl ammonium was maintained under 1 atm of molecular oxygen at 90 ° C for 9 hours in a closed vessel. The oxygen solution was cooled to room temperature and 11.2 mg of cyclooctene were added. After 2 hours the solution was analyzed by GLC. The analysis showed a conversion of 63.7% to cyclooctene oxide. EXAMPLE 5 A 5 ml solution of degassed 1,2-dichloroethane containing 100 μmol of Q ?? WZnRu2 (ZnW9? 34) 2, in which Q is tricaprylmethyl ammonium was maintained under 1 atm of molecular oxygen at 90 ° C for 9 hours in a closed container. The oxygen solution was cooled to room temperature and 8.4 mg of 2,3-dimethyl-2-butene were added. After 2 hours the solution was analyzed by GLC. The analysis showed a conversion of 78.4% to 2,3-dimethyl-2-butene oxide.

EXAMPLE 6 A degassed 1,2-dichloroethane solution containing 100 μmol of QnWZnRu2 (ZnW9? 34) 2 in which Q is tricaprilmethyl ammonium was maintained under 1 atm of molecular oxygen at 90 ° C for 9 hours in a closed vessel. The oxygen solution was cooled to room temperature and the solution was purged and repressurized with 1 atm of propene. After 2 hours at 80 ° C the solution was analyzed by GLC. The analysis showed 96% propene oxide and 4% acrolein as the only products.

EXAMPLE 7 A 5 ml solution of degassed 1,2-dichloroethane containing 100 μmol of QnWZnRu2 (ZnWg? 34) 2 in which Q is tricaprilmethyl ammonium was maintained under 1 atm of molecular oxygen at 120 ° C for 6 hours in a closed vessel . The oxygen solution was cooled to room temperature and the solution was purged and repressurized with 1 atm of propene. After 2 hours at room temperature the solution was analyzed by GLC. The analysis showed 98% propene oxide and 2% acrolein as the only products.

EXAMPLE 8 A 5 ml solution of degassed 1,2-dichloroethane containing 100 μmol of Q ?? WZnRu2 (ZnW9? 34) 2 in which Q is tricaprylmethyl ammonium was maintained under 1 atm of molecular oxygen at 90 ° C for 18 hours in a closed container. The oxygen solution was cooled to room temperature and 11.2 mg of 1-ketene was added. After 18 hours at 60 ° C the solution was analyzed by GLC. The analysis showed a conversion of 76% to 1-octene oxide.

EXAMPLE 9 A 5 ml solution of degassed toluene containing 2.5 μmol of QnWZnRu2 (ZnWg? 34) 2 in which Q is tricaprylmethyl ammonium and 280 mg was kept under 5 atmospheres of molecular oxygen at 90 ° C for 24 hours in a closed vessel. After cooling the GLC analysis showed a 15% conversion of cyclooctene to cyclooctene oxide. It will be apparent to those skilled in the art that the invention is not limited to the details of the illustrative examples mentioned above and that the present invention can be carried out in other specific forms without departing from the essential attributes thereof, and wishes therefore that the present embodiments and examples be considered in all respects as illustrative and not restrictive, with reference to the appended claims, rather than the above-mentioned description, and that all changes that come within the meaning and equivalence scope of the claims are therefore designed to be encompassed therein.

Claims (11)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for the catalytic epoxidation of an alkene which comprises contacting said alkene with molecular oxygen and with a polyoxometalate substituted by transition metal of the formula [RU2 Zn W (X W9 O34) 2] q, characterized in that X is a heteroatom selected from Zn, Co, Fe, P, Si, Ge, B and As and Q is a counter cation

2. A method according to claim 1, wherein X is selected from Zn and Co.

3.- A process according to claim 1, wherein said counter cation is a cation selected from an alkali, alkaline earth metal or transition metal cation or an organic cation

4. A process according to claim 1, wherein said polyoxometalate substituted by transition metal has the formula [Ru2 Zn W (X W9 O3) 2] 11"Qi i.

5. A process according to claim 4, wherein Q is tricaprylmethyl ammonium.

6. A process according to claim 1, wherein said alkene is selected from the group consisting of branched, linear and cyclic alkenes.

7. - A method according to claim 1, wherein said polyoxometalate substituted by transition metal is first contacted with molecular oxygen, followed by contact with said alkene.

8- A method according to claim 1, wherein said polyoxometalate substituted by transition metal is contacted simultaneously with molecular oxygen and said alkene.

9. A process according to claim 1, wherein said epoxidation is carried out at a temperature in the range between 25 ° C and 250 ° C.

10. A process according to claim 1, wherein said epoxidation is carried out at superatmospheric pressure.

11. A process according to claim 1, wherein said molecular oxygen is diluted with at least inert gas.