Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-01-07
2001-12-04
Lambkin, Deborah C. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S532000, C549S523000
Reexamination Certificate
active
06326502
ABSTRACT:
The present invention relates to a process for preparing epoxides by catalytic oxidation of olefins using air or oxygen.
Epoxides (oxiranes), for example ethylene oxide, propylene oxide, 1,2-butene oxide or similar epoxides, are widely used intermediates in the production of a great number of products. The oxirane function in such compounds is very reactive and can undergo ring-opening reactions with nucleophilic reactants. Thus, for example, epoxides can be hydrolyzed to form glycols which are employed as deicing agents or as reactive monomers for preparing condensation polymers.
Polyether polyols prepared by ring-opening polymerization of epoxides are widely used as intermediates in the production of polyurethane foams, elastomers, coatings, sealants or similar products.
The reaction of epoxides with alcohols leads to glycol ethers which are used, for example, as polar solvents.
For the preparation of epoxides, a wide variety of processes which are supposed to selectively catalyze the epoxidation of alkenes have been developed.
Thus, for example, Huybrecht (J. Mol. Catal. 71, 129 (1992); EP-A-311 983) describes the epoxidation of olefins using hydrogen peroxide in the presence of titanium silicate compounds as catalyst. However, the range of products which is obtained in the oxidation of alkenes using titanium silicate catalysts is not sufficiently controllable, so that even minimal changes in the reaction conditions or in the reactants used lead to drastic changes in the proportions of the end products.
The epoxidation of olefins using atmospheric oxygen in the presence of tungsten- or molybdenum-containing catalysts is described in DE-C-22 35 229. The epoxidation reaction is carried out in a solvent which can be oxidized by oxygen to form hydroperoxides. However, the hydroperoxides formed lead, in further reactions, to oxygen-containing by-products, generally alcohols, which are formed as coproducts of the reaction.
A process for the epoxidation of ethylene using t-butyl hydroperoxide (TBHP) in the presence of molybdenum complexes as catalysts is described by Kelly et al. (Polyhedron, Vol. 5, 271-275, (1986)). As compounds having a high catalyst activity, mention is made of complexes such as MoO
2
(8-hydroxyquinoline)
2
, MoO
2
(phenylenebissalicylimine) (=MoO
2
(salphen)), MoO
2
(salicylaldoxime)
2
and MoO
2
(5-nitroso-8-hydroxyquinoline)
2
. The actual active catalyst is a molybdenum complex which has undergone an addition reaction with TBHP and one equivalent of epoxide.
The process does proceed with high selectivity, but an expensive oxidizing agent is used. Furthermore, reproducibility problems occur, which prevents industrial use of the process.
The oxidation of olefins using air or oxygen as oxidizing agent would be of great advantage in industry, since the oxidizing agent is available at low cost and the reaction could proceed without formation of reduced by-products.
A process for preparing epoxides in the catalyzed liquid-phase oxidation of olefins using molecular oxygen or air is described in DD-B-159 075. Catalysts used are epoxidation-active transition metal salts or complexes of molybdenum, e.g. chloro, carbonyl or chloronitrosyl complexes which additionally contain donor ligands such as hexamethylphosphoramide (HMPA), triphenyl phosphite or acetonitrile. The most active compounds here are those which contain HMPA as donor ligands, but HMPA is known to be carcinogenic.
The epoxidation of 1-octene using molybdenum catalysts has been subject matter of a study in J. Prakt. Chem. (1992, 334, 165-175). A selectivity to 1,2-epoxyoctane of 34% is found in the presence of molybdenum acetylacetonate, and a selectivity of 28% is found in the presence of molybdenum trioxide. Likewise, it is confirmed that the position of the transition metal in the Periodic Table and its oxidation state have by far the greatest influence on the catalyst activity, while the structure of the catalyst complex itself plays only a subordinate role.
FR-A-2115752 discloses a process for the epoxidation of olefins in a titanium-lined autoclave. However, this is a non-catalytic process.
The best epoxide selectivities to date are known from DE-A-444 7231. This publication discloses molybdenum catalysts which contain an organic donor ligand. However, the catalytic activities of these catalysts are still capable of improvement.
It is an object of the present invention to provide a process which allows olefins to be oxidized highly selectively using oxygen or air to give the corresponding epoxides.
It has surprisingly been found that improved epoxide selectivities and yields are obtained using molybdenum catalysts under particular reaction conditions or when a particular procedure is employed.
The present invention provides a process for the epoxidation of alkenes of the formula (1)
where R
1
, R
2
, R
3
and R
4
are, independently of one another, hydrogen, C
1
-C
20
-alkyl, C
1
-C
12
-alkoxy, C
6
-C
10
-aryl, —CHOH—CH
3
, —CH—NH
2
—CH
3
or carboxy, using air or oxygen over a catalyst comprising compounds of the formula (2)
Mo
x
O
y
(L)
z
(2)
where
x is1,2 or 3,
y is an integer from 0 to 2x+1, preferably from<1 to 2x+1,
z is an integer from 1 to 2x,
and 2y+z is preferably 5 or 6,
where the ligand L is a compound of the formula (3) or (4)
where
x is a nitrogen, oxygen or sulfur atom,
Y is hydrogen, C
1
-C
8
-alkyl, C
1
-C
8
-alkoxy, F, Cl, Br, I, COOCH
3
,
C
6
-C
14
-aryl or C
3
-C
8
-cycloalkyl,
R
7
and R
8
form a ring containing from 4 to 8 carbon atoms onto which one or two aromatic rings may be fused,
R
5
and R
6
are hydrogen, branched or straight-chain C
1
-C
12
-alkyl or branched or straight-chain C
1
-C12-haloalkyl which are substituents on the ring formed by R
7
and R
8
and/or the rings fused onto this ring,
or the ligand L is a compound of the formula (5), (6) or (7)
where R is hydrogen, C
1
-C
8
-alkyl, C
1
-C
8
-haloalkyl, C
1
-C
8
-alkoxy, COOCH
3
, C
6
-C
14
-aryl or C
3
-C
8
-cycloalkyl and n is 1 or 2 and m is from 1 to 6, wherein the reaction is carried out in a pressure vessel which is completely lined with an inert material.
The ligand is generally bound in a bidentate manner to the metal center which can bind up to two such ligands. In the case of the tetradentate ligand (7), only one ligand is bound. Both cis and trans isomers of the dioxo complexes are possible.
Examples of preferred ligands L are the following compounds:
where R=CH
3
, C
2
H
5
, i-C
3
H
7
, n-C
3
H
7
and n-C
4
H
9
.
Complexes of the formula (2) are prepared by reacting a suitable precursor with the appropriate ligands in an organic solvent. Suitable precursors are, for example, the commercially available oxo-acetylacetonates such as molybdenyl acetylacetonate MoO
2
(acac)
2
or oxo-dithiocarbamates, e.g. molybdenyl bis(N,N-diethyldithiocarbamate), the pyridyl and/or acetate complexes of the oxides, the higher oxides, e.g. molybdenum trioxide, or the corresponding acids and their salts.
The precursor is suspended in an organic solvent. The most suitable organic solvents are polar protic solvents such as methanol or ethanol and protic solvents such as acetonitrile or methyl tert-butyl ether (MTBE) or halogenated hydrocarbons such as CH
2
Cl
2
, CHCl
3
or CCl
4
. The appropriate ligand is subsequently added while stirring. The amount of ligand used is preferably twice that of the precursor used.
After the reaction is complete, the mixture is filtered off and the residue is washed. The filtration residue obtained can be used as catalyst in this form or after drying under reduced pressure.
Supported complexes can be prepared by adding a suitable carrier material during and/or after the synthesis of the complex. For this purpose, the starting complex of the formula (2) is dissolved in an organic solvent or water, the carrier material is added and the mixture is stirred. The ratio of complex/carrier material is preferably in the range from 1:1 to 1:1000, in particular in the range from 1:2 to 1:100.
Suitable carrier materials are inorganic and organic carrier
Dingerdissen Uwe
Herrmann Wolfgang Anton
Lobmaier Gerhard
Schulz Rolf Peter
Aventis Research & Technologies GmbH & Co. KG
Connolly Bove & Lodge & Hutz LLP
Lambkin Deborah C.
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