Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1993-12-28
1995-07-04
Evans, Joseph E.
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
502150, 549546, C07D30112, C07D30304
Patent
active
054301610
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for epoxidation, and more particularly to such a process employing hydrogen peroxide and catalysed by a metal. The invention further relates to metal catalysts which are suitable for use in such epoxidation processes and the production of such catalysts.
In a well known process for epoxidising an olefinic group of formula >C.dbd.C< in a substrate to an epoxide of formula ##STR1## the substrate is reacted with hydrogen peroxide in a suitable reaction medium which often comprises an halogenated hydrocarbon, in which a heavy or transition metal catalyst is dissolved. Such a reaction employs the catalyst homogeneously, which can be very effective because it enables the catalyst to contact the substrate intimately throughout the liquid reaction medium, but as a result the reaction mixture is contaminated by the presence of such metals. In the past, the cheapest method of disposal of spent reaction mixtures or extracts therefrom containing such catalysts comprised their discharge into municipal sewage systems or into watercourses. Such means of disposal, however, are being tolerated to an ever decreasing extent in Western Europe, America and Japan as controls on discharges in to the environment are generally tightened, and in any event such disposal is wasteful of the metal. The metals are dissolved in the reaction mixture, so that their removal from the mixture, possibly for future recycle or re-use, may often be neither a simple nor cheap proposition.
From an environmental viewpoint, it would be desirable for a heavy metal catalyst to be incorporated in a distinctly separate and separable phase from the remainder of the reaction mixture, for example by supporting the catalytic material on a substantially insoluble solid support. However, there are a number of potential difficulties to be overcome to translate a theoretical possibility into a practical reality, pre-eminent amongst which there is the question of whether the catalyst would continue to function. The act of supporting the catalyst transforms any catalyst from a homogeneous to a heterogeneous system. It has been observed that apparently the same catalyst can perform differently in homogeneous and heterogeneous systems under the same general reaction conditions in attempting a desired reaction such as epoxidation. Thus, there is real doubt as to whether the catalyst would be able to perform if a truly heterogeneous system is employed.
A number of explanations may be advanced as to why a different outcome may arise. For example, it may be asserted that the local environment of the catalyst is different in a homogeneous system from that in a heterogeneous system. In the former, the catalyst is dissolved in and therefore dispersed in intimate contact with reactants and solvent throughout the liquid medium, whereas in the latter, the reaction typically takes place at the interface between the catalyst and the liquid phase of the reaction mixture in the immediate vicinity of the support surface. The presence of support can influence the ease with which the reactants can meet and react, and the surface of the support may even promote alternative reactions with one or other of the reactants or intermediates. Moreover, interactions between the catalyst and its support during production of the supported catalyst may modify both. The possible differences in outcome are such that the skilled man cannot predict with any real certainty how to create a heterogeneous system employing heavy or transition metals for the same reaction, and in particular for an epoxidation reaction, starting from homogeneous systems.
On the other hand, if the system created is not truly heterogeneous, in that the catalyst is not firmly attached to the support, it can leach into the reaction mixture during the course of the reaction, so that the reaction still suffers from the waste disposal problems of the catalyst metal in the spent reaction mixture.
It has previously been suggested in U.S. Pat. No. 2,870,171 (Gable) assigned to Shell D
REFERENCES:
patent: 2833787 (1958-05-01), Carlson et al.
patent: 4731482 (1988-03-01), Venturello et al.
patent: 5274140 (1993-12-01), Venturello et al.
patent: 5286885 (1994-02-01), Goetz et al.
Brown Scott W.
Hackett Anthony
Johnstone Alexander
Johnstone Robert A. W.
Evans Joseph E.
Solvay Interox Limited
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