Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing organic compound
Reexamination Certificate
2000-12-22
2002-06-04
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing organic compound
C205S422000, C205S431000, C205S434000, C205S440000, C205S441000, C205S450000, C205S460000
Reexamination Certificate
active
06398938
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for electrochemical oxidation of organic compounds.
2. Discussion of the Background
Cell types of the most diverse nature are described for oxidation reactions, including the so-called capillary cracking cell, which was developed by Beck and Guthke in 1969. In these cells, electrochemical oxidation reactions take place on graphite electrodes, such as the methoxylation of furan to dimethoxydihydrofuran or the Kolbe electrolysis of adipic acid esters to 1,10-sebacic acid esters. By the use of graphite, particles of graphite can lead to short circuits due to the rough surface and graphite abrasion during electrolysis. Graphite blocks coated with metal foil have proved to be too unstable, since the metal foils wrinkle and split (F. Wenisch, H. Nohe, H. Hannebaum, D. Degner, R. K. Horn, M. Stroczel,
AIChE Symposium Series
1979, 75, 14; H. Nohe,
AIChE Symposium Series
1979, 75, 69).
In addition, numerous oxidation reactions of aromatics on graphite are known. For example, a yield of >85% of anisaldehyde dimethylacetal is obtained in the oxidation of p-methoxytoluene on graphite in methanol and KF (D. Degner,
Topics in Current Chemistry
1988, 148, 3-95).
A large number of mediator-assisted oxidation reactions have also been described (E. Steckhan,
Topics in Current Chemistry
1987, 142, 3-69). Furthermore, the use of the Ce(III)/Ce(IV) mediator system has industrial importance (WO 93/18208; U.S. Pat. No. 4,794,172 and U.S. Pat. No. 4,639,298).
In addition, it is known from publications on preparative organic electrochemistry that cathodes and anodes used on a preparative scale must have special electrochemical properties. Such electrodes are frequently manufactured by coating metal or carbon-like support electrodes by appropriate coating methods such as plasma sputtering, impregnation and baking, hot pressing, galvanic deposition, etc., as is described in EP 0435434 B.
Furthermore, in German Patent Application 19911746.2 A the manufacture of a diamond-coated electrode is described as well as its use in oxidation reactions of organic compounds.
A disadvantage in such manufacturing processes is that the electrodes must be frequently removed from the electrolysis apparatus and sent to external regeneration after inactivation of the catalytically active layer. Thus, short catalyst service lives and poisoning phenomena rule out economic use of the electrochemical system. A further disadvantage is found in the complex manufacture of the catalytically active layer as such and the achievement of adequate stability of this layer on the support electrode. The development expense for classical electrode-coating processes therefore pays for itself only in very large-scale processes, such as alkali metal chloride electrolysis or dimerization of acrylonitrile.
In European Patent Application 808920 A, a process is described for reduction of organic compounds by bringing the organic compound into contact with a cathode, wherein the cathode includes a support of an electrically conductive material and an electrically conductive, cathodically polarized layer formed in situ thereon by precoating. Oxidation reactions are not described therein. German Patent Application 19954323.2 A relates to the oxidation of phosphonomethyliminodiacetic acid to glyphosates.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for the oxidation of organic compounds, which makes possible high space-time yields.
It is another object of the present invention to provide a process for the oxidation of organic compounds, which makes possible high selectivities for repeatedly oxidized compounds.
It is another object of the present invention to provide a process for the oxidation of organic compounds, which suppresses oxidation of the solvent as much as possible.
It is another object of the present invention to provide a process for the oxidation of organic compounds, which permits high current densities.
It is another object of the present invention to provide a process for the oxidation of organic compounds, which is industrially usable.
The objects of the present invention, and others, may be accomplished with a process, which includes:
electrochemically oxidizing at least one organic compound by bringing the organic compound into contact with an anode, wherein the anode includes:
an electrically conductive support; and
an electrically conductive, anodically polarized layer on the support;
wherein the anodically polarized layer is formed in situ upon the support by precoating; and
wherein the organic compound is not phosphonomethyliminodiacetic acid.
Another embodiment of the present invention provides a product, produced by the above process.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description of the preferred embodiments of the invention.
Preferably, the present invention relates to a process for electrochemical oxidation of at least one organic compound by bringing an organic compound into contact with an anode, characterized in that the anode includes a support of electrically conductive material and an electrically conductive, anodically polarized layer formed in situ thereon by precoating, wherein phosphonomethyliminodiacetic acid is ruled out as the organic compound.
Preferably, the catalytically active electrode is stabilized in the operating condition by the pressure loss at the electrically conductive anodically polarized layer formed by precoating. In this connection the term “in situ” used according to the invention covers all alternative versions of such precoating with the material for the anodically polarized layer, which can therefore take place together with or also after introduction of the reaction mixture into the reactor. The term “in situ” therefore directly expresses the fact that the anode is formed in the oxidation cell and, in fact, by precoating. For regeneration the layer can be resuspended by stopping the pumped circulation and discharged by blowing out. Thus oxidation reactions are performed on a system which is suitable for forming a catalytically active electrode and decomposing it once again in the process, without the need to open the cell or extract electrodes.
Preferable supports for the electrically conductive, anodically polarized layer there include electrically conductive materials. Compared with the reductive processes already described, the oxidative side imposes more stringent requirements on the stability of the material. Suitable materials are platinum or platinized metals, such as platinized titanium. The materials from which the support is made preferably depend on, among other factors, the solvent of the anolyte. Preferably, coated Ti, Ta and/or Nb supports are used. For this purpose there can be mentioned in particular platinized supports or supports provided with mixed oxides of Subgroups IV to VI, with Ru/Ta mixed oxide, with Ru/Ir mixed oxide, with coatings based on Ru oxide (DSA®), with IrO
2
, with PbO
2
, with SnO
2
, with Co oxides or with Ni/Ni oxides (basic pH) or also Fe/Fe oxides (basic pH) or spinels. Furthermore, there can also be used electrode carbon and graphite, from which matching support materials can be prepared by a new machining process, or in other words water-jet cutting. Furthermore, there can also be used fabric forms of graphite or carbon that are commercially available in the form of technical fabric.
Preferably, these supports exist as permeable, porous materials. These can have the form of commercial filter fabrics which include or are composed of metal wires or graphite/carbon fibers, graphite/carbon fabrics and graphite/carbon sponges. Other preferable supports include filter fabrics of the linen weave, twill weave, twilled braiding weave, braiding weave and satin weave type. More preferably, perforated metal foils, metal felts,
Huber Günther
Merk Claudia
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wong Edna
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