Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2002-12-31
2004-10-26
Raymond, Richard L. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
Reexamination Certificate
active
06809215
ABSTRACT:
The invention relates to a method for hydrogenation of aromatic urethanes, which contain one or more aromatic rings and one or more urethane groups bonded directly and/or indirectly to one aromatic ring or to different aromatic rings, wherein the hydrogenation reaction is performed with hydrogen in the presence of a supported catalyst, which contains ruthenium as active metal. The catalyst to be used in the inventive method contains a catalyst support having a special combination of properties. In particular, the invention relates to a method for hydrogenation of dibutyl 4,4′-methylenedicarbanilate (hereinafter abbreviated as MDU) to dibutyl 4,4′-methylenedicyclohexylcarbamate (hereinafter abbreviated as H
12
MDU) with a trans-trans isomer content of <30%, preferably of <20%, particularly preferably of 5 to 15%.
It is known that cycloaliphatic urethanes containing one or more urethane groups can be synthesized by catalytic hydrogenation of the corresponding mononuclear or polynuclear aromatic urethanes containing one or more urethane groups and possibly other substituents.
The obtained cycloaliphatic urethanes can be reacted directly with polyols to form high-quality polyurethanes that are stable to light. Rather than the cycloaliphatic urethanes, however, there are preferably used, for synthesis of polyurethanes, the corresponding cycloaliphatic isocyanates, which are accessible from the cycloaliphatic urethanes by elimination of the alcohol groups.
It is also known that, during hydrogenation of the said aromatic urethanes, there are formed aliphatic urethanes in which cis-trans isomerism is possible. In the case of hydrogenation of MDU to H
12
MDU, three cis-trans isomers are possible: cis-trans-, cis-cis- and trans-trans-H
12
MDU. The elimination of the alcohol groups of a mixture of H
12
MDU isomers to form bis[4-isocyanatocyclohexyl]methane (hereinafter abbreviated as H
12
MDI) leads to a mixture of H
12
MDI isomers whose proportions are substantially equal to the proportions of the H
12
MDU isomers in the starting product.
The practical industrial properties of H
12
MDI are directly related to the proportion of isomers, especially to the content of the 4,4′-trans-trans isomers. In order to ensure constant product quality of the polyurethanes synthesized from the H
12
MDI and to achieve easier handling capability, it is particularly important that the H
12
MDI have the form, at room temperature, of a homogeneous liquid that does not contain solids. The temperature at which the first solid particles form in the H
12
MDI becomes lower with increasing content of the 4,4′-trans-trans isomer. Thus products with low 4,4′-trans-trans content are liquid in a broader temperature range and therefore have considerable advantages for industrial application.
As already mentioned in the foregoing, the proportion of isomers in an H
12
MDI synthesized from H
12
MDU by elimination of the alcohol groups is substantially equal to the proportion of isomers in the H
12
MDU itself. Thus, if a low 4,4′-trans-trans content is to be achieved in the H
12
MDI, it will be particularly economic to produce an H
12
MDU with low 4,4′-trans-trans content during hydrogenation of the MDU, so that it can then be directly further processed to an H
12
MDI with correspondingly low 4,4′-trans-trans content.
As follows from the documents cited hereinafter, the hydrogenation of aromatic urethanes to the corresponding cycloaliphatic urethanes is achieved in some cases by using supported catalysts.
U.S. Pat. No. 5,360,934 teaches the method of the class in question, but uses a supported catalyst containing rhodium for the purpose. Ruthenium can also be present as the active metal. According to the teaching of that document, the catalyst activity depends considerably on the modification of the aluminum oxide used as support. Apparently catalysts containing delta, theta and kappa aluminum oxide are more active as support material than a catalyst containing commercial gamma aluminum oxide as support material.
In the method according to European Patent 0813906, organic compounds can be hydrogenated using a supported ruthenium catalyst. These compounds also include aromatic compounds in which at least one functional group is bonded to an aromatic nucleus. In addition to ruthenium, the catalyst can also contain other metals from the subgroups of Groups I, VII or VIII of the Periodic Table. The support material has a BET surface of at most 30 m
2
/g and an average pore diameter of at least 50 nm. The catalyst used here is also characterized by a ratio of surface area of the active metal to surface area of the catalyst support of smaller than 0.05. The macroporous support materials with an average pore diameter of preferably 500 nm to approximately 50 &mgr;m are mainly aluminum oxide and zirconium oxide. Details on the hydrogenation of MDU to HMDU cannot be inferred from that document. In particular, there is described the hydrogenation of substituted aromatic compounds, in which either at least one hydroxy group or one amino group is bonded to an aromatic nucleus. In contrast, the object set by the inventors of the present application was to convert substituted aromatic urethanes to cycloaliphatic urethanes with low 4,4′-trans-trans content.
A method similar to that of European Patent 0813906 is taught in European Patent 0814098: In this case there are used, as support material for the supported ruthenium hydrogenation catalyst, materials in which 10 to 50% of the pore volume is represented by macropores with a pore diameter ranging from 50 to 10,000 nm and 50 to 90% is represented by mesopores with a pore diameter ranging from 2 to 50 nm. The BET surface of the support is specified as 50 to 500 m
2
/g, especially 200 to 350 m
2
/g. The ratio of the surface area of the active metal to that of the support is supposed to be smaller than 0.3, especially smaller than 0.1. Particulars on the activity of such catalysts and on the proportions of isomers during the hydrogenation of MDU to H
12
MDU cannot be inferred from that document.
From European Patent 0653243 there are known catalysts suitable for hydrogenation of aromatic compounds. The catalysts listed therein are systems formed by introduction of the dissolved active component into an organic polymer. This mixture must be mixed in turn with a support material, then molded and heat-treated. This method of producing the catalyst is relatively complex, since numerous individual partial steps must be considered. In total, these steps are cost-intensive, since several chemical additives are necessary. Moreover, the active component becomes homogeneously mixed with the support compound, and so only part of this component is available for catalytic reaction.
German Unexamined Application 2639842 describes a method for synthesis of cycloaliphatic urethanes by hydrogenation of aromatic urethanes. Transition metals of Group VIII of the Periodic Table are used as hydrogenation catalysts, rhodium being particularly preferred. Among other reactions, the hydrogenation of dimethyl 4,4′-methylenedicarbanilate to dimethyl 4,4′-methylenedicyclohexylcarbamate is also described. The hydrogenation reaction is performed in an inert solvent, preferably an aliphatic alcohol. A disadvantage of this method is that the catalysts used rapidly lose activity and can be only partly regenerated by rinsing with sulfuric acid, methanol and 2-propanol. Moreover, no particulars are given regarding the 4,4′-trans-trans content in the product and, moreover, no indication of any kind can be found that this is of importance.
In German Unexamined Application 4407019 there is described a method for hydrogenation of aromatic urethanes in an inert solvent with metals of Group VIII of the Periodic Table or compounds thereof as hydrogenation catalysts, ruthenium being particularly preferred. The synthesis of H
12
MDI from MDI is cited as an example. This example describes the hydrogenation of dimethyl 4,4′-methylenedicarban
Finke Norbert
Lettmann Christian
Lomoelder Ranier
Stochniol Guido
Degussa - AG
Raymond Richard L.
Tucker Zachary C.
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