Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-08-22
2002-09-10
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06448437
ABSTRACT:
FIELD OF THE INVENTION
This invention is generally related to the disproportionation/isomerization of salts of aromatic carboxylic acids. More particularly, this invention is related to catalysts used in the disproportionation/isomerization of salts of aromatic carboxylic acids. The present invention provides halide-free, copper based catalyst alternatives to the metal halide catalysts typically used in the art for disproportionation reactions. The catalysts demonstrate particularly good yields and high selectivity in the disproportionation of potassium naphthoate to the potassium salts of 2,6 NDA. In one embodiment the catalyst comprises a mixed catalyst of compounds of copper, zinc, and zirconium; and, in a second embodiment, the catalyst comprises a copper compound treated with a base, used with an alkali metal promoter. The halide-free catalysts of this invention provide good stability, activity, and selectivity in a disproportionation/isomerization reaction.
BACKGROUND OF THE INVENTION
It is known in the art that aromatic carboxylic acids are useful as raw materials for the production of polyesters for fibers, films and plasticizers. One method for making aromatic carboxylic acids is oxidation. An alkyl or acyl substituted aromatic compound is converted to the corresponding aromatic carboxylic acid using a heavy metal catalyst in the liquid phase. For example, U.S. Pat. Nos. 2,833,816; 3,870, 754; 4,933,491; and 4,950,786 disclose methods for making naphthlene dicarboxylic acid by oxidation.
In another method, naphthalene monocarboxylic acid and naphthalene dicarboxylic acids other than 2,6-naphthalene dicarboxylic acid can be converted to 2,6-naphthalene dicarboxylic acid using a disproportionation/isomerization reaction, the so called Henkel rearrangement reaction. Henkel and Cie first patented the reaction of naphthoic acid salts to 2,6-naphthalene dicarboxylic acid in the late 1950s. (See U.S. Pat. Nos. 2,823,231 and 2,849,482.)
The Henkel and Cie patents, as well as many other references in the prior art teach the preferential use of cadmium halide, as well as other metal halides as catalysts in disproportionation reactions.
U.S. Pat. No. 3,546,282 discloses the use of iron, zinc, cadmium, and copper oxides, however the examples demonstrate cadmium salts were the most effective.
One patent that takes another view is U.S. Pat. No. 3,766,258 that teaches the use of a catalyst composition consisting of basic copper carbonate, cadmium fluoride and potassium carbonate. At Col. 1, line 60, it is stated the invention is particularly useful in a process for making terephthalic acid from a metallic salt of benzoic acid. In the examples water extraction and subsequent acidification/filtration isolate the products. No analytical technique is disclosed, and it is likely unreacted potassium napthoate is mistakenly counted as a diacid product. In the present invention, it is demonstrated in Ex. 10 that basic copper carbonate which has not been treated as taught in the present invention promotes a deleterious side reaction.
It would provide a significant improvement in the art if there were available a disproportionation/isomerization catalyst which affords good selectivity to the 2,6-isomer of the potassium salt of naphthalene dicarboxylic acid without the extreme toxicity and reactor corrosion concerns which are typical of the heavy metal halides currently accepted in the art.
The present invention provides effective, halide-free catalysts for a disproportionation reaction.
SUMMARY
In accordance with the foregoing, the present invention provides the option of two very effective halide-free disproportionation/isomerization catalysts, the first comprising a copper compound, a zinc compound, and at least one compound selected from the group consisting of aluminum, zirconium, magnesium, a rare earth, and mixtures thereof. The first embodiment is exemplified by a catalyst comprising sintered copper (II) carbonate, zinc carbonate, and zirconium carbonate. Another embodiment is a catalyst comprising a copper compound that is treated with a base and optionally used with a promoter. The second embodiment is exemplified by a catalyst comprising copper (II) carbonate treated with potassium hydroxide, optionally with a cesium carbonate promoter. The copper (II)-based catalyst with a cesium carbonate promoter has been demonstrated to be kinectically faster at lower temperatures. Specific examples demonstrate good yields and high selectivity in the disproportionation of naphthoic acid salts to 2,6-naphthalene dicarboxylic acid, using the catalysts of this invention.
DETAILED DESCRIPTION OF THE INVENTION
Starting materials for a disproportionation in which the catalyst of the invention is useful include salts of aromatic mono-, di-, or polycarboxylic acids. Such acids include, for example, benzoic acid, &agr;- and &bgr;-naphthoic acid, diphenyl monocarboxylic acids, as well as phthalic acid, isophthalic acid, terephthalic acid, naphthalic acid and other naphthalene dicarboxylic acids or diphenic acid and other diphenyl dicarboxylic acids. In addition, mono- or dicarboxylic acids in which the carboxylic groups are attached to another aromatic ring system, for example to anthracene, terphenyl, diphenyl methane or benzophenone radicals, are suitable for use as starting materials for the process of the invention, as well as tri- and polycarboxylic acids which are derived from aromatic ring systems. Also, mixtures of such acids which are formed, for example, by oxidation, or mixtures of alkyl aromatic compounds may be used.
The starting materials may also be salts of monobasic heterocyclic carboxylic acids, the carboxyl groups of which are attached to heterocyclic rings having an aromatic structure. Such acids are derived, for example, from pyridine, pyrazine, pyrimidine, pyridazine, &agr;-pyran, furan, thiophene, thiazole, quinoline, isoquinoline, indole, benzotriazole and benzimidazole.
In all of these carboxylic acids the aromatic ring or the heterocyclic ring having an aromatic structure can, in addition to the carboxyl group, also carry other substituents such as halogen atoms or alkyl radicals, provided that they do not decompose at temperatures below the reaction temperature. The term aromatic carboxylic acid is intended to include both compounds having a homocyclic aromatic ring and compounds having a heterocyclic ring.
When aromatic monocarboxylic acids are used as starting materials for a disproportionation reaction, the reaction products obtained are industrially valuable dicarboxylic acids or the salts thereof, such as, for example, terephthalic acid and 2,6-naphthalene dicarboxylic acid. Aromatic monocarboxylate includes benzoate, methyl benzoate, naphthoate, and similar compounds.
It is advantageous to use the above-mentioned carboxylic acids in the form of an alkali metal salt. Preferably the potassium salts or the sodium salts are used. The lithium, rubidium and cesium salts, may be used, but generally are not for reasons of economy. It is also possible to use mixtures of salts of two different metals. Reaction materials that form the above-mentioned salts may also be used.
Suitable temperatures for the disproportionation reaction are in the range of from about 340° C. to 500° C. Better results are observed where the temperature is from about 400° C. to 480° C. The preferred temperature is from about 440° C. to 460° C. This temperature range is, however, very limited. Raising the temperature generally improves conversion, however decomposition through decarboxylation and tarring becomes more severe at higher temperatures. Generally, at temperatures over 500° C. the decomposition of the organic material and product become substantial and lead to carbonization, so temperatures this high for very long periods of time should be avoided.
The disproportionation reaction is carried out under the pressure of gaseous carbon dioxide. The gaseous mixture may contain an inert gas or gases such as nitrogen, methane, or other gaseous paraffinic, olefinic, and aromatic hydrocarbons. In the case of
DuBois Donn Anthony
Murray Brendan Dermot
Killos Paul J.
Mossi & Ghisolfi Overseas S.A.
Renner Kenner Greive Bobak Taylor & Weber
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