Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-08-22
2002-08-27
Killos, Paul J. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S481000, C562S482000
Reexamination Certificate
active
06441224
ABSTRACT:
FIELD OF INVENTION
This invention is related to the production of aromatic dicarboxylic acids. More particularly this invention is related to a process for selectively carboxylating an aromatic mono-acid to form primarily an aromatic diacid. One embodiment of the invention is the selective carboxylation of naphthoic acid to form primarily 2,3-naphthalene dicarboxylic acid (2,3-NDA). A second part of the invention is the incorporation of the selective carboxylation into a two-stage process for producing greatly increased yields of aromatic diacid. The invention makes greater use of aromatic rings and obtains a surprisingly high yield of an aromatic dicarboxylic acid, such as, for example, 2,6-naphthalene dicarboxylic acid (2,6-NDA).
BACKGROUND OF THE INVENTION
Aromatic dicarboxylic acids are highly useful organic compounds. They are often used as monomers for the preparation of polymeric materials. For example, terephthalic acid is used to prepare polyethylene terephthalate, a widely used polyester material and the naphthalene dicarboxylic acids, i. e. 2,6-naphthalene dicarboxylic acid, is a particularly useful aromatic carboxylic acid because it can be reacted with ethylene glycol to prepare poly(ethylene-2,6-naphthalate), PEN. Fibers and films manufactured from PEN display improved strength and superior thermal properties compared with other polyester materials such as polyethylene terephthalate. High strength fibers made from PEN can be used to make tire cords, and films made from PEN are advantageously used to manufacture magnetic recording tape and components for electronic applications. It is desirable to use as pure as possible forms of these dicarboxylic acids in the various applications. It is also desirable to obtain as high a yield as possible of the aromatic dicarboxylic acids.
It is known in the art to prepare aromatic dicarboxylic acids by primarily two methods. One is the liquid phase, metal catalyzed oxidation of an alkyl or acyl substituted aromatic compound. This method is described, for example, in U.S. Pat. Nos. 2,833,816; 3,856,855; 3,870,754; 4,933,491; and 4,950,786. This method has drawbacks. The primary disadvantage of the method that involves direct oxidation to 2,6 NDA, is that impurities are trapped in the 2,6 NDA oxidation product which forms upon oxidation as a solid in the oxidation solvent. In order to remove these impurities to a sufficiently low level acceptable for polymerization, the 2,6 NDA product must be purified via multiple steps. These steps typically involve esterification, so that the resulting end product is 2,6-naphthalene dicarboxylate, an ester, rather than the preferred 2,6 napthalene dicarboxylic acid.
Alternatively, naphthalene monocarboxylic acid and naphthalene dicarboxylic acids other than 2,6-naphthalene dicarboxylic acid can be converted to 2,6-NDA using a disproportionation reaction in the case of the monocarboxylic acids or a rearrangement reaction in the case of other naphthalene dicarboxylic acids. Henkel and Cie first patented a reaction of naphthoic acid salts to 2,6 NDA in the late 1950s. (See U.S. Pat. Nos. 2,823,231 and 2,849,482). In these references, it can be observed that excess base was neutralized out of the feed with HCl with the objective of having precisely a 1:1 ratio of K:carboxyl. These references demonstrate the disproportionation of benzene to terephthalic acid+benzene. Isomerization of a diacid such as phthalic to terephthalic was demonstrated, as well. It can be observed that the best yield of diacid in this work was about 65%.
It is known in the art that in normal Henkel disproportionation reactions, a significant yield loss occurs during the reaction. This loss, even in the best of circumstances, is usually 3% or more of the weight of the naphthalene dicarboxylic acids (NDAs) theoretically expected to be produced. This loss arises from a mixture of causes, such as coupling of aromatic radicals to form binaphthyls and higher condensed species, decarboxylation of naphthoic acids to naphthalene, and other undesired reactions.
In the absence of charging other carboxylic acid salts (e.g. tricarboxylic benzene acids, or potassium formates, and the like) there is no precedent for obtaining a yield of NDA which exceeds the theoretical yield given by the equation for the Henkel II reaction:
2(potassium naphthoate)→1 napthalene+1 naphthalene dicarboxylic acid,
where the naphthalene dicarboxylic acid is a mixture of isomers, usually mostly 2,6-naphthalene dicarboxylic acid.
A perplexing question has been how one could more fully use all of the rings present in a feed of aromatic monoacids without the need for alkylation or subsequent oxidation. For example, there has not been a method available in the art to fully use all of the naphthalene rings present in a feed of naphthoic acid.
There does not appear to be any work in the art relating to the possibility of selective carboxylation of monoacids to aromatic diacids using inorganic salts. One Japanese reference claims carboxylation in the presence of oxalates, another organic salt, however only very low molar conversion was demonstrated, with only about 2% of the carboxyl groups present in the oxalate being transferred. (cite unavailable)
There is a great demand for dicarboxylic acids in the production of polymers, yet it has been difficult to produce dicarboxylic acids of good purity and in high yields. It would be a great advance in the art if it were possible to significantly increase the yield of dicarboxylic acids in a disproportionation/isomerization type reaction.
If there were a method available for direct carboxylation of an aromatic monoacid it would provide a significant advance in the art. It would be particularly valuable if there were a method for producing the much sought after 2,6-napthalene dicarboxylic acid in significantly greater yields by direct carboxylation of a feed which is simple to purify and oxidize, such as napthoic acid.
SUMMARY
In the present invention it has been discovered that by operating in an unusual regime of high base and lower temperature, it is possible to produce a significantly higher ratio of NDA to naphthalene than the theoretical ratio of 1.0.
In accordance with the foregoing, the present invention comprises a method of directly carboxylating an aromatic monoacid to an aromatic diacid, which comprises:
Reacting said aromatic monoacid with excess base in the presence of a catalyst comprising a metal oxide, particularly an oxide of Group IIB, at a temperature of from about 350° to 500°.
A second embodiment of the present invention also comprises substantially increasing the yield per pass in a disproportionation/isomerization reaction by a two-stage process comprising:
Heating overbased naphthoic acid salt at a temperature up to about 420° C. for a relatively short period of time to form 2,3-NDA by carboxylation, followed by a heating the product for a relatively longer period of time at a higher temperature, say above 420° C., to isomerize the mainly 2,3-NDA product of the first step to 2,6-NDA.
The invention demonstrates an increase in yield per pass in the disproportionation reaction to form naphthalene dicarboxylic acid, as well as increased throughput, and the reduced recycling of naphthalene. The present invention more fully utilizes all of the naphthalene rings present in a naphthoic acid feed to form naphthalene dicarboxylic acid, without the need for alkylation or subsequent oxidation. The examples demonstrate the direct carboxylation of 2-naphthoic acid, and mixtures of 1- and 2-naphthoic.
The present invention makes it possible to have a low capital, highly efficient disproportionation/isomerization type process to produce naphthalene dicarboxylic acid from naphthoic acid without the need for recycle of naphthalene for alkylation to naphthoic acid. The present invention could greatly simplify and make more productive any process for producing aromatic dicarboxylic acids, especially those that utilize a disproportionation/isomerization reaction.
DETAILED DESCRIPTION OF THE INVENTION
Dispr
Brownscombe Thomas Fairchild
DuBois Donn Anthony
King William Larry
Pfrehm Susan Secor
Mossi & Ghisolfi Overseas, S. A.
Renner Kenner Greive Bobak Taylor & Weber
Tucker Zachary
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