Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1998-11-17
2000-08-22
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
562423, C07C 5115
Patent
active
061075167
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention concerns a process for the production of aromatic hydroxycarboxylic acids by contacting an aromatic hydroxy compound and carbon dioxide in the presence of fluoride ion.
TECHNICAL BACKGROUND
Aromatic hydroxy acids are important items of commerce. For instance o-hydroxybenzoic acid (salicylic acid) is used as a chemical intermediate, for instance to make aspirin, while p-hydroxybenzoic acid is used to make parabens and is also used as a monomer in making polyesters. Aromatic hydroxy acids can be manufactured using the Kolbe-Schmitt reaction, which is a reaction of an alkali metal salt of an aromatic hydroxy compound with carbon dioxide, usually under elevated temperature and pressure. The Kolbe-Schmitt reaction has been a standard procedure for the preparation of aromatic hydroxy acids for over 100 years, see for instance A. S. Lindsey, et al., Chem. Rev., vol. 57, p. 583-620 (1957). However, this process is complex and difficult to run, involving several manufacturing steps, which adds to the cost of the final product. Also, substantial cost is incurred for the use of corrosive compounds such as NaOH or KOH which are subsequently discarded (as sodium or potassium salts).
SUMMARY OF THE INVENTION
This invention concerns a process for the production of aromatic hydroxycarboxylic acids, comprising contacting, at a temperature of about 100.degree. C. to about 300.degree. C., an aromatic hydroxy compound and carbon dioxide, in the presence of fluoride ion, wherein the carbon dioxide has a partial pressure of at least about 0.1 MPa.
DETAILS OF THE INVENTION
The product of the process is an aromatic hydroxycarboxylic acid. By an aromatic hydroxycarboxylic acid is meant a compound that contains at least one aromatic carbocyclic ring, and at least one hydroxyl group and one or more carboxyl groups (preferably one carboxyl group) attached to carbon atoms of an aromatic carbocyclic ring. This compound may contain one or more aromatic rings, and if more than one such ring is present they may be fused, as in naphthalene, connected by a covalent bond, as in biphenyl, or by a divalent group, as in diphenyl ether. There may also be inert groups attached to the aromatic ring(s), such as one or more alkyl groups. Without intending to be limited to any particular theory or explanation, it is believed that the positions in the aromatic rings which may be substituted by a carboxyl group herein are similar to those which are substituted in the Kolbe-Schmitt reaction. Therefore, at least one of these positions should preferably be unsubstituted in the aromatic hydroxy compound. Compounds which may be produced by this process include p-hydroxybenzoic acid, o-hydroxybenzoic acid, 2-hydroxy-3-methylbenzoic acid, 2-hydroxy-5-methylbenzoic acid, 2,4-dihydroxybenzoic acid, and a hydroxynapthoic acid. Preferred products are p-hydroxybenzoic acid, o-hydroxybenzoic acid, and 6-hydroxy-2-naphthoic acid.
One of the starting materials for the instant process is an aromatic hydroxy compound. By an aromatic hydroxy compound is meant a compound that contains at least one aromatic carbocyclic ring, and also contains at least one hydroxyl group attached to a carbon atom of an aromatic carbocyclic ring. This compound may contain one or more aromatic rings, and if more than one such ring is present they may be fused, as in naphthalene, connected by a covalent bond, as in biphenyl, or by a divalent group, as in diphenyl ether. There may also be inert groups attached to the aromatic ring(s), such as one or more alkyl groups. Useful aromatic hydroxy compounds include phenol, 1-naphthol, 2-naphthol, o-cresol, p-cresol, m-cresol, and resorcinol. Phenol and 2-naphthol are preferred aromatic hydroxy compounds, and phenol is especially preferred.
Another ingredient in the process is carbon dioxide. While the partial pressure of CO.sub.2 in the process is not critical, it is preferred that it is at least about 0.1 MPa, more preferably in the range of about 5 MPa to about 70 MPa, and especially preferably about
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E. I. Du Pont de Nemours and Company
Killos Paul J.
Oh Taylor Victor
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