Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1992-07-31
1994-05-17
Shippen, Michael L.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C07C 5115
Patent
active
053129768
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the technical field of intermediate products which can be employed, for example, for the synthesis of azo dyestuffs and polyester base materials.
2-Hydroxy-naphthalene-6-carboxylic acid is not only a useful synthesis unit for pharmaceuticals, textile auxiliaries and dyestuffs (cf., for example, European Patent Application Publication No. 0,292,955A), but in particular is also an important monomer for the preparation of liquid crystalline high-performance plastics and fibers having outstanding properties (cf. U.S. Pat. No. 4,393,191).
2-Hydroxy-naphthalene-6-carboxylic acid is synthesized industrially by a procedure analogous to the so-called Kolbe-Schmitt reaction, i.e. by reaction of the potassium salt of .beta.-naphthol with carbon dioxide, under pressure at 200.degree.-300.degree. C. (cf., for example, U.S. Pat. Nos. 1,593,816, 4,329,494 and 4,287,357). However, the procedures described in these publications have some industrial disadvantages; considerable amounts of decomposition products, such as tars and resins, are formed which, like the 2-hydroxy-naphthalene-3-carboxylic acid and 2-hydroxy-naphthalene-3,6-dicarboxylic acid formed in side reactions, can be removed only with difficulty. Attempts have indeed been made to improve the reaction procedure and to reduce the formation of the intermediate products by the procedures described in European Patent Application Publications Nos. 0,053,824 and 0,081,753 by carrying out the process in a solvent, preferably kerosene. In spite of this advantage over the solvent-free Kolbe-Schmitt reaction, however, these two process variants still have the fundamental disadvantage that in each case 1 mol of .beta.-naphthol remains unreacted in the reaction mass per mole of 2-hydroxy-naphthalene-6-carboxylic acid formed, which is why even in the best possible reaction procedure the yield is limited to a maximum of 50% in accordance with the equation: ##STR1## In the preparation of the isomeric compound 2-hydroxy-naphthalene-3-carboxylic acid, it has already been proposed to avoid this disadvantage of incomplete conversion of the .beta.-naphthol into naphtholcarboxylic acid by carrying out the reaction of potassium .beta.-naphtholate with potassium carbonate in the presence of carbon monoxide in accordance with the equation: ##STR2## (see British Patent Specification 1,155,776). However, if attempts are made to modify this procedure with the aim of preparing 2-hydroxy-naphthalene-6-carboxylic acid by varying the reaction conditions of temperature and carbon monoxide pressure, the synthesis of this 6-carboxy derivative remains unsuccessful.
It has now been found that 2-hydroxy-naphthalene6-carboxylic acid is obtained in a good yield and purity in a surprising manner if the reaction of the potassium .beta.-naphtholate with potassium carbonate and carbon monoxide is carried out at a temperature above 260.degree. C., such as at a temperature between 270.degree. C. and 360.degree. C., preferably between 280.degree. and 320.degree. C., and under a carbon monoxide pressure of above 10 bar, such as under a CO pressure of 50 to 150 bar, preferably between 70 and 140 bar, and in particular under a CO pressure between 80 and 120 bar, in potassium formate as the solvent (diluent).
The reaction according to the invention in potassium formate as the solvent or diluent (potassium formate melts above 167.5.degree. C. to give a clear liquid) is carried out in accordance with the equation: ##STR3## The formate used as the solvent (diluent) is employed in at least the same molar amount as the potassium .beta.-naphtholate starting substance; the amount of potassium formate used is not critical and can vary within wide limits. However, it is advantageous to employ a relatively large amount of potassium formate as the solvent (diluent), such as, for example, 2.5 to 18 times, preferably 6 to 15 times, the amount by weight of the potassium .beta.-naphtholate employed, in order to ensure the best possible thorough mixing of the reactants potassium .beta.-naphtho
REFERENCES:
patent: 1593816 (1926-07-01), Andre
patent: 3655744 (1972-04-01), Yasuhara
patent: 4287357 (1981-09-01), Mueller
patent: 4329494 (1982-05-01), Montgomery
patent: 4345095 (1982-08-01), Mueller
Lindsey, Chem. Rev. 57, pp. 583-620 (1957).
Hautzel Volker
Rittner Siegbert
Hoechst Aktiengesellschaft
Shippen Michael L.
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