Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1997-09-26
2002-05-21
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S405000
Reexamination Certificate
active
06392090
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a process for preparing hydroxybenzoic acids. More specifically, it relates to an industrially advantageous process for preparing alkylsalicylic acids such as a 3,5-dialkylsalicylic acid which are useful as synthetic materials of chemicals such as developers for pressure-sensitive recording papers, agricultural chemicals and antioxidants.
(ii) Description of the Prior Art
As a process for preparing a hydroxybenzoic acid, there is known the Kolbe-Schmidt reaction from old days which comprises reacting an alkali metal salt of a phenol with carbon dioxide.
In recent years, as improved techniques of the Kolbe-Schmidt reaction, methods in which the reaction proceeds in the state of a solution or a slurry instead of a solid phase reaction have intensively been researched from the viewpoint of some industrial advantages.
For example, Japanese Patent Application Laid-open No. 165341/1988 discloses a method for preparing a 3,5-dialkylsalicylic acid which comprises adding an aqueous alkali metal hydroxide solution and a 2,4-dialkylphenol to a hydrocarbon solvent, the amount of the 2,4-dialkylphenol being in excess of the alkali, removing water by azeotropic dehydration to synthesize an anhydrous alkali metal salt of the 2,4-dialkylphenol, and reacting this salt with carbon dioxide. In this method, however, the reaction mass tends to form a paste, which makes stirring difficult. In consequence, as shown in comparative examples which will be described hereinafter, a sufficient reaction yield cannot be obtained.
Japanese Patent Application Laid-open No. 34944/1989 discloses a reaction in a mixed solvent of a hydrocarbon solvent such as toluene and sulfolane, but sulfolane is a viscous and high-boiling solvent; and hence, because of the adhesion of sulfolane to crystals, it is difficult to recover all of the sulfolane.
In a method disclosed in Japanese Patent,Application Laid-open No. 178947/1991, a 2,4-dialkylphenol is reacted with an alkali metal hydroxide in a lower alcohol, and the lower alcohol and produced water are then distilled off. The resulting anhydrous alkali metal salt of the 2,4-dialkylphenol is next reacted with carbon dioxide. However, the reaction with carbon dioxide is carried out in a non-solvent solid phase state, which is not considered to be an industrially advantageous method.
In Japanese Patent Application Laid-open No. 90047/1991, there is disclosed a method which comprises heating a 2,4-dialkylphenol and an alkali metal hydroxide in a mixed solvent of a hydrocarbon solvent and 1,3-dimethyl-2-imidizolidinone, carrying out azeotropic dehydration to form an anhydrous alkali metal salt of the 2,4-dialkylphenol, reacting the same with carbon dioxide in the mixed solvent to obtain a 3,5-dialkylsalicylic acid. In this method, the reaction solution is directly discharged into an acidic liquid to take out the product. However, it is difficult to recover expensive 1,3-dimethyl-2-imidazolidinone from the aqueous layer, and so this method is not considered to be an industrially advantageous method. In addition, it is described in the disclosed specification that the amount of 1,3-dimethyl-2-imidazolidinone to be used is preferably in the range of 1 to 5 wt % based on the weight of the raw material phenol from an economical viewpoint, but when the compound is used in such an amount, the reaction system becomes a paste at the time of the dehydration, so that the reaction system is substantially close to the state of a solid reaction and hence stirring by a conventional of stirrer is impossible. Even if the reaction is forcedly continued, a sufficient reaction yield cannot be obtained.
In the case that the reaction is carried out in an aprotic polar organic solvent such as sulfolane or 1,3-dimethyl-2-imidazolidinone, the high reaction yield can be obtained, but as described above, there are large problems regarding the recovery of the product from the reaction solution and the recovery of the solvent.
That is to say, in the case that the aprotic copolar organic solvent is used as the reaction solvent, the reaction proceeds to a the high reaction yield, but o after the reaction, even if it is attempted that the alkali metal salt of the 3,5-dialkylsalicylic acid is crystallized and collected from the reaction solution, the recovery yield is much lower as compared with the reaction yield, because the solubility of this metal salt in the aprotic polar organic solvent is high. It is also possible that a large amount of a poor solvent can be added to recover the product, but the volume efficiency is very poor. Furthermore, a wet type of the obtained alkali metal salt of the 3,5-dialkylsalicylic acid contains a large amount of the aprotic polar organic solvent. Since a certain interaction is present between the alkali metal salt of the 3,5-dialkylsalicylic acid and the aprotic polar organic solvent, the removal of the aprotic polar solvent by washing with the poor solvent is difficult. If the thus obtained alkali metal salt of the 3,5-dialkylsalicylic acid containing the aprotic polar organic solvent is dissolved in water to do acidifying-out, all of the contained aprotic organic solvent transfers to the crystallization by acidification filtrate and it is consequently lost.
As a technique other than the above crystallization for recovering the alkali metal salt of the 3,5-dialkylsalicylic acid, there is a method which comprises concentrating the reaction solution. In this method, however, the distillation efficiency of a high-boiling solvent such as 1,3-dimethyl-2-imidazolidinone or sulfolane is poor, and as described above, a certain interaction is present between the alkali metal salt of the 3,5-dialkylsalicylic acid and the aprotic polar organic solvent, so that the recovery of its total amount by the distillation is impossible.
On the other hand, even in the case that the reaction solution is directly dissolved in water with-out the alkali metal salt of the 3,5-dialkyl-salicylic acid and then separated, wherein the separated aqueous layer is further subjected to the acidifying-out, almost all aprotic polar organic solvent transfers to the acidifying-out filtrate and is finally lost. In order to recover the aprotic polar organic solvent in a large amount of water, it is necessary to distill a large amount of water, and for this reason, the technique is not industrially applicable in view of an energy efficiency. Thus, on the basis of the conception that the loss of the aprotic polar organic solvent is unavoidable, it can also be considered to reduce the amount of the aprotic polar organic solvent to be used from an economical viewpoint, but if the amount of the aprotic polar organic solvent is reduced, the reaction solution correspondingly becomes a substantially solid phase reaction in a paste state, so that the reaction yield also deteriorates.
SUMMARY OF THE INVENTION
In consequence, an object of the present invention is to provide an industrially applicable process for preparing a hydroxybenzoic acid from a phenol in accordance with the Kolbe-Schmidt reaction by the use of an aprotic polar organic solvent as a reaction solvent, and this process is excellent in reaction yield and product recovery yield and can substantially completely recover the used aprotic polar organic solvent.
The present inventors have intensively investigated with the intention of solving the problems of the conventional technique, and as a result, it has been found that in a process which comprises reacting a phenol with an alkali metal compound by the use of an aprotic polar organic solvent as a reaction solvent to form an alkali metal salt of the phenol, and then reacting this alkali metal salt with carbon dioxide to obtain a hydroxybenzoic acid, an alkali metal salt of the hydroxybenzoic acid can be quantitatively recovered by sufficiently raising the ratio of the phenol to the hydroxybenzoic acid and the aprotic polar organic solvent even after the reaction, and the obtained wet product does not contain any aproti
Furuya Masayuki
Nagatomo Akinori
Wada Masaru
Killos Paul J.
Mitsui Chemicals Inc.
Oh Taylor V.
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