Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-05-19
2001-08-14
Killos, Paul J. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S512000
Reexamination Certificate
active
06274766
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved process for purifying &agr;-keto acids. In particular, the present invention pertains to the isolation of pivalic acid and other organic impurities from &agr;-keto acids. In a preferred embodiment, the present invention relates to the preparation of trimethylpyruvic acid (TMPA) of enhanced purity.
BACKGROUND OF THE INVENTION
It is known that &agr;-keto acids and salts thereof are useful as starting materials in the production of herbicides. In particular, ar aqueous solution of the sodium salt of TMPA is used in the synthesis of the herbicide Sencor. In the prior art, various processes for producing &agr;-keto acids and salts thereof have been proposed. These processes include (1) reacting sodium cyanide and acetyl chloride to form acetyl cyanide and then hydrolyzing the cyanide; (2) dry-distilling tartaric acid in the presence of potassium hydrogensulfate; (3) fermenting lactic acid; (4) oxidizing lactic esters with potassium permanganate; and (5) oxidizing propylene glycol.
In U.S. Pat. No. 4,175,188, a process is described for producing TMPA from trimethylpyruvic acid N-t-butylamide. The process includes the acid hydrolysis of trimethylpyruvic acid N-t-butylamide by heating under reflux in hydrochloric acid, and then extracting with dilute sodium hydroxide, hydrochloric acid and ethyl acetate. The yield of the desired product is only 75% of theory.
In U.S. Pat. No. 4,614,822, a process is described for preparing TMPA by oxidation of the corresponding &agr;-hydroxy acid.
The above-identified processes have various disadvantages which include the following: (i) the yield of the desired product is low, and (ii) the formation of considerable amounts of by-products makes it difficult to separate and purify the desired product.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for preparing &agr;-keto acids of enhanced purity. The object of the invention is realized by (i) adding to an aqueous solution of a sodium salt of the &agr;-keto acid (a “keto salt”) a mineral acid in an amount such that the pH of the acidified solution is from about 3.0 to about 4.0; (ii) adding a solvent to the acidified solution and allowing the resultant mixture to separate into a first organic phase and a first aqueous phase; (iii) removing the first organic phase from the first aqueous phase, wherein the first organic phase includes the solvent and organic impurities, and wherein the first aqueous phase includes water and the sodium salt of the &agr;-keto acid (“keto salt”); (iv) adding a mineral acid to the first aqueous phase in an amount such that the pH of the acidified first aqueous phase is less than 1; (v) adding a solvent to the acidified first aqueous phase and allowing the resultant mixture to separate into a second organic phase and a second aqueous phase; (vi) removing the second organic phase from the second aqueous phase, wherein the second organic phase includes the solvent and &agr;-keto acid, and the second aqueous phase includes water; and (vii) recovering the &agr;-keto acid of enhanced purity from the second organic phase.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention relates to preparing &agr;-keto acids of enhanced purity. The process generally includes the partial acidification of an aqueous solution of a sodium salt of the &agr;-keto acid (a “keto salt”), a first solvent extraction of the keto salt solution to remove organic impurities, further acidification of the keto salt solution, a second solvent extraction to remove the &agr;-keto acid, and isolation of the &agr;-keto acid from the solvent.
In the present invention, a mineral acid is added to an aqueous solution of a sodium salt of the &agr;-keto acid (a “keto salt”). Suitable mineral acids include hydrochloric acid, sulfuric acid, and phosphoric acid. In a preferred embodiment, the mineral acid is hydrochloric acid. The mineral acid is added in an amount such that the pH of the acidified solution is from about 3.0 to about 4.0, and preferably from about 3.3 to about 3.7. The mineral acid used in the reaction mixture is preferably an aqueous solution containing from about 30% by weight to about 100% by weight of mineral acid, and preferably from about 37% to about 85% by weight of mineral acid. The precise amount of mineral acid used in the reaction depends on the particular mineral acid selected. Further, in a preferred embodiment, the keto salt solution is an aqueous trimethylpyruvic acid (TMPA) salt solution, and the purified &agr;-keto acid is TMPA.
A solvent is then added to the acidified keto salt solution. Preferably, the solvent is an organic solvent. Such suitable organic solvents are known in the art and include any water insoluble ketones, esters, ethers, alcohols, hydrocarbons, and chlorinated hydrocarbons. In a preferred embodiment, the solvent is either ethyl acetate or methyl-isobutyl ketone (MIBK). The ratio of the keto salt solution to solvent by volume is from about 1:1 to about 10:1, and preferably from about 3:1 to about 5:1. Addition of the solvent to the keto salt solution results in a mixture that is separated into a first organic phase and a first aqueous phase. The first organic phase contains the solvent and organic impurities. The first aqueous phase includes water and keto salt. The first organic phase, containing the impurities, is removed from the first aqueous phase.
A mineral acid is then added to the first aqueous phase. The mineral acid for this second acidification step may be selected from the same group as that previously indicated for the first acidification step of the invention. In a preferred embodiment, the mineral acid is hydrochloric acid. The mineral acid is added in an amount such that the pH of the acidified solution is less than 1, and preferably from about 0.4 to about 0.8. The mineral acid has a concentration of from about 30% to about 100% by weight, and preferably from about 37% to about 85% by weight. The precise amount of mineral acid used in the reaction will depend on the particular mineral acid selected.
A solvent is then added to the acidified first aqueous phase. The solvent may be selected from the same group as that indicated in the previous solvent extraction step. In a preferred embodiment, the solvent is MIBK. The ratio of keto salt solution to solvent by volume is from about 1:1 to about 10:1, and preferably from about 3:1 to about 5:1. Addition of the solvent results in a mixture that is separated into a second organic phase and a second aqueous phase. The second organic phase contains the solvent and &agr;-keto acid. The second aqueous phase includes water and inorganic salts. The second organic phase is removed from the second aqueous phase.
The &agr;-keto acid of enhanced purity is then isolated from the solvent in the second organic phase. In a preferred embodiment, isolation of the desired product is accomplished by distillation of the solvent from the second organic phase.
The process of the present invention may be carried out as either a batch process or a continuous process. Further, the solvent may be recovered from the first and second organic phases, and recycled for subsequent use in the process of the present invention.
The following examples illustrate preferred embodiments of the present invention and are not limiting of the specification and claims in any way.
REFERENCES:
patent: 2092494 (1937-09-01), Bass et al.
patent: 3524877 (1970-08-01), Haage et al.
patent: 4013680 (1977-03-01), Johnson et al.
patent: 4175188 (1979-11-01), Klenk et al.
patent: 4204044 (1980-05-01), Suhara et al.
patent: 4614822 (1986-09-01), Jackman et al.
Howerton Cathy L.
Jackman Dennis E.
Bayer Corporation
Chaudhry Mahreen
Gil Joseph C.
Killos Paul J.
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