The way to preparation of 2,4-Difluorobenzoic acid

2,4-Difluorobenzoic acid is a kind of white to light yellow crystal powders with Molecular Formula: C7H4F2O2 and Molecular Weight: 158.1. It is soluble in water, stable at room temperature in closed containers under normal storage and handling conditions. We should store it in a tightly closed container. Store it in a cool, dry, well-ventilated area away from incompatible substances. The CAS Registry Number is 1583-58-0.

This invention relates to a method for the preparation of 2,4-Difluorobenzoic acid. It has been prepared by the oxidation of the corresponding toluene derivative. More particularly, this invention relates to a process for the preparation of 2,4-Difluorobenzoic acid by the decarboxylation of 4,5,-difluorophthalic anhydride or 4,5-difluorophthalic acid in which the decarboxylation reaction is conducted in N-methylpyrrolidone or dimethyl acetamide. Copper catalysts may be used in this reaction.

2,4-Difluorobenzoic acid(CAS NO: 1583-58-0)  is a useful chemical intermediate.  For example, it has been used as an intermediate in the preparation of potential anti-cancer agents. In addition, it has been used in the synthesis of antidepressant drugs. Attempts were made to prepare 2,4-Difluorobenzoic acid by decarboxylation of 4,5-difluorophthalic anhydride. It may be readily prepared by the reaction of 4,5-dichlorophthalic anhydride with potassium fluoride as disclosed in U.S. Pat. No. 4,374,266 . The acid may be readily prepared by reacting the anhydride with water.

The decarboxylation of 4,5-difluorophthalic anhydride proved to be difficult, since previously known methods of decarboxylation led to a low yield of the desired product along with numerous by-products. The following chart illustrates the decarboxylation methods which were tested. The percentage product shown in the results were those obtained by gas chromatographic analysis, DFBA stands for 2,4-Difluorobenzoic acid s.m. stands for starting material.

The difluorobenzoic acid may be isolated from the reaction mixture by acidifying the mixture and extracting with a suitable solvent such as ethyl acetate or diethyl ether. Evaporation of the solvent yields crude difluorobenzoic acid which may be recrystallized/decolorized by using water and activated carbon.

We have found that 4,5-difluorophthalic anhydride and 4,5-difluorophthalic acid may be decarboxylated in high yield to 2,4-Difluorobenzoic acid in N-methyl-2-pyrrolidone or dimethyl acetamide using copper, copper oxide, copper salts, or halides and salts of Zn, Cd, Ag and Ni as a catalyst.

Surprisingly, we have found that 4,5-difluorophthalic anhydride and 4,5-difluorophthalic acid may be selectively decarboxylated in N-methyl-pyrrolidone, dimethyl acetamide or quinoline to yield 2,4-Difluorobenzoic acid.

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