GB793230A - Improvements in or relating to the preparation of gamma-phenoxybutyric acids and salts thereof - Google Patents

Abstract

Purified gamma phenoxybutyric acids, the phenyl group of which may be unsubstituted or substituted with two halogen groups or an alkyl and a halogen group, are obtained by reacting, in aqueous medium, an impure alkali metal salt of the acid with an ion exchanger solid capable of replacing metal ions by hydrogen ions and then separating the aqueous medium from the ion exchanger solid and purified phenoxybutyric acid. The process is particularly applicable to the preparation of a purified gamma phenoxybutyric acid derived by reacting an alkali metal phenoxide with gamma chloro-butyronitrile followed by hydrolysis, or with gamma butyrolactone, or with an alkali metal salt of gamma chlorobutyric acid. The ion exchanger solid and the impure alkali metal phenoxybutyrate are preferably employed in approximately chemically equivalent proportions. The ion exchanger solid is preferably stirred with an aqueous solution of the impure alkali metal gamma phenoxybutyrate and the solid material filtered off. Any water-soluble impurities remaining in the solid material are preferably washed off with water and the purified phenoxybutyric acid separated from the ion exchanger solid with a suitable solvent, e.g. ether, acetone or an alcohol such as methyl, ethyl or isopropyl alcohol. The solvent may then be removed from the extract by distillation. When an alcohol is used as solvent it may also be used to esterify the phenoxybutyric acid using the acidic ion-exchanger solid as an esterification catalyst. The mixture of ion-exchanger solid and purified phenoxybutyric acid may be treated with an organic or inorganic base or basic acting substance, to convert the acid into the corresponding salt of the base. This reaction may be effected in a liquid reaction medium, e.g. an aqueous or aqueous alcoholic medium. Suitable bases are mono-, di- or triethanolamines, ethylamine, isopropylamine, alkali metal hydroxides or alkali metal carbonates or bicarbonates. After removing the purified gamma phenoxybutyric acid from the ion exchanger solid, the latter may be regenerated by treatment with a mineral acid such as hydrochloric or sulphuric acid. Suitable ion-exchanger solids are the sulphonic acid cation-exchange resins and products obtained by condensing phenol, an aldehyde and a sulphonic acid or a sulphite. An example is given of the preparation of pure gamma (2-methyl-4-chlorophenoxy) butyric acid from impure sodium gamma (2 - methyl - 4 - chlorophenoxy) butyric acid, and details are given of its scorch effect at various concentrations on clover seedlings, when used as a selective weed killer. Other compounds mentioned are gammaphenoxy butyric acid and gamma-(2 : 4-dichloro-phenoxy) butyric acid. Specification 758,980 is referred to.