Abstract: A method for recovering purified m-hydroxybenzoic acid from crude m-hydroxybenzoic acid alkali metal salt. The method comprises dissolving the crude m-hydroxy benzoic acid alkali metal salt in water at a ratio of between about 13 and 20 milliliters of water per gram of pure m-hydroxybenzoic acid alkali metal salt contained in the crude salt; acidifying the resulting solution to a pH of below 2 with a mineral acid to neutralize all alkali metal hydroxide present and to convert the m-hydroxybenzoic acid alkali metal salt to free m-hydroxybenzoic acid; and cooling the solution to from about 0.degree. C. to about 15.degree. C. for a sufficient time to crystallize purified m-hydroxybenzoic acid from the solution.The method is particularly effective for removing impurities of parahydroxybenzoic acid, alkali metal hydroxide and water soluble inorganic salts.

Abstract: A process for purifying 4,4'-dihydroxydiphenyl comprising contacting a solution of 4,4'-dihydroxydiphenyl alkali metal salt with activated carbon followed by removing the activated carbon from the solution and acidifying the solution with sufficient acid to convert essentially all of the 4,4'-dihydroxydiphenyl alkali metal salt to water insoluble 4,4'-dihydroxydiphenyl and 4,4'-dihydroxydiphenyl product containing less than 0.45 weight percent of 4-monohydroxydiphenyl impurity.

Abstract: A process for the preparation of 4,4' dihydroxydiphenyl by acidifying an alkali metal salt of 4,4' dihydroxydiphenyl. The alkali metal salt of 4,4' dihydroxydiphenyl is prepared by fusion of an alkali metal hydroxide with alkali metal diphenyl 4,4' disulfonic acid. Because the reaction may be carried out in granular form, or in a reaction which is made highly fluid by using potassium hydroxide with potassium diphenyl 4,4' disulfonic acid, or by reacting the alkali metal 4,4' disulfonic acid in increments with the hydroxide, low molar ratios of hydroxide to alkali metal diphenyl 4'4, disulfonic acid may be used. When potassium diphenyl 4,4' disulfonic acid is used in accordance with the invention, it is prepared by reacting 4,4' diphenyl disulfonic acid with an inorganic neutral potassium salt.