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.