Process for the simultaneous recovery of 4-hydroxy-diphenyl and 4,4'-dihydroxydiphenyl

摘要

4-Hydroxydiphenyl (mono-OD) and 4,4'-dihydroxydiphenyl (DOD) are obtained simultaneously from a mixture which contains these two substances, if such a mixture is treated with an aqueous alkali, and the resulting solution and the solid phase formed are separated at a temperature from -28 DEG C. to +40 DEG C. and the solution and the solid phase are acidified separately in order to form the free mono-OD and DOD. Mono-OD and DOD can be present in the starting mixture in the free form or in the form of the alkali metal phenolates. After formation of the alkali metal phenolates, where this is required, the aqueous alkali still contains 1-15 mol of alkali metal hydroxide per mol of the diphenyl compounds. The concentration of alkali metal hydroxide should be 4-25% by weight, relative to the amount of water present. In this process, it is also possible to employ industrial mixtures of the alkali melts of the associated diphenyl-sulphonic acids.