Method for continuous production of dihydroxydiarylalkanes

A continuous process for producing dihydroxydiarylalkane in a series of at least two reactors comprising

• (i) reacting phenol with at least some ketone and at least some isoalkenylphenol at the lowest possible temperature in a first reactor to form a reaction mixture and continuing the reaction at increasing temperatures in the succeeding at least one reactor and introducing at least portions of the remaining ketone and isoalkenylphenol in said at least one succeeding reactor to form at least one succeeding reaction mixture, and
• (ii) distilling off and removing unreacted ketone from the reaction mixture, and
• (iii) separating dihydroxydiarylalkane from the reaction mixture by crystallization to obtain mother liquor and crystals and washing the crystals thus obtained with washing phenol, and
• (iv) combining the mother liquor with said washing phenol, distilling off the phenol and returning said phenol to the reaction, and
• (v) decomposing the bottoms which include dihydroxydiarylalkane, isomers in the presence of a catalytic quantity of base in a first reactive rectification to produce (a) phenol and isoalkenylphenol distillate which leave at the top and (b) high boiling residue at the bottom, and
• (vi) acidifying said high boiling residue so that it contains a catalytic quantity of acid, and decomposing said residue in a second reactive rectification to produce (c) phenol and (d) bottoms, and
• (vii) returning the phenol produced in (vi) and the distillate produced in (v) to the reaction to produce dihydroxydiarylalkane.