The present invention relates to a process for reacting chemical compounds comprising the step of reacting a compound of formula (IV) wherein Hal is independently selected from CI or Br, and X is a monovalent anion, in the presence of an inorganic acid, wherein the aqueous inorganic acid has a concentration of at least about 60%, at a temperature of about 140 C. to Cabout 250 C., to obtain a compound of formula (V) wherein Hal is as defined above.

##STR00001##

The present invention relates to a process for reacting chemical compounds comprising the step of reacting a compound of formula (IV) wherein Hal is independently selected from CI or Br, and X is a monovalent anion, in the presence of an inorganic acid, wherein the aqueous inorganic acid has a concentration of at least about 60%, at a temperature of about 140 C. to Cabout 250 C., to obtain a compound of formula (V) wherein Hal is as defined above.

##STR00001##

Provided are an apparatus and a method for preparing bisphenol A. In the present invention, all or some of a mother liquid stream is circulated to a flash rector through a bypass line after crystallization in a process of preparing bisphenol A so as to increase a conversion rate of bisphenol A in a reactor, reduce energy, and use a heating source of phenol to be discharged to an upper side of the flash reactor, and thus the reaction efficiency of the whole process can be increased.

Provided are an apparatus and a method for preparing bisphenol A. In the present invention, all or some of a mother liquid stream is circulated to a flash rector through a bypass line after crystallization in a process of preparing bisphenol A so as to increase a conversion rate of bisphenol A in a reactor, reduce energy, and use a heating source of phenol to be discharged to an upper side of the flash reactor, and thus the reaction efficiency of the whole process can be increased.