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