Abstract: Ⅲumination of a solution contahing hypocrellih B(or A)and Na₂SO₃ leads to the formation of 5 or 8-sulfonated and 5,8-disulfonated hypocrellin B (or A).The photo induced sulfonation of hypocrellins is very susceptible to the changes of reaction conditions such as the concentration of oxygen,pH value of the solution,and polarity of the solvent.In aeratedsolution,the rate of sulfonation is much faster than that in deaerated solution,and some sidereactions(e. g self-sensitized)which are favourable under oxygen can be prevented.The optimum pH value for the sulfonation is pH 7.0～7.7.The rate of the photo-sulfonation declines with the decrease of the polarity of the solvent.strongly polar solventsfacilitate the sulfonation of hypocrellins.

Key words: hypocrellins, photosulfonation, polarity of solvent