[curiouscat]

At what H2SO4 conc. does H2SO4 char organics typically? I'm trying out a liq. phase alkene sulfonation and things go all fine and dandy till a concentration of about 78% H2SO4. But if I use anything higher in conc. the alkene chars / polymerizes.

Is there anything I can do about this? Any ways to avoid charring? I'd like to test higher acid concentrations to see if it will speed up the reaction. Is it possible to use H2SO4 analogs that might char less?

On a more fundamental level, what determines how easily an organic will char? I think I've seen other reactions using 90% or more H2SO4 and wonder how they get around the charring issues.