# Kinetic and thermodynamic control of sulphonation of toluene

Sulfonation of toluene with conc. $$\ce{H2SO4}$$ at room temperature gives ortho- and para-toluenesulphonic acid (with $$95 \%$$ yield), whereas sulfonation of toluene with conc. $$\ce{H2SO4}$$ at $$\pu{150-200 °C}$$ gives meta-toluenesulphonic acid (with $$95 \%$$ yield). Why is this so?

What I thought is that at room temperature, the reaction is kinetically controlled, and the ortho-/para- directive effects of methyl group operate leading to ortho- and para-toluenesulphonic acid.

At high temperature, the reaction would be thermodynamically controlled. So the more stable product would be formed, which happens to be meta toluene sulfonic acid. Why is this more stable?

Does it have anything to do with the equilibrium of the sulfonation reaction?