What is the product when phenol reacts with conc. $\ce{H2SO4}$ in excess?

I have been told that the major product will be ortho at low temperature and para at high temperature. Why cannot it form both ortho- and para-substituted product as in the case of picric acid?


1 Answer 1


It's a reversible reaction, so at higher temperature the thermodynamic para product is formed from the kinetic ortho product.

Further reading here.

  • $\begingroup$ Why does it only form a monosulphonated product and why not a trisulphonated product $\endgroup$
    – Jash
    Nov 26, 2019 at 11:54
  • 1
    $\begingroup$ Because the mono-product is strongly electron-withdrawn and the electrophile is not as good as NO2+ $\endgroup$
    – Waylander
    Nov 26, 2019 at 12:07
  • 2
    $\begingroup$ And because the forcing conditions needed to further sulfonate cause a range of other oxidative reactions leading to a complex mixture. $\endgroup$
    – Waylander
    Nov 27, 2019 at 14:20
  • $\begingroup$ Why is the ortho product the kinetically controlled product? I would've assumed that the attack at the para position is faster since the ortho position suffers the negative inductive effect of the oxygen. $\endgroup$ Jun 24, 2021 at 9:56

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