Why does thiophene possess a greater tendency to undergo sulphonation than benzene? I came across this reaction which employs the use of sulphuric acid to separate thiophene from commercially prepared benzene.
In the chapter Aromatic five-membered ring heterocycles with one heteroatom in Organic Chemistry by J. William Suggs (2002) the following explanation can be found (pp. 403-404) which summarizes the thoughts already pointed out in the comments:
The resonance stabilization energy of benzene is greater than that of these heteroaromatic compounds. The order of aromaticity is benzene > thiophene > pyrrole > furan.
All three of these ring systems undergo electrophilic aromatic substitution and are much more reactive than benzene. In part, this reactivity difference arises because the rate-determining step in electrophilic aromatic substitution is the first step, which breaks up the aromatic $\pi$ system. Since thiophene, pyrrole, and furan have less stabilization to lose than benzene, the intermediate is lower in energy and the overall reaction proceeds more rapidly.
All three of these heteroaromatic rings undergo electrophilic aromatic substitution, preferentially at C-2. The reactivity order is pyrrole > furan > thiophene because of several factors, including the electronegativity of the heteroatom and the resonance stabilization of the aromatic ring.