The mechanisms of introducing sulphur surface groups in porous carbons was deduced from the model carbon material carbide derived carbon (CDC) based on titanium carbide. The electrophilic substitution reaction at the aromatic ring system was identified as the predominant mechanism, even in highly amorphous carbons. The finding was deduced from TG-MS and XPS analysis. Upon varying the aromaticity and the amount of oxygen surface groups of the porous carbons, no change in mechanism was observed. This neglects an effect of spatial hindrance of the electrophilic substitution reaction within micropores. The introduced sulphur groups were found to be highly acidic sulphonic acid groups, which enable the functionalized carbons to be used as solid acid catalysts. The performance evaluation of the functionalized carbons catalyst in the esterification reaction of levulinic acid with ethanol supported the mechanistic findings. The activity correlated with the amount of sulphuric acid groups. The maximum amount of 0.86 mmol m(-2) and, thus, the highest activity was determined for the most graphitic porous carbon material.