Deactivation of sulfonated hydrothermal carbons in the presence of alcohols: Evidences for sulfonic esters formation

Deactivation of sulfonated hydrothermal carbon in the presence of alcohols depends on the type of alcohol and temperature, and it is mainly due to the formation of sulfonic esters, as shown by solid state NMR. [Display omitted] ► Activity of sulfonated hydrothermal carbons in esterification. ► Deactivation linked to the presence of alcohols. ► Detection of chemically bound alkyl groups. ► Alkyl sulfonates formation as responsible for deactivation. Sulfonated hydrothermal carbons present high activity for esterification of palmitic acid with alcohols. However, the catalyst is significantly deactivated upon recovery. Leaching of sulfonated species does not account for this deactivation, which is observed even by pretreatment only with the alcohol under reflux. Solid state NMR shows the presence of chemically bound alkyl groups coming from the alcohol, clearly different from strongly physisorbed species obtained by pretreatment at room temperature. The formation of sulfonate esters accounts for the deactivation behavior in reactions taking place in alcohols as solvents, mainly with methanol due to its higher reactivity.