Sulfonated sucrose-derived carbon: efficient carbocatalysts for ester hydrolysis†

A series of sulfonated carbon acid catalysts with strong acidity was prepared by simultaneous carbonization and sulfonation of biomass sucrose in the presence of the organic sulfonating agent sulfosalicylic acid under hydrothermal conditions at temperatures ranging from 150 to 200 °C. It was found from FTIR and XPS spectra that the surface of carbon was efficiently functionalized with –SO₃H groups. Research on the mechanism of the sulfonation process indicated that the intermediate 5-hydroxymethyl furfural (5-HMF), which was easily hydrolyzed from sucrose, was prone to carbonization and functionalized with –SO₃H groups simultaneously. Compared with 5-HMF and fructose used as the initial carbon precursor, the slow hydrolysis of sucrose to intermediate 5-HMF to suppress its rapid carbonization is favorable for the efficient grafting of –SO₃H groups when sucrose is used as the initial carbon precursor. The prepared sulfonated carbons were evaluated as acid catalysts in a typical ester hydrolysis reaction, namely, hydrolysis of ethyl acetate. The sulfonic acid groups were identified to be the active sites and quantified by a cation-exchange process. The activity of the sulfonated carbon was primarily correlated with the total number of active sites. However, when the total number of the –SO₃H groups did not change, higher activities were shown on the sulfonated carbon with higher surface S content.