Montmorillonite—environmentally friendly catalyst for esterification of carvacrol with acetic anhydride

Abstract Carvacryl acetate (5-isopropyl-2-methylphenyl acetate) is a monoterpenoid ester, which is characterized by similar or even higher pharmacological properties as its precursor—carvacrol, including anti-inflammatory, antibacterial, antinociceptive activity. Traditional synthesis of carvacryl acetate is the reaction of carvacrol with acetyl chloride or acetic anhydride using homogeneous basic catalyst. Such homogeneous reaction arrangement suffers from the necessity of ester isolation from homogeneous catalyst together with formation of a significant amount of chlorinated waste (in case of acetyl chloride use). In our work we present solvent—free synthesis of carvacryl acetate with acetic anhydride using a cheap, eco-friendly and available heterogeneous catalyst—montmorillonite K10, which was used as commercially available or in acid treated (nitric or sulfuric acid) form. Prepared acid treated montmorillonites were thoroughly characterized (XRD, XRF, nitrogen physisorption, static laser light scattering, FTIR) and its acidity was studied using temperature programmed desorption of pyridine and DR–UV–Vis spectroscopy. In the case of using montmorillonite treated with sulfuric or nitric acid as catalyst total conversion of carvacrol after 10–15 min of reaction at room temperature was observed (100% selectivity to the desired ester). Reaction kinetic parameters were evaluated using ERA3.0 software package.