The polymerization of carvacrol catalyzed by Mn-porphyrins: obtaining the desired product guided by the choice of solvent, oxidant, and catalyst

Abstract

Carvacrol is a monoterpene obtained in large quantities from renewable raw materials, such as oregano. Carvacrol oxidation to produce more valuable and useful compounds using different catalysts and oxidants has been studied since the 1980s and the main described product has been thymoquinone. For metalloporphyrin-mediated oxidation, we expand the research field by using for the first time less polar solvents and iodoarenes as oxidants. Under mild conditions, up to 100% of carvacrol oxidation was observed and the major product was not the expected thymoquinone. Further investigation of the products revealed the formation of a polymeric product, observed exclusively for carvacrol oxidation mediated by the manganese porphyrins studied as catalysts. The polymer can be classified as a low-molar-mass polymer, with applicability in epoxy resin synthesis. A radical mechanism has been proposed to explain carvacrol polymerization catalyzed by manganese porphyrins and it may be useful for further investigations on the oxidation of other triterpenes in systems with iodoarenes/metalloporphyrins. This study confirms the versatility of metalloporphyrin catalysts by showing that their activity can be modulated by varying the reaction conditions.