Valorization of Glycerol: Synthesis of Glyceryl Salicylates, Components of Endodontic Sealants, from Methyl Salicylate Using Red Mud Alkaline Solution as a Basic Catalyst

An aqueous solution of red mud, or red mud waste alkaline solution (RMWAS), with a pH of 13 obtained from the production of alumina and containing high concentrations of soluble hematite (Fe2O3), goethite (FeOOH), gibbsite γ Al(OH)3, boehmite (AlOOH), anatase (tetragonal TiO2), rutile (ditetragonal dipyramidal TiO2), hydrogarnets Ca3Al2(SiO4)3–x(OH)4x, and perovskite (CaTiO3) was used as a basic catalyst in the synthesis of glyceryl salicylate resin (endodontic sealants). Alkoxide anions were generated during the reaction of glycerol with RMWAS for 1 h. The resulting reaction mixture was treated with methyl salicylate (MS) at room temperature (25 °C) for 2 h, affording a resinous mixture composed of 2,3-dihydroxypropyl 2-hydroxybenzoate (1-glyceryl salicylate, 1-GS) and 1,3-dihydroxypropan-2-yl 2-hydroxybenzoate (2-glyceryl salicylate, 2-GS) in 91.91% yield. The RMWAS catalyst was then reused in 10 additional transesterification cycles, each producing mixtures of 1-GS and 2-GS with consistently high yields. The yields obtained for the 1st through 10th reuse cycles were 89.23%, 89.03%, 88.10%, 88.01%, 86.08%, 85.53%, 85.08%, 82.65%, 80.05%, and 79.43% respectively, after 2 h of reaction following glycerol anion formation. The RMWAS used in this work has the advantage of exhibiting catalytic activity in an aqueous medium at room temperature (25 °C) and under an air atmosphere. It is a recyclable and environmentally friendly waste material. The use of a renewable base in aqueous medium makes the protocol highly significant from green and sustainable chemistry perspectives. 1-GS and 2-GS are relevant components of endodontic cement formulations. Antimicrobial evaluation showed that the mixture of 1-GS and 2-GS exhibited effective activity against E. coli, S. aureus, and S. Typhimurium. In addition, no hemolytic effect was observed at concentrations equal to or below 2%, indicating minimal cytotoxicity and suggesting low toxicity at the effective antimicrobial concentrations.