Solid superacid SO42−-S2O82−/SnO2-Nd2O3-catalyzed esterification of α-aromatic amino acids

•SO42−-S2O82−/SnO2-Nd2O3 catalyzed the methyl esterification of α-aromatic amino acids (L-Tyr and L-Trp).•High ester yields of ≥ 92% was achieved within 3-6 h, and catalyst was reused > 6 times.•Nd-doping enhanced electron-withdrawing inductive effect of SO42−/S2O82−, and increased Brönsted and Lewis acidity.•Nd-doping reduced activation energy of L-Tyr esterification. α-Aromatic amino acid esters are important platform compound for drugs, sweeteners and fluorescent sensors. Due to the amphoteric dissociation and steric effect, the esterification of α-aromatic amino acids is difficult. Here, a green and efficient solid superacid, SO42−-S2O82−/SnO2-Nd2O3 (SSSN), was synthesized and firstly used for the methyl esterification of α-aromatic L-tyrosine and L-tryptophan. The methyl esters yield was optimized with the highest L-TyrOMe yield of 93.1% and L-TrpOMe yield of 92% over SSSN-650 (SO42−-S2O82−/SnO2-Nd2O3 calcined under 650 °C). Furthermore, it was clarified that the doping of Nd enhanced the electron-withdrawing inductive effect of SO42−/S2O82− with increased Brønsted and Lewis acidity, which were beneficial to the esterification of L-tyrosine and L-tryptophan. Besides, Nd-doping reduced the activation energy during L-Tyr esterification by kinetics study. Finally, SSSN-650 could be recycled six times with > 70% of their initial ester yield. The decrease of catalyst activity was caused by carbon deposition and species leaching. This work launched a novelty, rapid and environmental-benign technology for the esterification of α-aromatic amino acid using solid superacid. [Display omitted]