Green approach to semisynthesis of apigenin from naringin isolated from very immature pomelo peels

Abstract The flavanone glycoside naringin, which is abundant in the very immature pomelo peel cultivated in Vietnam, has been demonstrated to have potential use in semisynthesis into other flavonoid compounds, especially apigenin, which exhibits several biological properties and has a greater commercial value. In this study, we carried out an oxidation reaction on flavanone backbone to semisynthesize apigenin with I 2 catalyst in some environmentally friendly solvents such as a replacement for the reaction in the pyridine solvent, which is thought to be a non‐green solvent. These solvents which were employed in this investigation included water, DMSO, ethyl acetate, ethanol, ethylene glycol, and vegetable oil. The degree of conversion and the purity of the isolated product were evaluated using the RP‐HPLC‐DAD method, the yield was calculated according to the mass of the obtained crystals, and the synthetic compounds were confirmed by NMR spectra. The results showed that the solvents of DMSO, DMSO:H 2 O gave the total yield of 93% and the purity of apigenin greater than 95% as compared to 74% and 93%, respectively, with the reaction in pyridine. Our findings revealed that using 10% mol of I 2 catalyst was more cost‐effective than conducting the reaction in pyridine, which required an equivalency of substrate and catalyst of 1:1. The solubility of naringin in the solvent combination should be taken into account, though, since this might result in a low yield and influence the degree of conversion.