Sustainable synthesis of 1,8-dioxooctahydroxanthenes in deep eutectic solvents (DESs)

Abstract

Deep eutectic solvents are obtained by the fusion of two or more compounds: hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs). They are formed by mixing the constituents with moderate heating (via hydrogen bond interactions). In this manuscript, the dual activities (as catalysts and reaction media) of six deep eutectic solvents were compared for the synthesis of 1,8-dioxooctahydroxanthenes at room temperature. Here DES 2, a combination of ZrOCl₂·8H₂O with ethylene glycol at a 1 : 2 ratio, was found to be the supreme catalyst among the six DESs and was reused for five batches. The photophysical properties of the xanthene derivatives were examined by UV-vis and fluorescence spectroscopy in THF. The synthesised molecules showed absorption maxima around 285–295 nm and emission maxima around 403–404 nm. The ground state dipole moments of all the molecules were calculated by the Debye–Guggenheim method using toluene as the non-polar solvent. All the synthesised molecules showed significant dipole moment values and are in good agreement with theoretical values.