Selective synthesis of phosphate mono-esters with an acidic modified niobium oxide catalyst

The atom-efficient esterification of phosphoric acid was investigated for the selective synthesis of phosphate mono-esters using an acid treated niobium oxide catalyst, avoiding the use of amines as is common in literature. Kinetic studies revealed that the heterogeneous catalyst exhibited higher selectivity for mono-esters compared to homogeneous acid catalysts, as supported by calculation of the relative reactivity of mono-ester and phosphoric acid with different catalysts. To characterize the catalyst, its Hammett acidity value (H₀) was determined, while solid state ³¹P NMR enabled studying the adsorption of H₃PO₄. Due to the mild acidity of the niobium oxide, alcohols with acid-sensitive functions, including substituted double bonds, could be phosphorylated, enabling the synthesis of surfactants such as oleyl phosphate.