Synthesis of mono-dodecyl phosphate ester with high selectivity over the bicationic-heteropoly acid catalysts

A series of ionic liquid-heteropoly acid hybrid catalysts with bi-imidazolium cation were prepared via a two-step method. The structures of catalysts were characterized by FT-IR. The catalytic performances of direct esterification of phosphoric acid with lauryl alcohol to mono-dodecyl phosphate with high selectivity were studied. The results indicated that the hybrid catalysts had the same Keggin type structure as that of heteropoly acid. The catalytic activity of hybrid catalyst was higher than that of the pure heteropoly acid catalyst. With 0.67% (mass fraction) catalyst dosage, the bis-(3-methyl-1-imidazolium) butylene phosphotungstate catalyst possessed the best catalytic performance with 43.5% yield and 99.9% selectivity of mono-dodecyl phosphate under 90°C for 1 h reaction among the hybrid catalysts. With toluene as dehydrant, a high yield of 93.5% with a very high selectivity of 99.8% for mono-dodecyl phosphate was achieved when the direct esterification of phosphoric acid with lauryl alcohol was carried out at 120°C for 24 h under the optimum catalyst dosage of 0.8% (mass fraction) . The excellent activity and perfect reusability during a six-recycle test demonstrated that the bi-imidazolium cation ionic liquid-heteropoly acid was a very potential organic-inorganic hybrid catalyst.