Metal−organic frameworks as recyclable catalysts for efficient esterification to synthesize traditional plasticizers

Abstract Practically the traditional plasticizers are produced via homogeneous esterification reaction in millions of tons annually as additives for modulating the properties of polymeric materials, facing great environment pressure such as a huge amount of wastewater produced to remove the detrimental metal catalyst. In this work, a series of MOFs, MIL-101, MIL-125, MIL-125-NH2, UiO-66, UiO-66-NH2, and UiO-66-SO3H, have been synthesized and employed as heterogeneous catalysts for the syntheses of plasticizers. MIL-125 and MIL-125-NH2 were found to show the superior catalytic efficiency compared with other MOFs. Catalyzed by only 1.0 mol% of MIL-125 within 1.0 h at 190 °C, the heterogeneous reaction achieved 99.9 % yield of Di-(2-ethylhexyl)terephthalate (DOTP). In addition, MIL-125 also showed excellent catalytic performance for the syntheses of other plasticizers (DOP, TOTM, DOA and DOS). The control experiments demonstrated that the titanium metal nodes of the MOFs dominate this kind of esterification reaction while functional groups on the ligands and structural defects give a certain positive effect. MIL-125 has been proved to be a heterogeneous catalyst with high efficiency and good recyclability, mitigating the pollution and promising for economic and environmental friendliness in the practical production of traditional plasticizers.