Study On The Catalytic Synthesis Of The Green Plasticizer Citrate Esters

Tributyl citrate (TBC) received more and more attention as the green plasticizer for the substitution of the traditional plasticizer of DOP. Ionic liquids are widely applied to esterification, Mannich reaction, Bechmann rearrangement and hydrolysis reactions as the environment-friendly catalytic materials. The results show that the catalysts own the advantages of high activities, high selectivities and reusability. Solid acids such as the carbon based solid acids are also used in widely in the organic synthesis. The novel heterogeneous catalysts have many advantages such as high activity, strikingly simple workup procedure, non-pollution and reusability, so the materials own great potential as catalyst in the green chemical process.In this paper, room temperature ionic liquids, acids impregnated on silica gel and carbon based solid acids as the novel catalysts have been used high efficiently in the synthesis of the green plasticizer of citrate esters.Firstly, a series of Brφnsted acidic ionic liquids with non-volatility and low melting point have been synthesized under solvent-free conditions. These ionic liquids were used as catalyst for the synthesis of tri-butyl citrate and other citrate esters. The results showed that the Brφnsted acidic ionic liquids were very efficient for the reactions. Under the optimical reaction conditions, the yields of all citrate esters were over 96%.Second, from the view point of environment and economy, the decline of the usage of sulfuric acid in the chemical process and simplification in handling procedures are highly required. So developing heterogeneous catalytic process became more and more important. Here the different heterogeneous catalytic processes were carried out for the synthesis of TBC. First, different active acids impregnated on silica gel were applied to the synthesis of TBC, which showed high activity with the disadvantages of instability. In order to resolve the problem, the novel carbon based solid acids were synthezed for the reaction. The catalyst was characterized by XRD, FT-IR, SEM. The results showed great potential for the substitute of H₂SO₄ with attractive features such as high activity, high selectivity and reusability. The procedure owned many advantages such as the reusability, environment benign, and a waste-free. Under the optimical reaction conditions, the yield of TBC was over 97% and decreases no more than 2% after the catalyst was recycled for 5 times.Finally, the simple and efficient procedure for the synthesis of ATBC was also carried out through the acetylation of TBC with Ac₂O using the above-mentioned catalysts. The notable advantages were (1) mild reaction conditions, (2) short reaction time, (3) excellent yields, (4) high selectivity. The yield of the acetyl tri-butyl citrate was over 97% within 30 minutes at room temperature under solvent-free conditions.