Green Catalytic Synthesis Of Ester Plasticizer

Liquid acids are usually selected as the catalysts of esterification. However, they are difficult to separate and recycle from the product, and they also unfavorably affects corrosion prevention of synthesis equipment. Green catalysis technology may make up for these deficiencies.In this paper, some novel green catalytic materials were synthsized by molecular design, and their properties were investigated through modern characterization methods. Various acidic ionic liquids can be synthesized by introduction of long carbochains and functional carboxyl-group (B acid center) to the ring of imidazole via substituent reaction,elimination reaction,addition reaction and multiple step synthesis. Since Imidazolium ions exist potential lewis-acid centers, N, N-dialkyl imidazole ionic liquid, Gemini ionic liquid and N, N-disubstituent imidazolium ionic liquid with carboxy group were synthesized from imidazole and methyl imidazole. FT-IR, and elemental analysis were employed to characterize the structure of the products. In addition, the obtained ionic liquids (ILs) were used as catalysts to prepare plasticizers, such as tributyl citrate and diisobutyl adipate, respectively. Taking the advantage of supported catalyst, which has the integration feature of heterogeneous catalysts and homogeneous catalysts, in to account, ionic liquids supported on the montmorillonite (MMT) were prepared by intercalation and absorption. Thermal and chemical stability of these supported catalysts was analyzed by using TG and XRD. While the properties of catalytic activity, separation and reuse of the so prepared supported ionic liquids were investigated, an optimal green preparation process was also worked out with the evaluation of result catalytic materials.Results revealed that the target products obtained, which were expected to be N, N-dialkyl imidazole ionic liquid, Gemini ionic liquid and N, N-disubstituent imidazolium ionic liquid with carboxy group, were all exactly the same and tally with the requirement of molecular design.The onset decomposition temperatures of the long-chain substituted N, N-dialkyl imidazole ionic liquid and Gemini ionic liquid were relatively high, which can be nearly 300℃. Via ion exchanging method, The ILs mentioned above can be succeeded intercalating into the interlayer of MMT to form the supported ILs with higher thermal stability, compared with unsupported ILs. Moreover, results showed that supported ILs has high selectivity and obvious catalytic activity towards the preparation of tributyl citrate and diisobutyl adipate. Though the d-space of the composites with supported Gemini ILs will decrease after use, which implies that there exists escape of activity sites. Single long-chain substituted N, N-dialkyl imidazole supported ILs appear to be with high chemical stability, the color of the corresponding esterification products was light and the amount of the by-product was little. In particular, the catalyst can be easily seperated and recycled. Thus, supported ILs can be considered as a kind of solid catalyst with potential environmental benign feature.