| According to the relevant references, in this paper, we used N-methylimidazole, pyridine, and triethylmine as materials to prepare several functionalized acidic ionic liquids, such as l-methyl-3-(3-sulfo-propyl)-imidazolium hydrogen sulfate ([HSO3-pMIM]HSO4),l-methyl-3-(3-sulfo-propyl)-imidazolium p-toluenesulfonate ([HSO3-pMIM]pTSA),l-(3-sulfo-propyl)-pyridine hydrogen sulfate ([HSO3-pPy]HSO4),l-(3-sulfo-propyl)-pyridine p-toluenesulfonate ([HSO3-pPy]pTSA),N-(3-sulfo-propyl)-N,N,N-triethylamine hydrogen sulfate ([HSO3-pTEA]HSO4) and N-(3-sulfo-propyl)-N,N,N-triethylamine p-toluenesulfonate ([HSO3-pTEA]pTSA). And the structure of these ionic liquids were characterized by IR, 1 H NMR,13C NMR and TG-DSC. The acidity of these ionic liquids were determined by using pyridine as IR spectroscopic probe.The esterification synthesis of plasticizer esters—Diisoctyl maleate ( DOM ), Dibutyl maleate ( DBM ), Diisoctyl itaconate ( DOIA ), Dibutyl itaconate ( DBIA ) and preservative Nipagin esters were studied using various ionic liquids as catalysts. The catalytic and reusable performances of these ionic liquids are different, which can be explained with the acidity, polarity or solubility difference of these ionic liquids. Using the better ionic liquid as catalyst, we further optimized the reaction conditions, thereby an environment friendly approach for the synthesis of those esters are provided.Among those ionic liquids, the neutral ionic liquids showed weak catalytic activity due to their weak acidity; the acidic ionic liquids were dissolved in the reaction fluids and cannot be separated even cool to the room temperature; however the -SO3H functionalized ionic liquids showed good catalytic activity and reused performance. Lighter color, higher purity, better yield products were gained which catalyzed by these functionalized ionic liquids under mild reaction conditions. In the synthesis of maleate and itaconate esters, the functionalized ionic liquids were immiscible with the product and could be reused without any disposal; While in the synthesis of Nipagin esters which with -OH, the functionalized ionic liquids were dissolved in the product. However, ionic liquids can be simply separated through extracting method due to the series predominances of its own. At the same time, as the length of the alcohol carbon chain increases, the melting point of the Nipagin ester decreases, and the crystallization becomes more difficult, resulting in the lossing of ionic liquids. Therefore we need further exploration.The recycling performance of ionic liquids were investigated. The results showed that the catalytic activity of ionic liquids were still high after they were used for several times, and the deactivtion may be the lose of in the procedure of separation. However, when some ionic liquids were added to the system, the catalytic activity could be recovered. Compared with classical methods, the reaction showed simpler product procedure, less catalyst consumption and less pollution of environment. The study provides guidances for ionic liquids to be used in esterification. |
