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Synthesis of [RMIM] Acetate Halogen-Free Ionic Liquids for Use as Greener Solvents in Diels-Alder Reaction

 

Susan D. Arco1*, Rosalie T. Laxamana2, Ofelia D. Giron1, and Judy M. Obliosca1

1Institute of Chemistry and 2Natural Sciences Research Institute
University of the Philippines, Diliman, Quezon City 1101

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endo and exo TS in Diels

 

Representations of the endo- and exo- TS in the Diels-Alder reaction of methyl acrylate and cyclopentadiene in [RMIM]OAc medium; (a) and (c) are 2D models of endo TS and exo TS, respectively; (b) and (d) are 3D models of endo TS and exo TS, respectively.

 


ABSTRACT


A halogen-free ionic liquid 1-alkyl-3-methylimidazolium acetate, [RMIM]OAc, with its cation based on 1-alkyl-3-methyl imidazolium and with the halogen-free anion acetate (OAc) was synthesized. This ionic liquid’s distinctive solvent properties and its application as greener solvent for the Diels-Alder reaction were examined. Its efficiency as medium for the Diels-Alder reaction between cyclopentadiene and methyl acrylate was evaluated in terms of product yield and stereoselectivity. Using these parameters, [RMIM]OAc was compared with other solvents such as benzene, methanol, and water as alternative solvent for the Diels-Alder reaction. Results showed a decrease in product yield as the length of the alkyl group chain on the imidazolium cation is increased from C6 to C12. In terms of stereoselectivity, there is a general preference for the endo-product in all of the solvents tested. The endo-selectivity obtained with [HMIM]OAc (endo:exo=91:9) is remarkably high and is more desirable compared to that obtained with water (endo:exo=76:24)......

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