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Benzimidazolium-based high temperature ionic liquid-in-oil microemulsion for regioselective nitration reaction

Kar, Barnali and Ghosh, Prasanjit and Kundu, Kaushik and Bardhan, Soumik and Paul, Bidyut K. and Das, Sajal (2018) Benzimidazolium-based high temperature ionic liquid-in-oil microemulsion for regioselective nitration reaction. In: JOURNAL OF MOLECULAR LIQUIDS, 268 . pp. 122-130.

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Official URL: http://dx.doi.org/10.1016/j.molliq.2018.07.010

Abstract

Owing to the fascinating applications of ionic liquids (ILs) based non-aqueous microemulsions (MEs) in the field of chemical reactions due to their high thermal stability compared to that of aqueous MEs and requirement of water-free environment, we designed a high-temperature stable cationic IL-in-oil microemulsions using 1-ethyl-3-propylbenzimidazolium bromide (EPbim]Br) as a polar phase for the first time. In order to determine the thermodynamic stability of such type of MEs, we measured the distribution of cosurfactant (herein, 1-octanol) between bulk n-decane phase and interface covered by quaternary ammonium head group of cetyltrimethylammonium bromide (CTAB) at elevated temperature. The spontaneous formulation of high-temperature IL-in-oil MEs with organized IL-oil interface was identified by the negative free energy and entropy change at studied temperature range (358-370 K). Interestingly, we observed temperature-independent exothermic behavior at a specific composition, which probably comes from the cation-pi interaction between quaternary ammonium head group of CTAB and aromatic moiety of ILs. We performed phase behavior study to demonstrate a wide range of thermally stable of EPbim](Br]/CTAB/decane MEs. Surprisingly, the droplet size was decreased with progressive addition of IL, which may be due to the difficulty of formation of strong and favourable H-bond between the polar head groups of CTAB and EPbim]Br] at higher temperature. Furthermore, the aggregation number and molecular interfacial area at higher temperature were calculated, which have direct correlation with the droplet size. Finally, the nitration reaction with three different aromatic compounds was performed in this MEs media at the temperature-independent composition. The reaction was completed with the highest regioseletivity-of para isomer product over the ortho one. Moreover, these results clearly highlight an efficient way towards the formulation of high temperature stable MEs with ILs at ambient pressure and open a wide field of potential applications. (C) 2018 Elsevier B.V. All rights reserved.

Item Type: Journal Article
Additional Information: Copy right for this article belong to ELSEVIER SCIENCE BV
Keywords: Ionic liquid; Microemulsion; Thermodynamics; Dynamic light scattering; Nitration
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Depositing User: Id for Latest eprints
Date Deposited: 14 Nov 2018 15:11
Last Modified: 14 Nov 2018 15:11
URI: http://eprints.iisc.ac.in/id/eprint/61053

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