3-Methylpiperidinium ionic liquids

Tayeb Belhocine, Stewart A Forsyth, H Q Nimal Gunaratne, Mark Nieuwenhuyzen, Peter Nockemann, Alberto V Puga, Kenneth R Seddon, Geetha Srinivasan, Keith Whiston

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12 Citations (Scopus)

Abstract

A wide range of room temperature ionic liquids based on the 3-methylpiperdinium cation core were produced from 3-methylpiperidine, which is a derivative of DYTEK® A amine. First, reaction with 1-bromoalkanes or 1-bromoalkoxyalkanes generated the corresponding tertiary amines (Rmβpip, R = alkyl or alkoxyalkyl); further quaternisation reactions with the appropriate methylating agents yielded the quaternary [Rmmβpip]X salts (X(-) = I(-), [CF3CO2](-) or [OTf](-); Tf = -SO2CF3), and [Rmmβpip][NTf2] were prepared by anion metathesis from the corresponding iodides. All [NTf2](-) salts are liquids at room temperature. [Rmmβpip]X (X(-) = I(-), [CF3CO2](-) or [OTf](-)) are low-melting solids when R = alkyl, but room temperature liquids upon introduction of ether functionalities on R. Neither of the 3-methylpiperdinium ionic liquids showed any signs of crystallisation, even well below 0 °C. Some related non-C-substituted piperidinium and pyrrolidinium analogues were prepared and studied for comparison. Crystal structures of 1-hexyl-1,3-dimethylpiperidinium tetraphenylborate, 1-butyl-3-methylpiperidinium bromide, 1-(2-methoxyethyl)-1-methylpiperidinium chloride and 1-(2-methoxyethyl)-1-methylpyrrolidinium bromide are reported. Extensive structural and physical data are collected and compared to literature data, with special emphasis on the systematic study of the cation ring size and/or asymmetry effects on density, viscosity and ionic conductivity, allowing general trends to be outlined. Cyclic voltammetry shows that 3-methylpiperidinium ionic liquids, similarly to azepanium, piperidinium or pyrrolidinium counterparts, are extremely electrochemically stable; the portfolio of useful alternatives for safe and high-performing electrolytes is thus greatly extended.

Original languageEnglish
Pages (from-to)10398-10416
Number of pages19
JournalPhysical Chemistry Chemical Physics
Volume17
Issue number16
Early online date28 Jan 2015
DOIs
Publication statusPublished - 28 Apr 2015

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    Belhocine, T., Forsyth, S. A., Gunaratne, H. Q. N., Nieuwenhuyzen, M., Nockemann, P., Puga, A. V., Seddon, K. R., Srinivasan, G., & Whiston, K. (2015). 3-Methylpiperidinium ionic liquids. Physical Chemistry Chemical Physics, 17(16), 10398-10416. https://doi.org/10.1039/c4cp05936k