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The seven-member alicyclic secondary amine, azepane, has been used as starting material to synthesise a new family of room temperature ionic liquids. Such useful transformations of this coproduct of diamine production processes, generated in large amounts in the polyamide industry, would mitigate its disposal, which usually involves combustion. Reaction of azepane with 1-bromoalkanes or 1-bromoalkoxyalkanes produced the corresponding tertiary amines with good selectivity; further quaternisation reactions with the appropriate methylating agents yielded quaternary azepanium salts, [Rmazp]X (R = alkyl or alkoxyalkyl; X− = I−, [CF3CO2]− or [OTf]−; Tf = (trifluoromethyl)sulfonyl). Analogous [NTf2]− salts have also been produced by metathetic reactions. Liquid temperature ranges are significantly affected by the nature of the anion and the substituents on the azepanium cation core; for example, [CF3CO2]− or [OTf]− salts based on cations with alkyl substitution are solids, whereas those with alkoxyalkyl substitution are liquids at ambient temperature. The crystal structures of [C4mazp][CF3CO2], [C4mazp]I and [C6mazp][NTf2] (C4 = butyl, C6 = hexyl) are reported. The effects of the structural features of cations and anions on density, viscosity and conductivity data are discussed. The presence of ether linkages in the cationic side chains causes a marked decrease in viscosities and an increase in conductivities. Cyclic voltammetry showed that azepanium ionic liquids exhibit extremely wide electrochemical windows, thus becoming promising and safe alternatives to electrolytes based on volatile organic compounds. [ABSTRACT FROM AUTHOR]

The preparation and characterisation of a series of ionic liquids based on S-alkylthiouronium cations prepared from thiourea, 1,3-dimethylthiourea, 1,3-diethylthiourea and 1,3-tetramethylthiourea coupled with bis{(trifluoromethane)sulfonyl}imide, bromide, methylsulfate or ethylsulfate anions are reported. All are liquids at room temperature or solids with melting points close to room temperature, except for the bromide salts, which have melting points below 92 °C. Systematic variation in the N- and S-alkyl substituents demonstrates how the physical properties of these ionic liquids can be readily controlled. The mutual miscibility limits of representative examples with octane, dodecane and toluene have been determined as a function of temperature, and the extraction of dibenzothiophene from dodecane as a model for desulfurisation of diesel has been investigated. [ABSTRACT FROM AUTHOR]