Physicochemical Properties of Tri-n-butylalkylphosphonium Cation-Based Room-Temperature Ionic Liquids
2013
Yoshii, Kazuki | Yamaji, Keisuke | Tsuda, Tetsuya | Tsunashima, Katsuhiko | Yoshida, Hiroyuki | Ozaki, Masanori | Kuwabata, Susumu
The physicochemical properties of novel four tri-n-butylalkylphosphonium-based room-temperature ionic liquids (RTILs), tri-n-butylmethylphosphonium dimethylphosphate ([P₄,₄,₄,₁][DMP]), tri-n-butyl(2-hydroxymethyl)phosphonium bis(trifluoromethylsulfonyl)amide ([P₄,₄,₄,₂OH][Tf₂N]), tetra-n-butylphosphonium O,O′-diethylphosphorodithioate ([P₄,₄,₄,₄][DEPDT]), and tri-n-butyldodecylphosphonium 3,5-bis(methoxycarbonyl)benzenesulfonate ([P₄,₄,₄,₁₂][MCBS]), were examined in this study. All RTILs showed a favorable thermal decomposition temperature exceeding 560 K. Of these, [P₄,₄,₄,₁₂][MCBS] exhibited a fairly high thermal stability compared with common phosphonium cation-based RTILs reported to date. Interestingly [P₄,₄,₄,₁][DMP] formed an ionic plastic crystal phase within a range of 279–290 K, but that was not the case with [P₄,₄,₄,₄][DEPDT], which is similar in the cation and anion structures to the [P₄,₄,₄,₁]⁺ and [DMP]⁻. [P₄,₄,₄,₂OH][Tf₂N] showed a relatively high conductivity of 0.48 mS cm–¹ at 303 K among the RTILs consisting of tri-n-butylalkylphosphonium cation and usual fluoroanion.
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