Heat Capacities and Low Temperature Thermal Transitions of 1-Hexyl and 1-Octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide

详细信息    查看全文

• 作者：Thomas J. Hughes ; Tauqir Syed ; Brendan F. Graham ; Kenneth N. Marsh ; Eric F. May
• 刊名：Journal of Chemical & Engineering Data
• 出版年：2011
• 出版时间：May 12, 2011
• 年：2011
• 卷：56
• 期：5
• 页码：2153-2159
• 全文大小：803K
• 年卷期：v.56,no.5(May 12, 2011)
• ISSN：1520-5134

文摘

Several previous measurements of the isobaric heat capacity of the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([Hmim][Tf₂N]) differ relative to the IUPAC recommended value by 卤 8 %. Specifically, the results obtained by differential scanning calorimetry (DSC) showed relative difference from each other and from values determined by adiabatic calorimetry by up to 12 % and by 6 % on average. The aim of this work was to explore the reason for these discrepancies in DSC measurements. Accordingly, measurements of the isobaric heat capacity and low temperature thermal transitions of [Hmim][Tf₂N] and 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([Omim][Tf₂N]) made by DSC are reported here. The isobaric heat capacities for both ionic liquids were measured on samples of (5 to 9) g over the temperature ranges (303 to 373) K for [Hmim][Tf₂N] and (288 to 373) K for [Omim][Tf₂N] using steps of 10 K and a scan rate of 0.025 K路min^鈭?. These heat capacity measurements were consistent, within their estimated relative uncertainty of 3 %, with the values measured by adiabatic calorimetry and with the DSC measurements made at scan rates of less than 1 K路min^鈭? on samples of 5 g or greater. In addition, several thermal transitions were observed for these ionic liquids at temperatures down to 140 K. For [Hmim][Tf₂N] a melting temperature of (272 卤 1) K and an enthalpy of fusion of (62 卤 2) J路g^鈭? were measured, which are consistent within the combined uncertainties with those of Shimizu et al. (J. Phys. Chem. B2006, 110, 13970鈭?3975). After tempering the [Omim][Tf₂N] sample, a melting temperature of (250 卤 1) K and an enthalpy of fusion of (58 卤 2) J路g^鈭? was obtained, which differ by 1.6 K and 3.7 % respectively from values reported by Paulechka et al. (J. Chem. Thermodyn.2007, 39, 866鈭?77).