Chemistry Honors Theses
Heats of Dissolution of Several Imidazolium-Based Ionic Liquids into Low Dielectric MediaIonic liquids (ILs) are salts that are liquid at or near room temperature. They have unique properties since they are completely composed of ions and therefore have many potential applications. This thesis research focuses on the properties of ILs in low polarity solvent, chloroform (CHCl3). The motivation for this research was to further confirm the presence of particularly stable, long-lived ion pairs for several different imidazolium-based ILs dissolved in chloroform, as evidenced in prior research by the presence of two resonance sets in 1H NMR spectra.1 Specifically, it was shown that the variation of experimental conditions such as temperature and concentration changed the relative intensities of the two sets of resonances in the 1H NMR spectrum for the particular IL 1-ethyl-3-methylimidazolium bis(triflyl)amide ([C2mim][NTf2]), indicating an equilibrium between freely dissolved ions and ion pairs. From this discovery, it became relevant and of interest to measure the heats of dissolution of [C2mim][NTf2], which are useful to assess the thermodynamic stability of the ion pair formation. For comparison, the heats of dissolution were also obtained for the structurally similar ILs 1-hexyl-3-methylimidazolium bis(triflyl)amide ([C6mim][NTf2]) and 1-hexyl-3-methylimidazolium tris(triflyl)methide ([C6mim][MeTf3]). These ILs serve as comparisons for the effect of imidazolium chain length and anion. An RC1 calorimeter was used to obtain the heats of dissolution measurements of three imidazolium-based ILs using adiabatic controls. The dissolution of [C2mim][NTf2], [C6mim][NTf2], and [C6mim][MeTf3] were observed to be exothermic, releasing a small amount of heat into the solution, varying from -2.5 kJ/mol for [C6mim][MeTf3] up to -5.5 kJ/mol for [C2mim][NTf2]. To assess the reliability and accuracy of the measurements, the effect of different potential contaminants were examined, dissolved gas and solvent stabilizers (amylenes). It was determined that these potential contaminants did not affect the heats of dissolution. Heats of dissolution measurements were found to be lower for [C2mim][NTf2] when dissolving into 96:4 CHCl3:acetone solvent as compared to pure CHCl3. Using Hess’ Law, the change in enthalpy for the equilibrium between the freely dissolved ions and ion pairs in CHCl3 was determined to be between -1.0 and -2.1 kJ/mol IL for each of the temperatures investigated in this study, the largest change in enthalpy being at the lower temperatures.
Intermolecular Interactions of Two Non-Ionic Surfactants with Water Studied Through Nuclear Magnetic ResonanceThrough the use of various nuclear magnetic resonance (NMR) spectroscopic experiments we have studied the intermolecular interactions of two non-ionic surfactants with water. For the two surfactants used in these studies a proton NMR peak assignment has been completed. From the spectral assignments there are several different structures that the surfactant forms depending on the water content of the samples. First, we investigated the intermolecular interactions between water and a non-ionic surfactant, CHEM 1260, having an average of five ethoxy groups per alkyl chain (CaE5, where a is the number of alkyl carbons present in the surfactant and E stands for ethoxy). Proton NMR (1H-NMR) has allowed for the identification of several cross-linking structures formed by the surfactant as water content increases. The second part of this research investigated the intermolecular interactions of a non-ionic surfactant, CHEM 29, consisting of seven ethoxy groups and two isopropoxy groups (CaE7P2, where P stands for iospropoxy) and water. Both 1H-NMR and 13C-NMR were employed in this study. In the CHEM 29 study the presence of water in two different chemical environments was not observed as in the CHEM 1260 study, which lead to the idea that CHEM 29 behaves differently than CHEM 1260 in the presence of water.
NMR Diffusion and Relaxation Studies on Surfactant SystemsThe unique bilateral structure of surfactants allows for a variety of interesting applications in society and industry. In this study, we focused on one particular non-ionic surfactant referred to as C10E7P2OH. Six solutions were analyzed by DOSY, T1 and T2 experiments in order to determine the structure and size of the aggregates formed in solution. Three of these solutions contain the surfactant C10E7P2OH in water at concentrations by mass of 2, 3.5 and 5%. Three solutions contain surfactant at identical concentrations, and also D-limonene at 2% by mass.