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Investigation of the spectroscopic, chemical and physical properties of Cyrene and its hydrate

Misefari, Antonio (2017) Investigation of the spectroscopic, chemical and physical properties of Cyrene and its hydrate. MSc by research thesis, University of York.

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This work examines distinct properties of Cyrene notably the occurrence of a carbonyl doublet in the IR spectrum and the formation of the Cyrene-hydrate (= Cyrene's geminal diol) when mixing Cyrene with water. To this extent a thorough analysis by FT-IR, Raman, 1H NMR and 13C NMR spectroscopy was undertaken. FT-IR spectroscopy was also performed with variable temperatures as to gain more understanding on the chemical/physical reasons for the carbonyl doublet presence. Surprisingly limited influence of this phenomenon by both temperature and use of different solvents was seen. The possible occurrence of Fermi resonance was also investigated but Raman spectroscopy, using polarized and non-polarized light, largely ruled out this hypothesis. Calculation of the IR spectrum of pure Cyrene was also performed suggesting the occurrence of Cyrene dimers in the least – potentially extending into oligomeric structures. The presence of such structures are consistent with the high value of the enthalpy of vaporization as calculated by the classic Clausius Clapeyron equation. Calorimetric analysis (covering the -70 to 20 C range) of both pure Cyrene and its solutions in different solvents was equally performed. The data suggested an amorphous structure, not showing a unique and consistent peak for the crystallization and melting point. Also, a strong dependence of the thermograph on the thermal history of the sample could be observed. Analysis by diffuse light scattering (DLS), small angle X-ray scattering (SAXS) and polarized light microscopy ruled out the occurrence of a long-range structural order (as one can encounter with ionic liquids and liquid crystals) for Cyrene. The Cyrene hydrate case was found very complex in that mixing Cyrene with water yielded a ternary mixture consisting of Cyrene, its hydrate or geminal diol and remaining unreacted water. This was established by state of the art solvent free 1H and 13C NMR analysis. Density and viscosity measurements of Cyrene/water combinations revealed two distinct zones: a) the addition of >50 wt% Cyrene to water is characterized by high densities and viscosities b) <50 wt% Cyrene in water the properties are largely dominated by the water component. NMR at different temperatures was also performed showing that an increase in the temperature shifts the Cyrene/geminal diol equilibrium to Cyrene and a decrease in the temperature favours the Cyrene hydrate. Interestingly the Cyrene/geminal diol equilbrium does not fit the intuitive stoichiometry of one water molecule reacting with one Cyrene to form a single geminal diol. It is shown that at least two waters are implicated in this equilibrium, hinting at the formation of clathrates. Interestingly the presence of Cyrene and geminal diol in water actively depresses the latter's freezing point much alike in water/ethylene glycol mixtures. Also, the ternary mixture is a clear example of a NAtural Deep Eutetic Solvent (NADES) but then, unusually, as a solvent mixture. Lastly the solubility of a range of compounds was investigated in a range of Cyrene/geminal diol/water ternary mixtures. To this end solvent-free 1H and 13C NMR spectroscopy was used. Through this investigation it was found that the ternary mixture can be exploited as a chameleon solvent and a switchable hydrotrope. On the one side, the addition of a small amount of water to Cyrene switches on the amphiphilic geminal diol chameleon solvent, increasing the solubility of a range of compounds vis-à-vis their solubility in pure Cyrene with up to a factor of 9. Alternatively, the addition of Cyrene to water creates in situ the amphiphilic geminal diol as a switchable hydrotrope, which leads to a remarkable increase in solubility up to 10000-fold. The dissolved compounds can generally be recovered by simply adding (or removing) water, potentially aided by lowering the temperature, decreasing naturally their solubility.

Item Type: Thesis (MSc by research)
Academic Units: The University of York > Chemistry (York)
Depositing User: Mr Antonio Misefari
Date Deposited: 04 Oct 2017 15:29
Last Modified: 21 Sep 2018 00:18
URI: http://etheses.whiterose.ac.uk/id/eprint/18284

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