Analytical Sciences

Simultaneous XRD-DSC Measurements of Water-2-Propanol at Sub-Zero Temperatures

Yuko NISHIMOTO,* Yoichi KANEKI,* and Akira KISHI**

*Department of Chemistry, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293, Japan
**X-Ray Research Division, Rigaku Corporation, Akishima, Tokyo 196-8666, Japan

A simultaneous low-temperature X-ray powder-diffractometric (XRD)-DSC technique was applied to the solid state and melting process of frozen aqueous solutions of 2-propanol. ¹H NMR spectra were also obtained at low temperatures. The chemical shifts of the CH₃ proton and the CH proton can be classified into four temperature regions: higher than -20°C, around -20°C, -50 to -20°C, and lower than -50°C. In the XRD data, five small diffraction peaks for 2 θ at 21.0°, 25.2°, 27.8°, 31.1° and 32.1° can be attributed to the peritectic, while five diffraction peaks at 22.5°, 24°, 25.6°, 33.4° and 39.8° can be attributed to ice; these peaks are due to the hexagonal form of ice, which disappears upon melting. However, the diffraction peak at 33.4° showed a different pattern than the other peaks due to hexagonal ice. These results indicate that the temperature dependence of the diffraction peak at 33.4° for 2 θ is related to the formation of hydrogen bonds between 2-propanol and water. The simultaneous XRD-DSC technique was effective for investigating this water-alcohol mixture at low temperatures.

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