Light scattering investigations in the system methyl ethyl ketone + water + secondary butyl alcohol with traces of potassium thiocyanate

Abstract

The effect of trace amounts of potassium thiocyanate (KSCN) at weight fractions XKSCN = 0.0300, 0.0319 and 0.0320 – the weight fractions at which no particular structural peculiarities exist in the phase diagram of MEK + W + sBA + KSCN; presence of critical endpoints (CEPs) are detected and coexistence domes with minimal separation between the vertices containing double critical points (DCPs) are formed in the phase diagram, respectively [Naseer A. P. et. al., J. mol. Liq. 296 (2019)] – on the critical behaviour of the system methyl ethyl ketone (MEK) + water(W) + secondary butyl alcohol (sBA) are investigated through thelight scattering technique. For MEK weight fractions (x) in the range of 0.1000 ≤ x ≤ 0.1800 at constant XKSCN = 0.0300 near Ising-type behavior is observed for experimental paths approaching both TL from below and TU from the above, while in the range of 0.2000 ≤ x ≤ 0.2100 the samples show a clear mean-field type of behavior both at the TL as well as TU. Investigations near the DCPs corresponding to the minimum approach of the two coexistence domes (i.e., at x = 0.1419 and 0.1608 at XKSCN = 0.0320) do not result in the well-established, doubling of critical exponents γ and ν due to inherent chemical complexities in the system MEK + W + sBA + KSCN. FTIR and LC-HRMS studies establish that the formation of the isothiocyanate-isomer of α-thiocyanated methyl-ethyl-ketone resulting from prolonged exposure to elevated temperatures during the course of the light-scattering experiments, is responsible for the results.