Molecular Association in Binary Mixtures of tert-Butyl Alcohol−Water and Tetrahydrofuran−Heavy Water Studied by Mass Spectrometry of Clusters from Liquid Droplets

Abstract

The cluster structures observed by means of mass spectrometry for binary mixturestert-butyl alcohol (TBA)−H2O and tetrahydrofuran (THF)−D2Owith varying mixing ratios exhibit striking contrast, even though both TBA and THF are miscible with water at any mixing ratio. In the TBA−H2O mixtures at TBA mole fractions of (XTBA) ≤ 0.01−0.025, some of the H2O molecules in the H2O clusters are replaced by TBA molecules. For 0.01−0.025 ≤ XTBA ≤ 0.2−0.3, the self-aggregation of TBA forms dominant cluster structures, and the hydrogen-bonded water clusters are disintegrated with increasing XTBA. This TBA self-aggregation is reduced with further increasing TBA at XTBA ≥ 0.3. However, in the THF−D2O mixtures, THF molecules have a weak additional interaction with D2O clusters, and the self-aggregation of THF is not promoted in the THF−D2O mixtures. The D2O clusters still exist, even at a THF mole fraction of XTHF = 0.3. On the basis of the observed cluster structure, the mechanism for the mixing between water and the organic solvent and the controlling factors in the self-aggregation are proposed.