HYDRATE CLUSTER FORMATION OF DIOL COMPOUNDS IN AQUEOUS-SOLUTION

Dilute aqueous solutions of seven diols (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-pentanediol, 2,4-pentanediol, 1,4-pentanediol, and 1,5-pentanediol) were examined by mass spectrometric analysis of the clusters isolated through adiabatic expansion of liquid droplets in vacuum. Stability constants of the solute m-mer hydrate clusters k(m) (m = 1, 2) were estimated by analyzing the obtained mass spectra. All the stability constants for the diols were found to be approximately equal to or less than 1.0, suggesting that the hydrate clusters of the solute species are as strong as or weaker than those of pure water clusters. Stabilities of the diol hydrate clusters are also dependent on the distance between the two OH groups and/or the number of methylene groups between the two OH groups. From the temperature dependence of the population ratio of the diol-hydrate clusters to pure water ones, we evaluated thermochemical values for the elemental association-dissociation processes.