Water Solubility, Vapor Pressure, and Activity Coefficients of Terpenes and Terpenoids

Water solubilities, activity coefficients, and vapor pressures of some terpenes and terpenoids were determined from two sets of experiments. The first involved liquid−liquid contacting until saturation of an aqueous layer, which gave solubility and activity coefficient at infinite dilution γ^∞. The second set involved stripping a solute from a nonsaturated aqueous solution by an air stream. This last experiment gave the product γ^∞P° from which vapor pressure P° was deduced. Reliability of the results was established from predicted P° values, and data for 12 compounds are now available. Data obtained at 25 °C showed low solubilities (0.037−0.22 mmol/L) and high activity coefficients (10⁵−10⁶) for terpenes, whereas oxygenated monoterpenes exhibited solubilities 20 orders of magnitude higher, in the range of 2−20 mmol/L and 10³−10⁴ for activity coefficients. Vapor pressures ranged from 100 to 550 Pa for terpenes and from 1 to 130 Pa for terpenoids. Attempts to estimate water solubility showed that recent equations in the literature are unable to predict this property with an accuracy better than 140%.