Solubilities of ferrocene and acetylferrocene in supercritical carbon dioxide

Abstract

In this work, the solubilities of ferrocene and acetylferrocene in supercritical carbon dioxide (scCO2) were measured using an analytical method in a quasi-flow apparatus. High-performance liquid chromatography was applied through an online sampling procedure to determine the concentration of ferrocene and acetylferrocene in the scCO2 phase. The experiments were performed within a temperature range of 308–348K and at pressures ranging from 7.7 to 24.4MPa. Acetylferrocene is the product of the Friedel–Crafts acylation reaction of ferrocene and has many applications in the material and pharmaceutical industries. The molar solubilities at the applied conditions range from 8.9 to 31.2×10−4 for ferrocene and 2.5 to 79.2×10−4 for acetylferrocene. The existence of a cross-over area for acetylferrocene was detected at a pressure of around 15MPa and for ferrocene at a pressure of around 10MPa. The comparison between the experimental solubility data shows that ferrocene is more soluble in scCO2 at lower pressures, while at higher pressures acetylferrocene is more soluble in scCO2. The reason for this behavior is a trade-off between the lower polarity of ferrocene (more dominant at lower pressures) and the higher volatility of acetylferrocene (more dominant at higher pressures). Results obtained in this work show that the solubility of the reaction product acetylferrocene in scCO2 is sufficiently high to use scCO2 extraction at high pressures to separate it from its reactant ferrocene in Friedel–Crafts acylation processes.