The high CO₂-solubility of per-acetylated α-, β-, and γ-cyclodextrin

Per-acetylated cyclic hexa-, hepta-, and octa-saccharide, (α-cyclodextrin octadecaacetate, β-cyclodextrin heneiicosaacetate and γ-cyclodextrin tetracosaacetate, respectively) exhibit melting point reduction and high solubility in dense CO₂. Two-phase boundaries of the CO₂-acetylated sugar mixtures were determined for per-acetylated cyclodextrin concentrations of 2-30wt.%. The dew-point locus of the CO₂ per-acetylated cyclodextrin binary systems shifted to higher pressures as the number of saccharides in the acetylated cyclodextrin increased. The CO₂-solubility of per-acetylated cyclodextrins was comparable to oligomers of poly(vinyl acetate) (PVAc) (the most CO₂ soluble non-fluorous vinyl homopolymer) that contained an equivalent number of acetate groups. This very high degree of miscibility implies that the acyl groups of the per-acetylated cyclodextrins were readily accessible for favorable Lewis acid:Lewis base interactions with CO₂. Upon depressurization, each per-acetylated cyclodextrin formed rigid, brittle foams within the vessel as the boiling per-acetylated cyclodextrin-rich phase solidified during the removal of CO₂.