Recovery of host crystals from inclusion crystals of p-tert-butylcalix[4]arene and p-tert-butylthiacalix[4]arene by the treatment with a solvent and/or supercritical CO2

Upon stirring inclusion crystals of p-tert-butylthiacalix[4]arene (2) in solvents with heating, guest compounds were efficiently desorbed to yield guest-free crystals. More specifically, upon treatment with methanol, the exchange of guest compounds with methanol in the crystals, followed by the desorption of the methanol afforded metastable host crystals 2 beta, whereas, upon treatment with heptane, the dissolution of the inclusion crystals and simultaneous crystallization of compound 2 afforded stable host crystals 2 alpha. Further, a host crystal of p-tert-butylcalix[4]arene (1) was recovered by the treatment of 2:1 (host/guest) inclusion crystals of compound 1 with supercritical carbon dioxide (scCO(2)), and through the combination of the guest exchange of 1:1 inclusion crystals of compound 1 with hexane and scCO(2) treatment of the resulting 2:1 inclusion crystals 1 (2)center dot hexane. Although the recovered host crystal of compound 1 contained a small amount of CO2, it could be reused for the inclusion of organic compounds.