CYCLODEXTRIN PRECIPITATES WITH NORMAL-ALCOHOLS IN AN AQUEOUS-MEDIUM AND THEIR STABILITY ON BEING LEFT STANDING IN AIR

Cyclodextrin (CyD) precipitates with normal alcohols (guests, 1-butano l to 1-decanol) were prepared at 25 degrees C by introducing an alcoho l vapor into an aqueous CyD solution and circulating it in a closed sy stem. The guest/CyD molar ratio of the precipitates was measured immed iately after preparation and after having been allowed to stand in air at room temperature for 30 or 40 d. Precipitates were obtained with a lcohols higher than 1-pentanol for alpha-CyD, 1-hexanol for beta-CyD, and 1-butanol for gamma-CyD. The reason that CyD does not precipitate with lower alcohols could be explained in terms of the solubility prod uct. There was a linear relationship between the apparent solubility ( derived from the solubility product) of the CyD precipitates in water and the guest-CyD association constant. Upon drying in air, the guest/ CyD molar ratio in the precipitates gradually decreased with days allo wed to stand. In the cases of alpha- and gamma-CyDs, the ratio remaine d constant after one week.