ASSOCIATION CONSTANTS OF FERROCENE WITH CYCLODEXTRINS IN AQUEOUS-MEDIUM DETERMINED BY SOLUBILITY MEASUREMENTS OF FERROCENE

The association constants of ferrocene with cyclodextrins (CyD's) in a n aqueous medium at 25 degrees C have been determined by solubility me asurements of ferrocene in both the absence and presence of CBD. The s olubility of ferrocene in pure water was found to be (4.25 +/- 0.02) x 10(-5) mol dm(-3) at 25.0 +/- 0.1 degrees C. The beta- and gamma-CyD' s form only 1 : 1 complexes with ferrocene. The 1 : 1 association cons tants were determined to be (1.39 +/- 0.21) x 10(2) (alpha), (1.65 +/- 0.04) x 10(4) (beta), and (9.04 +/- 0.11) x 10(2) dm(3) mol(-1) (gamm a). The 2 : 1 (CyD : ferrocene) association constant was (2.36 +/- 0.0 6) x 10(3) dm(3) mol(-1) (alpha). Ferrocene-included CyD precipitates were also prepared in water, and their stability upon drying in air wa s studied. The sublimation enthalpy of ferrocene in the temperature ra nge of 290.65 to 298.15 K was estimated to be 74.2 +/- 1.5 kJ mol(-1).