SOLUBILITY OF BUCKMINSTERFULLERENE (C_(60)) IN ORGANIC SOLVENT MIXTURES

摘要

The potential large scale production of C_(60) and its widespread use in consumer products may translate into occupational and public exposure and in long-term environmental exposure. To assess the risk and fate of C_(60) in the environment, it is important to understand its solvate formation in common industrial solvents as the solvates may affect various properties of C_(60) including reactivity and toxicity. Solid solvates of C_(60) have been reported in a number of solvents and have been studied by differential scanning calorimetry (DSC), X-ray diffraction, infrared and Raman spectroscopy and NMR spectroscopy. However, such methods are unsuitable when investigating solvate formation in solvents for which C_(60) has limited solubility, due to the large sample volumes that would be required to form precipitates for analysis. Solvate formation has also been reported to lead to unusual temperature dependences of solubility in a variety of solvents. For example, Figure 1 shows results obtained by Zhou et al. for the solubility of C_(60) in toluene, o-xylene and carbon disulfide over a temperature range of -40 to 80oC. In each solvent, at temperatures below the temperature of maximum solubility, a saturated solution is in equilibrium with the solvate which melts at temperatures above the temperature of the maximum solubility to yield another solvate or pure crystalline C_(60) in equilibrium with the dissolved molecules. Measuring solubility in solvent mixtures can be helpful in predicting whether solvates form with a solvent whenever other methods of analysis are unsuitable. Moreover, the solubility curve indicates maximum concentration that can be analyzed while avoiding C_(60) precipitation or cluster formation. Solubility of C_(60) has been measured in more than 150 solvents; however, solubility studies in mixed solvent systems are few.