STABILITY OF C_(60) FULLERENE UNDER THERMAL TREATMENT IN HYDROCARBONACEOUS SOLVENTS

摘要

The stability of fullerenes in low concentrations in boiling toluene under reflux was studied in order to answer some of the questions raised in previous works dealing with extraction and analysis of fullerenes from rocks. It was observed that small concentrations of C_(60) fullerene in the toluene (10 mg l~(-1)) were highly susceptible to any trace of molecular oxygen (or any other oxidizing agent) and quickly decomposed. This was accompanied by change of color of the solution from light violet to pale yellow, typical for oxidation adducts of fullerenes. Various grades of toulene purity and C_(60) standard were tested, as well as toluene deoxygenation before the treatment and keeping the apparatus under argon. However, only bubbling of argon through the boiling solution during the whole experiment was able to quench the decomposition of C_(60). This finding has serious consequences on results of extractions made by higher temperature treatments (e.g. Soxhlet), reported earlier by other groups. The decomposition in experiments with no safety precautions against oxygen takes place also in solutions with higher concentrations of C_(60) (1 g l~(-1)), the loss being "only" ca. 5%. This shows that only a limited number of reactive species is readily available to decompose C_(60). ~(13)C nuclear magnetic resonance showed that the principle products of pure toluene oxidation are benzoic acid, benzylalcohol and benzaldehyde. Comparative experiments were performed in cyclohexane and n-heptane (initial concentration of 10 mg l~(-1)), only negligible loss of fullerenes was observed.