EVIDENCE OF HEMIKETALS INCORPORATED IN THE STRUCTURE OF FULLEROLS DERIVED FROM AQUEOUS ACID CHEMISTRY

We have characterized and elucidated the chemical structure of fullerols, prepared from the aqueous acid reaction of C60 in the presence of sulfuric acid and nitric acid, consisting of hemiketal moieties in addition to tertiary hydroxy groups, In the aqueous reaction, a high yield of fullerols was obtained utilizing potassium nitrate as an effective precursor for generating nitric acid in situ. Evidence for the hemiketal structure is given by an observation of chemical shifts of vinyl ether carbons and ketal carbons centered at delta 170.3 and 100.0, respectively, in the C-13 NMR spectrum of fullerols. This structure was also substantiated by several spectroscopic methods including XPS, TGA-MS, and TGA-FTIR. Interestingly, the reversible interconversion reaction of hemiketal moieties in fullerol to the corresponding ketone upon variation of pH in aqueous solution provided conclusive results to verify the presence of hemiketal functions. This is the first observation of hemiketal functions incorporated onto the fullerene cage structure.