EFFICIENT SYNTHESIS OF POLYHYDROXYLATED FULLERENE DERIVATIVES VIA HYDROLYSIS OF POLYCYCLOSULFATED PRECURSORS

Novel cyclosulfation chemistry for the functionalization of C-60 and i ts analogs is described. The cyclosulfation of C-60 is accomplished in neat fuming sulfuric acid at 55-60 degrees C under N-2 to afford poly cyclosulfated fullerene derivatives. Hydrolysis of these derivatives, either in the presence of water at 85-90 degrees C or in aqueous NaOH solution at ambient temperature, gives the corresponding polyhydroxyla ted fullerenes (fullerenols) in high yield. The functional characteris tics and number of sulfate moieties per C-60 molecule in the polycyclo sulfated fullerene precursors, and the structure of fullerenols, were determined primarily by the analysis of the TGA-mass spectrum and the sulfur (S-2p) and carbon (C-1s) absorption bands in the XPS spectrum. We resolved an average of 10 to 12 hydroxyl addends in the chemical st ructure of fullerenols that can be correlated to the structure of poly cyclosulfated fullerene precursors containing 5 to 6 cyclosulfate unit s. The cyclosulfation chemistry is, presumably, initiated by a one-ele ctron oxidation of C-60, followed by the attack of anionic sulfate spe cies on the resulting cationic C-60 radical intermediates, to form the corresponding hydrogen sulfated C-60 radicals. Further oxidation and intramolecular cyclization of this hydrogen-sulfated C-60 yields the p olycyclosulfated C-60 products.