A RAPID PREPARATION OF BROMINATED BUCKMINSTERFULLERENE (C60Br24)
Martin R. Schultz and Mark D. Timken
Widener University, Chester,
PA 19013, USA
September 16, 1996
We describe here a rapid and simple method for preparing fully brominated C60. In the current literature method1 solid C60 is allowed to react with neat, liquid bromine for 5-8 days, after which C60Br24 is isolated by filtration (yield ca. 86%). This method is straightforward, but slow. As described in detail below, we have modified this method simply by adding an iron wire to the reaction mixture. This modification reduces the reaction time from at least five days to ca. one hour, presumably due to the in-situ formation of FeBr3, a Lewis acid that is known to catalyze electrophilic aromatic substitutions by polarizing Br2 for electrophilic attack, and that probably plays a similar catalytic role in the addition of bromine to C60.
C60 was synthesized and purified in-house by following literature methods.2-4 In a closed container, neat bromine (5 mL) was combined with 50 mg C60 and ca. 1 g of large-gauge iron wire. The mixture was stirred vigorously at room temperature for one hour, after which the excess liquid bromine was removed by evaporation under a vacuum. The resulting dark solid was treated with 20 mL of methanol, a procedure that dissolves the ferric bromide that forms during the reaction. The iron wire was removed, and the methanol mixture was filtered to give a yellow powder which was washed with additional methanol. The infrared spectrum of the product is identical to the reported spectrum of C60Br24.1 In a typical preparation, 50.5 mg of C60 gives 197.1 mg of product, an increase in mass that corresponds to an empirical formula of C60Br24.Br2, consistent with previous reports.1 The product should be stored away from light and heat.
Note: The reason large-gauge iron wire is used in the reaction is to facilitate the removal of the unreacted iron. If iron powder is used it is difficult to remove the unreacted iron from the product. Small gauge wire will separate into many small pieces and become difficult to remove.
1. F.N. Tebbe, R.L. Harlow, D.B. Chase, D.L. Thorn, G.C. Campbell, J.C. Calabrese, N. Herron, R.J. Young, and E. Wasserman, Science, 1992, 256, 822.
2. H. Ajie, M.M. Alvarez, S.J. Anz, R.D. Beck, F. Diederich, K. Fostiropoulos, D.R. Huffman, W. Kraetschmer, Y. Rubin, K.E. Shriver, D. Sensharma, R.L. Whetten, J. Phys. Chem., 1990, 94, 8630.
3. R.E. Haufler, Y. Chai, L.P.F. Chibante, J. Conceicao, C.-M. Jin, L.-S. Wang, S. Maruyama, and R.E. Smalley, Mat. Res. Soc. Symp. Proc., 1991, 206, 627.
4. K.C. Khemani, M. Prato, F.Wudl, J. Org. Chem., 1992, 57, 3254.