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Buckminsterfullerene synthesis Maryam Ebrahimi Chem 7530 Feb. 7th, 2006 1 Outline ● ● ● ● ● Discovery of C60 & Smalley's apparatus Natural Sources Different Techniques for Synthesis of C60 Rational Synthesis of Buckminsterfullerene Significance of Fullerene yield 2 Discovery of C60 For generations diamond and graphite were considered to be the only pure forms of carbon. In 1985, a group of discoverers (R.F. Curl, R.E.Smalley & H.W.Kroto) found a third form, C60 which was named Buckminsterfullerene owing to the structural similarity of C60 to geodesic domes designed by Buckminster Fuller. C60, is the exact structure of a soccer ball, having both pentagonal and hexagonal rings arranged in an alternating fashion . This 5/6-ring cage provides remarkable stability In fact, C60 is the smallest fullerene for which all pentagons are isolated. 3 Smalley's apparatus for generating and detecting buckyball H. W. Kroto, J. R. Heath, S. C. O'Brien, R. F. Curl and R. E. Smalley "C(60) Buckminsterfullerene" (1985) Nature, 318, 6042, 162-163 http://www.chem.wisc.edu/~newtrad/CurrRef/BDGTopic/BDGtext/BDGBucky.html 4 How the apparatus works? ● generate long chain carbon molecules so that their spectroscopic fingerprints could be measured. ● a laser is aimed at a rotating graphite disk in a helium-filled vacuum chamber. ● lasers deliver short, high energy bursts of energy in the form of light. The rapid, intense heating of the graphite surface by the laser enables many of the C-C bonds in the graphite to rupture. ● carbon atoms and small clusters of carbon atoms sputter from the graphite surface. Thus, the energy of the light produced in the laser is used to break the bonds between atoms in graphite, a process that involves the conversion of light energy to chemical energy. ● The high energy C atoms and small clusters of carbon atoms cool and collide in the He atmosphere yielding new bonding arrangements of C atoms. ● These new materials can be characterized by different instruments like mass spectrometers & nuclear magnetic resonance spectrometers. 5 H. W. Kroto, J. R. Heath, S. C. O'Brien, R. F. Curl and R. E. Smalley "C(60) Buckminsterfullerene" (1985) Nature, 318, 6042, 162-163 6 Do fullerenes form spontaneously in nature? ● It is believed that fullerenes form in the cosmos due to evidence that polyynes (such as HC7N) are produced by ambient starlight photofragmentation of dust, and the fact that carbon species of 30-100 atoms are formed on carbon photofragmentation ● Fullerenes also appear to form spontaneously on earth whenever carbon condenses, i.e. any sooting flame H. W. Kroto, “Space, Stars, C60, and Soot”, Science 242, 1139-1145 (1988) J. B. Howard, et al., Fullerenes C60 and C70 in flames, Nature 352, 139-141 (1991) R. E. Smalley, “Self-Assembly of the Fullerenes”, Acc. Chem. Res. 25, 98-105 (1992) 7 ● This is the first natural example of carbon in the "Bucky Ball" configuration of C-60 carbon atoms. It is called "shungite" - which is the Russian name for this type of graphite. It came from the Shunga River, in Karelia, Russia. Shungite is a rare Precambrian carbonaceous rock. This black rock contains small veins of stacked spheres that are precisely buckminsterfullerene in their configuration. http://www.sciencemall-usa.com/c60buc.html 8 Different Techniques for Synthesis of C60 ● ● ● ● Graphite vaporization (Smalley's technique) Resistive heating of graphite Graphite arching Pyrolysis of hydrocarbons 9 Resistive Heating of Graphite (K-H method) ● The first macroscopic quantities of C60 were produced in 1990 by what is now known as the Kratschmer-Huffman (K-H) method. ● Instead of vaporizing carbon with a laser, a graphite rod was slowly evaporated using resistive heating. ● This slower, more ‘gentle’ technique allowed for more control over the conditions that make C60 formation possible. W. Krätschmer,et al., “Solid C60: a new form of carbon”, Nature 347, 354-357 (1990) F. Diederich,et al., “The Higher Fullerenes: Isolation and Characterization of C76, C84, C90, C94, and C70O, an Oxide of D5h-C70”, Science 252, 548-551 (1991) 10 Graphite Arching (Haufler et. al.) ● The apparatus for this technique is comprised of graphite electrodes over which an ac or dc arc is produced, generating the necessary carbon soot. ● The graphite rod and disk are connected to an external 60 Hz ac power source. The graphite is vaporized with a 100-200A current at an rms voltage of 10-20V. ● Not shown in this diagram is the helium source that condenses the carbon. ● The graphite arcing technique is currently the most commonly used technique and is also used commercially. R. E. Smalley, “Self-Assembly of the Fullerenes”, Acc. Chem. Res. 25, 98-105 (1992) R. E. Smalley, et al., “Efficient Production of C60 (Buckminsterfullerene), C60H36, and the 11 Solvated Buckide Ion”, J. Phys. Chem. 94, 8634-8636 (1990) Pyrolysis of Hydrocarbons Hydrocarbons (mostly PAH) as starting material mechanism of formation of a partial C60 cage from naphthalene ● The removal of hydrogen, as well as the curling of joined rings into a cage structure ● Two proposed mechanism by Taylor and Baum R. Taylor, G. J. Langley, H. W. Kroto, & D. R. M. Walton, “Formation of C60 by pyrolysis of naphthalene”, Nature 366, 728-731 (1993) T. Baum, S. Löffler, P. Löffler, P. Weilmünster, K. H. Homann, Ber. Bunsenges. Phys. 12 Chem. 96, 841-857 (1992) Pyrolysis of Hydrocarbons The decomposition of a hydrocarbon to produce fullerene-containing soot can be accomplished through a variety of means such as: ● flame combustion flame (combustion of benzene), ● laser, ● a general heat source such as a torch or a tube furnace (pyrolysis of naphthalene). Typical pyrolysis apparatus R. Taylor, G. J. Langley, H. W. Kroto, & D. R. M. Walton, “Formation of C60 by pyrolysis of naphthalene”, Nature 366, 728-731 (1993) 13 Separation of Fullerenes from Soot Fullerene soot Toluene extraction Toluene extract with C60 to ~C100 C60 pure Toluene-insoluble soot Alumina, hexane/toluene (95:5) ~C100 to ~C250 C70 pure Alumina, hexane/toluene (95:5) Higher fullerenes C76, C78, C84, traces of C90, C94, residual C70 2-3 HPLC runs on C18 reversed phase CH3CN/toluene (1:1) C76 pure C2v-C78 pure D3-C78 pure C84, mixture of at least 2 isomers Fullerene separation scheme F. Diederich, & R. L. Whetten, “Beyond C60: The Higher Fullerenes”, Acc. Chem. 14 Res. 25, 119-126 (1992) Rational Synthesis of Buckminsterfullerene http://www.trincoll.edu/depts/chem/toms/REUsite/facproj/mitzel/mitzel.html Tom Mitzel, Trinity College, Connecticut 15 Significance of Fullerene yield ● ● ● ● ● ● Lubrication Superconductors Semiconductors Photoconductors Optical Limiters Atom Encapsulation R. E. Smalley, “Self-Assembly of the Fullerenes”, Acc. Chem. Res. 25, 98-105 (1992) Wang, “Photoconductivity of fullerene doped polymers”, Nature 356, 585-587 (1992) http://www.science.org.au/nova/024/024box02.htm, Australian Academy of Science 16