Purification of fullerenes

The explosion of interest that followed the identification of buckminsterfullerene, CgO) by Kroto and co-workers in 1985 [1] has yet to subside. Together with the discovery of related fullerenes and buckytubes, the isolation of heralded the start of a new chapter in the now ubiquitous field of nanotechnology. Like nanotechnology, which dates from Feynman s There s plenty of room at the bottom lecture to the American Physical Society in 1959 [2], the identification of Q,o s soccer ball shape can also be traced back to an earlier origin, Osawa s paper in 1970 [3]. 

Recently it has been shown that single-walled carbon nanotubes and fullerenes are capable of blocking cellular transmembrane ion channels [9]. Given global interest in the potential toxicity of nanomaterials, including C6o, the macrocyclic 

4-Methyl(iV-benzyl)azacalix[ 3 ]arene (34) Test tubes 

Note this experiment should be carried out in a fume hood. 

In a test tube, dissolve 4-mcthyl(/V-bcnzyl )azacalix[3]arene (34, 36 mg, 0.05 mmol) in toluene (5 mL) to give a colourless solution. In a second test tube, dissolve C60 (7 mg, 0.01 mmol) in toluene (5 mL), heating if necessary, to give a characteristic purple solution. Add the solution of the macrocycle to the Cgo solution and heat briefly. The purple solution will slowly turn pale brown if left standing at room temperature for several days indicating the formation of an inclusion complex of Cgo- 

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For the purification of fullerenes from the fullerene oxides the activated alumina and silica can be used. Fulllerene oxides are adsorbed strongly on such adsorbents from solution and the oxides are removed from fullerene samples. For the preparative separation of fullerenes at present activated carbons and graphite are used [11-14], For this purpose silica with the deposited carbon layer [16] can be used also. In this case it is very easily to regulate the pore diameter and specific surface area of adsorbents as well as particle diameter. Such adsorbents is very important for the decreasing of fullerenes loss. On preparative separation of fullerenes on LiChrosorb SI 60 with deposited carbon layer by modified method [15] on glass column first fractions contained quite pure Csq. 

Relatively few molecular separations have been studied from the utilitarian standpoint. One of these, the purification of fullerenes via 8 , is discussed on p. 170. In a reciprocal experiment the separation of 4 " , 6 , and 8 with a column using a chemically-bonded C o silica stationary phase has been re-ported. Chromatographic selectivity has been achieved for amino acid esters and alkali metal cations on silica-bonded calix[4]arene tetraesters, the structure of which has been explored by and Si-CP-MAS NMR. Silica-bonded calixarenes have also been used as packing materials for HPLC columns that are capable of separating disubstituted aromatics, peptides, and nucleosides. The HPLC separation of phenols using 6 ° as a constituent of the eluent has been described. ... 

An interesting example of the interplay between solid-state clathrands and solution-phase cavitands is provided by cyclotriveratrylene (CTV, 8). In the solid state, the saucer-shaped CTV molecules stack one on top of another in the two most common phases (x and and hence, while the molecules possess shallow molecular cavities, they do not include guests such as solvent molecules, which instead are located in voids between host stacks. However, larger guests such as buckminsterfuller-ene C6o, organometallic sandwich compounds,or carboranes form intracavity inclusion compounds, and the association persists in the solid state, with potential applications, for example, in the selective purification of fullerenes. Thus, CTV is both a cavitand and a clathrand. The cavitand behavior of CTV is highlighted by the chemistry of the double-CTV cryptophanes that form very stable solution complexes with a variety of halocarbon guests. 

The synthesis and purification of fullerenes were very difficult, and the prices of purified materials were high at the beginning. Later, a cheaper method was discovered, and grams of Ceo, the most important fullerene, are now available at reasonable cost [255]. 

This review has described the supramolecular chemistry of fullerenes and CNTs. Although the non-covalent chemistry of heterocyclic molecules has been highlighted in this review, the supramolecular chemistry of other host molecules, as well as covalent chemistry, has also contributed enormously to the progress of this interdisciplinary field in science. One of the landmarks must be the application of the supramolecular interaction of Ceo with calix[8]arenes to the practical purification of fullerenes, which was reported independently by Shinkai et al. and Atwood et al. in 1994 [243,244]. Quite recently, the host-guest strategy has been successfully applied to structure-... 

CATALYTIC PRODUCTION AND PURIFICATION OF NANOTUBULES HAVING FULLERENE-SCALE DIAMETERS... 

Isaacs, L., Wehrsig, A., and Diederich, F. (1993) Improved purification of C60 and formation of S- and 7i-homoaromatic methano-bridged fullerenes by reaction with alkyl diazoacetates. Helv. Chim. Acta 76, 1231-1250. 

Ge Z, Duchamp JC, Cai T, Gibson HW, Dorn HC (2005) Purification of endohedral trimetallic nitride fullerenes in a single, facile step. J. Am. Chem. Soc. 127 16292-16298. 

Stevenson S, Stephen RR, Amos TM, Cadorette VR, Reid JE, Phillips JP (2005) Synthesis and purification of a metallic nitride fullerene bisadduct exploring the reactivity of Gd(NZ ,C80. J. Am. Chem. Soc. 127 12776-12777. 

Purification of Cjq by fractional crystallization in 1,3-diphenylacetone represents another inexpensive method [230]. After three steps, 99.5% pure was obtained with a total yield of 69%. The purity of Cgg can be increased up to 99.99% by adsorption of the residual C7Q fullerene on charcoal. Preferential precipitation of C7Q over Cgo has been obtained by the addition ofp-trihalohomocalix[3]arenes [231]. 

In the reaction of cyclotetragermane 27c, products 28c and 29c were obtained in 43% and 37% yields, respectively, based on unreacted Cgo- In order to examine the reactivity of fullerene-silicon derivatives, 29b was irradiated with a carbon disulfide solution of bromine. Purification of the product by means of gel-permeation chromatography afforded C6o and 33 in 93% and 45% yields, respectively (equation ll)23. The structure of 33 was determined by X-ray crystallographic analysis (Figure 13). Adduct 33b did not react with bromine in the dark, and therefore a bromine radical seems to participate in this reaction. 

Since efficient methods for the synthesis and purification of gram quantities of C60 and C70 became available in the early 1990s, fullerene chemistry has developed at a phenomenal pace. There are many reactions which can generate... 

Cyclotriveratrylene synthesis is a poorly understood process, as with many reactions between phenols and aldehydes, and yields are as variable as the methods to prepare them a review lists fifteen different conditions that give between 21 and 89% yield. Despite this the compounds are worth preparing as they have an interesting affinity for buckminsterfullerene, C6o, and are cited in papers and patents that describe methods to isolate pure C6o from a mixture of fullerenes [50], It transpires that the threefold symmetry of cyclotriveratrylene is complementary to the threefold axis of C6o and that the two form very stable complexes in toluene as shown in Fig. 1.12, which precipitate leaving other fullerenes in solution. If the precipitate is isolated and taken up in chloroform the complex dissociates leaving cyclotriveratrylene in solution and precipitates C6o- The purity of the C6o treated in this way is significantly enriched and can approach 100%. At the time of this discovery fullerene research was very much in its infancy, and the material available was of variable purity, making the purification technique an important milestone in the history of fullerene chemistry. 

In addition to quinone reduction and hydroquinone oxidation, electrode reactions of many organic compounds are also inner-sphere. In these charge transfer is accompanied by profound transformation of the organic molecules. Some reactions are complicated by reactant and/or product adsorption. Anodic oxidation of chlorpro-mazine [54], ascorbic acid [127], anthraquinone-2,6-disulfonate [128], amines [129], phenol, and isopropanol [130] have been investigated. The latter reaction can be used for purification of wastewater. The cyclic voltammogram for cathodic reduction of fullerene Cm in acetonitrile solution exhibits 5 current peaks corresponding to different redox steps [131]. 

But a wide application of such substances is hampered by their high costs of synthesis and purification. The most popular synthesis methods are the arc-discharge and laser-ablation method which have the disadvantage of either small fullerene yield or small quantity of the fullerene containing soot. Moreover it is necessary to use vacuum technique for maintaining of low pressure of helium for these methods. For the hydrocarbon combustion method it is necessary to use the additional expenses for fullerene purification [1-3], Thus, the search for improved methods of fullerene synthesis is of considerable importance. 

A special attention has been given to the purification of the working solution components from impurities. Commercial toluene used as the fullerene solvent has been subjected to double purification by distillation. Ethanol for purification from water and some impurities has been subjected to electrolysis within 1-2 h at the operating voltage about 380-400 V. The active additives used in the base electrolyte composition have not been purified additionally because they correspond to the classification as "pure for analysis". The TF solution has been purified from the undissolved particles by filtration using the laboratory filter paper of the "F" make-up. 

An unusual C2 complex contained within a carbon cluster is contained in the soot formed by an arc discharge between graphite containing Sc203. Purification of the endohedral scandium fullerenes by HPLC gave Sc2C2 C84 (Fig. 11). X-ray powder diffraction and 13C NMR data (8 92) were interpreted in terms of a disordered Sc2C2 cluster encapsulated by D2d-Cs4 (Sc-C 2.26, C-C 1.43 A).487... 

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