Graphite lamellar compounds

Berthelot, J., M. Jubault, and J. Simonet. Tetra-alkylmmonium-graphite lamellar compounds—A new class of reducing agent in organic chemistry. J. Chem. Soc., Chem. Commun. (1982) 759. 

Alkali-metal graphites are extremely reactive in air and may explode with water. In general, reactivity decreases with ease of ionization of M in the sequence Li > Na > K > Rb > Cs. Under controlled conditions H2O or ROH produce only H2, MOH and graphite, unlike the alkali-metal carbides M2C2 (p. 297) which produce hydrocarbons such as acetylene. In an important new reaction CgK has been found to react smoothly with transition metal salts in tetrahydrofuran at room temperature to give the corresponding transition metal lamellar compounds ... 

The effect of delicate adjustments of the catalytic site parameters on the activation modes of hydrocarbons (such as CH4) is further supported by Ichikawa s studies [51] on lamellar compounds. Graphite-K-lamellar entities promote the H -D c.xchangc in methane, but the rate greatly depends on C/K ratio Cj4K gives higher rate (X 2) thanC K at 300°C. Molecular sieves are also active for Ol4- D]0 exchange reactions at 600 C 52]. 

Molecules and ions can penetrate between the layers of graphite to form interstitial or lamellar compounds. These so-called intercalation compounds are of two types, namely, nonconducting compounds, in which the planarity of the graphite layers is destroyed, and conducting compounds, in which the planarity of the graphite layers is preserved (see Intercalation Chemistry) ... 

It is well known that graphite and fluorine gas do not interact at room temperature and ordinary pressures. At higher temperatures (380-600 °C), the lamellar compounds (CjF) and (CF) are formed, in which the carbon atoms are disposed in puckered sheets (Riidorff Riidorff 1947a Kita et al. 1979). In the presence of HF, graphite is spontaneously intercalated by fluorine, at room temperature. The first accounts (Riidorff Riidorff of such a... 

Once graphite is formed, then it may react with a large number of substances to give lamellar compounds in which the reactant is present in the form of monolayers separated by one or more carbon layers.These compounds have been found to be active catalysts for various reactions in which the catalytic activity should not be described in terms of the reactant supported on graphite but, rather, in terms of formation of a new composite material. These intercalate catalysts will be considered below, but it should be stressed that they differ from a combination of alkali and carbon black (say), where the reactant is physically held in the pores of the carbon and acts as a supported catalyst. 

A very loose, layered structure of graphite makes it possible for many molecules or ions to penetrate between the layers, forming interstitial or lamellar compounds. 

Residue compounds of graphite are prepared from the corresponding lamellar compounds by partial deintercalation. This process ultimately yields residue compounds via more dilute lamellar compounds. Figure 1 shows a typical composition isotherm for an intercalation-deintercalation cycle. Lamellar compounds that form spontaneously by action of the intercalant on graphite can be deintercalated simply by thermal or in vacuo treatment deintercalation of graphite salts requires a reductant. 

In residue compounds prepared from lamellar compounds based on artificial polycrystalline graphite, 1/3 of the original intercalant may be retained depending on particle size and crystallinity of the material. Lamellar compounds prepared from large crystals decompose only slowly, not just because of longer diffusion pathways in the interlayer gap but because the amount of retained intercalant also increases with the thickness of the graphite flakes °. 

Lamellar compounds based on highly oriented graphite can be deintercalated more completely. By electrochemical deintercalation of first-stage acid salts (cf. 16.4.2.1.4) based on highly oriented pyrolytic or natural graphite 95% of the intercalant can be removed under quasi-equilibrium conditions " for much less crystalline carbon fibers, the corresponding value is 80 %. ... 

The electronic conductivity of residue compounds is several times higher than that of the parent graphite, but still below the conductivity of either donor- or acceptor-type lamellar compounds. Thus conductivity is a sensitive probe for the reversibility of an intercalation reaction. 

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