Graphite, intercalation compounds reduction properties

The properties of the intercalation compound, potassium graphite, KCg, have been detailed in several review articles.34/35 The bonding in potassium graphite is described in terms of the limiting structure, K+Cg", and it is believed that the anion forms as a result of the transfer of an electron from the alkali metal to the conduction band of graphite. Novikov and Volpin35 have noted a similarity between aromatic radical-anions and alkali metal-graphite intercalation compounds. Their observation was based on inspection of reduction potentials of aromatic hydrocarbons relative to biphenyl, Table 9.2 ... 

Graphite reacts with alkali metals - potassium, cesium and rubidium - to form lamellar compounds with different stoichiometries. The most widely known intercalate is the potassium-graphite which has the stoichiometry of CgK. In this intercalate the space between the graphite layers is occupied by K atoms. CgK functions as a reducing agent in various reactions such as reduction of double bonds in a,fl-unsaturated ketones [19], carboxylic acids and Schiff bases alkylation of nitriles [20], esters and imines [21] reductive cleavage of carbon-sulfur bonds in vinylic and allylic sulfones [22]. The detailed reaction mechanism of CgK is not known, and the special properties which are ascribed to the intercalate come either from the equilibrium between K+/K [23], or topochemical observations (the layer structure) [24]. 

As already mentioned the fundamental condition which must be fulfilled for intercalation to occur is electron transfer from the graphite macromolecule to intercalate or vice versa. This quantity determines directly many physiocochemical properties of GICs. For example, it is obvious that for an acceptor compound the quantity of electrons lost by the graphene layers (some other time understood as the hole concentration), must exactly be compensated by the amount of electrons accumulated in the intercalate layers to assure the electrical balance of the intercalation system. The formation of acceptor and donor-type compounds in the reactions of anodic oxidation and cathodic reduction may be represented by the following equations, respectively,... 

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