Intercalation halides

Solid Superacids. Most large-scale petrochemical and chemical industrial processes ate preferably done, whenever possible, over soHd catalysts. SoHd acid systems have been developed with considerably higher acidity than those of acidic oxides. Graphite-intercalated AlCl is an effective sohd Friedel-Crafts catalyst but loses catalytic activity because of partial hydrolysis and leaching of the Lewis acid halide from the graphite. Aluminum chloride can also be complexed to sulfonate polystyrene resins but again the stabiUty of the catalyst is limited. 

First metal halide-graphite intercalation compound made with FeCl.i. 

A quite different sort of graphite intercalation compound is formed by the halides of many elements, particularly those halides which themselves have layer structures or weak intermolecular binding. The first such compound (1932) was with FeCl3 chlorides, in general, have been the most studied, but fluoride and bromide intercalates are also known. Halides which have been reported to intercalate include the following ... 

HOPG cylinders showed that intercalation starts close to the basal planes and proceeds thence to the central layers. Cylinders capped at both ends with glass caps and grease are not intercalated. The layer system is split into a number of discs at a rate that increases with the degree of alignment of layer planes. For non-heat-treated PG, the threshold pressure increases with the number of layer planes in the sample. Similar results confirming this mechanism have been obtained with metal halides (H13). A mechanism of intercalation based on these results has been discussed by Hooley (H22). 

The graphite-metal halides constitute the most populous group of intercalation compounds. Most of the investigative efforts have been directed towards the metal chlorides, particularly FeCls, whereas considerably less is known about the metal bromides S21). Compounds... 

Intercalation from solutions in nonaqueous solvents (S21). This method may suffer from the drawback that final stoichiometries may not correspond to equilibrium conditions, because of partial leaching out of metal halide. For this reason, some chlorides can be intercalated only from solvents in which they have limited solubility iLS). It has often been the practice to wash intercalates with solvents to remove the excess of intercalant this may lead to stoichiometries lower than the original ones. The two-ampoule method may, therefore, be preferable (H24). 

At this time, no all-inclusive rule can be given that will predict whether a given compound will intercalate or not. Most of the information available seems to have been obtained empirically. Such analogies as similar chemical properties have been helpful. The many factors that infiuence the intercalation process have been surveyed by Herold (H14). In Tables II-VI are listed metal halides considered to intercalate into graphite, together with some structural information (S2J, i 9). Several general characteristics have been ascribed to intercalat-... 

Elastic-inelastic collision model, Szilard-Chalmers reaction and, 1 269 Electrical conduction, in organic superconductors, 29 278-286 Electrical conductivity of chalcogenide halide compounds, 23 331 of Group IB, 23 337-339, 342, 346-349 photoelectric effects, 23 368, 410 semiconductors, 23 368, 390, 395-396, 400-402, 410-412 superconductors, 23 375-377 of graphite intercalation compounds, 23 290, 294, 309-310, 312, 317-318 Electric discharges arc type, 6 146-147 chemical reactions in, 6 189-191 chemical reactions in, 6 143-206... 

Thus, for example, for a system of benzyl chloride, butyl bromide, and the hydrotalcite-like material, we expect the following reactions to occur. Butyl bromide would undergo a halide substitution by the interlayer Cl anions, leaving Br anions in the interlayer space the intercalated Br anions would, in turn, attack benzyl chloride to yield benzyl bromide leaving Cl anions in the interlayer space, the interlayer Cl anions being cycled as follows ... 

Lalancette et al.188 indicated that intercalation process can be carried out in CCI4 solution only if the Lewis acid halide is slightly soluble in the solvent. Therefore, AICI3 is probably eluted from the graphite by the feed. The rate of this process will increase with the increase in temperature, which increases the vapor pressure of Lewis acid halide. Hence, there are several drawbacks in using these graphite intercalates. 

Table 5.22. Transethylation of Benzene with Diethylbenzene over Graphite-Intercalated Metal Halides.112...

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