Graphite Compounds with Homopolar Bonding

The composition of graphite oxide is most suitably characterized by the C 0 ratio, after taking into account the hydrogen found in combustion S3). If all four of the valencies of each carbon atom were satisfied by bonding to oxygen this ratio would be two, but this value is never reached. Values for C 0 of 2.4 to 2.9 are found for well-oxidized preparations and values of 2.7 to 2.8 are particularly common. Less oxidized preparations with C 0 ratios of 3.5 to 4 are, however, homogeneous phases, and show the same characteristic properties as more highly oxidized specimens. 

In connection with the constitution of graphite oxide, the question of the number and nature of the acid groups and the point of their attachment is especially interesting. Comprehensive studies by Hofmann and his co-workers 36, 35, 8, 74) on the extent of base exchange and on the methylation of graphite oxide have made a substantial contribution towards solving this problem. The results of these investigations may be summarized as follows. 

Only a part of the —OH groups—about 700 meq per 100 gm—can be methylated with diazomethane or acetylated with acetic anhydride. That it is the —OH groups attached to the carbon planes which react in this way follows from the fact that, after methylation or acetylation, the interplanar distance in the dry graphite oxide is increased by 3-4 A. Methylated graphite oxide preparations retain the property of base exchange with sodium methylate solution to an extent corresponding with the number of -—OH groups not involved in the methylation reaction. 

The number of carboxyl groups has the comparatively small value of 30-100 meq per 100 gm. These groups may be determined by methylation with methanol and hydrochloric acid. In this case the weakly acid —OH groups of the layer planes do not react. Carboxyl groups can probably be attached only at the edges of the crystal or at the edges of cavities in the layer planes, for preparations methylated with methanol show the same interplanar distance as unmethylated specimens. 

Layer of graphite oxide with tertiary OH-groups (Ruess, 74). 

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