RESUMEN
Carbon materials including carbon nanoparticles, such as nanographite, graphene and graphenic materials, and carbon nanotubes are known to be highly hydrophobic. Oxidation treatments are widely used as the best methods to improve their affinity in a liquid medium or a polymer matrix so that they can be dispersed, handled and processed. Here, we have applied eight different oxidation treatments in order to graft oxygen-containing functional groups at the surface of polyhedral graphitic particles synthesized by arc discharge from graphite, also called astralenes. The used functionalization approaches include both standard chemical attack by strong oxidants and radical functionalization of the sp2 network by direct C[double bond, length as m-dash]C bond opening. Commonly efficient functionalization methods were unsuccessful to functionalize astralenes while radicals generated from arylhydrazine could lead to functionalization of the outer surface of astralenes. The occurrence of functionalization could be shown by TGA coupled with MS and XPS. The reported method represents the first example of functionalization of astralenes. The efficiency of the applied functionalization methods is discussed considering the chemical reactivity of different carbon nanomaterials including graphene and carbon nanotubes.
RESUMEN
The preparation of 27 isomers of chiral hexahalogeno-4,4'-bipyridines by means of two complementary methods is described. The first one is convergent and based on the LDA-induced 4,4'-dimerization of trihalopyridines, whereas the second method is divergent and achieved through regioselective halogenation reactions of 4,4'-bipyridine-2,2'-diones. Iodine in 2,2'-positions of the 4,4'-bipyridines was introduced by a copper-catalyzed Finkelstein reaction (Buchwald procedure) performed on 2,2'-dibromo derivatives. Selected compounds of this new family of atropisomeric 4,4'-bipyridines were enantioseparated by high performance liquid chromatography on chiral stationary phases, and the absolute configurations of the separated enantiomers were assigned by using X-ray diffraction analysis. The latter revealed that various halogen bond types are responsible for crystal cohesion.