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Hexacyclohexylcyclohexane

27 July 2020 - Chemical Zoo

Dillenburger et al. report the chemical anaysis of hexacyclohexylcyclohexane which is cyclohexane with on every carbon atom a cyclohexyl unit (DOI). To arrive at this result hexaphenylbenzene was hydrogenated in an autoclave with hydrogen and palladium on carbon at 250 bar and 150 degrees for four days. A seemingly simple reaction but the authors noted that while the starting compound had disappeared after 1 day, from then on product increase was only marginal. It also did not help that in MS-APCI a compound may partially dehydrogenate again. The final reaction product (76% yield) did contain two compounds, the sought-after and fully hydrogenated one and hexahexylbenzene which is an intermediate. Although both compounds were well resolved in HPLC it was not possible to separate them with a regular silica column. In one recrystallisation method it was however possible to separate the two compounds as individual crystals. From X-ray crystallography it was then found that the central cyclohexyl chain in one isomer forms a chair configuration and in another isomer a twisted boat. All cyclohexyl substituents are chairs.
Not sure what to make of it. The authors do not mention synthesis because the desired compound was not isolated. But with an additional effort? The reaction was not repeated with a reaction time of just one day. If compounds resolve in HPLC, preparative HPLC must be in reach. Hexaphenylbenzene costs just 115 euro per gram and will not blow the research budget. Do people still do melting points? Vacuum sublimation?