Weygand/Hilgetag Preparative Organic Chemistry

1086 Rearrangement of carbon compounds
Inhoffen 151 achieved the aromatization of ring A of l,4-cholestadien-3-one
under similar conditions:
4. Isomerization of hydrocarbons 152
The action of aluminum chloride on aliphatic hydrocarbons has been investigated
by Nenitzescu and Dragan. 153 Even at the boiling point hexane
is largely isomerized to a mixture of methylpentanes but a small proportion
is dehydrogenated to cyclohexane. These reactions proceed by way of cations.
Nenitzescu and Cantuniari 154 cleared up contradicatory statements in the
literature. They showed that pure anhydrous aluminum chloride is almost
without action on cyclohexane, but that isomerization occurs if water is
present:
Cyclohexane (1500 ml) is boiled for 3 h with freshly sublimed aluminum chloride (500 g)
and water (13.6 ml). The supernatant liquid is then washed and dried. Fractionation gave
material (330 ml), b.p. 71.3-72.3°, that was almost pure methylcyclopentane.
On the other hand, a mixture of cyclohexane and methylcyclopentane is
obtained from methylcyclopentane under the same conditions. Thus an
equilibrium is established between the two ring systems; it was shown by
measurement of the refractive index of the product mixture to contain 23%
of methylcyclopentane.
The conversion of methylcyclopentane into cyclohexane has been used by
Turner and Werne 155 for the preparation of [ 14 C1]benzene, as follows:
14 COOH
Dehydration of cyclopentanemethanol over aluminum oxide at 320° kgave an olefin
mixture whence hydrogenation afforded a mixture (94%) of [ 14 C]methylcyclopentane with
about 34% of [ 14 C]cyclohexane. The mixed cycloalkanes were transformed into [ 14 C]cyclohexane
by Nenitzescu and Cantuniari's method, 154 and dehydrogenation on a platinumcharcoal
catalyst at 360° then yielded [^CJbenzene.
151 H. H. Inhoffen, Angew. Chem., 53, 471 (1940).
152 L. Schmerling, Ind. Eng. Chem., 45, 1447 (1953) (review).
153 C. D. Nenitzescu and A. Dragan, Ber. Deut. Chem. Ges., 66, 1892 (1933).
154 C. D. Nenitzescu and P. Cantuniari, Ber. Deut. Chem. Ges., 66,1097 (1933).
155 H. S. Turner and R. J. Werne, /. Chem. Soc, 1953, 789.