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National Advisory Committee for Aeronautics, Technical Notes - Synthesis and Purification of Alkyldiphenylmethane Hydrocarbons

The syntheses of five alkyldiphenylmethane hydrocarbons ,.
2-methyldiphenylmethane, 3-methyldiphenylmethane, 2-ethyldiphenylmethans,
4-ethyldipheny1methane, and 4—isopropyldipheny1methane, are described.
The preparation of these hydrocarbons was based on the reaction of the
appropriate arylmagnesium halides with benzaldehyde to yield the cor-
responding alkylbenzhydrols, which were subsequently converted to the
hydrocarbons by hydrogenolysis. The physical properties tabulated
include melting point, boiling point, index of refraction, density,
viscosity, heat‘ of fusion, and heat of combustion. Time-temperature
melting curves are plotted for all compounds prepared.

The synthesis and the purification of several alkyldiphenylmethane
hydrocarbons, 2-methy1 diphenylmethane , 5-methy1 diphenylmethane ,
2-ethyldipheny1methane, 4-ethyldipheny1methane, and
4-isopropyldiphenylmethane, were undertaken in conJunction
with a. program being conducted at the NACA Lewis laboratory to study
hydrocarbons as possible fuels for Jet-propulsion aircraft engines. A
review of the literature disclosed few data on this series of
compounds.

The hydrocarbon 2-methy1diphenylmethane has been prepared by the
Clemensen reduction of 2-methylbenzhydrol or 2-methylbecnzophenone
(reference 1) and by the catalytic reduction of ethyl o-benzoylbenzoate.

Methods of synthesis that have been employed for the preparation
of 5-methyldiphenylmethane include the reduction of 5-methy1benzophenone
by hydriodic acid and phosphorus (reference 5) and the reaction of
m—methylbenzylchloride with benzene in the presence of aluminum chlo-
ride (reference 4).

No mention of 2-ethy1diphenylmethane has appeared in the literature
and the only reference to 4-isopropyldipheny1methane described a prep-
aration by the reduction of 4-isopropylbenzophenone with sodium in
ethyl alcohol (reference 5).

Three methods for the synthesis of 4-ethyldiphenylmethane are
given: the reaction of ethyl benzene with benzyl chloride in the pres-
ence of zinc dust (reference 6) and in the presence of beryllium chlo-
ride (reference 7) and the reduction of 4-ethylbenzophenone with
hydriodic acid and, phosphorus (reference 8).

Except for those cited in references 1 and 2, the methods of
preparation previously mentioned could not be expected to yield pure
products. Each of the five alkyldiphenylmethane hydrocarbons dis-
cussed herein was prepared by hydrogenolysis of the solid benzhydrol
(reference 1), which was synthesized by the condensation of the appro-
priate arylmaaesium halide with benzaldehyde. The hydrogenolysis was
accomplished catalytically instead of by the Clemensen reaction as
in reference 1.