On Assembling Polychlorinated Aromatic Hydrocarbons from Carbon Tetrachloride via Dichlorocarbene Intermediary by a Solvothermal Reaction: A Reaction Pattern from Carbene−Ylide Interconversion

The forced one-electron reduction of carbon tetrachloride with sodium in a sealed steel vessel is
shown to have a narrow window of conditions to arrest the reaction at the polychlorinated aromatic
hydrocarbons (PCAHs), as well as to prevent the reaction from proceeding all the way to the final
stage of graphite and other carbon solids. The intermediates are quenched with toluene or benzene
to give electrophilic substitution products and with water to give a quinomethine as the major
product. The product pattern leads us to propose the carbene, perchlorobenzo[c,d]pyren-6-ylidene,
or its reversible dimer as the major intermediate among others, that survives the severe conditions
until coming into contact with these nucleophiles. Mainly from aromatic resonance stabilization,
the carbene is proposed to have a delocalized singlet state analogous to a ylide electronic structure
and, thus, undergoes observed ionic reactions instead of typical carbene reactions. This work serves
as a mechanistic link on the structural evolution of carbon networks between molecular chemistry
and nanomaterial chemistry.