The polarographic reduction of aromatic carbodiimides in anhydrous aprotic
solvents goes through a carbene intermediate by a diffusion controlled process in two
one-electron steps. The first step is the rate-determining step and converts the
carbodiirnide to a radical anion (6) that reduces further by a fast one-electron step to
a carbene dianion intermediate (7). This abstracts an oxygen, along with protons,
from the solvent to give diphenyl urea (9) or reduces further to methylene dianiline
(12) .