N-substituted trichloroacetamides (NTCAs), which serve
as blocked
isocyanates, were synthesized in ∼97% yields by in situ photo-on-demand
trichloroacetylation of amines with tetrachloroethylene (TCE). The
reactions were performed by photo-irradiation of TCE solutions containing
an amine under O2 bubbling over 70 °C with a low-pressure
mercury lamp. TCE underwent photochemical oxidation to afford trichloroacetyl
chloride having high toxicity and corrosivity, which then reacts in
situ with the amine to afford NTCA. Compared with conventional NTCA
synthesis with hexachloroacetone, the present reaction has the advantage
of being widely applicable to a variety of amines, even those with
low nucleophilicity such as amides, fluorinated amines, and amine
HCl salts. NTCAs could be converted to the corresponding N-substituted
ureas and carbamates through base-catalyzed condensation with amines
and alcohols, respectively, with the elimination of CHCl3. The reaction may proceed by the initial formation of isocyanate
and its subsequent addition reaction with the amine or alcohol. This
photochemical reaction also enables the synthesis of fluorinated NTCAs,
which accelerate the reactions, and realizes the synthesis of novel
fluorinated chemicals including polyurethanes.
Presented is a method involving TM–As–Q (TM = Hg, Cd; Q = S, Se) quaternary arsenic chalcogenides and different mixed solvents which has been used to synthesize four new quaternary chalcogenide compounds.
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