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Typical procedure for thiocyanation
To a mixture of heterocyclic aromatic compounds (1 mmol),
ammonium thiocyanate (3 mmol) in appropriate solvent, 0.8%
Ag/TNT as the catalyst was added and the mixture was irra-
diated with visible light (irradiation light was under 12 W
compact fluorescent lamp (CFL), 12 W blue LED, 12 W green
LED and 12 W red LED) and was open to air at room tempera-
ture. The progress of the reactions was screened by TLC. After
completion of the reactions, we separated the catalyst from
reaction solvent by centrifugation and then, 20 mL H2O was
added to the reaction solvent and the mixture was extracted by
CH2Cl2 in a decanter. The organic layer was further cleaned
with distilled water (2 ꢂ 15 mL) and dried over Na2SO4. Then,
the solvent was removed from the mixture under reduced
pressure and the resulting crude product was purified by silica
gel column chromatography with petroleum ether/ethyl acetate
(20 : 1) to give the desired thiocyanation products in good to
excellent isolated yields. Furthermore, 2-amino-4-phenylthiazole
derivatives were purified by recrystallization in acetone.
Conclusions
In conclusion, Ag/TNT heterojunctions exhibit much higher
photocatalytic performance than pure TiO2-NTs and P25 under
visible light, which is due to the LSPR effect and the restraining
effect for recombination of photogenerated electrons and
holes. Considering sulfur affinity of silver metals, we exploited
Ag/TNT photocatalyst in thiocyanation reactions. This easily
prepared, nontoxic and cheap photocatalyst exhibited high
activity toward thiocyanation of indoles, anilines, pyrroles
and 2-amino thiazoles for the first time under visible light
(except indoles). These photoinduced reactions have been
developed using Ag/TNT as a photoredox catalyst at room
temperature without an external oxidant. Simple work-up, good
to excellent yields, mild reaction conditions and reusability of
the catalyst are the major advantages of this unprecedented
procedure.
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There are no conflicts to declare.
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