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Catalysis Science & Technology
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between FT-IR spectra of recovered ARS-TiO2 (after third run) purification was done through silica gel column chVroiemw AarttoiclgerOanplihnye
and untreated ARS-TiO2 revealed no significant change in the
absorption peaks of the remaining dye on the surface of
DOI: 10.1039/C9CY02268F
using petroleum ether/ethyl acetate.
titanium dioxide (See SI Figure S3). Moreover, the XRD patterns
of photocatalysts, before and after recycling (after third run),
exhibited no considerable change in the structure of TiO2 during
the reaction (See SI Figure S4).
Finally, we surveyed the possibility of
a gram-scale
thiocyanation reaction under our optimized condition. In this
context, 3.01 g (86%) of target product (3a) was obtained,
upon isolation which showed the merit of a practical
procedure in thiocyanation reaction (scheme 8).
Notes and references
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NCS
ARS-TiO2
atmospheric O2
S
S
NH4SCN
+
4.
THF, blue LED
24h ,rt
N
N
NH2
NH2
1a, 15 mmol, 2.6 g
3a, 3.01 g, 86%
2, 3eq, 2.3 g
5.
6.
X. Lang, X. Chen and J. Zhao, Chemical Society Reviews,
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Scheme 8. Gram-scale thiocyanation of 2-phenylamino-
thiazole.
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Conclusions
In conclusion, we have developed a versatile, sustainable and
regioselective thiocyanation protocol through direct C–S bond
formation as well as the first visible light-driven synthesis of 2-
9.
10.
11.
12.
13.
14.
15.
aminobenzothiazole.
A vast majority of important precursors
treated with ammonium thiocyanate in satisfactory yields. Notably,
the method is scalable and compatible with varied functional
groups.
Experimental section
Preparation of ARS-TiO2 photocatalyst.
At first, the TiO2 powder was heated at 110 °C in air for 3 h to
remove adsorbed water on the surface. Dyes-TiO2 were prepared
by a minor modified reported procedure45. Typically, three different
molar concentration of ARS dye (0.1 mol/L, 0.2 mol/L and 0.4
mol/L) in ethanol were added to 1g of pre-heated nano TiO2 (P25)
and stirred at room temperature in the dark for 12 h. The solid was
centrifuged and washed with ethanol five times and dried at 40 °C
for 30 h on the vacuum oven and kept in the dark.
16.
17.
18.
19.
20.
21.
General procedure for thiocynation reactions.
A mixture of aromatic compounds and (1 mmol) and ammonium
thiocyanate (3 mmol) in THF or CH3CN (6 mL) placed in 10 mL round
bottom flask, ARS-TiO2 (7.0 mg, 0.97 μmol g−1) was added and the
reaction was irradiated by 15 W blue LED Lamp (λ > 440 nm,
distance app. 4.0 cm) in open air condition. The reaction was stirred
for appropriate time at room temperature (25 °C) and monitored by
TLC. After completion, the reaction mixture was centrifuged to
separate the photocatalyst, then, the reaction was diluted with
CH2Cl2 /EtOAc (15mL) and washed with brine. The combined organic
phases were dried over MgSO4 and the solvent was evaporated
under reduced pressure to obtain the crude. Final product
22.
23.
24.
25.
26.
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