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S. Koguchi et al. / Tetrahedron 72 (2016) 7633e7637
(Table 2, Entry 1e6). We also investigated the oxidation reaction
of benzyl alcohol (Table 2, Entry 7e13). Benzyl alcohols were
efficiently oxidized by this reaction. However, methoxybenzyl
alcohol was observed to exhibit a different behavior in the reac-
tion according to its positional isomers. The oxidation of 3-
methoxybenzyl alcohol resulted in low yields (Table 2, Entry 11).
Finally, we have examined the oxidation reaction of 4-
hydroxybenzyl alcohol and 4-aminobenzyl alcohol. However, the
corresponding aldehyde was not obtained.
coupling constants (J) are in Hz. The mass analyses were performed
using a JEOL AccuTOF LC-plus JMS-T100LP spectrometer. The
courses of the reactions were monitored using TLC aluminum
sheets with silica gel 60 F254 (Merck). The column chromatography
was performed using silica gel 60 (Kanto Chemical).
1.2. 5-Hydroxy-2-iodobenzoic acid (2)
Finally, we examined the reusability of this reaction system.
After the oxidation reaction was complete, the product was washed
with water and extracted with ether. We successfully extracted
a pure product and removed the inorganic material by-product
using this process. Thus, it was possible to convert the hydropho-
bic ionic liquid-supported 1-hydroxy-1,2-benziodoxole-3(1H)-one
(IBA) to the hydrophobic ionic liquid-supported IBX using Oxone. A
reclaimed reaction system (hydrophobic ionic liquid-supported IBX
and hydrophobic ion liquid [bmim]PF6) could be recycled and
reused for the oxidation reaction. As previously mentioned, the
synthesis of this novel ionic liquid catalyst, the ionic liquid sepa-
ration, and the recycling of the product were easily achievable.
Excellent conversions were obtained for up to five consecutive
cycles of recycling and reuse (Table 3).
The solution of 5-hydroxyanthoranic acid (1.99 g, 1.33 mmol) in
water (20 ml) was added to HCl (10 ml) and NaNO2 (1.08 g,
45.6 mmol). The mixture was stirred at 0 ꢁC for 30 min and then
mixture was added KI (3.24 g, 19.5 mmol) and water (5 ml). The
result mixture was stirred at 90 ꢁC for 30 min. The mixture
extracted with ethyl acetate, and organic layer was washed with
H2O, dried (MgSO4) and evaporated. The product was isolated by
silica gel column chromatography to give the title compound 2
(2.15 g, 88%) as brown solid mp¼180 ꢁC; IR (KBr) nmax¼3293, 1700,
1666, 1583, 1477, 1427, 1307, 1265, 1241, 1222, 1018, 933, 877, 827,
782 cmꢀ1; 1H NMR (500 MHz, DMSO):
d
¼6.69 (1H, d, J¼8.5 Hz), 7.13
(1H, s), 7.71 (1H, d, J¼8.5 Hz), 9.9 (1H, s), 13C NMR (DMSO)
¼80.5,
d
117.8, 120.6, 137.9, 141.7, 157.8, 168.3. HRMS (APCI): m/z [MþH]þ
calcd for C7H5IO3: 264.9361; found: 264.9377.
Table 3
Recovery and reuse of the ionic liquid phase containing hydrophobic ionic liquid-supported IBX
Run
1
95
2
92
3
91
4
93
5
90
Yield (%)a
a
Isolated yield
In summary, we reported the synthesis of hydrophobic ionic
liquid-supported IBX and demonstrated that it is capable of cata-
lyzing the oxidation reactions of primary and secondary alcohols.
This system is advantageous because of its environmental friend-
liness and good yields. Additionally, this reaction system can be
washed with water and is formed by oxidizing the hydrophobic
ionic liquid-supported IBA using Oxone, which can be recycled and
reused at least five times.
1.3. Methyl-5-hydroxy-2-iodobenzoate (3)
The solution of 5-hydroxy-2-iodobenzoic acid
2
(2.21 g,
8.4 mmol) in methanol (40 ml) was added to H2SO4 (0.3 ml). The
result mixture was stirred at reflux for 2 days. The mixture
extracted with ethyl acetate, and organic layer was washed with
NaHCO3 aq, dried (MgSO4) and evaporated. The product was iso-
lated by silica gel column chromatography to give the title com-
pound 3 (1.95 g, 88%) as colorless solid mp¼90 ꢁC; IR (KBr)
nmax¼3339, 2956, 1710, 1604, 1565, 1427, 1294, 1265, 1222, 1097,
1. Experimental section
1.1. General
1016, 981 cmꢀ1
;
1H NMR (500 MHz, CDCl3):
d
¼3.92 (3H, s), 6.72
(1H, d, J¼8.57 Hz), 7.32 (1H, s), 7.81 (1H, d, J¼8.5 Hz), 13C NMR
(CDCl3)
d
¼52.8, 82.0, 118.4, 120.8, 135.8, 142.2, 155.9, 167.4. HRMS
(APCI): m/z [MþH]þ calcd for C8H8IO3: 278.9518; found: 278.9508.
All reagents and chemicals received from commercial suppliers
were of reagent grade and were used unmodified. NMR spectra
were performed on Bruker Advance DRX 500 (1H: 500 MHz, 13C:
125 MHz) spectrometers. Deuterated solvents used are indicated in
1.4. Methyl-5-(2-chloroethoxy)-2-iodobenzoate (4)
each case. Chemical shifts (
residual peak of the solvent or TMS as an internal standard;
d
) are expressed in ppm and refer to the
The solution of methyl-5-hydroxy-2-iodobenzoate 3 (1.11 g,
4 mmol) in DMF (10 ml) was added to TBAB (0.13 g, 4 mmol) and