Cong et al.
FULL PAPER
attentions in the synthetic organic chemistry,
[
19,20]
and
NMR (400 MHz, CDCl
3
) δ: 10.00 (s, 1H), 7.87 (d, J=
7.6 Hz, 2H), 7.55 (d, J=7.6 Hz, 2H), 4.81 (s, 2H).
[
21-23]
[24,25]
exhibits effective oxidation of alcohol,
phenol,
[26,27]
1
and amine
with the formation of intermediate in
Compound 3c, terephthalaldehyde. H NMR (400
which the heteroatom on substrate binds to the iodoxyl
moiety with the dehydration. Accordingly, the aqueous
solvent is unfavorable to the oxidation, and the utiliza-
tion of the hydrophobic cavity of Q[8] in our previous
work, has been served as an effectual way to perform
the IBX oxidation of benzyl alcohols in water di-
3
MHz, CDCl ) δ: 10.15 (s, 2H), 8.06 (s, 4H).
Host-guest interactions by isothermal titration calo-
rimetry
Isothermal titration calorimetry (ITC) experiments
were carried out on an isothermal titration calorimeter of
Nano ITC (TA) at 25 ℃. Concentrations of benzenedi-
[15-17]
rectly.
With this ideal, we report the IBX oxidation
−3
−1
methanol in aqueous solutions were 1.0×10 mol•L ,
and concentration of Q[8] in aqueous solution was 1.0×
of benzenedimethanols in the presence of Q[8] based on
the host-guest interactions hereby (Scheme 1).
−4
−1
1
0
mol•L . The benzenedimethanol solutions were
titrated into Q[8] solution.
Experimental
Materials and apparatus
Results and Discussion
Q[8] was prepared and purified according to the
[
28]
Following the reaction conditions of IBX oxidation
of benzyl alcohols in the presence of Q[8], the substrate
o-benzenedimethanol (compound 1a, Scheme 1) has
been subjected to this oxidation. In the absence of Q[8]
at room temperature, o-benzenedimethanol has been
oxidized by 1 equiv. IBX to provide o-(hydroxymethyl)-
benzaldehyde (compound 2a, Scheme 1), the one and
only product with the yield of 28% (Entry 1, Table 1),
namely, the oxidation should be a thermodynamic con-
trol process and the secondary oxidation could not occur
here. In the presence of 10% Q[8], which is the standard
methods developed in our laboratory.
The benzene-
dimethanols were purchased from Alfa Aesar (Tianjin)
Chemical Co., Ltd. and used without further purification.
IBX was prepared with 2-iodobenzoic acid and
[
29] 1
oxone.
6
H NMR (d -DMSO) δ: 7.96 (d, J=7.6 Hz,
1
7
H), 7.68 (d, J=7.6 Hz, 1H), 7.46 (t, J=7.6 Hz, 1H),
.22 (t, J=7.6 Hz, 1H). m.p. 230-233 ℃ with explo-
sive decomposition.
High Performance Liquid Chromatography (HPLC)
was performed using a Shimadzu LC-20A with a Photo-
Diode Array Detector detector (PDA). The alcohols and
corresponding aldehydes were successfully separated by
a Sipore ODS-3 chromatographic column (150 mm×
[15-17]
condition in our previous work,
the yield of 2a is
increased to 48% with trace 3a product, o-phthalal-
dehyde, (Entry 2, Table 1), and furthermore the em-
ployment of 10% more catalyst for the two hydroxy-
methyl groups on benzene ring is not able to improve
this oxidation (Entry 3, Table 1). At reflux, the oxidation
is so fast that the reaction time has been shortened to 5
min, and the conversion of IBX oxidation of 1a is
slightly increased by 6% in the absence of Q[8] (Entry 4,
Table 1), while 62% yield of 2a has been observed in
the presence of either 10% or 20% macrocyclic com-
pound (Entries 5 and 6, Table 1). To promote the oxida-
tion of IBX, 2 equiv. IBX has been subjected to the sys-
tem, which obviously enhances the conversion of 1a. It
is surprisingly that the substrate 1a shows almost the
same activity in the absence or presence of Q[8] at room
temperature (Entries 7-9, Table 1), however, the yield
of 2a has been increased by about 15% with the 10% or
20% Q[8]’s catalysis at reflux (Entries 10-12, Table 1).
The 1 equiv. IBX oxidation of substrate m-benzene-
dimethanol (compound 1b, Scheme 1) affords m-(hy-
droxymethyl)benzaldehyde (compound 2b, Scheme 1)
with only 13% yield in the absence of Q[8] (Entry 1,
Table 2). With the participant of 10% or 20% cucur-
bit[8]uril, about 35% 2b and little 3b, isophthalaldehy-
dehyde, have been observed (Entries 2-3, Table 2), and
therefore 10% more Q[8] could not improve the oxida-
tion. As the case of o-benzenedimethanol (1a), the IBX
oxidation of 1b is accelerated by increasing temperature.
At reflux, 33% 2b has been produced in the absence of
0
.21 mm×5 μm), and the oxidation results were calcu-
lated from the integrated peak areas and expressed in
terms of the percentages of the aldehyde formed.
Catalytic oxidation experiments
Benzenedimethanol (28 mg, 0.2 mmol) was added to
the suspended solution of IBX and Q[8] in a proportion
in 25 mL distilled water with vigorously stirring. The
aqueous solution were directly used for the HPLC
analysis after Q[8] was removed by filtration. The
products were extracted with ethyl acetate (10 mL×3)
form the aqueous solution followed by separation by
1
TLC, and then identified by H NMR.
1
Compound 2a, 2-(hydroxymethyl)benzaldehyde. H
NMR (400 MHz, CDCl
5
1
3
) δ: 10.40 (s, 1H), 7.85 (d, J=
.6 Hz, 1H), 7.74 (t, J=5.6 Hz, 1H), 7.59 (d, J=5.6 Hz,
H), 7.56 (t, J=5.6 Hz, 1H), 4.69 (s, 2H).
1
Compound 3a, phthalaldehyde. H NMR (400 MHz,
CDCl
d, J=5.6 Hz, 2H).
Compound 2b, 3-(hydroxymethyl)benzaldehyde. H
NMR (400 MHz, CDCl ) δ: 10.03 (s, 1H), 7.89 (s, 1H),
.81 (d, J=7.6 Hz,1H), 7.65 (d, J=7.6 Hz, 1H), 7.54 (t,
J=7.6 Hz, 1H), 4.80 (s, 2H).
Compound 3b, isophthalaldehyde. H NMR (400
MHz, CDCl ) δ: 10.13 (s, 2H), 8.39 (s, 1H), 8.17 (d, J=
.6 Hz, 2H), 7.74 (t, J=7.6 Hz, 1H).
3
) δ: 10.55 (s, 2H), 7.99 (d, J=5.6 Hz, 2H), 7.78
(
1
3
7
1
3
7
1
Compound 2c, 4-(hydroxymethyl)benzaldehyde. H
546
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© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2015, 33, 545—549