Yongle Chen et al. / Chinese Journal of Catalysis 37 (2016) 2114–2121
2115
mmol/L) of PGTACs and other catalysts at room temperature
(25 °C). Dimethyl yellow (pKa(I)aq = 3.3) was used as the indi‐
cator (0.085 mmol/L), and the UV‐visible determination was
carried out in the range of 200–700 nm.
+
+
-
+
-
+
N1
2N
Hb
N
H
N
N
H
N
H
Ha
2.3. Synthesis and characterization of PGTACs
-
-
X
X
X
X
X
[Phen-H][X] (1b-3b)
1a-3a
1c-3c
[Phen-2H][X]2 ( )
[Phen-H][X]---HX (
)
To a vigorously stirred ethanol solution (100 mL) of
1,10‐phenanthroline (18.02 g, 0.1 mol), ethanol solution (50
mL) of sulfuric acid (19.60 g, 0.2 mol) was added at 0 °C. The
mixture was stirred for a further 12 h at reflux temperature.
The ethanol was removed by evaporation to give a reddish
liquid. Then, the colored residue was washed with benzene
three times and dried in vacuum to give the purified PGTACs
1a. This catalyst was solidified on cooling (yield: 99%). PGTACs
2a to 3b were synthesized similarly to the preparation of
PGTACs 1a. The yields of these PGTACs were all above 99%.
The structural maps of 1a–3b are shown in Figure 1.
PGTACs 1a. 1H NMR (400 MHz, DMSO‐d6) δ = 9.34 (1 H, d),
9.33 (1 H, d), 9.13 (1 H, d), 9.10 (1 H, d), 8.39 (2 H, s), 8.27 (1 H,
d), 8.25 (1 H, d), 2.44 (6 H, s). 13C NMR (100 MHz, DMSO‐d6) δ =
148.22, 141.98, 138.03, 129.77, 127.82, 126.03, 40.37. MS
(ESI): m/z = 181.08 [M + H]+. Anal. Calcd. for C14H16N2O6S2: C
45.16, H 4.30, N 7.53; Found: C 45.14, H 4.31, N 7.55.
PGTACs 3a. 1H NMR (400 MHz, DMSO‐d6) δ = 9.33 (1 H, d),
9.32 (1 H, d), 9.12 (1 H, d), 9.10 (1 H, d), 8.38 (2 H, s), 8.26 (1 H,
d), 8.25 (1 H, d), 7.49 (4 H, d), 7.13 (4 H, t), 2.29 (6 H, s). 13C
NMR (100 MHz, DMSO‐d6) δ = 147.62, 145.29, 142.03, 137.82,
137.30, 129.58, 128.10, 127.54, 125.77, 125.46, 20.75. MS
(ESI): m/z = 181.08 [M + H]+. Anal. Calcd. for C26H24N2O6S2: C
59.54, H 4.58, N 5.34; Found: C 59.50, H 4.63, N 5.30.
Scheme 1. Structure of [Phen–H][X]···HX, [Phen–H][X] and
[Phen–2H][X]2. X– = CH3SO3 (1), HSO4 (2), and CH3PhSO3 (3).
In contrast to these widely known PILs, we reported here a
new bonding mode between the Brönsted acid and base. They
are called proton gradient transfer acid complexes (PGTACs).
The PGTACs were generated by a reaction between phenan‐
throline (Phen) and acid in 1:2 mole ratio ([Phen–H][X]···HX,
1a–3a in Scheme 1). These complexes are interesting because
only one proton (Ha) formed a covalent bond with the N atom
of Phen, and another proton (Hb) formed a hydrogen bond with
another N atom. Furthermore, Hb can transfer between the N
atom and X anion with a low barrier. That is, the transfer abili‐
ties of the Ha and Hb protons are different. The PGTACs are a
good compromise between the free acid (HX) and [Phen–H][X]
when both catalytic activity and selectivity are taken into con‐
sideration. In particular, these PGTACs can be easily separated
and reused because of the nature of the salts, so a green reac‐
tion separation integration is enabled.
2. Experimental
2.1. Materials
PGTACs 1b. 1H NMR (400 MHz, DMSO‐d6) δ = 9.31 (1 H, d),
9.30 (1 H, d), 9.06(1 H, d), 9.04 (1 H, d), 8.35 (2 H, s), 8.21 (1 H,
d), 8.19 (1 H, d), 2.31 (3 H, s). 13C NMR (100 MHz, DMSO‐d6) δ =
148.09, 142.44, 137.59, 129.94, 127.95, 126.23, 40.18. MS
(ESI): m/z = 181.08 [M + H]+. Anal. Calcd. for C13H12N2O3S: C
56.52, H 4.35, N 10.14; Found: C 56.55, H 4.35, N 10.13.
PGTACs 3b. 1H NMR (400 MHz, DMSO‐d6) δ = 9.32 (1 H, d),
9.31 (1 H, d), 9.09 (1 H, d), 9.07 (1 H, d), 8.37 (2 H, s), 8.24 (1 H,
d), 8.23 (1 H, d), 2.28 (3 H, s). 13C NMR (100 MHz, DMSO‐d6) δ =
148.14, 146.14, 142.30, 138.13, 137.85, 129.94, 128.54, 127.94,
126.17, 125.99, 21.24. MS (ESI): m/z = 181.08 [M + H]+. Anal.
Calcd. for C19H16N2O3S: C 64.77, H 4.55, N 7.95; Found: C 64.70,
H 4.57, N 8.04. Data for PGTACs 2a and 2b have been reported
in other being published articles.
All chemicals were analytical grade and used without any
purification. 1,10‐Phenanthroline (Phen) was purchased from
Sun Chemical Technology (Shanghai) Co. Ltd. Geraniol, acetic
anhydride, methylsulfonic acid (MSA), H2SO4, p‐toluenesulfonic
acid (PTS), and D72 resin were obtained from Jintan Huagong
Chemical Research Institute (Jiangsu, China). Lewatit® K 2620
resin was purchased from Aladdin Industrial Corporation
(Shanghai, China). The other alcohols were obtained from En‐
ergy Chemical (China) Co. Ltd.
2.2. Methods
1H and 13C NMR spectra were collected on an Agilent DD2
400MR equipment operating at 400 and 100 MHz, respectively.
The elemental analysis (EA) was obtained using a Herae‐
us‐CHN‐O‐Rapid analyzer. The ESI MS spectra were deter‐
mined with a LCQ‐fleet ESI Mass Spectrometer. The FTIR spec‐
tra of the samples were recorded on a PerkinElmer Spectrum
100 Series FTIR spectrometer with a universal ATR accessory.
Thermogravimetry characterization for these PGTACs was
carried out on a PerkinElmer Diamond TG/DTA from room
temperature to 800 °C with a heating rate of 10 °C/min under
N2 atmosphere. An Angilent 8453 UV‐visible spectrometer was
used to determinate the Hammett functions (H0) of the PGTACs.
The experiments were carried out in methanol solution (2
Fig. 1. Prepared PGTACs samples1a, 2a, 3a, 1b, 2b and 3b.