261
Table 3
Synthesis of 3-acetyl-5-bromo-indole.
Run
Catalyst
T(◦C)/t (h)
Solventa
Conv.[%]
V[%]
VI[%]
VII[%]
1
2
3
4
5
6
7
8
Aquivion-Ga
Aquivion-Ga b
Aquivion-Ga b
Aquivion-Ga b
Aquivion-Ga b
Aquivion-Gac
Aquivion-Gac
Aquivion-Gac
Aquivion-Fe
Aquivion-Feb
Aquivion-Feb
Aquivion-Feb
Aquivion-Feb
Aquivion-Fec
Aquivion-H
AA
AA
AC
AA
AA
90/2
90/2
90/2
90/2
90/2
90/2
90/2
90/16
90/2
90/2
90/2
90 / 2
90/2
90/4
90/2
90/2
90/2
90/22
90/22
90/2
AA
AA
AA
AA
100
100
100
92
95
91
92
92
93
92
90
91
74
70
90
94
92
92
90
51
73
–
5
5
5
4
5
-
-
-
-
4
5
5
4
-
5
–
–
–
4
5
3
3
2
4
5
–
–
30
10
2
3
2
AA
ACN
ACN
ACN
AA
AA
AA
AA
AA
ACN
AA
AA
74
100
100
100
100
99
98
51
91
–
–
20
99
100
9
10
11
13
14
15
16
17
18
19
20
21
4
traces
13
–
–
–
Aquivion-Hb
d
SiO2/ZrO2
SiO2/ZrO2
AA
ACN
AA
–
e
20
92
88
Nafion-Fef
Nafion-Feg
3
7
AA
a
AA = acetic anhydride, AC = acetyl chloride, ACN = acetonitrile.
Catalyst recovered from the previous run and used as such.
Reaction conditions: 2.22 g (0.011 mol) of IV in 3 mL of ACN and equimolar amount of acylating agent (AA or AC).
Reaction conditions: 2.22 g (0.011 mol) of IV in 3 mL of AA and 0.2 g of catalyst.
Reaction conditions: 2.22 g (0.011 mol) of IV in 3 mL of ACN and 0.89 g (0.011 mol) of AC and 0.2 g of catalyst.
Pelletized Nafion-Fe.
b
c
d
e
f
g
Coarse powder Nafion-Fe.
mer, after a rapid drying under vacuum, is ready for use as a Lewis
catalyst. This protocol was also applied to prepare the correspond-
ing Nafion salts. However, using commercial available pelletized
Nafion-H, the reaction only led to a 28% transformation in the
desired Nafion-Fe, as determined by the analysis, after many days
and working also with a larger amount of acetonitrile. Conversely,
after a freezing treatment with liquid nitrogen and manual crush-
ing of commercial Nafion-H into a coarse powder, the reaction was
Nafion-H is that Aquivion-H is already sold as powder and does not
require any difficult processing before use.
agreement with other studies [17]. This mass loss is clearly present
in the TG-DSC Aquivion-H curve (Fig. 2a), however it is less evident
for the Aquivion-Fe and Aquivion-Ga (Fig. 2b and c, respectively).
Both the Aquivion salts seem to have a more stable temperature
profile also in the range 300-400 ◦C with a minimum mass loss. This
enhancement would enable both Aquivion salts to be also used in
Lewis acid catalyzed gas phase reactions.
Finally, Aquivion-Fe and –Ga samples compared with Aquivion-
H by optical microscopy show a nearly homogeneous distribution
of metallic cationic species in the polymer, although the presence
of small amounts of unreacted metallic particles cannot be ruled
With ATR-FTIR useful information can be collected without any
manipulation of the sample [16]; for this reason it was used for
registering spectra of Aquivion-H and its salts (Fig. SM1 a–c, Sup-
plementary material). The most interesting diagnostic zone seemed
to be between 1800 cm−1 and 1400 cm−1, where the spectrum of
Aquivion-H (a) presented a broad band centered at 1735 cm−1 and
both Aquivion-Fe and –Ga spectra (b and c respectively) had three
peaks between 1660 and 1450 cm−1. However, after treatment with
acetonitrile at reflux temperature for 8 h, a sample of Aquivion-H
powder was filtered with some difficulty (a film was formed instead
of the starting powder), dried under vacuum and reanalyzed by
ATR-FTIR; (Fig. SM1 d, supplementary material). In the spectrum
obtained three peaks, instead of the previous broad band, were
lation of two heterocylic compounds was studied (Scheme 2). A
representation of mechanism of Friedel–Crafts acylation catalyzed
by Aquivion-Fe is reported in Fig. 3.
Table 2 reports the results obtained in the acylation of the thio-
phene substrate I with Aquivion-H and its salts, compared with
those found using the traditional Friedel–Crafts Lewis acid cat-
alyst SnCl4, used in stoichiometric amount, or a heterogeneous
commercial acid catalyst EPZG-10, activated before use. If not oth-
erwise indicated, the experimental conditions are those described
in the experimental section. Two acylating agents and different
kinds of catalysts were compared in this reaction. This application is
interesting because it permits to obtain, in particular, 2-propionyl-
5-ethyl-thiophene (III) which was originally prepared using EtCd
and 5-ethyl-2-thiophenecarboxylic acid chloride [18]. This com-
and a low odor threshold. Initially a general procedure described
in the literature for thiophene acylation was followed [19] but
carrying out the reaction at 25 ◦C in dichloromethane, instead of
in a stoichiometric amount, was SnCl4 and the acylating agent
was propionyl chloride. After 2 h, a quantitative conversion of the
starting material into the desired product was observed and, after
work-up, an 80 % yield of III was obtained (Table 2, run 10). This
result is satisfactory but it should be underlined that the synthe-
observed between 1800 cm−1 and 1400 cm−1
.
One possible interpretation of this different result is that in
spectrum (a) there were also bands due to a small amount of
attributed to the bending of OH bond) and water was removed
by treatment with acetonitrile. Thus no substantial difference was
found between Aquivion-H and its salts with this technique.
Fig. 2 reports the TG-DSC curves of the Aquivion-H and its
salts, obtained from 30 to 650 ◦C under N2 flow rate. All thermo-
grams show three mass losses and a similar behaviour to Nafion-H
and Nafion-Fe (Fig. SM2) and also in comparison with the liter-
ature [16,17]. The mass loss observed in the temperature range
180–300 ◦C may be related to the decomposition of SO3 groups, in