Regioselective synthesis of 5-aryl azo salicylaldehydes catalyzed by Zn/SBA-15

Article abstract of DOI:10.1007/s11696-019-00790-1

Synthesis of (E)-2-hydroxy-5-(aryldiazenyl)benzaldehydes was investigated. Various Lewis acids were tested as catalyst to achieve regioselectivity. In addition to various commercial catalysts, mesoporous Zn/SBA-15 was synthesized through a modified direct

Full text of DOI:10.1007/s11696-019-00790-1

Chemical Papers
https://doi.org/10.1007/s11696-019-00790-1
ORIGINAL PAPER
Regioselective synthesis of 5‑aryl azo salicylaldehydes catalyzed
by Zn/SBA‑15
Forouzan Zonouzi1 · Alireza Rahmani2 · Hamid Dezhampanah1,3 · Bahram Ghalami‑Choobar1,3
Afsaneh Zonouzi2,4
·
Received: 17 October 2018 / Accepted: 19 April 2019
© Institute of Chemistry, Slovak Academy of Sciences 2019
Abstract
Synthesis of (E)-2-hydroxy-5-(aryldiazenyl)benzaldehydes was investigated. Various Lewis acids were tested as catalyst
to achieve regioselectivity. In addition to various commercial catalysts, mesoporous Zn/SBA-15 was synthesized through
a modifed direct method with chloride salt as zinc precursor and characterized using N2-physisorption, low-angle XRD,
FESEM and EDX methods; specifc surface area of 832 m2 g−1 is a noteworthy result compared to the literature. The synthe-
sized catalyst showed the best results in terms of both total yield and regioselectivity. A scalable two-phase reaction media
was used to facilitate both reaction progress monitoring and fnal product separation. Minimizing solvent consumption, this
method can be considered for larger scale production of aryl azo dyes and related compounds.
Keywords Catalyst · Azo dyes · Regioselective · Synthesis · Lewis acids
Introduction
(İnan et al. 2018), and also pharmaceuticals (Pérez-Ibarbia
et al. 2016). Aryl azo salicylaldehydes were frst synthe-
sized by Tummeley (1889) and they have since been used for
the synthesis of more complex azo dyes (Odabaşoğlu et al.
2007; Sivaguru et al. 2016; Chopde et al. 2017; Xu et al.
2018). Conventional synthesis route for such compounds
requires the use of NaNO2 and HCl as reagents and yields
two regioisomers 2 and 3. Obtaining each of 2 or 3 in pure
form is possible only through expensive and time consuming
separation (Scheme 1). In continuation of our quest explor-
ing earth abundant nanocatalysts for the synthesis of organic
compounds (Zonouzi et al. 2016, 2017, 2018), herein we
report efcient regioselective synthesis for 5-arylazo salicy-
laldehydes 2 using Zn/SBA-15 as catalyst by which pure
form of the compounds 2a–d can be easily obtained by sim-
ple and rapid work-up (Scheme 1).
As one of the largest and oldest classes of synthetic indus-
trial dyes, azo compounds (Marmion 1991) have been used
in a wide variety of applications including but not limited to
textile industry (O’Neill et al. 1999), inkjet printing (Green-
wood 1988), LEDs (Liu et al. 2009), data storage (Pham
et al. 1997), dye-sensitized solar cells (Chen et al. 2016),
sensors (Salmani et al. 2016), antiproliferative, antioxidant
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11696-019-00790-1) contains
supplementary material, which is available to authorized users.
* Bahram Ghalami-Choobar
B-ghalami@guilan.ac.ir
SBA-15 type mesoporous silica was frst synthesized by
Zhao et al. (1998) at UC Santa Barbara (SBA-15 stands for
Santa Barbara Amorphous). Their pioneering publication
led to numerous follow-ups and widespread usage of SBA-
15 in a variety of applications including catalyst support
(Huirache-Acuña et al. 2013), hard-template (Han et al.
2000), and drug delivery (Song et al. 2005). Many methods
and procedures have been proposed to modify SBA-15 to
intensify or create desired properties which can be either
direct or post-synthetic. Wang and co-workers reported a
* Afsaneh Zonouzi
zonouzi@khayam.ut.ac.ir
1
Department of Chemistry, University Campus 2, University
of Guilan, Rasht, Iran
2
School of Chemistry, College of Science, University
of Tehran, Tehran 14155-6455, Iran
3
Department of Chemistry, Faculty of Science, University
of Guilan, Rasht 19141, Iran
4
Pharmaceutical and Cosmetic Research Center (PCRC),
University of Tehran, Tehran, Iran
Vol.:(0123456789)
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Chemical Papers
Scheme 1 Synthesis of the compounds under study
general route to synthesize metal oxide containing SBA-15
(Wang et al. 2005). Zn/SBA-15 was synthesized by impreg-
nation method and studied as a catalyst for desulfurization
of H2S (Ren et al. 2011). A similar catalyst was used in
the cracking of industrial dipentene (Du et al. 2005). Direct
method was used to synthesize Zn/SBA-15 as a catalyst for
selective coupling of CO2 and epoxides (Liu et al. 2016) and
the cycloaddition of CO2 to propylene oxide (in synergy with
DMF) (Zhong et al. 2015); these two studies used nitrate salt
as the source of zinc which resulted to the surface area of
around 500 m2 g−1.
Experimental
Chemicals and instruments
Chemicals and solvents were of synthetic grade and obtained
from Merck (Germany), Aldrich (US) and Fluka (Switzer-
land) and were used without further purifcation except for
aniline which was steam distilled prior to use. TLC on pre-
coated plastic sheets (25 DCUV-254), respectively. Melting
points were measured on a Barnstead Electrothermal (UK)
melting point apparatus and are not corrected. Elemental
analysis for C, H and N were obtained using a Thermo
Finnigan (US) Flash EA1112 instrument. UV–Vis spectra
were measured using a PG instruments (UK) T80+. FTIR
spectra were recorded on a Bruker (Germany) EQUINOX
For the abovementioned reaction, Zn/SBA-15 was synthe-
sized with chloride salt as the precursor of zinc and charac-
terized using N2-physisorption (surface area of 832 m2 g−1
among other results), Low-angle XRD, FESEM and EDX.
This catalyst was used in a two phase (water/petroleum
ether) reaction route. Dyes 2 and 3 are insoluble in water
and they have been obtained as deposits in the literature
(Tummeley 1889); such compounds have been produced
in similar time and energy consuming manner ever since
(Baul et al. 2009). Herein we present a new procedure for the
Zn/SBA-15 catalyzed synthesis of regioisomer 2 benefting
from the immiscibility of water with petroleum ether and
the solubility of the fnal product in the later solvent. Using
this method, it is much easier to monitor the production of 2
using TLC and to obtain the product after completion with-
out the separation from catalyst and reaction mixture. Fur-
thermore, the product is much easier to purify by aqueous
washing due to regioselectivity.
55 spectrophotometer as ATR method. H NMR and 13C
1
NMR spectra were determined in DMSO-d6 on Agilent (US)
500 spectrometer and chemical shifts were expressed in ppm
downfeld from tetramethylsilane. Low angle powder X-ray
difraction patterns were obtained on a Philips (Holland)
PW1730 difractometer with CuKα (λ=1.54 Å) radiation.
N2-physisorption isotherms were obtained at 77 K on a Bel-
sorp (Japan) Mini II instrument. Field-emission scanning
election micrographs were obtained on a TSCAN (Czech
Republic) MIRA 3 equipped with a Bruker (Germany)
XFlash detector for EDX analysis.
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Chemical Papers
Table 1 Yields of azo dyes 2a and 3a obtained using various cata-
Catalyst synthesis
lysts (0.5 w/w%)
Zn/SBA-15 was synthesized by a direct method (Liu et al.
2016; Zhong et al. 2015) with modifcations. 1 g of Pluronic
P123 was added to 50 mL of water and 0.7 mL of HCl (37%
aq) while stirring. Afterwards ZnCl2 was added (the amount
was calculated to achieve the Zn/Si molar ratio of 0.1) and
the stirring was continued for 30 min at room temperature.
2 g of tetraethylorthosilicate (TEOS) was added slowly and
the temperature was raised to 40 °C for 24 h; then it was
transferred to a Tefon® lined autoclave and kept at 100 °C
for another 24 h. The obtained white solid was centrifuged
and washed with distilled water several times (until reaching
pH≈7). After drying at room temperature for several days
the pre-ceramic was calcined at 550 °C for 5 h in a static air
mufe furnace and let to cool down to room temperature
slowly. The obtained powder was fnely grinded and used
for characterization and catalytic tests.
Entry
Catalyst
Total yield %a
% in fnal
productb
2a
3a
1
2
3
4
5
6
7
8
–
ZnO
ZnCl2
ZrO2
Nano-ZrO2
SBA-15
Zn/SBA-15
Zn/SBA-15c
55
65
62
60
68
60
65
85
65
75
78
75
80
70
98
98
30
20
15
15
15
20
–
–
aBased on total precipitate weight containing both 2 and 3
bObtained by PLC separation
cWith double solvent approach
phase was removed and the precipitate was washed with
petroleum ether several times to separate the fnal products
from solid catalyst. Obtained catalyst was stored and the
petroleum ether phase was washed with ice cold water sev-
eral times. Products were obtained as powder by solvent
evaporation. Regioisomers 2a and 3a were separated as
above (Table 1, entries 2–7).
Synthesis of 2a–d
Traditional procedure
To a magnetically stirred solution of anilines 1 (0.05 mol)
was added 8 mL of HCl (37% aq) drop wise at 0 °C and then
20 mL of NaNO2 solution (4 g in 20 mL of H2O) was added
to the above mixture and stirring continued for 20 min. At
the same time another solution was prepared from salicylal-
dehyde (0.05 mol in 5 mL NaOH 10% aq) and magnetically
stirred for 10 min. The frst solution was added slowly to
the second and stirred further for 5–7 h at 0 °C; the reactor
was then transferred to a refrigerator and kept overnight.
Yellow to light brown precipitates were fltered and washed
thoroughly with cold distilled water several times. TLC
of the products shows two adjacent distinguishable spots
(Rf ≈ 0.7–0.9, ethyl acetate: n-hexane 1:3 on silica gel)
related to 2 and 3. The regioisomers 2a and 3a were sepa-
rated by PLC (Table 1, entry 1).
Double solvent approach for catalyzed regioselective
synthesis
To a magnetically stirred solution of anilines 1 (0.05 mol)
was added 8 mL of HCl (37% aq) drop wise at 0 °C and then
20 mL of NaNO2 solution (4 g in 20 mL of H2O) was added
to the above mixture and stirring continued for 20 min. In
a separate Erlenmeyer, 0.05 mol of salicylaldehyde was
mixed with 10 mL petroleum ether (40–60 °C) and stirred
for 10 min; then 0.5 w/w% of Zn/SBA-15 was added (the
amount was optimized by preliminary experiments), then
5 mL NaOH 10% aq was added drop wise. The petroleum
ether phase was added to the aqueous solution while being
vigorously agitated. Both liquid phases can in practice wet
the solid catalyst (contact angles of 7° and 14° were meas-
ured for water and petroleum ether, respectively). The reac-
tion progress was monitored both visually and by TLC every
5 min. After about 45 min, a foggy lemon colored aqueous
phase was separated from a yellow to brown organic phase.
The TLC of this stage showed only one spot (Rf≈0.7, ethyl
acetate: n-hexane 1:3 on silica gel) related to regioisomers
2a–d. The fnal products were obtained as petroleum ether
solutions and then as powder upon solvent evaporation at
reduced pressure and washed thrice with distilled water.
Obtained pure products were used for spectroscopic char-
acterization (see Supporting Information).
Catalyzed synthesis
To a magnetically stirred solution of anilines 1 (0.05 mol)
was added 8 mL of HCl (37% aq) drop wise at 0 °C and then
20 mL of NaNO2 solution (4 g in 20 mL of H2O) was added
to the above mixture and stirring continued for 20 min (A).
At the same time 0.05 mol of salicylaldehyde was added
to 5 mL distilled water in another Erlenmeyer; 0.5 w/w %
of catalysts listed in Table 1 were added after fne grinding
with agate mortar and pestle (the amount was optimized by
preliminary experiments). After some stirring, 5 mL NaOH
10% aq was added (B). Addition of (B) to (A) followed by
vigorous stirring for 5–7 h at 0 °C; the reactor was then
transferred to a refrigerator and kept overnight. Aqueous
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Zinc and zirconium-based Lewis acid catalysts can inter-
act with oxygen moiety from salicylaldehyde hence hinder
the ArN2+ electrophilic attack on the ortho position of aro-
matic ring. Application of such materials can bring about
regioselectivity as presented in Table 1; preliminary experi-
ments showed the optimized catalyst ratio of 0.5 w/w%. Pris-
tine SBA-15 did not show a signifcant efect on the reac-
tion yield and regioselectivity suggesting that not all acid
surface groups can take part in the present reaction. Cu/
SBA-15 (from our previous studies) were also put to test, but
the results were even worse, proving that only certain metals
with high afnity toward oxygen can lead to regioselectivity
in this synthesis. To obtain a fairly inexpensive and recov-
erable catalyst without the complications associated with
nanoparticles (both in terms of synthesis and recovery), we
investigated Zn/SBA-15. In this approach, appropriate sur-
face acid groups take part in the reaction while the benign
framework of SBA-15 bring about material economy and
catalyst robustness.
Results and discussion
Recent advances in using catalysts for the synthesis of
organic compounds are focused on the development of new
reaction systems which ofer more control over stereo-and/or
regiochemistry (Schmalz 2008). Such selective protocols can
provide economic and environmentally benign procedures
for the scalable synthesis of key organic intermediates. In
continuation of our studies on using Lewis acid catalysts for
the synthesis of organic frameworks (Zonouzi et al. 2016,
2017, 2018, 2012, 2013), in the present research frst we
tried using some commercially available Lewis acids (ZnO,
ZnCl2, ZrO2 and nano-sized ZrO2 also pristine SBA-15) for
the synthesis of aryl azo dyes 2a, 3a; while they did enhance
the regioselectivity they could not completely eliminate the
second spot related to 3a in TLC. Obtained results for vari-
ous catalysts are presented in Table 1.
In the traditional reaction procedure for the dyes under
study, the fnal product is not soluble in the reaction medium
and is likely to precipitate on the heterogeneous catalyst.
As seen in this study, the fnal products are obtained as pre-
cipitate on the heterogenous catalyst particles. Several steps
of washing with organic solvents and water should be per-
formed to achieve pure products. Therefore, we tried design-
ing a new procedure based on two immiscible phases (water/
petroleum ether); water provides the suitable medium for
diazonium salt formation while petroleum ether dissolves the
fnal product. Monitoring the reaction is much easier. Con-
tact angle measurements showed that petroleum ether has
the ability to wet our synthesized catalyst (less than water
but still considerably), this means that during the course of
reaction, products are constantly washed from the surface;
making active sites available for the unreacted species.
Dyes synthesized using the double solvent catalytic
method were washed and purifed and used for characteri-
zation. Melting points, and elemental analysis data for com-
pounds 2a–d are summarized in Table 2.
The structures 2a–d were assigned based on their elemen-
tal analysis, FTIR, 1H and 13C NMR spectral data (see Sup-
porting Information). The IR spectra of compounds 2a–d
showed a broad absorption for O–H (3198–3214 cm−1)
and did not change upon dilution with CCl4. The IR spec-
tra also displayed carbonyl absorption of aldehyde group
at (1653–1662 cm−1); these absorption values are less than
expected for C=O groups. The above mentioned phenom-
ena are an evidence for intramolecular hydrogen bonding
between C=O and O–H groups in the molecules.
Table 2 The structure, melting
Elemental Analysis
points and elemental analysis
(Found)
H
Code
Structure
M.p. (˚C)
130
of 2a–d
C
N
69.02
4.46
(4.31)
12.38
(12.51)
2a
(69.22)
59.90
3.48
10.57
2b
2c
2d
215
219
128
(59.84)
(3.58)
(10.71)
51.17
(51.25)
2.97
(3.04)
9.18
(9.24)
70.85
(70.79)
5.55
(5.69)
11.02
(11.13)
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Chemical Papers
Fig. 1 UV–Vis spectra of 2a–d (5×10−5 M in DMSO, 1 cm standard quartz cell), λmax
, and their visual appearances
ꢀ
Fig. 2 a Adsorption/desorption
isotherms of N2 for Zn/SBA-15
and b BJH-plot of pore radius
distribution
1
The H NMR and 13C NMR spectral data for com-
pounds 2a–d (see Supporting Information) confrm their
proposed structures. For example a broad single peak at
(11.495–11.539 ppm) for hydroxyl groups which further
confrms the intramolecular hydrogen bonding as discussed
above; this tends to distance the proton from oxygen in the
hydroxyl group and the proton becomes less available for
the solvent.
BJH-plot (Fig. 2b) shows the pore radius distribution in the
meso-range. It is apparent that the use of zinc chloride rather
than nitrate (Zhong et al. 2015) led to higher surface area
5 × 10−5 M solutions of 2a–d in DMSO were prepared
and UV–Vis spectra were recorded in 200–600 nm range.
UV–Vis spectra and related information (λmax values and
absorption coefcients) along with visible appearances of
the synthesized dyes are presented in Fig. 1.
Specifc data for the characterization of the catalyst can be
helpful in understanding its efectiveness. N2-physisorption
isotherm is presented in Fig. 2a. Application of BET
model gave the surface area of 832.13 m2 g−1, pore volume
of 0.55 cm3 g−1 and the mean pore diameter of 2.64 nm.
Fig. 3 Low-angle XRD pattern for Zn/SBA-15
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Fig. 4 Field-emission scanning electron micrographs at diferent magnifcations and EDX spectrum of Zn/SBA-15
and smaller pore size and this is the point for the efective-
ness of the new catalyst.
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