Synthesis, characterization and application of nitrogen–sulfur-doped carbon spheres as an efficient catalyst for the preparation of novel α-aminophosphonates

Article abstract of DOI:10.1007/s13738-017-1135-8

Abstract: Nitrogen–sulfur-doped carbon spheres (NS-CSs) were prepared from sucrose and thiourea through a simple hydrothermal process. NS-CSs were characterized by TEM, FTIR, TGA, XRD, Raman spectroscopy and elemental analyses. The results revealed that the synthesized carbon spheres have an amorphous structure with diameters of 300–500?nm. The microspherical carbon catalyst that is recyclable has been used in the synthesis of α-aminophosphonates derived from 2-aminobenzothiazoles. Three-component reaction was performed between 2-aminobenzothiazoles, aromatic aldehydes and trimethyl phosphite in the presence of NS-CSs as microorganocatalyst at 50?°C under solvent-free conditions in high yield.

Full text of DOI:10.1007/s13738-017-1135-8

J IRAN CHEM SOC
DOI 10.1007/s13738-017-1135-8
ORIGINAL PAPER
Synthesis, characterization and application of nitrogen–
sulfur‑doped carbon spheres as an effcient catalyst for the
preparation of novel α‑aminophosphonates
Mina Taheri‑Torbati1 · Hossein Eshghi1 · Seyyed Amin Rounaghi2 · Ali Shiri1 ·
Mahdi Mirzaei1
Received: 30 April 2017 / Accepted: 3 May 2017
© Iranian Chemical Society 2017
Abstract Nitrogen–sulfur-doped carbon spheres (NS-
CSs) were prepared from sucrose and thiourea through a
simple hydrothermal process. NS-CSs were characterized
by TEM, FTIR, TGA, XRD, Raman spectroscopy and
elemental analyses. The results revealed that the synthe-
sized carbon spheres have an amorphous structure with
diameters of 300–500 nm. The microspherical carbon
catalyst that is recyclable has been used in the synthe-
sis of α-aminophosphonates derived from 2-aminoben-
zothiazoles. Three-component reaction was performed
between 2-aminobenzothiazoles, aromatic aldehydes
and trimethyl phosphite in the presence of NS-CSs as
microorganocatalyst at 50 °C under solvent-free condi-
tions in high yield.
Keywords Heterogeneous carbon · Hydrothermal
synthesis catalyst · α-Aminophosphonates · Kabachnik–
Fields reaction · Carbon microspheres
Introduction
During the past years, carbon materials with various shapes
such as fbers, onion, sphere, horns and fasks, have been
synthesized and implemented in different catalytical appli-
cations. Among them, carbon spheres are an important
class, due to the high level of thermal stability, unique
electronic properties and low density. Carbon spheres are
used in lithium-ion batteries, as well as catalytic coatings,
Graphical Abstract
* Hossein Eshghi
heshghi@um.ac.ir
1
Department of Chemistry, Faculty of Science, Ferdowsi
University of Mashhad, 91775-1436 Mashhad, Iran
2
Department of Materials Engineering, Birjand University
of Technology, 9719866981-236 Birjand, Iran
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J IRAN CHEM SOC
injectable scaffolds for tissue regeneration, drug delivery,
water purifcation, protecting the enzymes and proteins
and magnetic data storage applications [1]. One of the
main applications for carbon spheres is known to be as a
catalyst in Heck, Suzuki and Sonogashira coupling reac-
tions [2]. α-Aminophosphonates as structural analogs of
α-amino acid esters are of interest for potential anticancer
drugs [3, 4], enzymes inhibitors [5], haptens of catalytic
antibodies [6, 7], pharmacologic agents [8], antifungals
[9], insecticides [10], plant growth regulators [11], anti-
HIV agents [12] and interesting carriers for the transport of
hydrophilic molecules across bilayer lipid membranes [13].
Several multi-step synthetic approaches for the synthesis of
α-aminophosphonates have been reported in the literature
including alkylation of nucleophilic Schiff bases, Hofmann
rearrangement of substituted phosphonoacetic esters and
conversion of 1-hydroxyphosphonates to the correspond-
ing α-aminophosphonates [14]. An alternative synthesis
of α-aminophosphonates involves nucleophilic addition of
phosphite to imine [15–20]. However, since many imines
are hygroscopic and are not suffciently stable for isola-
tion, this method has certain limitations. The most simple
and straightforward synthetic method for the synthesis of
α-aminophosphonates is the Kabachnik–Fields reaction
which involves a one-pot three-component coupling of an
aldehyde, amine and phosphite ester [21]. In this regard,
numerous protocols for the synthesis of these compounds
have been developed using various catalysts such as molec-
ular iodine [22], xanthan sulfuric acid [23], DTP/SiO2 [24],
succinic acid [25], phenylphosphonic acid [26], SnCl2 [27],
SiO2–AlCl3 [28], Mg(ClO4)2 [29], CeCl3·7H2O [30], TiO2
[31], NaHSO4–SiO2 [32], nano-Fe3O4 [33], γ-Fe2O3@
SiO2-PA [34], DHAA–Fe3O4 [35], IRMOF-3 nano [36],
Fe/SWCNTs [37], ZrOCl2·8H2O [38] and ethyl ammo-
nium nitrate [39]. Herein, nitrogen–sulfur co-doped carbon
spheres (NS-CSs) were synthesized by a simple hydrother-
mal process [40] and the catalytical activity of the new het-
erogeneous and recyclable micro carbon sphere was inves-
tigated for the one-pot synthesis of α-aminophosphonates
directly from aldehydes, 2-aminobenzothiazoles and trime-
thyl phosphites.
microscope Leo 912 AB120 kV Zeiss, Germany. The
FTIR spectra were recorded on an Avatar 370 FTIR Ther-
mal Nicolet spectrometer. X-ray diffraction (XRD) meas-
urements were performed using a Philips X’Pert X-ray
diffractometer with Cu Kα radiation (λ = 0.154056 nm).
1
The H NMR spectra were recorded on a Bruker DRX
300 spectrometer. Thermogravimetric analysis (TGA)
was performed using a Shimadzu thermogravimetric ana-
lyzer (TG-50). The Raman spectrum was recorded at the
ambient temperature using a Renishaw RM2000 Raman
microspectrometer with an argon ion laser at an excita-
tion wavelength of 514.5 nm.
Hydrothermal synthesis of the nitrogen
and sulfur‑doped carbon
In a typical experiment, sucrose (2.7 g, 7.9 mmol) and thi-
ourea (0.6 g, 7.9 mmol) were dissolved in distilled water
(200 ml) and the solution was stirred for 30 min. After-
ward, the solution was transferred into a Tefon-lined stain-
less steel autoclave and heated at 190 °C for 20 h. The
synthesized material, then, was fltered and washed sev-
eral times with excess amount of distilled water to remove
impurities. The obtained black powder was dried in oven at
80 °C overnight.
General procedure for preparation
of α‑aminophosphonates
(CN-CSs) (3 mg) was added to a mixture of aldehydes
(1 mmol), 2-aminobenzothiazoles (1 mmol) and trimethyl
phosphite (1 mmol, 0.12 gr), and the mixture was stirred
at 50 °C. After completion of the reaction as monitored by
TLC, the mixture was washed With CH2Cl2 (3 × 3 mL).
The combined extracts were fltered, and the solvent was
removed under reduced pressure. The product was purifed
by column chromatography by using hexane-ethyl acetate
as solvent system in different concentration to obtain the
pure compound.
Spectral data phosphonate compounds
Dimethyl ((benzo[d]thiazol‑2‑ylamino) (phenyl)methyl)
phosphonate (4a)
Experimental
White powder; yield 90%; mp 166–167 °C; IR (KBr,
cm−1): ν 3223, 3031, 2952, 2850, 1596, 1567, 1530, 1237,
1217, 1056, 1033; 1H NMR (CDCl3, 300 MHz): δH 3.57 (d,
Chemicals and instruments
3
3
All reagents were purchased from Merck and Aldrich
and used without further purifcation. The melting point
of the products was determined with an electrothermal
type 9100 melting point apparatus. Transmission elec-
tron microscope (TEM) images were acquired on a TEM
3H, JHP = 10.5 Hz, OCH3), 3.85 (d, 3H, JHP = 10.8 Hz,
2
OCH3), 5.63 (d, 1H, JHP =21.9 Hz, CHP), 7.09 (td, 1H,
J = 7.5, 1.2 Hz), 7.30 (td, 1H, J = 8.4, 1.2 Hz), 7.34–7.43
(m, 3H), 7.56 (ddd, 2H, J = 8.1, 3.3, 0.6 Hz, CH–Ph),
7.61–7.64 (m, 2H); 13C NMR (CDCl3, 75 MHz): δC 165.6
1 3

J IRAN CHEM SOC
3
(d, JCP = 12 Hz, N=C–NH), 151.9, 134.8, 131.2, 128.7
1251, 1030; 1H NMR (CDCl3, 300 MHz): δH 3.58 (d,
3
3
3
(d, JCP = 2.25 Hz), 128.4 (d, JCP = 2.25 Hz), 128.1
3H, JHP = 10.5 Hz, OCH3), 3.80 (s, 3H, CH3), 3.84 (d,
2
3
2
(d, JCP = 6 Hz), 125.8, 121.9, 120.7, 119.4, 55.33 (d,
3H, JHP = 10.8 Hz, OCH3), 5.54 (d, 1H, JHP = 21.6 Hz,
CHP), 6.92 (d, 2H, J = 8.7 Hz, CH–Ph), 7.03 (b, NH), 7.08
(td, 1H, J = 7.5 Hz), 7.29 (td, 1H, J = 8.4 Hz), 7.53–7.58
(m, 4H); MS (m/z): 379 (M+).
1JCP = 153 Hz, CHP), 54.1 (d, 2JCP = 6.7 Hz, OCH3), 53.9
(d, 2JCP = 6.7 Hz, OCH3); 31P NMR (CDCl3, 121 MHz): δp
23.28; MS (m/z): 348 (M+).
Dimethyl ((benzo[d]thiazol‑2‑ylamino) (4‑(diethylamino)
Dimethyl ((benzo[d]thiazol‑2‑ylamino) (2‑methoxyphenyl)
phenyl)methyl)phosphonate (4b)
methyl) phosphonate (4f)
Brownish yellow solide; yield 92%; mp 160–161 °C; IR
White powder; yield 80%; mp 169–170 °C; IR (KBr,
cm−1): ν 3229, 3045, 2952, 1600, 1570, 1535, 1443,1241,
1232, 1055, 1023; 1H NMR (CDCl3, 300 MHz): δH
(KBr, cm−1): ν 3233, 3027, 2974, 1949, 1532, 1443, 1236,
1
1203, 1056, 1036; H NMR (CDCl3, 300 MHz): δH 1.16
3
(t, 6H, J = 7.2 Hz, CH2CH3), 3.35 (q, 4H, J = 6.9 Hz,
3.55 (d, 3H, JHP = 10.8 Hz, OCH3), 3.85 (d, 3H,
3
CH2), 3.58 (d, 3H, JHP = 10.5 Hz, OCH3), 3.82 (d, 3H,
3JHP = 10.8 Hz, OCH3), 3.99 (s, 3H, CH3), 5.95 (d, 1H,
2JHPJHP = 21.5 Hz, CHP), 6.98 (t, 2H, J = 8.1 Hz), 7.08
(t, 1H, J = 7.5 Hz), 7.26–7.34 (m, 2H), 7.30 (b, NH),
7.55–7.58 (m, 3H); 13C NMR (CDCl3, 75 MHz): δC 165.4
2
3JHP = 10.6 Hz, OCH3), 5.38 (d, 1H, JHP = 21.3 Hz,
CHP), 6.66 (d, 2H, J = 8.7 Hz, CH–Ph), 7.09 (t, 1H,
J = 7.5 Hz), 7.29 (t, 1H, J = 8.1 Hz), 7.30 (b, NH), 7.41 (d,
2H, J = 7.5 Hz, CH–Ph), 7.55 (d, 1H, J = 6.9 Hz), 7.57 (d,
1H, J = 7.2 Hz); 31P NMR (CDCl3, 121 MHz): δp 23.83;
MS (m/z): 420 (M+).
3
(d, JCP = 12 Hz, N=C–NH), 151.8, 134.4, 134.3, 133.6,
131.1, 129.5, 128.9, 125.9, 122.1, 120.8, 119.5, 54.5 (d,
1JCP = 153.7 Hz, CHP), 54.2, 54.1, 30.9; MS (m/z): 379
(M+).
Dimethyl ((benzo[d]thiazol‑2‑ylamino)(4‑(dimethylamino)
phenyl)methyl)phosphonat (4c)
Dimethyl ((benzo[d]thiazol‑2‑ylamino) (4‑isopropylphenyl)
methyl) phosphonate (4g)
White powder; yield 90%; mp 168–169 °C; IR (KBr,
cm−1): ν 3228, 3032, 2951, 2847, 1569, 1534, 1443, 1242,
1235, 1053, 1029; 1H NMR (CDCl3, 300 MHz): δH 2.95 (s,
White powder; yield 89%; mp 168–169 °C; IR (KBr,
cm−1): ν 3229, 3032, 2956, 1598, 1567, 1534, 1443,
3
6H, NCH3), 3.57 (d, 3H, JHP = 10.5 Hz, OCH3), 3.83 (d,
1
3
2
1240, 1233, 1057, 1031; H NMR (CDCl3, 300 MHz):
3H, JHP = 10.8 Hz, OCH3), 5.49 (d, 1H, JHP =21.6 Hz,
CHP), 6.72 (d, 2H, J = 8.7 Hz, CH–Ph), 7.08 (t, 1H,
J = 7.5 Hz), 7.28 (t, 2H, J = 8.4 Hz), 7.30 (b, NH), 7.47
(dd, 2H, J = 8.7, 1.8 Hz, CH–Ph), 7.54 (d, 1H, J = 7.5 Hz),
7.57 (d, 1H, J = 7.8 Hz); MS (m/z): 392 (M+).
δH 1.24 (d, 6H, J = 6.9 Hz, CHCH3), 2.91 (m, 1H,
3
CHCH3), 3.57 (d, 3H, JHP = 10.8 Hz, OCH3), 3.84 (d,
3H, 3JHP = 10.5 Hz, OCH3), 5.62 (d, 1H, 2JHP = 21.6 Hz,
CHP), 7.09 (td, 1H, J = 7.5, 1.0 Hz), 7.23–7.32 (m, 3H),
7.30 (b, NH), 7.52–7.58 (m, 4H); 13C NMR (CDCl3,
3
75 MHz): δC 165.7 (d, JCP = 12 Hz, N=C–NH), 152.0,
Dimethyl ((benzo[d]thiazol‑2‑ylamino) (p‑tolyl)methyl)
Phosphonate (4d)
149.6, 132.3, 132.1, 131.2, 128.1, 126.9, 126.8, 125.7,
1
121.8, 120.7, 119.3, 55.0 (d, JCP = 155 Hz, CHP), 54.0,
53.9, 33.8, 23.9; 31P NMR (CDCl3, 121 MHz): δp 23.47;
MS (m/z): 391 (M+).
White powder; yield 91%; mp 173–174 °C; IR (KBr,
cm−1): ν 3228, 3031, 2952, 1597, 1567, 1534, 1240, 1031;
1H NMR (CDCl3, 300 MHz): δH 2.35 (s, 3H, CH3), 3.58 (d,
3
3
3H, JHP = 10.5 Hz, OCH3), 3.85 (d, 3H, JHP = 10.8 Hz,
2
Dimethyl ((benzo[d]thiazol‑2‑ylamino) (4‑chlorophenyl)
methyl) phosphonate (4h)
OCH3), 5.63 (d, 1H, JHP = 21.6 Hz, CHP), 7.08 (td, 1H,
J = 7.5, 1.2 Hz), 7.19 (d, 2H, J = 7.8 Hz, CH–Ph), 7.29
(td, 2H, J = 8.4, 1.2 Hz), 7.30 (b, NH), 7.52–7.58 (m, 4H);
MS (m/z): 363 (M+).
White powder; yield 84%; mp 164–165 °C; IR (KBr,
cm−1): ν 3236, 3056, 2645, 1598, 1538, 1444, 1236,
1044, 1017; 1H NMR (CDCl3, 300 MHz): δH 3.63 (d,
Dimethyl ((benzo[d]thiazol‑2‑ylamino) (4‑methoxyphenyl)
methyl) phosphonate (4e) [29]
3
3
3H, JHP = 10.5 Hz, OCH3), 3.86 (d, 3H, JHP = 10.8 Hz,
2
OCH3), 5.65 (d, 1H, JHP = 21.9 Hz, CHP), 7.11 (t, 1H,
J = 7.5 Hz), 7.27–7.37 (m, 3H), 7.55–7.57 (m, 4H); MS
(m/z): 383 (M+).
White powder; yield 85%; mp 170–171 °C; IR (KBr,
cm−1): ν 3228, 3032, 2952, 1597, 1534, 1443, 1234,
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J IRAN CHEM SOC
Dimethyl ((benzo[d]thiazol‑2‑ylamino) (2‑chlorophenyl)
Dimethyl ((4‑(diethylamino) phenyl) ((6‑ethoxybenzo[d]
methyl) phosphonate (4i)
thiazol‑2‑yl)amino)methyl) phosphonate (4l)
White powder; yield 80%; mp 169–170 °C; IR (KBr,
Red powder; yield 90%; mp 161–162 °C; IR (KBr, cm−1):
cm−1): ν 3218, 3047, 2951, 1596, 1578, 1535, 1442, 1252,
ν 3237, 3031, 2969, 1544, 1522, 1462, 1235, 1206, 1059,
1
1
1238, 1075, 1041, 1014; H NMR (CDCl3, 300 MHz):
1026; H NMR (CDCl3, 300): δH 1.15 (t, 6H, J = 7.1 Hz,
3
δH 3.55 (d, 3H, JHP = 10.5 Hz, OCH3), 3.91 (d, 3H,
NCH2CH3), 1.42 (t, 3H, J = 6.9 Hz, OCH2CH3), 3.35
2
3
3JHP = 10.9 Hz, OCH3), 6.07 (d, 1H, JHP = 21 Hz,
(q, 4H, J = 6.9 Hz, NCH2), 3.57 (d, 3H, JHP = 10.5 Hz,
3
CHP), 7.1 (td, 1H, J = 7.5, 1.2 Hz), 7.27–7.32 (m, 3H,
CH–Ph), 7.45–7.48 (m, 1H), 7.55–7.59 (m, 2H), 7.73–
7.76 (m, 1H); 13C NMR (CDCl3, 75 MHz): δC 165.5 (d,
3JCP = 12.7 Hz, N=C–NH), 152.0, 134.1, 133.2, 131.2,
129.7, 129.5, 127.3, 125.8, 121.9, 120.8, 119.7, 54.1 (2d,
OCH3), 3.82 (d, 3H, JHP = 10.5 Hz, OCH3), 4.02 (q, 2H,
2
J = 6.9 Hz, OCH2), 5.37 (d, 1H, JHP = 21.3 Hz, CHP),
6.65 (d, 2H, J = 8.7 Hz, CH–Ph), 6.88 (dd, 1H, J = 9,
2.4 Hz), 7.08 (d, 1H, J = 2.4 Hz), 7.40 (dd, 2H, J = 8.7,
1.8 Hz, CH–Ph), 7.45 (d, 1H, J = 9 Hz); 13C NMR (CDCl3,
1
3
2JCP = 7.5 Hz, OCH3), 52.1 (d, JCP = 154.5 Hz, CHP);
75 MHz): δC 164.2 (d, JCP = 12.7 Hz, N=C–NH), 154.5,
31P NMR (CDCl3, 121 MHz): δp 22.61; MS (m/z): 383
(M+).
147.8, 146.2, 132.0, 129.2, 120.6, 119.6, 114.0, 111.6,
1
106.0, 64.2, 55.0 (d, JCP = 157.0 Hz, CHP), 54.0 (d,
2
2JCP = 6.7 Hz, OCH3), 53.8 (d, JCP = 7.5 Hz, OCH3),
Dimethyl ((4‑(diethylamino) phenyl)((6‑methylbenzo[d]
thiazol‑2‑yl)amino)methyl) phosphonate (4j)
44.3, 149, 12.5; 31P NMR (CDCl3, 121 MHz): δp 24.01;
MS (m/z): 394 (M+).
Yellow powder; yield 95%; mp 167–168 °C; IR (KBr,
Dimethyl (((6‑ethoxybenzo[d]thiazol‑2‑yl) amino) (p‑tolyl)
methyl)phosphonate (4m)
cm−1): ν 3231, 3022, 2968, 1571, 1535, 1464, 1237,
1
1197, 1061, 1030; H NMR (CDCl3, 300 MHz): δH 1.15
(t, 6H, J = 7.1 Hz, CH2CH3), 2.39 (s, 3H, CH3) 3.34 (q,
White powder; yield 90%; mp 163–164 °C; IR (KBr,
3
4H, J = 6.9 Hz, CH2CH3), 3.58 (d, 3H, JHP = 10.2 Hz,
cm−1): ν 3244, 3035, 2973, 1576, 1545, 1459, 1241,1210,
3
1
OCH3), 3.81 (d, 3H, JHP = 10.5 Hz, OCH3), 5.37 (d, 1H,
1114, 1059, 1025; H NMR (CDCl3, 300 MHz): δH 1.42
2JHP = 21.3 Hz, CHP), 6.66 (d, 2H, J = 8.7 Hz, CH–Ph),
7.10 (dd, 1H, J = 8.3 Hz), 7.36 (s, 1H), 7.40 (dd, 2H,
J = 8.7, 1.8 Hz, CH–Ph), 7.46 (d, 1H, J = 8.4 Hz); 13C
NMR (CDCl3, 75 MHz): δC 165.2 (d, 3JCP = 12 Hz, N=C–
NH), 149.9, 147.8, 131.5, 131.2, 129.2, 126.9, 120.8,
(t, 3H, J = 6.9 Hz, OCH2CH3), 2.34 (s, 3H, CH3), 3.57 (d,
3
3
3H, JHP = 10.5 Hz, OCH3), 3.84 (d, 3H, JHP = 10.5 Hz,
OCH3), 4.02 (q, 2H, J = 6.9 Hz, OCH2), 5.55 (d, 1H, 2JHP
=21.9 Hz, CHP), 6.87 (dd, 1H, J = 9, 2.4 Hz), 7.07 (d,
1H, J = 2.4 Hz), 7.18 (d, 2H, J = 7.9 Hz, CH–Ph), 7.44
(d, 1H, J = 9 Hz), 7.51 (dd, 2H, J = 8.1, 1.8 Hz, CH–Ph);
1
120.5, 118.9, 111.6, 55.1 (d, JCP = 150 Hz, CHP), 53.9
2
2
3
(d, JCP = 7.5 Hz, OMe), 53.8 (d, JCP = 6.8 Hz, OMe),
44.3, 21.2, 12.6; 31P NMR (CDCl3, 121 MHz): δp 23.89;
MS (m/z): 434 (M+).
13C NMR (CDCl3, 75 MHz): δC 164.0 (d, JCP = 12.7 Hz,
N=C–NH), 154.6, 146.1, 138.1, 132.1, 131.9, 129.4, 128.1,
119.7, 114.0, 106.0, 64.2, 55.1 (d, 1JCP = 151.0 Hz, CHP),
2
2
54.0 (d, JCP = 4.5 Hz, OCH3), 53.9 (d, JCP = 5.2 Hz,
OCH3), 21.2, 14.9; 31P NMR (CDCl3, 121 MHz): δp 23.61;
MS (m/z): 407 (M+); CHN (%): C:56.23, H:5.66, N:6.88,
S:7.84.
Dimethyl (((6‑ethoxybenzo[d]thiazol‑2‑yl) amino) (phenyl)
methyl) Phosphonate (4k)
White powder; yield 90%, mp 170–171 °C; IR (KBr,
cm−1): ν 3225, 3032, 2957, 2851, 1594, 1563, 1529, 1237,
1210, 1056, 1030; 1H NMR (CDCl3, 300 MHz): δH 1.42 (t,
Dimethyl (((6‑ethoxybenzo[d]thiazol‑2‑yl) amino)
(4‑methoxyphenyl)methyl)phosphonate (4n)
3
3H, J = 6.9 Hz, OCH2CH3), 3.55 (d, 3H, JHP = 10.8 Hz,
3
OCH3), 3.84 (d, 3H, JHP = 10.8 Hz, OCH3), 4.02 (q, 2H,
White powder; yield 87%; mp 164–165 °C; IR (KBr,
2
J = 6.9 Hz, OCH2CH3), 5.57 (d, 1H, JHP = 22.2 Hz,
cm−1): ν 3235, 3031, 2953, 1542, 1458, 1237, 1213,
1
CHP), 6.81 (b, NH), 6.88 (dd, 1H, J = 9, 2.4 Hz), 7.08
(d, 1H, J = 2.4 Hz), 7.33–7.46 (m, 4H), 7.60 (dd, 2H,
J = 7.5, 1.4 Hz, CH–ph); 13C NMR (CDCl3, 75 MHz): δC
163.8 (d, 3JCP = 12 Hz, CNH), 154.7, 146.1, 134.9, 132.0,
128.7, 128.3, 128.1, 119.8, 114.11, 106.0, 64.2, 55.3 (d,
1058, 1029; H NMR (CDCl3, 300 MHz): δH 1.42 (t, 3H,
3
J = 6.9 Hz, OCH2CH3), 3.58 (d, 3H, JHP = 10.5 Hz,
3
OCH3), 3.80 (s, 3H, CH3), 3.84 (d, 3H, JHP = 10.8 Hz,
OCH3), 4.02 (q, 2H, J = 6.9 Hz, OCH2), 5.51 (d, 1H,
2JHP = 21.0 Hz, CHP), 6.90 (b, NH), 6.88 (dd, 1H,
J = 8.7, 2.4 Hz), 6.91 (d, 2H, J = 8.4 Hz, CH–Ph), 7.08
(d, 1H, J = 2.4 Hz), 7.44 (d, 1H, J = 8.7 Hz), 7.54 (dd, 2H,
J = 8.6, 1.8 Hz, CH–Ph); 13C NMR (CDCl3, 75 MHz): δC
2
1JCP = 153 Hz, CHP), 54.2 (d, JCP = 6.5 Hz), 53.9 (d,
2JCP = 6 Hz), 14.9; 31P NMR (CDCl3, 121 MHz): δp 23.43;
MS (m/z): 393 (M+).
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J IRAN CHEM SOC
3
3
163.9 (d, JCP = 12.7 Hz, N=C–NH), 159.6, 154.5, 146.1,
(d, JCP = 13.5 Hz), 154.7, 146.1134.1, 133.3, 132.1,
132.0, 129.4, 126.9, 119.7, 114.1, 114.0, 106.0, 64.2, 55.3,
129.7, 129.5, 129.1, 127.3, 120.0, 114.3, 105.9, 64.2, 54.1
1
2
2
54.7 (d, JCP = 154.5 Hz), 54.0, 53.8, 14.9; 31P NMR
(d, JCP = 3.0 Hz, OCH3), 54.0 (d, JCP = 3.7 Hz, OCH3),
52.2 (d, 1JCP = 154.5), 14.9; 31P NMR (CDCl3, 121 MHz):
δp 22.67; MS (m/z): 427 (M+).
(CDCl3, 121 MHz): δp 23.61; MS (m/z): 423 (M+).
Dimethyl (((6‑ethoxybenzo[d]thiazol‑2‑yl) amino)
(4‑isopropylphenyl)methyl) Phosphonate (4o)
Result and discussion
White powder; yield 89%; mp 162–163 °C; IR (KBr,
cm−1): ν 3230, 3031, 2956, 1574, 1542, 1460, 1241, 1221,
Hydrothermal synthesis of carbon spheres
1
1058, 1029; H NMR (CDCl3, 300 MHz): δH 1.24 (d, 6H,
J = 6.9 Hz, CHCH3), 1.42 (t, 3H, J = 6.9 Hz, OCH2CH3),
As shown in Scheme 1, an equimolar mixture of sucrose
and thiourea was dissolved in water. The solution, then,
was transferred to an autoclave and kept at 190 °C for 20 h.
The synthesized material was washed, fltered and dried to
get a black powder.
The synthesized nitrogen–sulfur-doped carbon spheres
(NS-CSs) were characterized by FTIR, X-ray diffrac-
tion (XRD), Raman spectroscopy, transmission electron
microscopy (TEM), thermogravimetric analysis (TGA)
and elemental analysis (CHN).
2.89 (q, 1H, J = 6.9 Hz, CH), 3.56 (d, 3H, 3JHP = 10.8 Hz,
3
OCH3), 3.84 (d, 3H, JHP = 10.8 Hz, OCH3), 4.02 (q, 2H,
2
J = 6.9 Hz, OCH2), 5.55 (d, 1H, JHP = 21.9 Hz, CHP),
6.88 (dd, 1H, J = 8.7, 2.4 Hz). 7.09 (d, 1H, J = 2.4 Hz),
7.24 (d, 2H, J = 8.1 Hz, CH–Ph), 7.45 (d, 1H, J = 8.7 Hz),
7.52 (dd, 2H, J = 8.1, 1.6 Hz, CH–Ph); 13C NMR (CDCl3,
3
75 MHz): δC 164.0 (d, JCP = 12 Hz, CNH), 154.5, 149.0,
146.1, 132.2, 132.0, 128.1, 126.8, 119.7, 114.0, 106.0, 64.2,
1
55.0 (d, JCP = 153.8 Hz), 54.0, 53.8, 33.9, 23.9, 14.9; 31P
NMR (CDCl3, 121 MHz): δp 23.62; MS (m/z): 435 (M+).
Dimethyl ((4‑chlorophenyl) ((6‑ethoxybenzo[d]
Catalyst characterization
thiazol‑2‑yl) amino)methyl)Phosphonate (4p)
X‑ray diffraction (XRD)
White powder; yield 83%; mp 160–161 °C; IR (KBr,
cm−1): ν 3240, 3035, 2973, 1542, 1460, 1230, 1217, 1113,
Figure 1 illustrates the XRD pattern of the synthesized cat-
alyst with a broad peak positioned at 2θ range of 20°–30°
indexed to the (002) plane of carbon in a graphitic carbon
structure. The observed peak broadening, however, indicates
that the structure possesses low crystallinity and is mainly
amorphous. The nanocrystalline structure of carbon is a
result of Scherrer equation which gives a value of 1.1 nm
for the in-plane crystallite size of carbon domains. This is
in agreement with other reports indicating to the amorphous
nature of carbonaceous phase prepared by the thermal
polymerization of glucose and its derivatives [41, 42].
1
1058, 1032; H NMR (CDCl3, 300 MHz): δH 1.42 (t, 3H,
3
J = 7.1 Hz, OCH2CH3), 3.61 (d, 3H, JHP = 10.8 Hz,
3
OCH3), 3.84 (d, 3H, JHP = 10.8 Hz, OCH3), 4.05 (q, 2H,
J = 6.9 Hz, OCH2), 5.55 (d, 1H, 2JHP = 22 Hz, CHP), 6.89
(dd, 1H, J = 9, 2.4 Hz), 7.09 (d, 1H, J = 2.4 Hz), 7.36 (d,
2H, J = 8.2 Hz, CH–Ph), 7.44 (d, 1H, J = 9 Hz), 7.54 (dd,
2H, J = 8.3, 1.8 Hz, CH–Ph); 13C NMR (CDCl3, 75 MHz):
3
δC 158.8 (d, JCP = 12 Hz, CNH), 150.1, 141.1, 129.6,
128.8, 127.2, 124.7, 124.1, 115.11, 109.5, 101.2, 59.4, 49.7
(d, 1JCP = 153.7 Hz, CHP), 49.4 (d, 2JCP = 7.5 Hz, OCH3),
49.1 (d, 2JCP = 6.7 Hz, OCH3), 10.1; MS (m/z): 427 (M+).
Raman spectroscopy
Dimethyl ((2‑chlorophenyl) ((6‑ethoxybenzo[d]
In accordance with XRD analysis, the Raman spectrum
of the synthesized material (bold solid line) shows typi-
cal characteristic features of an amorphous carbon struc-
ture (Fig. 2) [43]. For an accurate analysis, the spectrum
was curve-ftted with 8 distinct gaussian components.
The peak at 1584 cm−1 (G band) is assigned to the E2g
mode of graphite and is generated by in-plane bond-
stretching motion of pairs of sp2 carbon atoms [44]. The
two peaks located at 1413 cm−1 (V1), 1470 cm−1 (V2) are
assigned to aromatic rings with attached alkyl functional
groups (sp2 and sp3 bonded carbon) typically found in
thiazol‑2‑yl)amino)methyl)phosphonate (4q)
White powder; yield 78%; mp 165–166 °C; IR (KBr,
cm−1): ν 3236, 2986, 2953, 1573, 1544, 1463,1268, 1240,
1
1226, 1060, 1033; H NMR (CDCl3, 300 MHz): δH 1.42
3
(t, 3H, J = 7.2 Hz, CH3), 3.53 (d, 3H, JHP = 10.5 Hz,
3
OCH3), 3.90 (d, 3H, JHP = 10.8 Hz, OCH3), 4.02 (q, 2H,
2
J = 6.9 Hz, OCH2), 5.92 (d, 1H, JHP = 22.9 Hz, CHP),
6.4 (b, NH), 6.89 (dd, 1H, J = 9, 2.4 Hz), 7.10 (d, 1H,
J = 2.4 Hz), 7.28–7.32 (m, 3H), 7.46 (d, 1H, J = 9 Hz),
7.64–7.68 (m, 1H); 13C NMR (CDCl3, 75 MHz): δC 163.8
1 3

J IRAN CHEM SOC
Scheme 1 Chemical procedure
for the synthesis of NS-CSs
Fig. 1 XRD pattern of the carbonaceous catalyst (the dashed line
refers to (002) plane of carbon in a graphitic carbon structure)
Fig. 2 Raman spectrum of the carbonaceous catalyst
amorphous carbon materials. The band at 1519 cm−1 (GL)
represents small sp2 clusters of 3–5 fused aromatic rings
[45–48]. The Raman peak labeled as D at 1352 cm−1 is
attributed to defects in a graphitic structure or any con-
jugated aromatic systems having more than 6 fused car-
bon rings. The D side band (S) located at 1278 cm−1
represents Caromatic–Calkyl and sp2‒sp3 bonded carbon on
para-aromatics [47, 48]. Two small peaks at 1718 and
1755 cm−1 (labeled RCO) are ascribed to carbonyl (C=O)
functional groups [47].
spectrum of thiourea exhibits high intense transmission
bonds in the range 3100–3400 cm−1 assigned to amine
groups stretching vibration, while the band located at
1617 cm−1 attributed to NH2 bending vibration. The
N–C–N stretching vibration located at 1414 cm−1. The
characteristic bonds at 1084 and 730 cm−1 assigned
to C=S stretching vibration [49] (Fig. 4a). The FTIR
spectrum of sucrose shows the characteristic band at
3400 cm−1 assigned to OH stretching vibration. The
bonds at 2970 cm−1 assigned to CH stretching vibration,
while the band located at 1461 cm−1 attributed to CH
bending vibration. The strong bond at 1068 cm−1 can be
ascribed to C–O stretching [50–52] (Fig. 4b).
Transmission electron microscopy (TEM)
The size and morphology of synthesized carbonaceous
material were investigated by TEM (Fig. 3). As seen,
TEM micrographs present that the synthesized product
consisted of individual or aggregated carbon micro-
spheres with particles size distribution of 0.2–4 μm.
In the FTIR spectrum of NS-CSs, a weak band
around 300–3400 cm−1 may be related to N–H or O–H
stretching vibrations. The strong absorption bands at
1696 cm−1 attributed to the stretching vibration of the
C=O bond. Moreover, the bands at 1608 and 1431 cm−1
represent the typical stretching vibration of C=N and
C–N, respectively. The characteristic bonds at 1023 and
792 cm−1 assigned to C–S stretching vibrations of NS-
CSs [52, 53] (Fig. 4c). The above results and it’s insolu-
bility in water suggest that the NS-CSs were synthesized
successfully.
FTIR spectroscopy
Further chemical bonding structure of the product
was conducted by FTIR analysis (Fig. 4). The FTIR
1 3

J IRAN CHEM SOC
Fig. 3 TEM images of a an
individual and b aggregated
carbon spheres
Elemental analysis (CHN)
The amount of doped S and N atoms in the structure of
NS-CSs was determined by CHNSO elemental analyzer,
and the results are listed in Table 1 for both the reactants
(sucrose and thiourea) and NS–. Obviously, a large amount
of hydrogen and oxygen in the reactants is removed in
the form of H2O during the hydrothermal processes. By
elimination of these elements, the total mass reduces and
consequently the weight percent of the remained elements
increases in the solid-phase product. A signifcant increase
in the carbon contents (experimental/calculation) is justi-
fed by the fact that the sucrose is polymerized to the func-
tionalized spherical carbons during the hydrothermal pro-
cess. The measured values of 4.28 and 2.86, respectively,
for the weight percent of N and S in the product indicate
that these elements have successfully incorporated in the
structure of carbonaceous spheres and agree well with the
Fig. 4 FTIR spectra of a thiourea b sucrose c NS-CSs
Table 1 Comparison of the
amount of elemental analysis
Element
Reactants
Product (NS-CSs)
substrate and NS-CSs
Thiourea (cal. wt%)
Sucrose (cal. wt%)
(Cal. wt%)
(Experimental wt%)
C
H
N
S
15.78
5.30
36.80
42.12
–
42.11
6.68
–
37.32
6.26
62.68
3.41
6.70
4.28
–
7.66
2.86
O
51.42
42.06
26.77
1 3

J IRAN CHEM SOC
corresponding FTIR analysis (Fig. 4c). The lower sulfur
content in the product in comparison with the reactants is
mainly due to the sulfur elimination in the form of sulfur
containing species such as H2S and SO2 during the hydro-
thermal process.
Evaluation of catalytic activity of NS‑CSs in the synthesis
of α‑aminophosphonates
The NS-CSs were employed as a new heterogeneous
and recyclable microcatalyst for the one-pot synthesis of
α-aminophosphonates directly from aldehydes, 2-amin-
obenzothiazole and trimethyl phosphite (Scheme 2).
Thermo gravimetric analysis (TGA)
In order to know more about the thermal stability of the
product, the oxidation of NS-CSs was investigated by
heating the powder up to 800 °C in air (Fig. 5). As seen,
the TGA and DTG curves demonstrate a slight weight
loss at temperatures below 270 °C mainly attributed to
the evaporation of free water. The abrupt weight loss at
temperatures between 270 and 490 °C is due to the oxi-
dation and degradation of NS-CSs. These results exhibit
a good thermal stability for the NS-CSs and indicate
that the synthesized catalyst can be feasibly employed in
many organic reactions conducted at temperatures below
270 °C.
The optimal conditions for the Kabachnik–Fields reaction
in the presence of a NS‑CSs catalyst
Firstly, the reaction of benzaldehyde, 2-aminobenzoy-
hiazole and trimethyl phosphite was chosen to optimize
the reaction conditions such as, solvents, temperature and
molar ratio of the catalyst (Table 2, entries 1–14). The
effect of different parameters such as amount of catalyst,
solvent, reaction time and temperature were investigated on
the fnal yield.
To evaluate the effect of solvent on the reaction yield,
5 mg of NS-CSs were used to catalyze the reaction in
various solvents and solvent-free conditions. As shown in
Table 3, the reaction under solvent-free conditions gives
signifcantly higher yields in shorter reaction times than
the solution-based experiments. In the next step, the effect
of temperature on the reaction progress in the presence of
5 mg NS-CSs and under solvent-free conditions was inves-
tigated (Table 2, entries 6–9). As a result, the highest yield
was achieved at 50 °C (Table 2, entry 8), while increas-
ing the temperature to 70 °C gives the same yield level of
50 °C.
The catalyst amount is another factor which signifcantly
effects on the reaction yield (Table 2, entries 10–14). In this
regard, no product was obtained in the absence of the cata-
lyst (Table 2, entry 1) indicating that the catalyst is neces-
sary for the reaction. The reaction yield rapidly increases
when the catalyst amount enhances and reaches the high-
est level (92%) at 3 mg (Table 2, entry 12). Since further
increase in catalyst content beyond this value did not
Fig. 5 TGA and DTG curves of NS-CSs
Scheme 2 Synthesis of α-aminophosphonate derivatives in presence of NS-CSs
1 3

J IRAN CHEM SOC
Table 2 One-pot
Entry
Catalyst
(mg)
Solvent
Time
Temp (°C)
Isolated yield (%)
reaction of benzaldehyde,
2-aminobenzothiazole and
trimethyl phosphite under
different conditions
1
–
–
10 h
40
40
40
40
40
40
r. t
50
70
50
50
50
50
50
Trace
10
15
20
30
80
30
92
92
30
45
92
92
92
2
(NS-CSs)
(NS-CSs)
(NS-CSs)
(NS-CSs)
(NS-CSs)
(NS-CSs)
(NS-CSs)
(NS-CSs)
(NS-CSs)
(NS-CSs)
(NS-CSs)
(NS-CSs)
(NS-CSs)
5
5
5
5
5
5
5
5
1
2
3
6
12
MeCN
EtOH
H2O
CH2Cl2
Neat
Neat
Neat
Neat
Neat
Neat
Neat
Neat
Neat
1 h
3
1 h
4
1 h
5
1 h
6
30 min
30 min
30 min
30 min
30 min
30 min
30 min
30 min
1 h
7
8
9
10
11
12
13
14
change the reaction yield (Table 2, entries 13 and 14), the
optimum amount of catalyst is evaluated to be 3 mg. More-
over, increasing the reaction time more than 30 min did not
improve the yield.
Recyclability of the NS‑CSs catalyst was investigated
for the synthesis of α‑aminophosphonates by the one
catalyst in the Kabachnik–Fields reaction
After optimization of the reaction conditions, the cata-
lytic activities of NS-CSs were tested by different alde-
hydes, 2-aminobenzothiazole derivations and trimethyl-
phosphite. The novel compounds (4a–q) were synthesized
by the reaction of aldehydes, 2-aminobenzothiazole deriva-
tions and trimethylphosphite using 3-mg NS-CSs at 50 °C
and under solvent-free conditions. The results are shown in
Table 3.
The recyclability and recovery of the catalyst was inves-
tigated for the synthesis of α-aminophosphonates by the
one-pot three-component condensation of 2-aminobenzo-
thiazole and 4-dimethylaminobenzaldhyde with trimethyl
phosphite as model substrates at 50 °C under solvent-free
conditions for 30 min. The catalyst can be re-weighted and
reused at least for 6 times with only a slight reduction in
activity (as shown in Fig. 6).
Conclusion
The proposed mechanism of the Kabachnik–Fields reaction
in the presence of a NS‑CSs catalyst
In summary, novel nitrogen–sulfur-doped carbon spheres
(NS-CSs) were prepared by a facile hydrothermal pro-
cess. The results revealed that the size of NS-CSs vary
from a few hundred nanometers to a few micrometers
and have amorphous structure. The heterogeneous car-
bon catalyst was successfully employed for the synthe-
sis of α-aminophosphonate derivatives. The highest yield
(92%) was achieved when the reaction was carried out
at 50 °C for 15 min in the presence of 3 mg of catalyst
A plausible reaction mechanism is shown in Scheme 3. The
mechanism involves the activation of the carbonyl group
of the aldehyde by microorganocatalyst followed by the
nucleophilic addition of the amine to afford the imine by
the removal of water. The activated imine further reacts
with the trimethyl phosphite leading to the formation of
corresponding α-aminophosphonates.
1 3

J IRAN CHEM SOC
Table 3 Synthesis derivatives of α-aminophosphonate in the presence of the catalyst NS-CSs
Entry
2-aminobenzothiazole
Benzaldehyde (R2)
Products
Time (min)
Mp (oC)
Yield (%)
1
H
30
166-167
90
4a
2
3
4
5
4-N(Et)2
4-N(Me)2
4-Me
20
30
35
37
160-161
168-169
173-174
170-171
92
90
91
85
4b
4c
4d
4e
4-OMe
6
7
8
2-OMe
4-CH(CH3)2
4-Cl
38
34
53
169-170
168-169
164-165
80
89
84
4f
4g
4h
9
2-Cl
45
20
169-170
167-168
80
95
4i
4j
10
4-N(Et)2
11
12
13
14
15
16
17
H
4-N(Et)2
4-Me
25
15
24
37
32
40
44
170-171
161-162
163-164
164-165
162-163
160-161
167-168
90
92
90
87
89
78
83
4k
4l
4m
4n
4o
4p
4q
4-OMe
4-CH(CH3)2
4-Cl
2-Cl
Isolated yield, conditions: aldehyde (1 mmol), 2-aminobenzothiazole (1 mmol), trimethyl phosphite (1 mmol), catalyst (3 mg), 50 °C, under
solvent-free conditions. All the products were characterized by spectroscopic methods
1 3

J IRAN CHEM SOC
Scheme 3 Proposed mechanism of the Kabachnik–Fields reaction in the presence of a NS-CSs catalyst
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Acknowledgements The authors gratefully acknowledge the partial
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