Nanocrystalline magnesium oxide as a solid base catalyst promoted one pot synthesis of gem-dichloroaziridine derivatives under thermal conditions

Article abstract of DOI:10.1007/s13738-012-0137-9

In this study, efficient and mild synthesis of gem-dichloroaziridines from Schiff bases in the presence of nanocrystalline magnesium oxide/chloroform as a novel source of dichlorocarbene intermediate under thermal conditions have been described. The react

Full text of DOI:10.1007/s13738-012-0137-9

J IRAN CHEM SOC (2013) 10:161–167
DOI 10.1007/s13738-012-0137-9
ORIGINAL PAPER
Nanocrystalline magnesium oxide as a solid base catalyst
promoted one pot synthesis of gem-dichloroaziridine derivatives
under thermal conditions
•
•
•
H. Naeimi Kh. Rabiei M. Rezaei
F. Meshkani
Received: 17 December 2011 / Accepted: 5 July 2012 / Published online: 26 July 2012
Ó Iranian Chemical Society 2012
Abstract In this study, efficient and mild synthesis of
gem-dichloroaziridines from Schiff bases in the presence of
nanocrystalline magnesium oxide/chloroform as a novel
source of dichlorocarbene intermediate under thermal
conditions have been described. The reaction is dramati-
cally enhanced in the presence of nanocrystalline magne-
sium oxide, and any byproducts were detected during or
after the reaction. The corresponding products have been
obtained in excellent yields, high purity and short reaction
times.
oxide such as magnesium oxide has many applications as
catalyst [1–3], refractory materials [4], optically transpar-
ent ceramic windows [5, 6], etc. In the field of catalyst,
MgO has strong basic properties, which are associated with
catalysts by base in many organic reactions [7]. Asym-
metric Henry and Michael reaction [8], synthesis of organic
carbonates [9], aldol condensation [10], as a base catalyst
for Claisen–Schmidt condensation reaction [11], an effi-
cient catalyst for the synthesis of formamides [12], etc.,
are some of well-studied reactions catalyzed by MgO
nanoparticles.
Keywords Aziridine ꢀ Nanocrystalline magnesium
oxide ꢀ Schiff base ꢀ Dichlorocarbene ꢀ Catalyst
Gem-dichloroaziridines are valuable precursors for the
preparation of pharmacologically active compounds such
as indolinones [13], analogs of natural alkaloids such as
isoquinolinones [14] and isoquinolines [15] and nitrogen-
containing building blocks such as amidines [16] and
aziridinones [17]. As a result, several methods for syn-
thesis of gem-dichloroaziridines have been reported. The
preparation has been accomplished by the addition of di-
chlorocarbene generated from chloroform, hexachloroac-
etone or ethyl trichloroacetate with the appropriate bases
to imines [18–26]. Among these, dichlorocarbene, which
is generated from chloroform under phase transfer cata-
lyzed conditions, is most frequently used for the synthesis
of gem-dichloroaziridines because the yields are accept-
able. Also effective reaction between sodium hydroxide
and chloroform to produce dichlorocarbene normally
requires the use of phase transfer catalyst. Recently,
Komatsu and co-workers [27] have been reported novel
synthesis of gem-dichloroaziridines from imines via the
KF/Al2O3 generation of dichlorocarbene from chloroform.
Thus, herein we wish to report on the use of nanocrys-
tallines MgO as an efficient base for preparation of gem-
dichloroaziridine (2) from imine (1) and chloroform under
thermal conditions.
Introduction
Nanocrystalline oxides are of immense interest to scientist
due to their enriched surface chemistry and high surface
area. Ultrafine nanocrystallines of alkaline earth metal
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-012-0137-9) contains supplementary
material, which is available to authorized users.
H. Naeimi (&) ꢀ Kh. Rabiei
Department of Organic Chemistry, Faculty of Chemistry,
University of Kashan, Kashan 87317, Islamic Republic of Iran
e-mail: naeimi@kashanu.ac.ir
M. Rezaei ꢀ F. Meshkani
Catalyst and Advanced Materials Research Laboratory,
Department of Chemical Engineering, Faculty of Engineering,
University of Kashan, Kashan 87317, Islamic Republic of Iran
123

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J IRAN CHEM SOC (2013) 10:161–167
Experimental
Chemicals and apparatus
chlorophenyl] amine (0.01 mol, 3.3 g) were poured into
mortar and mix thoroughly together. The reaction mixture
was introduced to a 50 mL flask and mechanically stirred.
Then, 8 mL chloroform was added and uniformly was
heated at 60 °C. The progress of the reaction was monitored
by TLC. After the completion of the reaction, reaction
mixture was washed with dichloromethane (3 9 10 mL).
The organic solvent was stripped in a vacuum evaporator.
The white solid, 1,3-bis(4-chlorophenyl)-2,2-dichloroaziri-
dine, was obtained in 98 % yield, m.p. 139–141 °C. All of
the diarylaziridine products were identified by physical and
spectroscopic data as following:
All the materials were of commercial reagent grade. All the
Schiff bases have been prepared according with previously
reported procedure [28, 29].
IR spectra were recorded as KBr pellets on a Perkin-
Elmer 781 spectrophotometer and an Impact 400 Nicolet
FTIR spectrophotometer. H and 13C NMR were recorded
1
in DMSO/CDCl3 solvents on a Bruker DRX-400 spec-
trometer with tetramethylsilane as internal reference. Mass
spectra were recorded on a Finnigan MAT 44S by electron
ionization (EI) mode with an ionization voltage of 70 eV.
The elemental analyses (C, H, N) were obtained from a
Carlo ERBA Model EA 1108 analyzer. Melting points
obtained with a Yanagimoto micro melting point apparatus
are uncorrected. The N2 adsorption/desorption analysis
(BET) was performed at -196 °C using an automated gas
adsorption analyzer (Tristar 3000, Micromeritics). XRD
analysis was performed with an X-ray diffractometer
(PAnalytical X’Pert-Pro) using a Cu–Ka monochromatic
radiation source and a Ni filter. Transmission electron
microscopy (TEM) was performed with a Jeol JEM-
2100UHR, operated at 200 kV. The purity determination of
the substrates and reaction monitoring were accomplished
by TLC on silica-gel polygram SILG/UV 254 plates (from
Merck Company).
1,3-Diphenyl-2,2-dichloroaziridine (2a): pale yellow
solid; m.p. 100–102 °C (m.p. 98–99 °C) [20, 21, 25, 26].
1-(4-Bromophenyl)-2,2-dichloro-3-phenylaziridine (2b):
white solid; m.p. 143–145 °C; IR (KBr): m (cm-1) 3,100,
1
2,914, 1,600, 1,524 (C=C, Ar); H NMR (DMSO): d 4.40
(s, 1H, HCN), 7.107.80 (m, 9H, Ar); 13C NMR (DMSO): d
53.4, 77.1, 120.9, 121.3, 127.8, 128.1, 130.1, 131.2, 135.2,
142.1; MS: m/z 348 (M?6 ? 6, 10), 346 (M?4 ? 4, 25),
344 (M?2 ? 2, 45), 342 (M?, 30), 309 (85), 307 (100), 233
(65), 230 (45), 152 (80), 77 (85); Anal. Calcd for
C14H10BrCl2N: C, 49.02; H, 2.94; N, 4.08 %. Found: C,
49.15; H, 2.95; N, 4.12 %.
1-(4-Chlorophenyl)-2,2-dichloro-3-phenylaziridine (2c):
pale yellow solid; m.p. 72–74 °C (m.p. 71–72 °C) [22].
1,3-Bis(4-chlorophenyl)-2,2-dichloroaziridine
(2d):
white solid; m.p. 139–141 °C; IR (KBr): m (cm-1) 3,085,
1
2,910, 1,600, 1,504 (C=C, Ar); H NMR (DMSO): d 4.34
Preparation of nanocrystalline MgO
(s, 1H, HCN), 7.137.55 (m, 8 H, Ar); 13C NMR (DMSO): d
53.2, 75.9, 122.3, 128.9, 129.3, 129.7, 130.1, 132.2, 134.1,
143.6; MS: m/z 341 (M?8 ? 8, 4), 339 (M?6 ? 6,\3), 337
(M?4 ? 4, 4), 335 (M?2 ? 2, 10), 333 (M?, 20), 298 (70),
296 (65), 174 (60), 172 (95), 161 (80), 159 (100), 89 (50),
77 (55); Anal. Calcd for C14H9Cl4N: C, 50.49; H, 2.72; N,
4.20 %. Found: C, 50.48; H, 2.74; N, 4.21 %.
Nanocrystalline MgO was prepared by means of a proce-
dure reported elsewhere [30]. In short, poly(vinyl alcohol)
(PVA, MW70,000) was dissolved in water at 90 °C
under vigorous stirring to form a transparent solution.
Mg(NO3)2ꢀ6H2O was dissolved in water containing PVA.
The metal ion-to-PVA monomer unit molar ratio (M/PVA)
was chosen as 1:3. Aqueous ammonia (25 % w/w) was
added drop wise at room temperature to the resulting vis-
cous liquid mixture, with rapid stirring, to achieve careful
pH adjustment to 10.5. After precipitation, the slurry was
stirred for another 30 min and then heated under reflux at
80 °C for 20 h under continuous stirring. The mixture was
cooled at room temperature, filtered, and washed with hot
deionized water for effective removal of the PVA. The
final product was dried at 80 °C for 24 h and calcined at
700 °C.
1-(4-Bromophenyl)-2,2-dichloro-3-(4-chlorophenyl)azi-
ridine (2e): white solid; m.p. 134–136 °C; IR (KBr): m
1
(cm-1) 3,100, 2,920, 1,598, 1,509 (C=C, Ar); H NMR
(DMSO): d 4.33 (s, 1H, HCN), 7.077.59 (m, 8H, Ar); 13C
NMR (DMSO): d 53.1, 75.9, 122.7, 128.9, 129.7, 130.1,
132.2, 132.6, 134.1, 144.1; MS: m/z 384.5 (M?8 ? 8, 6),
382.5 (M?6 ? 6, \2), 380.5 (M?4 ? 4, 10), 378.5
(M?2 ? 2, 35), 376.5 (M?, 25), 341.5 (75), 339.5 (67),
217.5 (89), 205.5 (78), 204.5 (100), 202.5 (90), 89 (60);
Anal. Calcd for C14H9BrCl3N: C, 44.54; H, 2.40; N,
3.71 %. Found: C, 44.64; H, 2.42; N, 3.73 %.
1-(4-Bromophenyl)-2,2-dichloro-3-(4-nitrophenyl)aziri-
dine (2f): white solid; m.p. 141–143 °C; IR (KBr): m
Typical procedure for the synthesis of 1,3-bis
(4-chlorophenyl)-2,2-dichloroaziridine
1
(cm-1) 3,080, 2,924, 1,600, 1,522 (C=C, Ar); H NMR
(CDCl3): d 4.09 (s, 1H, HCN), 7.228.55 (m, 8H, Ar); 13C
NMR (CDCl3): d 53.9, 74.5, 121.2, 121.5, 123.7, 128.9,
132.3, 139.6, 143.3, 148.4; MS: m/z 392 (M?6 ? 6, 5), 390
Measured quantities of nanocrystalline MgO (0.02 mol,
0.8 g) and N-[1-(4-chlorophenyl)-methylidene]-N-[4-
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J IRAN CHEM SOC (2013) 10:161–167
163
(M?4 ? 4, 8), 388 (M?2 ? 2, 18), 386 (M?, 10), 353
(100), 351 (89), 307 (94), 305 (85), 153 (90), 77 (60); Anal.
Calcd for C14H9BrCl2N2O2: C, 43.33; H, 2.34; N, 7.22 %.
Found: C, 43.43; H, 2.35; N, 7.24 %.
As can be seen in Table 1, the reaction of 1a
(0.035 mol) with chloroform (8 mL) in the presence of
Na2CO3 or K2CO3 (0.3 g) as a base under thermal condi-
tions did not proceed at all (Table 1, entries 1 and 2), while
nanocrystalline MgO displays a substantially activity for
this reaction (Scheme 1) than commercial MgO under the
same condition (Table 1, entry 8 vs. 7).
2,2-Dichloro-1-(4-methylphenyl)-3-(4-nitrophenyl)azi-
ridine (2g): yellow solid; m.p. 140–142 °C; IR (KBr): m
(cm-1) 3,090, 2,918, 1,589, 1,490 (C=C, Ar); 1HNMR
(CDCl3): d 2.36 (s, 3H, CH3), 3.89 (s, 1H, HCN), 6.598.31
(m, 8H, Ar); 13C NMR (CDCl3): d 21.2, 53.5, 75.2, 119.6,
123.7, 128.9, 129.9, 134.6, 140.3, 141.7, 148.3; MS: m/z
326 (M?4 ? 4, 20), 324 (M?2 ? 2, 29), 322 (M?, 40), 289
(90), 287 (100), 243 (60), 241 (80), 154 (70), 152 (82), 91
(92); Anal. Calcd for C15H12Cl2N2O2: C, 55.74; H, 3.74; N,
8.67 %. Found: C, 55.75; H, 3.74; N, 8.67 %.
Because of the O-2, sites of MgO are influence to trigger
the reaction; in this regard, the nanocrystalline MgO should
have more reactive sites than commercial MgO (irregular
morphology with a surface area of 27 m2 g-1) and conse-
quently higher basic activity. Also nanocrystalline MgO has
more edges and corners which can lead to higher perfor-
mance of this basic catalyst. Also, presentation of Mg?2 as a
Lewis acid can be activated imine bond in Schiff base. In
addition to the above mentioned and with attention to spe-
cial structure of nanocrystalline MgO, it seems that the
organic species should be able to diffuse faster on the sur-
face of this solid base catalyst rather than commercial MgO.
The crystallite sizes determined by XRD were between
12.8 and 17.5 nm (determined by use of the Scherrer
equation), indicative of the nanocrystalline structure of the
prepared MgO. In addition, the surface area was approxi-
mately 116 m2 g-1. The pore volume and pore size were
also calculated from the N2 adsorption result; the pore size
was approximately 21.1 nm and the pore volume approx-
imately 0.69 cm3 g-1. The theoretical particle size was
also calculated from surface area, assuming spherical par-
ticles, from the equation:
1-(4-Bromophenyl)-2,2-dichloro-3-(4-methylphenyl)aziri-
dine (2h): yellow solid; m.p. 146–148 °C; IR (KBr): m
1
(cm-1) 3,100, 2,898, 1,600, 1,500 (C=C, Ar); H NMR
(CDCl3): d 2.31 (s, 3H, CH3), 3.75 (s, 1H, HCN), 7.047.48
(m, 8H, Ar); 13C NMR (CDCl3): d 20.1, 55.1, 74.1, 117.9,
121.9, 128.4, 129.6, 132.1, 134.1, 138.2, 141.1; MS: m/z
362 (M?6 ? 6, \2), 360 (M?4 ? 4, 10), 358 (M?2 ? 2,
27), 356 (M?, 15), 323 (100), 321 (89), 234 (84), 232 (70),
91 (97); Anal. Calcd for C15H12BrCl2N: C, 50.46; H, 3.39;
N, 3.92 %. Found: C, 50.59; H, 3.39; N, 3.94 %.
2,2-Dichloro-3-(4-chlorophenyl)-1-(4-methylphenyl)aziri-
dine (2i): white solid, m.p. 128–130 °C; IR (KBr): m (cm-1
)
3,090, 2,920, 1,600, 1,508 (C=C, Ar); 1H NMR (CDCl3): d
2.35 (s, 3H, CH3), 3.65 (s, 1H, HCN), 6.947.47 (m, 8H,
Ar); 13C NMR (CDCl3): d 22.1, 54.2, 76.1, 118.1, 121.5,
128.9, 129.6, 132.1, 134.1, 138.1, 144.1; MS: m/z 318
(M?6 ? 6, \2), 316 (M?4 ? 4, 7), 314 (M?2 ? 2, 12),
312 (M?, 15), 279 (85), 277 (95), 242 (70), 154 (90), 152
(100), 91 (95); Anal. Calcd for C15H12Cl3N: C, 57.62; H,
3.87; N, 4.48 %. Found: C, 57.64; H, 3.88; N, 4.49 %.
ꢀ
ꢁ
6; 000
q ꢁ S
DBET
¼
ð1Þ
where DBET is the equivalent particle diameter in nano-
meters, q is the density of the material in g cm-3, and S is
the specific surface area in m2 g-1. The particle size cal-
culated from Eq. 1 was 14.4 nm, which confirmed the
nanostructure of the MgO sample [30]. The TEM image of
MgO is shown in Fig. 1. As can be seen, the sample has a
nanocrystalline structure with a plate-like shape.
Results and discussion
Detailed studies of the reaction of N-phenyl-N-(1-phen-
ylmethylidene)amine (1a) with chloroform led to 1,3-
diphenyl-2,2-dichloroaziridine (2a). It was shown that this
addition reaction was influenced to a considerable extent
by the base as shown in Scheme 1 and Table 1.
Subsequent efforts were focused on optimizing condi-
tions to form the gem-dichloroaziridine using different
amounts of nanocrystalline magnesium oxide and various
temperatures (Table 2).
Scheme 1 Preparation of 1,3-
diphenyl-2,2-dichloroaziridine
from Schiff base (1a)
N
Cl
N
Cl
Nanocrystalline MgO
Heat
CHCl3
+
2a
1a
123

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J IRAN CHEM SOC (2013) 10:161–167
As indicated in this Table, the reaction showed an
improvement in yield using 0.8 g nanocrystalline MgO as a
solid base catalyst and the reaction temperature at 60 °C
(entry 6 in Table 2). Also, as can be seen in this Table, by
heating reaction mixture, the yield of desired product was
increased. It seems that a-elimination reaction on CHCl3 in
the presence of nanocrystalline MgO under thermal con-
ditions was occurred faster than the reaction at room
temperature conditions. Thus, addition reaction of the
generated CCl2 to imine bond occurred in excellent yields.
With attention to the importance of gem-dichloroaziri-
dine compounds, in continuation of our research, several
different Schiff bases were selected and the reaction of
them with nanocrystalline MgO (0.8 g) and CHCl3 have
been surveyed under thermal conditions (Scheme 2).
The corresponding results were summarized in Table 3.
As can be seen in Table 3, all of the gem-dichloroaziridine
products were obtained as crystalline solids in excellent
yields and short reaction times.
Table 1 Survey of different bases effect in the reaction of schiff base
with chloroform under thermal conditions at 40 °C
Entry
Base
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
Na2CO3
25
25
25
25
25
25
25
25
–
K2CO3
–
ZnO
\10
15
15
25
35
75
CuO
BaO
CaO
MgO
Nanocrystalline MgO
The synthesis of gem-dichloroaziridines in the presence
of nanocrystalline MgO and CHCl3 was compared with
previously reported methods. In this method, the used
nanocrystalline MgO:Schiff base mole ratio was 2:1 and
the desired product 2a was obtained in excellent yield
(95 %) after short reaction time (25 min) (Table 3, entry
1), while, in previously reported methods, the used
NaOCH3:Schiff base mole ratio was 4:1 and corresponding
product was obtained in 55 and 61 % yields after several
hours (Table 3, entries 2 and 5) [20, 21]. On the other hand,
synthesis of this compound 2a was reported in the presence
of TEBAC as a PTC in which used NaOH:Schiff base mole
ratio was 25:1 and the desired product was obtained in 74
and 88 % yields [25, 26]. Also preparation of product 2c
using this method was carried out in excellent yield and
very short reaction time that is comparable with the
reported method (Table 3, entry 7 vs. 8) [22].
Fig. 1 TEM image of nanocrystalline MgO
Table 2 Optimizing amount of nanocrystalline MgO and reaction
temperature conditions on the formation of 2a
Entry Amount of Time
nanocrystalline MgO (g) (min)
Temperature Yield
(°C)
(%)
1
2
3
4
5
6
7
8
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
25
25
25
25
25
25
25
25
40
50
60
60
60
60
60
r. t
75
75
80
85
88
95
95
65
It seems that this method for preparation of dichloroaz-
iridines has some advantages such as novelty, high effi-
ciency, appropriateness, being mild and useful in compare
to previously reported methods (Table 3, entries 2–5 and 8).
With attention to the importance of gem-dichloroaziri-
dine compounds, in continuation of our research, several
Scheme 2 Synthesis of gem-
dichloroaziridines in the
presence of nanocrystalline
MgO
Cl
N
Cl
N
Nanocrystalline MgO
60 0C
CHCl3
+
R
2
R
R
R
1
1
2
2a-i
1a-i
R1 = H, CH3, NO2, Cl
R2 = H, CH3, Cl, Br
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J IRAN CHEM SOC (2013) 10:161–167
165
Table 3 Synthesis of 1,3-diaryl-2,2-dichloroaziridine in the presence of nanocrystalline MgO under thermal condition at 60 °C
Entry
Substrate
Product
M.p. ( C)
Time (min)
Yield (%)a
Cl
N
N
Cl
Cl
Cl
Cl
Cl
1
100–102
25
95
61b
74c
Cl
N
N
N
2
3
4
5
6
98–99
98–99
99
360
40
–
Cl
N
Cl
N
N
88d
55e
Cl
N
N
98–99
143–145
400
20
Cl
N
N
Cl
Cl
Cl
94
95
Br
Cl
Br
Cl
Cl
Cl
N
N
N
7
8
72–74
71–72
20
Cl
N
68f
98
98
960
Cl
Cl
N
N
N
Cl
Cl
9
139–141
134–136
15
15
Cl
Br
Cl
Cl
Cl
Cl
Cl
N
10
Cl
Br
123

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J IRAN CHEM SOC (2013) 10:161–167
Table 3 continued
Entry
Substrate
N
Product
M.p. ( C)
141–143
Time (min)
20
Yield (%)a
93
Cl
Cl
11
N
Br
O2N
Br
O2N
Cl
Cl
N
12
140–142
146–148
15
15
92
96
N
CH3
O2N
CH3
O2N
Cl
Cl
N
13
N
Br
H3C
Br
H3C
N
Cl
N
Cl
14
128–130
15
97
CH3
Cl
CH3
Cl
a
Isolated yields based on Schiff base
b
c
d
e
f
By hexachloroacetone and sodium methoxide, Ref. [21]
By sodium hydroxide (50 %), chloroform in the presence of PTC, Ref. [25]
By sodium hydroxide (50 %), chloroform in the presence of PTC, Ref. [26]
By sodium methoxide and chloroform, Ref. [20]
By potassium t-butoxide and chloroform, Ref. [22]
different Schiff bases were selected and the reaction of
them with nanocrystalline MgO (0.8 g) and CHCl3 has
been surveyed under thermal conditions. The results were
summarized in Table 3.
nanocrystalline MgO as a base and CHCl3. The corre-
sponding products have been obtained in excellent yields,
high purity and short reaction times. The obtained diary-
laziridines have been characterized by physical and spec-
troscopic data such as IR, 1H NMR, 13C NMR, mass
spectroscopy and C, H, N analyses.
The structure of products has been confirmed by physical
1
and spectroscopic data such as IR, H NMR, 13C NMR,
mass spectroscopy and C, H, N analyses. In the IR spectra,
the stretching frequency of aromatic C=C is formed in the
region between m 1,490–1,600 cm-1. The stretching vibra-
tion of C–H in the alkyl groups was appeared at region
between m 2,898–2,930 cm-1. In the 1H NMR spectra, one
proton of CH–N has chemical shift in d 3.65–4.40.
The signals around d 6.59–8.55 are assigned by protons
of CH=CH of aromatic rings. In the 13C NMR spectra, one
carbon of C–N has chemical shift in d 52.1–55.1 and the
signal around d 74.1–77.1 is assigned by one carbon of
CCl2 of aziridine ring.
Acknowledgments The authors are grateful to University of
Kashan for supporting this work by Grant No. 159148/3.
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