Sonocatalyzed facile and mild one pot synthesis of gem-dichloroaziridine derivatives under alkaline conditions

Article abstract of DOI:10.1016/j.ultsonch.2011.06.012

In this research, rapid and efficient preparation of 2,2-dichloro-1,3- diarylaziridines through the reaction of Schiff base compounds with dichlorocarbene yielded in situ from chloroform and sodium hydroxide without any phase transfer catalyst under ultrasonic irradiation is described. The advantages of this reaction are very short reaction times, excellent product yields, simplicity of the method and high purity of products.

Full text of DOI:10.1016/j.ultsonch.2011.06.012

Ultrasonics Sonochemistry 19 (2012) 130–135
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
Sonocatalyzed facile and mild one pot synthesis of gem-dichloroaziridine
derivatives under alkaline conditions
⇑
Hossein Naeimi , Khadijeh Rabiei
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan 87317, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 April 2011
Received in revised form 15 June 2011
Accepted 20 June 2011
Available online 29 June 2011
In this research, rapid and efficient preparation of 2,2-dichloro-1,3-diarylaziridines through the reaction
of Schiff base compounds with dichlorocarbene yielded in situ from chloroform and sodium hydroxide
without any phase transfer catalyst under ultrasonic irradiation is described. The advantages of this reac-
tion are very short reaction times, excellent product yields, simplicity of the method and high purity of
products.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Aziridine
Ultrasonic
Schiff base
Dichlorocarbene
Dichloroaziridine
1. Introduction
temperatures [19]. A number of organic reactions have been revis-
ited by means of ultrasonic waves [17,19,22]. Also, some litera-
Aziridines, which are extremely important synthetic building
blocks, are nitrogen equivalents of epoxides, and can be similarly
opened in a stereo controlled manner with various nucleophiles,
providing access to a wide range of important nitrogen-containing
products [1]. These compounds are among the most fascinating
intermediates in organic synthesis, acting as precursors of many
complex molecules due to the strain incorporated in their skele-
tons [2]. Since the first synthesis of an aziridine reported by Gabriel
in 1888 [3], the synthetic scope of aziridine chemistry has blos-
somed in recent years. Thus, obtaining aziridines, has become of
great importance in organic chemistry. In particular, the antitumor
and antibiotic properties of a great number of aziridine-containing
compounds are of high significance among other biological proper-
ties, which make them attractive synthetic targets in their own
right [4]. As a result, several methods for synthesis of gem-dichlo
roaziridines have been reported. The preparation has been accom-
plished by the addition of dichlorocarbene generated from chloro-
form, hexachloroacetone or ethyltrichloroacetate with the
appropriate base under phase transfer catalyst, to imines [5–10].
The use of ultrasonic waves in organic synthesis has been
boosted in recent years [11–21]. Ultrasound is known to accelerate
diverse types of organic reactions and it is established as an impor-
tant technique in organic synthesis [17,19,22]. Sonication also
increases the reaction rate and avoids the use of high reaction
tures on ultrasonically prepared dichlorocarbene have been
reported [23–27]. Recently, syntheses of fluoro aziridines in the
presence of phase transfer catalyst under ultrasonic irradiation
have been reported [28]. The advantages of ultrasound procedures,
such as, good yields, short reaction times and mild reaction condi-
tions, are well documented [29].
In conjunction with ongoing work in our laboratory on the
preparation of Schiff base derivatives [30–33], here we decided
to report the synthesis of various dichloroaziridines through the
reaction of various Schiff base compounds and chloroform without
any phase transfer catalyst under ultrasonic irradiation.
2. Experimental section
2.1. Materials
All the materials were of commercial reagent grade. All the
Schiff bases have been prepared according to the previously
reported procedures [30,31].
2.2. Apparatus
IR spectra were recorded as KBr pellets on a Perkin-Elmer 781
spectrophotometer and an Impact 400 Nicolet FTIR spectropho-
tometer. 1H NMR and 13C NMR were recorded in DMSO/CDCl3 sol-
vents on a Bruker DRX-400 spectrometer with tetramethylsilane as
internal reference. Mass spectra were recorded on a Finnigan MAT
⇑
Corresponding author. Tel.: +98 361 5912388; fax: +98 361 5552935.
E-mail address: naeimi@kashanu.ac.ir (H. Naeimi).
1350-4177/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2011.06.012

H. Naeimi, K. Rabiei / Ultrasonics Sonochemistry 19 (2012) 130–135
131
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. The BANDELIN ultrasonic HD 3200
with probe model KE 76, 6 mm diameter, was used to produce
ultrasonic irradiation and homogenizing the reaction mixture. Pie-
zoelectric crystal of this kind of probe normally works in the range
of 700 kHz, but using through some proper clamps the output fre-
quency of piezoelectric crystal have controlled and reduced to
20 kHz. Therefore, the induced frequency of probe to the reaction
mixture is equal to 20 kHz. By changing the power of Tip the cav-
itations rate is displaced. Meaning the Tip frequency under all
amount of power is constant. Melting points obtained with a Yana-
gimoto micro melting point apparatus are uncorrected. The purity
determination of the substrates and reaction monitoring were
accomplished by TLC on silica-gel polygram SILG/UV 254 plates
(from Merck Company).
NMR/ (100 MHz, DMSO)/ d ppm: 53.15, 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), 337
(M+6 + 6,<3), 335 (M+4 + 4, 10), 333 (M+2 + 2, 25), 331 (M+, 15),
298 (70), 296 (65), 174 (60), 172 (98), 161 (80), 159 (100), 77
(55); Anal. Calcd. For C14H9NCl4: C, 50.45; H, 2.70; N, 4.20. Found:
C, 50.48; H, 2.74; N. 4.21.
2,2-dichloro-1-(4-bromophenyl), 3-(4-chlorophenyl) aziridine
(2e); white solid; m.p. = 134–136 °C; IR (KBr)/
t
(cmÀ1): 3100,
2920, 1598, 1509 (C@C, Ar); 1H NMR (400 MHz, DMSO)/d ppm:
4.34 (s,1 H, HCN), 7.08 (d, 2 H, Ar), 7.50–7.56 (m, 4 H, Ar), 7.58
(d, 2 H, Ar); 13C NMR/ (100 MHz, DMSO)/ d ppm: 53.0, 76.9,
122.3, 129.1, 129.3, 130.1, 131.8, 134.5, 137.6, 150.1; MS: m/z:
381 (M+6 + 6, 6), 379 (M+4 + 4, 25), 377 (M+2 + 2, 34), 375 (M+,
14), 342 (60), 340 (46), 218 (60), 216 (94), 205 (82), 203 (100);
Anal. Calcd. For C14H9NBrCl3: C, 44.62; H, 2.39; N, 3.72. Found: C,
44.64; H, 2.42: N, 3.73.
2,2-dichloro-1-(4-bromophenyl), 3-(4-nitrophenyl) aziridine
2.3. The power measurement by calorimetric method
(2f); white solid; m.p. = 141–143 °C; IR (KBr)/ t
(cmÀ1): 3080,
2924, 1600, 1522 (C@C, Ar); 1H NMR (400 MHz, CDCl3)/ d ppm:
3.79 (s, 1 H, HCN), 6.95 (d, 2 H, Ar), 7.50 (d, 2 H, Ar), 7.71 (d, 2 H,
Ar), 8.31 (d, 2 H, Ar); 13C NMR (100 MHz, DMSO)/ d ppm: 53.2,
75.9, 122.3, 128.9, 129.2, 129.7, 130.2, 132.2, 134.1, 143.6; MS:
m/z: 392 (M+6 + 6, 7), 390 (M+4 + 4, 20), 388 (M+2 + 2, 50), 386
(M+, 38), 353 (78), 351 (100), 307 (65), 305 (80), 218 (80), 216
(95), 77 (80); Anal. Calcd. For C14H9N2O2BrCl2: C, 43.41; H, 2.33;
N, 7.24. Found: C, 43.43; H, 2.35; N, 7.24.
We assessed the cavitational energy applied by ultrasonication
calorimetrically with water. The piezoelectric transducer was con-
nected to the frequency generator, HD-3200 (with frequency;
20 kHz). The probe (KE-76) was dipped in a jacketed cylindrical
vessel. For calorimetric measurement, the jacket was empty and
connected to vacuum to minimize heat losses. In this method, by
measuring the rate of temperature increase due to the conversion
of ultrasound energy into heat and calculating Pacoustic according
2,2-dichloro-1-(4-methylphenyl), 3-(4-nitrophenyl) aziridine
to: P = mc
D
T/t, where m is the mass of water (g), c is the specific
T is the difference in tem-
(2 g); yellow solid; m.p. = 140–142 °C; IR (KBr)/ t
(cmÀ1): 3090,
heat capacity of water (4.18 JgÀ1 kÀ1),
D
2918, 1589, 1490 (C@C, Ar); 1H NMR (400 MHz, DMSO)/ d ppm:
2.29 (s, 3 H, CH3) 4.45 (s, 1 H, HCN), 7.02 (d, 2 H, Ar), 7.21 (d, 2
H, Ar), 7.80 (d, 2 H, Ar)8.31 (d, 2 H, Ar); 13C NMR (100 MHz, CDCl3)/
d ppm: 20.9, 53.5, 75.1, 119.6123.7, 128.9, 134.6, 140.3, 141.7,
148.3; MS: m/z: 326 (M+4 + 4, 6), 324 (M+2 + 2, 29), 322 (M+, 40),
289 (70), 287 (100), 243 (60), 241 (80), 154 (70), 152 (82), 91
(92); Anal. Calcd. For C15H12N2O2Cl2: C, 55.73; H, 3.72; N, 8.67,
Found: C, 55.75; H, 3.74; N, 8.67.
perature (k) and t is the sonication time(s).
2.4. Typical procedure for the synthesis of 2,2-dichloro-1, 3-
diphenylaziridine
Measured quantities of NaOH (0.075 mol, 3 g) were dissolved in
30 ml of water and the obtained solution was introduced to a
100 ml flask. The ultrasonic probe was immersed directly in the
reactor. Then, Schiff base (organic reactant; 0.028 mol, 8.2 g) dis-
solved in chloroform (0.07 mol, 8.3 ml) was gradually added drop
wise to the NaOH solution under ultrasonic irradiation with power
67 W. The progress of the reaction was monitored by TLC. After the
completion of the reaction in 15 min, the solution was separated
and the portion of aqueous solution was extracted by diethylether.
Magnesium sulfate was also added to adsorb the residual water.
The organic solvent and other residues were stripped in a vacuum
evaporator. The pale yellow solid, 2,2-dichloro-1, 3-diphenylaziri
dine, was obtained in 96% yield, m.p. = 100–102 °C (reported
[5,8–10], m.p. = 98–99 °C), All of the diarylaziridine products were
identified by physical and spectroscopic data as following;
2,2-dichloro-1, 3-diphenylaziridine (2a); pale yellow solid;
m.p. = 100–102 °C (m.p. = 98–99 °C) [5,8–10].
2,2-dichloro-1-(4-bromophenyl), 3-(4-methylphenyl) aziridine
(2 h); yellow solid; m.p. = 146–148 °C; IR (KBr)/
t
(cmÀ1): 3100,
2898, 1600, 1500 (C@C, Ar); 1H NMR (400 MHz, CDCl3)/ d ppm:
2.38 (s, 3 H, CH3) 3.41 (s, 1 H, HCN), 7.15 (d, 2 H, Ar), 7.21 (d, 2
H, Ar), 7.45 (d, 2 H, Ar), 7.84 (d, 2 H, Ar); 13C NMR (100 MHz,
CDCl3)/ d ppm: 20.9, 51.0, 72.9, 120.1, 129.8, 130.1, 135.0, 136.7,
137.8, 149.3; MS: m/z: 361 (M+6 + 6,<2), 359 (M+4 + 4, 24), 357
(M+2 + 2, 47), 355 (M+, 35), 322 (85), 320 (100), 218 (64), 216
(80), 91 (95); Anal. Calcd. For C15H12NBrCl2: C, 50.56; H, 3.37; N,
3.93, Found: C, 50.59; H, 3.39; N, 3.94.
2,2-dichloro-1-(4-methylphenyl), 3-(4-chlorophenyl) aziridine
(2i); white solid, m.p. = 128–130 °C; IR (KBr)/
t
(cmÀ1); 3090,
2920, 1600, 1508 (C@C, Ar); 1HNMR (400 MHz, CDCl3)/ d ppm:
2.36 (s, 3 H, CH3) 3.65 (s, 1 H, HCN), 6.95 (d, 2 H, Ar), 7.18 (d, 2
H, Ar), 7.36–7.47 (m, 5 H, Ar); 13C NMR (100 MHz, CDCl3)/ d ppm:
21.5, 53.1, 73.1, 121.0, 128.5, 129.9, 130.1, 138.1, 138.5, 138.1,
139.0, 149.3; MS: m/z: 317 (M+6 + 6, 10), 315 (M+4 + 4, 20), 313
(M+2 + 2, 47), 311 (M+, 50), 283 (96), 281 (100), 154 (80), 152
(84), 91 (98); Anal. Calcd. For C15H12NCl3: C, 57.60; H, 3.84; N,
4.48, Found: C, 57.64; H, 3.88; N, 4.49.
2,2-dichloro-1-(4-bromophenyl)-3-phenylaziridine (2b); white
solid; m.p. = 143–145 °C; IR (KBr)/
t
(cmÀ1): 3100, 2914, 1600,
1524 (C@C, Ar); 1H NMR (DMSO)/ d ppm: 4.34 (s, 1 H, HCN), 7.14
(d, 2 H, Ar), 7.45 (d, 2 H, Ar), 7.50–7.55 (m, 5 H, Ar); 13C NMR/
(CDCl3) / d ppm: 50.0, 71.0, 119.4, 122.7, 128.9, 129.0, 131.9,
132.3, 136.2, 151; MS: m/z: 347 (M+6 + 6, 8), 345 (M+4 + 4, 20),
343 (M+2 + 2, 45), 341 (M+, 27), 308 (80), 306 (100), 229 (75),
227 (50), 77 (85); Anal. Calcd. For C14H10NBrCl2: C, 49.12: H,
2.92; N. 4.11. Found: C, 49.15; H, 2.95; N. 4.12.
3. Results and discussion
2,2-dichloro-1-(4-chlorophenyl)-3-phenylaziridine (2c); pale
yellow solid; m.p. = 72–74 °C (m.p. = 71–72 °C) [7].
In this research, the ultrasonic irradiation as a phase transfer
catalyzed reaction of dichloro aziridination of Schiff base com-
pounds has been studied. When 0.028 mol of Schiff base com-
pound was reacted with dichlorocarbene intermediate obtained
in situ from the reaction of chloroform and base under ultrasonic
irradiation, corresponding products, 2,2-dichloro-1, 3-diarylaziri-
2,2-dichloro-1, 3-bis(4-chlorophenyl)aziridine (2d); white so-
lid; m.p. = 139–141 °C; IR (KBr)/ t
(cmÀ1): 3085, 2910, 1600, 1504
(C@C, Ar); 1H NMR (400 MHz, DMSO)/ d ppm: 4.34 (s, 1 H, HCN),
7.14 (d, 2 H, Ar), 7.45 (d, 2 H, Ar), 7.50–7.58 (m, 4 H, Ar); 13C

132
H. Naeimi, K. Rabiei / Ultrasonics Sonochemistry 19 (2012) 130–135
Cl
N
Cl
dine compounds were obtained under alkaline conditions (10%
NaOH) (Scheme 1).
Firstly, we have carried out this reaction in the presence of
various amount of NaOH under ultrasonic irradiation (52 W). The
corresponding results are indicated in Table 1.
N
)))), NaOH
H2O
CHCl3
+
2
R
2
R
R
R
1
1
1a-i
2a-i
As can be seen in this Table, the desired product was obtained
with high yield using NaOH (10%) under ultrasonic irradiation
(52 W) (Table 1, entry 6). In order to determine enhancement
ultrasound irradiation with performance of this reaction under
magnetic stirring, the product was obtained in low yield and long
reaction times (Table 1, entry 8).
R1 = H, CH3, NO2, Cl
R2 = H, CH3, Cl, Br
Scheme 1. Preparation of 2,2-dichloro-1, 3-diarylaziridine compounds from Schiff
bases.
In continuation of this research, the effect of various powers of
ultrasonic irradiation has been surveyed. Initially we carried out
aziridination of (4-bromo-phenyl)methylene(4-chloro-phenyl)a-
mine as model reaction in order to optimize the best suited reac-
tion conditions. It was observed that the reaction in the presence
of NaOH 10% and ultrasonic irradiation with power 67 W was
afforded the best result as obtained product with 98% isolated yield
during 10 min (Table 2, entry 6).
Table 1
Enhancement of ultrasonic irradiation (52 W) on the formation of 2,2-dichloro-1-(4-
bromophenyl), 3-(4-chlorophenyl) aziridine in the presence of various amount of
NaOH.
Entry
Amount of NaOH (%)
Time (min)
Yielda (%)
1
2
3
4
5
6
7
8
5
90
70
60
50
45
40
37
840
53
60
64
72
80
90
90
40b
5.6
6.7
8.3
9.3
10
12
10
3.1. The effect of ultrasonic irradiation
Sonification of multiphasic systems accelerates the reaction by
ensuring a better contact between the different phases. By occur-
ring the reaction under sonication conditions dichloroscarbene
intermediate was produced very fast and thus corresponding prod-
ucts were obtained in excellent yields and very short reaction
times.
a
Isolated yields.
Isolated yield under silent conditions.
b
The effects of ultrasonic irradiation observed during organic
reactions are due to cavitations. In the case of volatile molecules
cavities are believed to act as a microreactor: as the volatile mole-
cules enter the microbubbles and the high temperature and pres-
sure produced during cavitations break their chemical bonds
thus reacting with other specie [34–36]. The presence of ultrasonic
irradiation in liquid–liquid system, cavitational collapse near the
liquid–liquid interface disrupts the interface and impels jets of
one liquid into the other forming fine emulsion, and leading to a
dramatic increase in the interfacial contact area across which
transfer of species can take place. Also, the ultrasonic irradiation
increase the produce of:CCl2 intermediate and cause the enhance-
ment of addition reaction rate.
Table 2
Survey the effect of ultrasonic irradiation on the formation of 2,2-dichloro-1-(4-
bromophenyl),3-(4-chlorophenyl) aziridine.
Entry Electric power (W) Measured power (W) Time (min) Yielda (%)
1
2
3
4
5
6
7
50
55
60
65
68
72
75
47
52
56
61
63
67
70
10
10
10
10
10
10
10
63
70
80
85
90
98
98
Then to ascertain the scope and limitation of the present reac-
tion, several Schiff base compounds were reacted with CHCl3 in
a
Isolated yields under 10% NaOH.
Table 3
Synthesis of gem-dichloro-1,3-diarylaziridines and NaOH (10%) under ultrasonic irradiation with 67 W power.
Entry
Substrate
Product
M.P. (°C)
Time (min)
Ultrasound
Yielda (%)
Silent
900
Ultrasound
Silent
35
1
Cl
N
N
N
N
Cl
100–102
15
–
95
–
2
3
Cl
N
Cl
Cl
98–99
98–99
360
40
61b
Cl
N
–
–
74c

H. Naeimi, K. Rabiei / Ultrasonics Sonochemistry 19 (2012) 130–135
133
Table 3 (continued)
Entry
Substrate
Product
M.P. (°C)
Time (min)
Ultrasound
Yielda (%)
Silent
–
Ultrasound
Silent
4
Cl
N
N
N
Cl
99
–
–
88d
5
6
Cl
N
Cl
Cl
98–99
400
12
Several hours
–
55e
Cl
N
N
32
143–145
970
94
Br
Cl
Br
Cl
Cl
7
8
9
Cl
N
N
N
Cl
Cl
36
72–74
12
998
960
840
95
Cl
N
71–72
–
–
68f
40
Cl
Cl
N
N
N
Cl
139–141
10
98
Cl
Br
B
Cl
Cl
Cl
Cl
10
11
Cl
Cl
N
134–136
141–143
10
13
840
870
98
93
40
30
Cl
Br
Cl
N
N
Cl
O2N
Br
O2N
O2N
12
13
Cl
N
Cl
Cl
N
140–142
146–148
14
11
910
845
92
96
27
38
C
O2N
H3C
CH3
Cl
N
N
Br
Br
H3C
14
N
Cl
N
Cl
128–130
10
840
97
40
CH3
Cl
CH3
Cl
a
b
c
d
e
f
Isolated yields based on Schiff base.
By hexachloroacetone and sodium methoxide, Ref. [5].
By sodium hydroxide(50%), chloroform in the presence of PTC, Ref. [8].
By sodium hydroxide(50%), chloroform in the presence of PTC Ref. [9].
By sodium methoxide and chloroform, Ref. [6].
By potassium t-butoxide and chloroform, Ref. [7].

134
H. Naeimi, K. Rabiei / Ultrasonics Sonochemistry 19 (2012) 130–135
the presence and optimum amount of NaOH (10%) under ultrasonic
irradiation and the desired dichloroaziridine derivatives were pre-
pared. The results are summarized in Table 3. As shown in this
Table, the reaction of the various Schiff bases with chloroform
and NaOH (10%), were catalyzed by ultrasonic irradiation. The cor-
responding products were obtained in excellent yields and appro-
priate reaction times under ultrasonic irradiation. It seems this
method for preparation of dichloroaziridines has some advantages
such as; highly efficiently, appropriately, mildly and useful in com-
pare to previously reported methods [5–9] (Table 3, entries 2–5
and 7). Among these, dichlorocarbene which is generated from
CHCl3 under PTC conditions is most frequently used because the
yields are acceptable. In our report on synthesis of dichloroaziri-
dine derivatives under ultrasonic irradiation, the mol ratio of NaOH
and CHCl3 into the Schiff base was ꢀ2.5, while in other reports
were 4 and 10. Also, in our research, NaOH with 10% concentration
was applied. The yields of products were higher and the reaction
time was shorter than the other previously reported methods
[6–9].
quency of aromatic C@C is formed in the region between
= 1490–1600 cmÀ1. The stretching vibration of C–H in the alkyl
groups was appeared at region between
= 2898–2930 cmÀ1. In
m
m
the 1H NMR spectra, the disappearance of imine proton signal
around the d = 8.42–8.75 in Schiff base compounds and followed
to appear the signal of CH-N around d = 3.41–4.45 ppm in gem-
dichloroaziridines was confirmed the formation of them in this
reaction (Fig. 1). The signals around d = 6.95–8.31 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 ppm and the sig-
nal around d = 71.0–76.9 is assigned by one carbon of CCl2 of aziri-
dine ring (Fig. 2).
4. Conclusion
In this study, we have synthesized gem-dichloroaziridine deriv-
atives through the reaction of various Schiff base compounds with
chloroform under ultrasonic irradiations as a phase transfer cata-
lyst. The corresponding products have been obtained in excellent
yields, high purity and short reaction times. The products have
been confirmed by physical and spectroscopic data such as; IR,
1H NMR, 13C NMR, MS spectroscopy and C. H. N. analyses.
The structure of products has been confirmed by physical and
spectroscopic data such as; IR, 1H NMR, 13C NMR, Mass spectros-
copy and C. H. N. analyses. In the IR spectra, the stretching fre-
Fig. 1. 1H NMR spectra of 2,2-dichloro-1-(4-bromophenyl), 3-(4-nitrophenyl)aziridine.
Fig. 2. 13C NMR spectra of 2,2-dichloro-1-(4-bromophenyl), 3-(4-nitrophenyl)aziridine.

H. Naeimi, K. Rabiei / Ultrasonics Sonochemistry 19 (2012) 130–135
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135
Acknowledgments
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Sonochem. 13 (2006) 32.
We are grateful to the University of Kashan research council for
the partial support of this work.
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