Microwave synthesis and antibacterial activities of some imidazolidine derivatives containing 1, 3, 4-oxadiazole moiety

Article abstract of DOI:10.14233/ajchem.2018.20970

5-(4-Aminophenyl)-2-thiol-1, 3, 4-oxadiazole (1) was synthesized via the reaction of carbon disulfide with 4-aminobenzoyl hydrazide in presence of potassium hydroxide in absolute ethanol. Compound 1 was converted to the corresponding diazonium salt which

Full text of DOI:10.14233/ajchem.2018.20970

Asian Journal of Chemistry; Vol. 30, No. 3 (2018), 546-550
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2018.20970
Microwave Synthesis and Antibacterial Activities of Some
Imidazolidine Derivatives Containing 1,3,4-Oxadiazole Moiety
*
ZEID HASSAN ABOOD , HAYDER RAHEEM ALI, HUSSEIN ALI QABEL and OSAMA HAMEED RASHEED
Chemistry Department, College of Science, University of Kerbala, Kerbala, Iraq
*
Corresponding author: E-mail: zeid.ab2013@yahoo.com
Received: 12 August 2017; Accepted: 9 November 2017;
Published online: 31 January 2018;
AJC-18741
5
-(4-Aminophenyl)-2-thiol-1,3,4-oxadiazole (1) was synthesized via the reaction of carbon disulfide with 4-aminobenzoyl hydrazide in
presence of potassium hydroxide in absolute ethanol. Compound 1 was converted to the corresponding diazonium salt which was introduced
in coupling reaction with alkaline solution of 2-hydroxybenzaldehyde as coupling reagent to give azooxadiazole derivative 2 containing
aldehyde group. The resulting aldehyde 2 was then introduced in condensation reactions with the primary aromatic amines including (4-
bromoaniline, 4-chloroaniline, 4-nitroaniline, 3-nitroaniline, 4-methoxyaniline and 4-hydroxyaniline) using microwave irradiation technique
in absolute ethanol to produce six imine derivatives of 1,3,4-oxadiazole (3a-f), respectively. Treatment of the resulting imines 3a-f with
glycine using microwave irradiation in tetrahydrofuran afforded six new imidazolidines 4a-f substituted with 1,3,4-oxadiazole moiety,
respectively. in vitro Antibacterial activity of the target compounds were investigated using two types of bacteria, Staphylococcus aureus
(Gram-positive) and Escherichia coli (Gram-negative). The results indicated that the newly synthesized imidazolidines (compounds 4d
and 4f) showed enhanced activity against Gram-negative bacteria when compared with that of the control drug (gentamycin).
Keywords: Imidazolidines, 1,3,4-Oxadiazoles, Imines, Antibacterial activity.
group with two pyridine typed nitrogen (-N=) [12]. Five-mem-
bered N-containing heterocyclic aromatic compounds found
in natural products [13]. Oxadiazoles have often been described
as bioisosteres for amides and esters [14]. Furthermore the
INTRODUCTION
The imidazolidine is five-membered heterocycles con-
taining two nitrogen atoms [1]. N-heterocyclic carbine (NHC)-
derived complexes have been used as powerful catalysts for
effecting many transformations [2]. Imidazolidine, a fully
saturated imidazole heterocycle, is an important intermediate
and building block in the construction of a variety of biolo-
gically active compounds [3]. Imidazolidine compounds
showed a variety of biological activities such as antibacterial,
antitubercular, antifungal, anti-HIV, antileishmanial, anti-
nociceptive, anti-inflammatory and analgesic activities [4,5].
They are also used for the treatment of schistosomiasis infec-
tions [6], anticonvulsant activity and reduced toxicity [7], anti-
diabetic [8]. Imidazolidines have antitumor, antiarrhytmic and
antiandrogenic activity. The activity of imidazolidin-2,4-diones
1,3,4-oxadiazole derivatives have some industrial applications
in the fields of dyes, photosensitivity electrical materials and
liquid crystals [15]. 1,3,4-Oxadiazoles and their derivatives
represent an important scaffold that has been found in many
natural and synthesized molecules because of their remarkable
biological activities [16] as anticancer [17], antifungal [18],
antitumor [19], antibacterial [20], antiparasitic [22], anti-HIV
[22], anti-infective [23], muscle relaxants [24], antiseptics [25]
and cathepsin K inhibitors [26].
EXPERIMENTAL
(
hydantoin) depends on the nature of substitution of imidazolidine
The chemicals were used as provided from Fluka, sigma
Aldrich, J.T. Baker and Merck. Microwave reactions were
performed on domestic microwave oven in crucible.Analytical
TLC was performed with silica gel 60 F254 plates. The reactions
were monitored by TLC and visualized by development of
the TLC plates with iodine vapour. Melting points were recorded
on an Electro thermal Stuart SMP 30 capillary melting point
apparatus and are uncorrected. Infrared spectra were recorded
ring [9]. Among imidazolidine-2-ones phenytoin is known as
antiepileptic drug and antihypertensive substance [10].
Oxadiazoles are cyclic compounds containing one oxygen
and two nitrogen atoms in a five- membered ring. The sequence
of these atoms may be different as 1,2,4-oxadiazole, 1,2,5-
oxadiazole, 1,2,3-oxadiazole or 1,3,4-oxadiazole [11]. Oxa-
diazole moiety is derived from furan by replacing two -CH=

Vol. 30, No. 3 (2018)
Microwave Synthesis and Antibacterial Activities of Some Imidazolidine Derivatives 547
on Shimadzu FTIR-8400S Infrared Spectrophotometer as
potassium bromide discs. H NMR spectra was collected on
Avance III 500, NMR spectrometer, Bruker, Germany at 500
ν(C=N) imine and ν(C=N) oxadiazole, vib. coupling, 1506s
1
ν(C=C) benzene and νas.( NO
2
) vib. coupling, 1411 ν(N=N),
1329 νs.(NO
benzene.
2
), 1066 ν(C=S) thione form, 840 δo.o.p.(C-H)
MHz in DMSO-d
at a Faculty of Science, University of Tarbiat Modares, Iran.
CHNS) ElementalAnalysis was carried out with Perkin Elmer
00A Elemental Analyzer at a Faculty of Science, University
of Tehran, Iran.
6
as solvent and TMS as an internal standard
4-((E)-(4-(5-Mercapto-1,3,4-oxadiazol-2-yl)phenyl)-
diazenyl)-2-((E)-((3-nitrophenyl)imino)methyl)phenol (3d):
(
3
-1
IR (cm ):3279 ν(O-H), 3072 ν(N-H) thione form and ν(C-H)
benzene, vib. coupling, 2933 and 2748 ν(N-H) intramolecularly
hydrogen bonded, thione form, 2573 ν(S-H) thiol form, 1604s
ν(C=N) imine and ν(C=N) oxadiazole, vib. coupling, 1525s
5
-(4-Aminophenyl)-2-thiol-1,3,4-oxadiazole (1) was
synthesized according to Yong and Wood method [27]. Pale
-1
yellow crystals, m.p. 234-236 °C, yield 82 %; IR (cm ): 3450
), 3354 νs.(NH ), 3095 ν(N-H) thione form and ν(C-
ν(C=C) benzene and νas.(NO
2
) vib. coupling, 1415 ν(N=N),
νas.(NH
2
2
1350 νs.(NO
2
), 1066 ν(C=S) thione form, 840 δo.o.p.(C-H)
H) benzene, vib. coupling, 2951 and 2767 ν(N-H) intramolecu-
larly hydrogen bonded, thione form, 2590 ν(S-H) thiol form,
benzene.
4-((E)-(4-(5-mercapto-1,3,4-oxadiazol-2-yl)phenyl)-
diazenyl)-2-((E)-((4-methoxyphenyl)imino)methyl)phenol
1
606s ν(C=N) oxadiazole and δ(NH ) vib. coupling, 1514
2
-1
and 1440 ν(C=C) benzene, 1066 ν(C=S) thione form, 839
δo.o.p.(C-H) benzene.
(3e): IR (cm ):3336 ν(O-H), 3055 ν(N-H) thione form and
ν(C-H) benzene, vib. coupling, 2931 and 2750 ν(N-H)
(
E)-2-Hydroxy-5-((4-(5-mercapto-1,3,4-oxadiazol-2-yl)-
intramolecularly hydrogen bonded, thione form, 2835 ν(CH ),
3
phenyl)diazenyl)benzaldehyde (2) was synthesized following
2555 ν(S-H) thiol form, 1610s ν(C=N) imine and ν(C=N)
oxadiazole, vib. coupling, 1510 ν(C=C) benzene, 1415 ν(N=N),
1068 ν(C=S) thione form, 831 δo.o.p.(C-H) benzene.
2-((E)-((4-Hydroxyphenyl)imino)methyl)-4-((E)-(4-(5-
mercapto-1,3,4-oxadiazol-2-yl)phenyl)diazenyl)phenol
the method described by Acton [28] as red solid, m.p.: 204-
-1
2
06 °C, yield 79 %; IR (cm ): 3402br ν(O-H), 3190 ν(N-H)
thione form, 3095 ν(C-H) benzene, 2937 and 2748 ν(N-H)
intramolecularly hydrogen bonded, thione form, 2885 ν(C-
H) aldehyde, 2580 ν(S-H) thiol form, 1662 ν(C=O) aldehyde,
-1
(3f): IR (cm ): 3340 and 3281 ν(O-H), 3032 ν(N-H) thione
form and ν(C-H) benzene, vib. coupling, 2928 and 2812 ν(N-H)
intramolecularly hydrogen bonded, thione form, 2596 ν(S-H)
thiol form, 1610s ν(C=N) imine and ν(C=N) oxadiazole, vib.
coupling, 1510 and 1479 ν(C=C) benzene, 1417 ν(N=N), 1072
ν(C=S) thione form, 829 δo.o.p.(C-H) benzene.
1
1
604 ν(C=N) oxadiazole, 1477 ν(C=C) benzene, 1411 ν(N=N),
068 ν(C=S) thione form, 842 δo.o.p.(C-H) benzene.
General procedure for the synthesis of imines 3a-f:All
reactions were carried out on domestic microwave oven in
crucible. Reactions contained the aldehyde derivative 2 (0.326
g, 1 mmol), equimolar amount (1 mmol) of aniline derivatives
General procedure for the synthesis of imidazolidines
(4a-f): A mixture of equimolar amounts of imine derivatives
3a-f (1 mmol) and glycine (0.075 g, 1 mmol) in tetrhydrofuran
(1 mL) was heated in microwave oven at (450-500 W) for 45
min. TLC (n-hexane:EtOAc) showed that the reactions were
completed. The products were washed with diethyl ether and
recrystallized from ethanol.
(
4-bromoaniline, 4-chloroaniline, 4-nitroaniline, 3-nitro-
aniline, 4-methoxyaniline and 4-hydroxyaniline, respectively)
and absolute ethanol (1 mL). The crucible was introduced to
the center of a domestic microwave oven and then heated at
(
300 W) for 25 min. TLC (n-hexane: EtOAc) showed that the
reactions were completed. The products were washed with
diethyl ether and recrystallized from ethanol.
3-(4-Bromophenyl)-2-(2-hydroxy-5-((4-(5-mercapto-
1,3,4-oxadiazol-2-yl)phenyl)diazenyl)phenyl)imidazolidin-
2
-((E)-((4-Bromophenyl)imino)methyl)-4-((E)-(4-(5-
-1
mercapto-1,3,4-oxadiazol-2-yl)phenyl)diazenyl)phenol
4-one (4a): IR (cm ): 3421br ν(O-H), ν(N-H) thione form,
ν(N-H) imidazolidine and ν(C-H) benzene, vib. coupling, 2955
and 2883 ν(N-H) intramolecularly hydrogen bonded, thione
form, 2600 ν(S-H) thiol form, 1716 ν(C=O) imidazolidine,
1653 δ(N-H) imidazolidine, 1606 ν(C=N) oxadiazole, 1506
and 1489 ν(C=C) benzene, 1410 ν(N=N), 1035 ν(C=S) thione
-1
(
3a): IR (cm ): 3352 ν(O-H), 3064 ν(N-H) thione form and
ν(C-H) benzene, vib. coupling, 2943 and 2758 ν(N-H) intra-
molecularly hydrogen bonded, thione form, 2553 ν(S-H) thiol
form, 1614s ν(C=N) imine and ν(C=N) oxadiazole, vib. coupling,
1
508 and 1487 ν(C=C) benzene, 1413 ν(N=N), 1070 ν(C=S)
thione form, 833 δo.o.p.(C-H) benzene.
-((E)-((4-Chlorophenyl)imino)methyl)-4-((E)-(4-(5-
mercapto-1,3,4-oxadiazol-2-yl)phenyl)diazenyl)phenol
1
form, 846 δo.o.p.(C-H) benzene; H NMR: δ (ppm) = 3.71 (s,
2
2H, CH imidazolidine, 5.06 (s, 1H, CH imidazolidine, 7.10–
2
8.11 (11H, Ar–H), 8.19 (s, 1H, N–H imidazolidine, 8.75 (s,
1H, O–H), 10.70 (s, 1H, S–H). The singlet signals around 2.48
-1
(
3b): IR (cm ): 3327 ν(O-H) and ν(N-H) thione form, vib.
coupling, 3074 ν(C-H) benzene, 2918 and 2756 ν(N-H)
intramolecularly hydrogen bonded, thione form, 2580 ν(S-H)
thiol form, 1612s ν(C=N) imine and ν(C=N) oxadiazole, vib.
coupling, 1504 and 1491 ν(C=C) benzene, 1413 ν(N=N), 1068
ν(C=S) thione form, 831 δo.o.p.(C-H) benzene.
ppm and 3.37 ppm attributed to DMSO and absorbed H
2
O in
DMSO, respectively; Anal. calcd. (%) for C23 SBr: C,
H
17
N O
6 3
51.40; H, 3.19; N, 15.64; S, 5.97; Found (%) C, 51.02; H,
3.46; N, 15.77; S, 5.95.
3-(4-Chlorophenyl)-2-(2-hydroxy-5-((4-(5-mercapto-
1,3,4-oxadiazol-2-yl)phenyl)diazenyl)phenyl)imidazolidin-
4
-((E)-(4-(5-mercapto-1,3,4-oxadiazol-2-yl)phenyl)-
-1
diazenyl)-2-((E)-((4-nitrophenyl)imino)methyl)phenol (3c):
4-one (4b): IR (cm ): 3389 ν(O-H), 3271 and 3194 ν(N-H)
thione form and ν(N-H) imidazolidine, 3095 and 3053 ν(C-
H) benzene, 2949 and 2883 ν(N-H) intramolecularly hydrogen
bonded, thione form, 2600 ν(S-H) thiol form, 1716 ν(C=O)
-1
IR (cm ): 3481 and 3363 ν(O-H), 3219 ν(N-H) thione form,
080 ν(C-H) benzene, 2935 and 2760 ν(N-H) intramolecularly
hydrogen bonded, thione form, 2594 ν(S-H) thiol form, 1597s
3

548 Abood et al.
Asian J. Chem.
imidazolidine, 1653s δ(N-H) imidazolidine, 1606 ν(C=N)
respectively; Anal. calcd. (%) for C24
4.13; N, 17.20; S, 6.56; Found (%) C, 58.97; H, 4.02; N, 16.83;
S, 6.21.
H
20
N
6
O
4
S:C, 59.01; H,
oxadiazole, 1533 and 1494 ν(C=C) benzene, 1411 ν(N=N),
1
1
035 ν(C=S) thione form, 846 δo.o.p.(C-H) benzene; H NMR:
δ (ppm) = 3.70 (d, J = 27.0 Hz, 2H, CH
d, J = 14.1 Hz, 1H, CH imidazolidine, 7.11–7.95 (11H, Ar–
H), 8.20 (s, 1H, N–H imidazolidine, 8.75 (s, 1H, O–H), 10.45
s, 1H, S–H).The singlet signals around 2.49 ppm and 3.38
ppm assigned to DMSO and absorbed H O in DMSO,
respectively;Anal. calcd. (%) for C23 SCl:C, 56.04; H,
.48; N, 17.05; S, 6.50; Found (%) C, 55.85; H, 3.66; N, 16.66;
S, 6.17.
-(2-Hydroxy-5-((4-(5-mercapto-1,3,4-oxadiazol-2-
yl)phenyl)diazenyl)phenyl)-3-(4-nitrophenyl)imidazolidin-
2
imidazolidine, 5.02
2-(2-Hydroxy-5-((4-(5-mercapto-1,3,4-oxadiazol-2-
yl)phenyl)diazenyl)phenyl)-3-(4-hydroxyphenyl)imidazo-
(
-1
lidin-4-one (4f): IR (cm ): 3230 br ν(O-H), 3180 ν(N-H) thione
form and ν(N-H) imidazolidine, 3066 ν(C-H) benzene, 2947
and 2885 ν(N-H) intramolecularly hydrogen bonded, thione
form, 2605 ν(S-H) thiol form, 1720 ν(C=O) imidazolidine,
1651 δ(N-H) imidazolidine, 1606 ν(C=N) oxadiazole, 1514
ν(C=C) benzene, 1411 ν(N=N), 1035 ν(C=S) thione form,
(
2
H
17
N
6
O
3
3
1
2
840 δo.o.p.(C-H) benzene; H NMR: δ (ppm) = 3.70 (s, 2H,
CH imidazolidine, 5.01 (d, J = 24.8 Hz, 1H, CH imidazolidine,
2
-1
4
-one (4c): IR (cm ): 3365 br ν(O-H), 3230 ν(N-H) thione form
and ν(N-H) imidazolidine, 3063 ν(C-H) benzene, 2935 and
877 ν(N-H) intramolecularly hydrogen bonded, thione form,
590 ν(S-H) thiol form, 1712 ν(C=O) imidazolidine, 1666
6.59–7.78 (11H,Ar–H), 8.21 (s, 1H, N–H imidazolidine, 10.35
(s, 2H, 2×O–H), 10.45 (s, 1H, S–H).The singlet signals around
2.49 ppm and 3.43 ppm due to DMSO and absorbed H
DMSO, respectively; Anal. calcd. (%) for C23
2
2
O in
S:
2
H
18
N
6
O
4
δ(N-H) imidazolidine, 1602 ν(C=N) oxadiazole, 1508 ν(C=C)
benzene and νas.(NO ) vib. coupling, 1413 ν(N=N), 1309 νs.(NO ),
051 ν(C=S) thione form, 844 δo.o.p.(C-H) benzene; H NMR:
imidazolidine, 6.57
d, J = 8.4 Hz, 1H, CH imidazolidine, 7.27–8.04 (11H, Ar–H),
C, 58.22; H, 3.82; N, 17.71; S, 6.76; Found (%) C, 57.87; H,
4.18; N, 17.44; S, 6.40.
2
2
1
1
Preliminary antibacterial assay: The antibacterial acti-
vities of the newly synthesized imidazolidines 4a-f were deter-
mined by the agar diffusion method [29] using representative
Gram-positive and Gram-negative bacteria on tryptic soya agar
media. The test microorganisms to evaluate the potential anti-
bacterial activity of the newly synthesized imidazolidines were
Staphylococcus aurous (Gram-positive) and Escherichia coli
(Gram-negative). The imidazolidines were dissolved in dimethyl
sulfoxide to prepare the test solutions of 10 mg/mL concen-
tration. Gentamycin was used as a reference and the activities
were presented as zones of inhibition for each compound
(Table-2).
δ (ppm) = 3.69 (d, J = 10.9 Hz, 2H, CH
2
(
8
1
.20 (s, 1H, N–H imidazolidine, 8.81 (s, 1H, O–H), 10.56 (s,
H, S–H).The signals around 2.49 ppm and 3.41 ppm due to
DMSO and absorbed H
S:C, 54.87; H, 3.40; N, 19.47; S, 6.37;
Found (%) C, 54.50; H, 3.68; N, 19.11; S, 5.98.
-(2-hydroxy-5-((4-(5-mercapto-1,3,4-oxadiazol-2-
yl)phenyl)diazenyl)phenyl)-3-(3-nitrophenyl)imidazolidin-
2
O in DMSO, respectively;Anal. calcd.
(
%) for C23
H
17
N O
7 5
2
-
1
4
-one (4d): IR (cm ): 3354 br ν(O-H), 3248 ν(N-H) thione form
and ν(N-H) imidazolidine, 3066 ν(C-H) benzene, 2937 and
877 ν(N-H) intramolecularly hydrogen bonded, thione form,
615 ν(S-H) thiol form, 1710 ν(C=O) imidazolidine, 1662 δ(N-
H) imidazolidine, 1606 ν(C=N) oxadiazole, 1527 νas.(NO
508 and 1473 ν(C=C) benzene, 1413 ν(N=N), 1330 νs.(NO
2
2
RESULTS AND DISCUSSION
2
),
),
4-Aminobenzoic hydrazide was converted to 5-(4-amino-
phenyl)-2-thiol-1,3,4-oxadiazole (1) by treating it with carbon
disulfide in presence of potassium hydroxide as catalyst in
absolute ethanol [27]. Diazotization of amino group in com-
pound 1 using sodium nitrite and hydrochloric acid generated
the corresponding diazonium salt which was directly intro-
duced in coupling reaction with 2-hydroxybenzaldehyde
dissolved in sodium hydroxide solution to give azo-oxadiazole
derivative 2 containing aldehyde group [28]. Aldehyde group
of azo-oxadiazole derivative 2 was condensed with the primary
aromatic amines including (4-bromoaniline, 4-chloroaniline,
4-nitroaniline, 3-nitroaniline, 4-methoxyaniline and 4-hydroxy-
aniline) using microwave irradiation in absolute ethanol to
produce six imine derivatives of 1,3,4-oxadiazole 3a-f respec-
tively, as the platforms for this work (Schemes I and II). The
resulting imines 3a-f were allowed to react with glycine using
microwave irradiation leading to the formation of imidazo-
lidine derivatives of oxadiazole 4a-f respectively in good yields
(Table-1).
1
1
2
1
049 ν(C=S) thione form, 840 δo.o.p.(C-H) benzene; H NMR:
imidazolidine, 6.64
d, J = 11.0 Hz, 1H, CH imidazolidine, 7.24–8.09 (11H, Ar–
H), 8.32 (s, 1H, N–H imidazolidine, 8.72 (s, 1H, O–H), 10.56
s, 1H, S–H).The signals around 2.49 ppm and 3.40 ppm
attributed to DMSO and absorbed H O in DMSO, respectively;
Anal. calcd. (%) for C23 S:C, 54.87; H, 3.40; N, 19.47;
S, 6.37; Found (%) C, 54.47; H, 3.79; N, 19.11; S, 6.01.
E)-2-(2-Hydroxy-5-((4-(5-mercapto-1,3,4-oxadiazol-
-yl)phenyl)diazenyl)phenyl)-3-(4-methoxyphenyl)imi-
δ (ppm) = 3.70 (d, J = 6.1 Hz, 2H, CH
2
(
(
2
H
17
N O
7 5
(
2
-1
dazolidin-4-one (4e): IR (cm ): 3325 br ν(O-H), ν(N-H), thione
form and ν(N-H), imidazolidine, vib. coupling, 3070 ν(C-H)
benzene, 2941 and 2727 ν(N-H) intramolecularly hydrogen
bonded, thione form, 2887 ν(C-H)
720 ν(C=O) imidazolidine, 1680 and 1653 (dN-H, thione
3
), 2594 ν(S-H) thiol form,
1
form and dN-H imidazolidine, 1606 ν(C=N) oxadiazole, 1512
and 1473 ν(C=C) benzene, 1413 ν(N=N), 1033 ν(C=S) thione
1
form, 839 δo.o.p.(C-H) benzene; H NMR: δ (ppm) = 3.71 (d,
The chemical structures of the target compounds synthe-
1
J = 27.2 Hz, 2H, CH
2
imidazolidine, 3.85 (s, 3H, O–CH
3
),
sized were confirmed from IR, H NMR spectral measurements
5
.02 (d, J = 22.2 Hz, 1H, CH imidazolidine, 6.65–8.18 (11H,
and (CHNS) elemental analysis and were in good agreement
with the proposed structures.
Ar–H), 8.25 (s, 1H, N–H imidazolidine, 8.76 (s, 1H, O–H),
1
3
0.57 (s, 1H, S–H).The singlet signals around 2.48 ppm and
.37 ppm assigned to DMSO and absorbed H O in DMSO,
The IR spectrum of oxadiazole derivative 1 showed the
disappearance of the sharp doublet band for hydrazide group
2

Vol. 30, No. 3 (2018)
Microwave Synthesis and Antibacterial Activities of Some Imidazolidine Derivatives 549
N
N
N
N
O
C
N
1
) i
OH
NH2
3) iii
4) iv
NH2
2
) ii
HS
N
H
2
N
N
O
HS
O
H
CHO
1
2
v
N
N
N
OH
N
N
N
OH
N
vi
HS
N
HS
N
O
Ar
HC
N
O
Ar
O
3a-f
HN
4a-f
Ar=
NO
2
Br
Cl
OCH
3
OH
NO
2
a
d
e
f
b
c
2 2
Scheme-I: Synthesis of imidazolidines, Reagents and conditions (i) CS , KOH, EtOH, 70 °C, 24 h; (ii) conc. HCl; (iii) NaNO , HCl, 0-5 °C;
(
(
2
iv) 2-hydroxybenzaldehyde, NaOH 10 %, 5 °C; (v) Ar-NH ,EtOH, MW (300W), 25 min; (vi) glycine, tetrahydrofuran, MW
450-500 W), 45 min
and (-NH ) bend due to the vibration coupling interaction.
2
H
C
-1
H
C
The weak and strong bands at 2590 and 1066 cm belong to
(S-H) str and (C=S) str in thioenol and thioketone forms,
respectively. The IR spectrum of azo-oxadiazole derivative 2
Ar
N
Ar
Ar
N
Ar
R
P.T
H
N
H
HO
C
CH
-1
HO
NH
2
indicated the absence of a doublet band at 3450 and 3354 cm
O
C
HC
for (-NH
2
) str and appearance of the following characteristic
O
R
-1
bands: the weak band at 1411 cm attributed to azo group
-1
(
N=N) str, the broad band at 3402 cm assigned to (O-H) str,
Ar
N
CH Ar
NH
Ar
N
CH Ar
NH
-
1
H O
the sharp and strong band at 1662 cm belong to aldehydic
(C=O) str, the oxadiazolic (C=N) str appeared as a weak band
2
C
H O
O
2
C
HC
CH
R
-1
at 1604 cm due to disappearance of the bending vibration of
-NH ) group. IR spectra of the oxadiazolic-imines 3a-f showed
O
R
(
2
Scheme-II: Proposed mechanism for the formation of imidazolidine ring
-1
disappearing the sharp and strong band at 1662 cm for
aldehydic (C=O) str, also disappearing the sharp doublet band
-1
-1
(-NHNH
2
) at (3307, 3236) cm and the strong band at 1627cm
due to (C=O) str, additionally the appearance of the following
characteristic bands: the doublet band at 3450 and 3354 cm
assigned to (-NH ) str that substituted in benzene ring, the
strong band at 1606 cm attributed to the oxadiazolic (C=N) str
for (-NH ) str in the starting amines at the general range (3400-
2
-
1
3250) cm and appearing a sharp and strong band at the range
-1
-1
(1614-1597) cm assigned to the iminic and oxadiazolic (C=N)
2
str due to the vibration coupling interaction. The IR spectra of
the imidazolidines 4a-f showed the appearance of strong band
-1
TABLE-1
PHYSICAL PROPERTIES OF THE SYNTHESIZED COMPOUNDS
Product
Colour
Red solid
Orange solid
Yellow solid
Dark orange solid
Yellow solid
Orange solid
Dark brown solid
Yellow solid
R (developer)
m.p. (°C)
204-206
206-208
181-183
175-177
158-160
219-221
156-158
224-226
204-206
201-203
189-191
177-179
170-172
Yield (%)
79
Time (min)
Microwave (W)
–
f
2
0.68 (n-hexane/EtOAc, 1:3)
0.81 (n-hexane/EtOAc, 1:3)
0.78 (n-hexane/EtOAc, 1:3)
0.56 (n-hexane/EtOAc, 1:3)
0.75 (n-hexane/EtOAc, 1:3)
0.68 (n-hexane/EtOAc, 1:3)
0.72 (n-hexane/EtOAc, 1:3)
0.67 (n-hexane/EtOAc, 1:3)
0.68 (n-hexane/EtOAc, 1:3)
0.56 (n-hexane/EtOAc, 1:3)
0.62 (n-hexane/EtOAc, 1:3)
0.62 (n-hexane/EtOAc, 1:3)
0.51 (n-hexane/EtOAc, 1:3)
–
3a
76
81
91
86
81
88
85
75
79
91
95
76
25
25
25
25
25
25
45
45
45
45
45
45
300-350
300-320
300
3b
3c
3d
300
3e
300-310
300-320
450-600
450-600
500-550
475-550
450-570
460-590
3f
4a
4b
Yellow solid
4c
Dark orange solid
Dark orange solid
Brown solid
4d
4e
4f
Grey solid

550 Abood et al.
Asian J. Chem.
-
1
at the range 1712-1720 cm attributed to the (C=O) str of the
imidazolidine ring. The spectra also showed the appearance
ACKNOWLEDGEMENTS
-1
The authors thanks for the University of Tarbiat Modares
and the Faculty of Science, University of Tehran, Iran for their
of absorption band at the range 1666-1651 cm assigned to
the (N-H)bend of the imidazolidine ring. The oxadiazolic
C=N) str appeared at the range 1606-1602 cm .
1
-1
significant assistance in H NMR and elemental analysis.
(
The structures of imidazolidine compounds 4a-f were
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The microwave irradiation is efficient technique including
short reaction time and high yield in comparison with the
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to the corresponding phenol salts to be totally soluble in water.
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