Synthesis, characterization and structural study of new ethyl thiourea compounds and the preliminary naked-eye sensors for mercury and argentum metal ions

Article abstract of DOI:10.13005/ojc/330227

Novel ethyl thiourea compounds 1a- 1f have been synthesized in good to high yields. The structure of all compounds were identified using FT-IR, ¹H NMR, ¹³C NMR spectroscopies, and ESI-Mass spectrometry. The compound 1-ethyl-3-(3-meth

Full text of DOI:10.13005/ojc/330227

ISSN: 0970-020 X
CODEN: OJCHEG
2017, Vol. 33, No. (2):
Pg. 800-806
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Synthesis, Characterization and Structural Study of New Ethyl
Thiourea Compounds and the Preliminary Naked-eye Sensors
for Mercury and Argentum Metal Ions
SITI AISHAH HASBULLAH*, SYAHIDATUL MUNIRAH RAFFIK, NURNADZIRAH
MAT NOH, EMMA IZZATI ZAKARIAH, FATIMATUL AKMA AWANG NGAH,
HAMZA MILAD ABOSADIYA and BOHARIYAMIN
School of Chemical Sciences and Food Technology, Faculty of Science and
Technology, Universitiy Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia.
*Corresponding author: aishah80@ukm.edu.my
http://dx.doi.org/10.13005/ojc/330227
(Received: October 09, 2017; Accepted: January 01, 2017)
ABSTRACT
Novel ethyl thiourea compounds 1a– 1f have been synthesized in good to high yields. The
structure of all compounds were identified using FT-IR, 1H NMR, 13CNMRspectroscopies,andESI-Mass
spectrometry.Thecompound1-ethyl-3-(3-methoxyphenyl)thiourea1e wasobtainedincrystallineformby
recrystallization from DMSO. Single crystal X-ray analysis revealed that 1e molecule crystallized in a
monoclinic crystal system with space group of P21/n and the unit cell dimensions are a = 11.0797(7)
Å, b = 8.6081(6) Å, c = 11.9698(7) Å, a = 90°, b =104.543(2)°, g = 90°, Z = 4 and V = 1105.04(12)
Å3. The preliminary optical sensor properties for metal ions of 1a, 1b and 1d were investigated using
naked-eye. The results determined that all compounds have the ability as naked eye sensors for
mercury (Hg) and argentum (Ag) metal ions.
Keywords: Synthesis; Structural study; Ethyl thiourea; Naked-eye Sensors
INTRODUCTION
greater electronegativity compare to sulphur. Many
applications can be done on behaviours.2 Thiourea
is a chemically interesting compound where it has
more than two functional groups in a compound:
amino, imino and thiol.3 Thiourea derivatives are
mostly crystalline compounds and thermally stable.
They can be produced in good yields from available
starting material by simple syntheses.3 Thiourea is
also one of the most famous studied compounds on
Thiourea is similar to urea compound
except the oxygen atom in urea is replaced by the
presence of sulphur atom in thiourea compound.1
The chemical properties of both compounds
are different because of the oxygen and sulphur
atoms in urea and thiourea. These atoms have
different in electronegativity where oxygen has

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HASBULLAH et al., Orient. J. Chem., Vol. 33(2), 800-806 (2017)
metallic electrodes.4 It can absorb to metal surface provide a multitude of bonding possibilities.15,16 The
and the absorption blocks the active sites.4 It is also structural characterization of the thiourea derivatives
1
one of the important industrial chemical products.5 were performed using FTIR, H NMR, 13C NMR
Now a days, the situation of environmental pollution spectroscopy devices and ESI-MS spectrometry.
by heavy metals is one of the critical issues due to the In order to investigate the sensor properties, the
development of modern industries and agriculture.
interaction of all compounds with metals in solvent
media was investigated using naked-eye sensor.
Many of heavy metals can be dangerous
towards human or animal health. Mercury (Hg2+) is
one of the most toxic and hazardous between all the
heavy metals.6 Mercury can cause cells damage and
MATERIALS AND METHODS
METHODS
All reactions were performed under
some diseases related to brain,7 kidney, and central conventional reflux method.Chemicals and solvents
nervous system. These are because the mercury were purchased from Sigma Aldrich and Across and
is unable to decay naturally and accumulates in used directly without any further purification.Melting
animal and human bodies.8 Silver ions (Ag+) also points were recorded on the open tube capillary
have long been known to have strong inhibitory and method using Electrothermal 9100 instrument
antimicrobial activities.9 Silver nano particles are (Electrothermal, England) and are uncorrected. All
showing very toxic effects on human health and the compounds were analyzed using FTIR Perkin Elmer
environment due to the antibacterial activity. Then, Model Spectrum GX in the range 400-4000 cm-1
1
1
chronic exposure to silver also can causes negative using KBr method, H and C NMR spectrometer
effects such as permanent bluish-grey discoloration model Bruker Advance 400 MHz and Liquid
of the skin (argyria) and eyes (argyrosis). Besides Chromatography Mass Spectroscopy (ToF) model
that, it also may produce other toxic effects like Dionex/BrukerMicroToF Q. Single-crystal X-ray
liver and kidney damage, irritation of the eyes, skin, experiments were performed on a Bruker D-QUEST
respiratory and intestinal tract and changes to blood diffractometer (Bruker, AXS Inc., Madison, WI, USA)
cell.10 For the above reasons, there is a high demand using graphite-monochromated Mo-Ka radiation
for tracking these metal ions.11 The aim of the present (g = 0.71073 Å).The w-scan measured the intensity
study was to synthesis thiourea compounds having data at room temperature. The full-matrix least-
alkyl and aryl group substitutes.
squares fit of 25 reflections determines the accurate
cell parameters and orientation matrix. Intensity
Chemical sensor is generally consisting data were collected for Lorentz and polarization
of two units; receptor unit and signalling unit, but in effects. Empirical absorption correction was carried
some cases spacer is also used to provide the shape out using multi-scan. The structure was solved by
and geometry in two armed molecule.12 Detecting direct methods and least-squares refinement of
metal cations is one of the great interests to many the structure was performed by the SHELXL-2007
scientists.13 Thioureas are well known having good program.17 All the non-hydrogen atoms were refined
affinity towards metals via thiono group (C=S) make anisotropically. The hydrogen atoms were placed in
them applicable as ion sensors.14 The nitrogen, the calculated positions except those of the terminal
oxygen and sulphur atom are donor atoms of thiourea nitrogen atoms of thiourea moieties located from
that can donate electrons to form bonding and Fourier maps and refined isotropically.
Scheme 1 Synthesis of ethylthioureas 1a – 1f

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HASBULLAH et al., Orient. J. Chem., Vol. 33(2), 800-806 (2017)
General procedure for synthesis of compounds
1a-1f
(ArC), 140.4 (ArC), 180.2 (C=S). m/z (ESI) (H+,
C10H14N2S requires 195.09)
A solution of ethylisothiocyanate (0.1394
g, 0.0016 mol) in dichloromethane (20 mL) was
added dropwise to a suspension of toluidine1a,1b
or 1c(0.1714 g, 0.0016 mol) and anisidine 1d, 1e
or 1f (0.1968 g, 0.0016 mol) in dichloromethane.
The reaction mixture was refluxed for 24 hours and
was monitored using thin layer chromatography
(TLC) until the reaction was completed. The white
precipitate was formed and filtered out. The solid
product was purified by recrystallization method
using ethanol: dichloromethane mixture.
1c Mp:97.4 – 98.8 0C.IR (KBr), NH:3198.00
cm-1, C-N:1317.00 cm-1, C=S:1249.00 cm-1. 1H NMR
(400 MHz, CDCl3-d6) d (ppm) 1.16(3H, t, J=7.2Hz,
CH3), 2.36(3H, s, CH3),3.64(2H, s, CH2), 5.95(1H,
s, NH), 7.10 (1H, d, J=7.6Hz, ArCH), 7.20(1H, d,
J=7.6Hz, ArCH), 7.32 – 7.33 (2H, m, ArCH), 8.06(1H,
s, NH). 13C NMR (100 MHz, CDCl3-d6) d (ppm) 14.3
(CH3), 21.1 (CH3), 40.3 (CH2), 128.0 – 130.8 (4 x
ArCH), 133.4 (ArC), 137.5 (ArC), 180.4 (C=S). m/z
(ESI) (H+, C10H14N2S requires 195.09)
1a Mp:81.9 – 83.6 0C.IR (KBr), NH:3193.00
cm-1, C-N:1371.00 cm-1, C=S:1245.00 cm-1. 1H NMR
(400 MHz, CDCl3-d6) d (ppm) 1.14 (3H, t J=7.2Hz,
CH3), 2.29 (3H, s, CH3), 3.63(2H, s, CH2), 5.65(1H,
s, NH), 7.25 (1H, d J=10.8Hz, ArCH), 7.26 (1H, t
J=7.8Hz, ArCH), 7.28 (1H, t J= 7.8Hz, ArCH), 7.30
(1H, d J=10.8Hz, ArCH), 7.84(1H, s, NH). 13C NMR
(100 MHz, CDCl3-d6) d (ppm) 14.5 (CH3), 17.8 (CH3),
40.2 (CH2), 127.5-131.8 (4 x ArCH), 135.9 (ArC),
134.4 (ArC), 180.6 (C=S). m/z (ESI) (H+, C10H14N2S
requires 195.09)
1d Mp: 72.5 – 72.5 0C. IR (KBr), NH:3335
cm-1, C-C aromatic: 1528 cm-1, C=S: 1263 cm-1.
1H NMR (400 MHz, CDCl3-d6) d (ppm) 1.20(3H,
t, J=7.2Hz, CH3), 3.67(2H, sex, J=5.6Hz, CH2),
3.85(3H, s, OCH3), 6.11(1H, s, NH), 6.98(1H, t,
J=7.6Hz, ArCH),7.23(1H, td J=6.4Hz and 1.6Hz,
ArCH), 7.31 (1H, s, ArCH), 7.52(1H, s, NH). 13C NMR
(100 MHz, CDCl3-d6) d (ppm) 14.3 (CH3), 40.3 (CH2),
55.7 (OCH3), 112.0 – 124.9 (4 x ArC), 127.5 (ArC),
152.4 (ArC), 180.3 (C=S).m/z (ESI) (Na, C10H14N2OS
requires 233.27g/mol)
1b Mp:84.9 – 85.6 0C.IR (KBr), NH:3011.00
cm-1, C-N:1355.00 cm-1, C=S:1148.00 cm-1. 1H NMR
(400 MHz, CDCl3-d6) d (ppm) 1.18 (3H, t J=7.2Hz,
CH3), 2.36(3H, s, CH3),3.66(2H, s, CH2), 6.01(1H,
s, NH),7.30(2H, d, J=7.2Hz, ArCH), 7.32 (2H, d
J=7.6Hz, ArCH), 8.20(1H, s, NH). 13C NMR (100
MHz, CDCl3-d6) d (ppm) 14.4 (CH3),21.4 (CH3), 40.3
(CH2), 122.2 (2 x ArCH), 129.9 (2 x ArCH), 136.1
1e Mp: 112.5 – 117.5 0C. IR(KBr)NH:3343
cm-1,C-C aromatic:1550 cm-1, C=S: 1284 cm-1.
1H NMR (400 MHz, CDCl3-d6) d (ppm) 1.19(3H,
t, J=7.2Hz, CH3), 3.67(2H, sex, J=5.4Hz, CH2),
3.80(3H, s, OCH3), 6.11(1H, s, NH),6.78(1H, dd,
J=6.0Hz and 2.0Hz, ArCH), 6.74(1H, t, J=2.0Hz,
ArCH), 6.82(1H, dd, J=6.0Hz and 2.4Hz, ArCH),
7.32(1H, t, J=8.0Hz, ArCH), 7.95(1H, s, NH). 13C
Fig. 2: Molecular packing of 1-ethyl-3-(3-
methoxyphenyl)thiourea 1e viewed down the b
axis.The dashed lines denote the N–H…S and
N–H…O hydrogen bonds
Fig. 1: ORTEP diagram of 1-Ethyl-3-(3-
methoxyphenyl)thiourea 1e

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HASBULLAH et al., Orient. J. Chem., Vol. 33(2), 800-806 (2017)
NMR (400 MHz, CDCl3-d6) d (ppm) 14.3(CH3), J=5.6Hz, CH2), 3.82(1H, s, OCH3), 5.78(1H, s, NH),
40.4(CH2), 55.5(OCH3), 110.7-130.9(4 x ArC), 137.3 6.93(1H, d, J=8.8Hz, ArCH), 7.14(1H, d, J=8.8Hz,
(ArC), 160.9 (ArC), 180.1(C=S). m/z (ESI) (Na, ArCH), 7.72(1H, s, NH). 13C NMR (400 MHz, CDCl3-
C10H14N2OS requires 233.27g/mol)
d6) d (ppm) 14.4 (CH3),40.2(CH2), 55.5(OCH3),
115.2 – 127.7(4 x ArC), 128.6(ArC), 158.8 (ArC),
1f Mp: 121.5 – 124.5 0C. IR(KBr), NH:3297 180.8(C=S). m/z (ESI) (Na, C10H14N2OS requires
cm-1, C-H:2988 cm-1C-C aromatic: 1520 cm-1, 233.27g/mol)
1
C=S:1289 cm-1. H NMR (400 MHz, CDCl3-d6)
d (ppm) 1.15(3H, t, J=7.2Hz, CH3), 3.64(2H, sex, General procedure for naked-eye sensor
For naked-eye sensor detection of metal
Table 1: Crystal data and structure refinement
of 1-ethyl-3-(3-methoxyphenyl)thiourea 1e
ions (Fe2+, Pb2+, Hg2+, Ni2+, Zn2+, Ag+, Cu2+, and Sn2+),
compounds 1a, 1b and 1d were dissolved in 25 ml
dimethyl sulfoxide (DMSO) to form 1 x 10-3 M solution.
Metal ion sources were prepared in deionized water
to form 1 x 10-3 M stock solution except SnCl2 in
DMSO.The color changes were observed by naked
eyes and the data were collected.
Crystal parameters
Data/values
Empirical formula
Formula weight
Temperature
C10H14N2OS
210.29
302(2) K
Wavelength l
Crystal system
Space group
0.71073 Å
Monoclinic
P21/c
RESULTS AND DISCUSSIONS
All ethyl thiourea compounds 1a – 1f
were synthesized in moderate to high yields from
the reaction of ethylisothiocyanate 2 with isomers
of toluidine 3a – 3c and anisidine 3d – 3f in
dichloromethane under reflux condition. Scheme 1
outlines the synthesis of ethyl thiourea compounds
1a – 1f.
Unit cell dimensions
a = 11.0797(7) Å
a = 90°
b = 8.6081(6)Å
b = 104.543(2)°°
c = 11.9698(7) Å
g = 90°
1105.04(12) Å3
4
Volume
Z
FT-IR spectra were taken with KBr pellets
between 4000 and 400 cm-1. In the FT-IR spectra
of all the synthesized compounds show sharp and
strong absorption band in the region of 3011 – 3335
cm-1 and it were attributed to the stretching vibration
of NH group, respectively. In addition, synthesized
compounds show strong intensity C=S stretching
vibration in the 1213 – 1284 cm-1 range. The proton
D, cal (Mg/m3)
1.264
0.263 mm”1
448
Absorption coefficient
F(000)
Crystal dimension (mm3)
Theta range for
data collection
Reflections collected
Ranges/indices (h,k,l)
Completeness to theta
Independent reflections
Max. and min.
0.44 x 0.37 x 0.29
2.89 to 28.40°
40490
-14, 14; -11, 11; -15, 15
28.40°, 99.6%
2753 [R(int) = 0.0791]
0.9275 and 0.8929
Table 2: Selected bond lengths and angles of
1-Ethyl-3-(3-methoxyphenyl)thiourea 1e
transmission
Data / restraints /
parameters
Goodness of fit on F2
R1, wR2 (I≥2s(I))
Bond
Length Å
Bond
Angles°
2753 / 2 / 137
S1-C8 1.6917(18)
C2-O1-C7
C8-N1-C6
C8-N2-C9
O1-C2-C3
O1-C2-C1
C5-C6-N1
C1-C6-N1
118.32(16)
124.92(16)
124.91(17)
115.78(16)
124.25(18)
119.26(18)
119.36(17)
1.100
R1 = 0.0580, wR2
= 0.1072
R1 = 0.1024, wR2
= 0.1220
0.230 and -0.285 e.Å-3
O1-C2
O1-C7
N1-C8
N1-C6
N2-C8
N2-C9
1.366(2)
1.420(3)
1.339(3)
1.436(2)
1.326(3)
1.456(3)
R1,wR2 indices (all data)
Largest diff. peak and
hole

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HASBULLAH et al., Orient. J. Chem., Vol. 33(2), 800-806 (2017)
NMR spectrum (1H and 13C) were in agreement
with compounds 1a – 1f.The peaks in the region of
7.60 – 8.20 ppm were attributed to NH proton near
the aromatic ring.This singlet NH resonance is more
de-shielded due to anisotropic effect.The distinctive
broad singlets in the range of 5.65 – 6.20 ppm were
attributed to NH proton attached to the ethyl terminal
ring.The present of electron donating ethyl moieties
increased the electron density and shifted the
protons of NH to the upfield position.The protons at
aromatic ring were assigned at 6.80 – 7.36 ppm.The
protons for methyl (1a – 1c) and methoxy (1d – 1f) at
aromatic ring exhibited signal as singlet in the range
of 2.28 – 2.36 ppm and 3.80 – 3.85 ppm, respectively.
The peaks in the region of 1.1 to 3.7 ppm were due
to the protons of methylene and methyl of ethyl ring.
According to the 13C NMR spectra, the signal of C=S
ring was found around 180.2 ppm and indicated the
formation of thiourea moiety. The aromatic carbons
were observed in the range of 110.7 – 160.9 ppm for
all compounds. The methyl (1a – 1c) and methoxy
(1d – 1f) carbons for aromatic ring were resonated at
21.0 and 55.5 ppm, respectively.All other carbons at
the ethyl terminal ring were resonated in the region of
14.3 – 40.3 ppm. The signal related to [M + H]+ and
[M + Na]+ for compounds 1b and 1d in the MS
spectrum were observed at 195.09 and 233.27,
respectively.
X-ray diffraction study indicates that the
compound 1e crystallizes in the monoclinic crystal
system with space group of P21/n and the unit cell
dimension are a = 11.0797(7) Å, b = 8.6081(6) Å, c =
11.9698(7) Å, a = 90°, b =104.543(2)°, g = 90°, Z = 4
and V = 1105.04(12) Å3. Crystallographic data have
been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication number
CCDC 1493627. Summary of the data collections
and details of the structure refinement is given in
Table 1.
Fig.1 shows the molecular structure
with numbering scheme of compound1e
which is analogous to the previously reported
1-(2-Hydroxyethyl)-3-(3-methoxyphenyl)thiourea
(Choi et al. 2010) except in 1e compound, there is
no hydroxyl group bonded to the terminal carbon of
ethyl group.
The molecule is not planar. However,
the thiourea fragment S1/N1/N2/C8/C9 and the
benzene ring (C1—C6) are essentially planar with a
maximum deviation of 0.003(2) Å for N2 atom from
the least square plane of the thiourea fragment.The
S
S
R
R
R
R
N
N
H
N
N
H
H
H
Scheme 2: Resonance structure of thiourea
Table 3: Hydrogen geometric parameters (Å) of 1-Ethyl-3-(3-methoxyphenyl)thiourea 1e
D¯H….A
D¯H
H….A
D….A
D¯H….A
N1¯H1A…..S1i
N2¯H2A…..O1ii
0.866(14)
0.865(19)
2.528(16)
2.331(17)
3.3678(18)
3.126(2)
163.6(16)
152.9(19)
Symmetry codes: i= -x,1-y,-z, ii= -x,1-y,1-z
Scheme 3: Reaction scheme of thiourea binding with metal ions

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HASBULLAH et al., Orient. J. Chem., Vol. 33(2), 800-806 (2017)
1a
1b
1d
Fig. 3:The interaction of compound 1a, 1b and 1d with metal cations
two planes forming a dihedral angle of 88.54(9)°, the naked-eye in DMSO solvent mixture in the
which is considerably bigger than that found in presence of metals such as Fe, Pb, Hg, Ni, Ag, Cu
1-(2-Hydroxyethyl)-3-(3-methoxyphenyl)thiourea and Sn. It was determined that ethyl thiourea as
of 62.57(4)°. Other bond lengths and angles are 1a – 1f did not exhibit naked-eye sensor properties
comparable to those in the analog and lie in normal for Fe, Pb, Ni, Cu and Sn metals. However, the
ranges (Table 2).
compounds exhibited selective sensor behavior for
Hg+ and Ag+ metal ions (Fig. 3).
The intramolecular hydrogen bonds does
not exists in the molecule while in the crystal
Thiourea derivatives contain a relatively
packing the molecules are linked by N1—H1A···S1 basic C=S group that interacts with the metal
and N2—H2A···O1 intermolecular hydrogen bonds ions. The C=S bond which was weak and had the
(Table 3), to form infinite one-dimensional chains resonance structure (Scheme 2) was the dominant
along the c axis (Fig. 2).
resonance contributor.8 The resonance structure will
be the nucleophile to attack the metal ions to form a
The ability and sensor features of stable complex (Scheme 3).
compounds 1a, 1b and 1d were investigated using

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HASBULLAH et al., Orient. J. Chem., Vol. 33(2), 800-806 (2017)
CONCLUSIONS
showed that ethyl thiourea 1a, 1b and 1d have the
ability as naked eye sensors for mercury (Hg) and
argentum (Ag) metal ions.
In the present work, ethyl thiourea
1a – 1f were prepared from the simple reaction
method and are characterised using various spectral
techniques. From the X-ray crystallography study
of 1e, molecule crystallized in a monoclinic crystal
system with space group of P21/n and the unit cell
dimensions are a = 11.0797(7) Å, b = 8.6081(6) Å,
c = 11.9698(7) Å, a = 90°, b =104.543(2)°, g = 90°,
Z = 4 and V = 1105.04(12) Å3. Preliminary study
ACKNOWLEDGEMENT
The authors thank the Ministry of Higher Education
of Malaysia and University Kebangsaan Malaysia
for the research grant FRGS1/2015/ST01/UKM/02/2
and PRGS/2/2015/SG01/UKM/02/1 for the X-ray
facility.
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