Synthesis, characterization, and study the inhibitory effect of thiazole and thiadiazole derivatives toward the corrosion of copper in acidic media

Article abstract of DOI:10.1080/15533174.2013.841226

The authors describe the synthesis and characterization of two different five-member heterocycle derivatives (thiazole and thiadiazole) by several organic procedures. These compounds were characterized by FTIR, ¹H NMR, and elemental analyses. A

Full text of DOI:10.1080/15533174.2013.841226

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Synthesis, Characterization, and Study the Inhibitory
Effect of Thiazole and Thiadiazole Derivatives Toward
the Corrosion of Copper in Acidic Media
Ivan Hameed R. Tomia, Ali. H. R. Al-Darajia & Sherien A. Aziza
a Department of Chemistry, College of Science, University of Al-Mustansiriya, Baghdad, Iraq
Accepted author version posted online: 02 Oct 2014.Published online: 24 Oct 2014.
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To cite this article: Ivan Hameed R. Tomi, Ali. H. R. Al-Daraji & Sherien A. Aziz (2015) Synthesis, Characterization, and Study
the Inhibitory Effect of Thiazole and Thiadiazole Derivatives Toward the Corrosion of Copper in Acidic Media, Synthesis and
Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 45:4, 605-613, DOI: 10.1080/15533174.2013.841226
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2015) 45, 605–613
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2013.841226
Synthesis, Characterization, and Study the Inhibitory Effect
of Thiazole and Thiadiazole Derivatives Toward the
Corrosion of Copper in Acidic Media
IVAN HAMEED R. TOMI, ALI. H. R. AL-DARAJI, and SHERIEN A. AZIZ
Department of Chemistry, College of Science, University of Al-Mustansiriya, Baghdad, Iraq
Received 1 July 2013; accepted 1 September 2013
The authors describe the synthesis and characterization of two different five-member heterocycle derivatives (thiazole and
thiadiazole) by several organic procedures. These compounds were characterized by FTIR, 1H NMR, and elemental analyses. Also,
the authors attempt to study the inhibition effects of these derivatives to the corrosion of copper in nitric acid media by weight loss
technique. The temperature factor affecting the inhibition efficiency of these derivatives is discussed. Also, the inhibition efficiency
depended on the changing substituents on the molecules. It was found from the results that the thiadiazole inhibitors have inhibition
efficiency more than thiazole inhibitors.
Keywords: thiazole, thiadiazole, corrosion, Synthesis, inhibitory effect
Introduction
adsorption of these derivatives on the metal surface good,
also these heterocyclic derivatives are considered as non-
The use of heterocycles compounds to inhibit corrosion has cytotoxic substances.[15] This environmentally friendly
assumed great significance due to their applications in pre- property makes them used as inhibitors to replacing some
venting corrosion under various corrosion environments.[1,2] toxic organic inhibitors that are used in the same fields.[16]
The interaction between these compounds and metallic sur-
This work was designed to study (a) corrosion inhibition
face is attributed by adsorption phenomenon. The structures of copper in nitric acid solution by some thiazole and thiadia-
of these compounds have a strong relationship in the inhibi- zole derivatives using weight loss method, (b) the effect of the
tion process, and thus the effect of the functional group in substituent groups in thiazole derivatives on the inhibition
adsorption processes varies because of the diversity of the efficiency, (c) the difference in inhibition ability between thia-
substitutes on these compounds.[3]
zole and thiadiazole derivatives, and also (d) the effect of tem-
Heteroatom derivatives with high electron density, which perature on the corrosion rate.
are considered as adsorption centers, are effective as corrosion
inhibitors.[4–7] The compounds containing both nitrogen and
sulfur atoms in their structures behaved as good inhibitors
when we compared with those containing only one of them.[8]
In the literature, various thiazole and thiadiazole deriv-
atives have been used as corrosion inhibitors for different
metals and solutions and it has been found that these
derivatives have good inhibition efficiency effects.[9–14]
The inhibition properties of these heteroatoms compounds
(thiazole and thiadiazole) are attributed to their molecular
structures. The planarity and pairs of free electrons in het-
eroatoms are an important reason that makes the
Experimental
The inhibitors (1–5) were synthesized in the laboratory
according to the following procedures. These compounds
were characterized by FTIR, 1H NMR, and elemental analy-
sis. All chemicals and solvents were of reagent grade (Aldrich
Chemicals Co.) and used without further purification. Infra-
red spectra were recorded with a Shimadzu 8000 FTIR spec-
trophotometer in the wave number range 4000–400 cm¡1
1
with samples embedded in KBr disc. H NMR spectra were
obtained with Bruker spectrometer model Ultra Shield at
300 MHz. The compounds were dissolved in DMSO-d6 solu-
tion with the TMS as internal standard. The CHNS data
were recorded on EuRO EA model EA3000.
The aggressive solutions used were made of 69% HNO3.
Appropriate concentrations of acid were prepared using
deionized water. The concentration range of inhibitor
Address correspondence to Ivan Hameed R. Tomi, Department
of Chemistry, College of Science, University of Al-Mustansiriya,
Baghdad, 00964 Iraq. E-mail: ivanhrtomy@yahoo.com
Color versions of one or more of the figures in the article can be
found online at www.tandfonline.com/lsrt.

606
Tomi et al.
employed was 50–250 ppm in the 1M HNO3 acid. The and asymm. NH2 group, 1627 (C D N); 1H NMR (DMSO-
weight loss measurements were carried out in 30, 40, 50, and d6, 300 MHz, d): 7.75–7.72 (d, 2H, phenyl), 7.55–7.53 (d, 2H,
60ꢀC for 3 h using sheets of pure copper with dimensions phenyl), 7.10 (s, 2H, NH2), 7.07 (s, 1H, thiazole ring); Anal.
(2 £ 2.5 cm2). Before the measurements, the copper speci- Calcd. for C9H7BrN2S (255 g/mol): C, 42.35; H, 2.75; N,
mens were polished successively with emery paper, degreased 10.98; S, 12.55. Found: C, 42.61; H, 2.77; N, 11.05; S, 12.43.
with acetone, washed with deionized water, and finally dried
4-(2-Aminothiazole-4-yl)-phenol (3): Yield (79%); mp: 208–
at room temperature. The coupons were weighted and 210ꢀC; FTIR (KBr disk cm¡1): 3447, 3304 symm. and
immersed in 1M of HNO3 solution with and without com- asymm. NH2 group, 3198 (O-H), 1616 (C D N); 1H NMR
pounds 1–5. At the end of the test, the coupons were taken
out, washed with distilled water, degreased with ethanol,
washed again with distilled water, dried, and then weighted
again. The loss in weight, corrosion rate (Rcorr.), the degree
of the surface coverage (u), and the percentage of inhibition
efficiency (%IE) were calculated at different inhibitors con-
centrations according to the following equation:-
W1 ¡ W2
DW D
(1)
(2)
(3)
A
DW
Rcorr:
D
t
ꢀ
ꢁ
ꢁ
W
ðWÞ
u D l ¡
W
ðWOÞ
ꢀ
W
ðWÞ
%IE D l ¡
£ 100
(4)
W
ðWOÞ
Where, W1 is the initial weight of the specimen (mg), W2
is the specimen weight (mg) after the immersion period, A is
the area of the specimen (cm2), t is the immersion time (s),
Rcorr. is the corrosion rate (mg/cm2.s), and W(w) and W(wo)
are weight loss of specimen with and without the inhibitors,
respectively.
Preparation of Compounds 1–5
General procedure for preparation the compounds 1–3
These compounds were prepared according to the proce-
dure that was described in Siddiqui et al.[17] The title com-
pounds were prepared by the addition of iodine (2.54 g,
0.01 mol) to the 4-substituted acetophenone (0.01 mol) and
thiourea (1.52 g, 0.02 mol), followed by heating of the mix-
ture overnight in an oil bath at 100ꢀC. After cooling, the
reaction mixture was washed with diethylether (100 mL) to
remove any unreacted iodine and substituted acetophenone.
The solid residue was put in (200 mL) of cold water and
treated with 25% aqueous ammonium hydroxide (to pH 9–
10). The precipitated thiazoles were collected and purified
by crystallization from hot ethanol.
2-Amino-4-(4-chlorophenyl)-thiazole (1): Yield (81%);
mp: 168–170ꢀC; FTIR (KBr disk cm¡1): 3439, 3284 symm.
and asymm. NH2 group, 1633 (C D N); 1H NMR (DMSO-
d6, 300 MHz, d): 7.81–7.79 (d, 2H, phenyl), 7.41–7.38 (d,
2H, phenyl), 7.12 (s, 2H, NH2), 7.04 (s, 1H, thiazole ring);
Anal. Calcd. for C9H7ClN2S (210.5 g/mol): C, 51.31; H,
3.33; N, 13.30; S, 15.20. Found: C, 51.55; H, 3.39; N, 13.50;
S, 15.33.
2-Amino-4-(4-bromophenyl)-thiazole (2): Yield (84%);
mp: 185–187ꢀC; FTIR (KBr disk cm¡1): 3429, 3286 symm.
Fig. 1. 1H NMR spectra of compounds 1, 2, and 3.

Synthesis of Thiadiazole and Thiazole
607
5,50-(Ethane-1, 2-diyldisulfanediyl) bis (1,3,4-thiadiazole-2-
amine) (4): Yield (73%); mp: 256–258ꢀC; FTIR (KBr disk
cm¡1): 3313, 3097 symm. and asymm. NH2 group, 2943 (C-
H) aliph.; 1631 (C D N); 1H NMR (DMSO-d6, 300 MHz, d):
7.32 (s, 4H, 2NH2), 3.49–3.52 (t, 4H, 2CH2); Anal. Calcd.
For C6H8N6S4 (292 g/mol): C, 24.66; H, 2.74; N, 28.77; S,
43.84. Found: C, 24.52; H, 2.71; N, 28.33; S, 43.21.
NH2
NH2
S
S
Br
Cl
N
N
( 2 )
( 1 )
NH2
S
HO
5,50-(Propane-1,3-diyldisulfanediyl)bis(1,3,4-thiadiazole-2-
amine) (5): Yield (77%); mp: 228–231ꢀC; FTIR (KBr disk
cm¡1): 3375, 3113 symm. and asymm. NH2 group, 2933 (C-
H) aliph.; 1602 (C D N); 1H NMR (DMSO-d6, 300 MHz, d):
7.30 (s, 4H, 2NH2), 3.14–3.16 (t, 4H, 2CH2 attached to thia-
diazole ring), 1.99 (m, 2H, CH2 center); Anal. Calcd. for
N
( 3 )
Sch. 1. The chemical structures of compounds 1–3.
(DMSO-d6, 300 MHz, d): 9.4 (br. 1H, phenolic OH), 7.62– C7H10N6S4 (306 g/mol): C, 27.45; H, 3.27; N, 27.45; S,
7.59 (d, 2H, phenyl), 6.98 (s, 2H, NH2), 6.77–6.74 (d, 2H, 41.83. Found: C, 27.33; H, 3.17; N, 27.51; S, 41.92.
phenyl), 6.70 (s, 1H, thiazole ring); Anal. Calcd. for
C9H8N2OS (192 g/mol): C, 56.25; H, 4.17; N, 14.58; S,
16.67. Found: C, 56.31; H, 3.99; N, 14.31; S, 16.42.
Results and Discussion
Synthesis
General procedure for preparation the compounds (4 and 5)
These compounds were prepared according to the modified The aminothiazoles (1–3) (Scheme 1) were synthesized by the
procedure that was described in Tomi et al.[18] To a stirred procedure that was described in Siddiqui et al.[17] The reac-
solution of 2-amino-5-mercapto-1,3,4-thiadiazole (X) tion between thiourea and 4-chloroacetophenone or 4-bro-
(1.00 g, 7.5 mmol) in (25 mL) of absolute ethanol, (0.42 g, moacetophenone or 4-hydroxyacetophenone in the presence
7.5 mmol) of potassium hydroxide that was dissolved in a of iodine as oxidant agent yielded the aminothiazoles 1–3.
minimum volume of water is added slowly. After heating the The suggested mechanism of this cyclization reaction may be
mixture for 15 minutes and cooling, (3.75 mmol) of 1,2- outlined in the Scheme 2.
dibromoethane for compound 4 and 1,3-dibromopropane for
The structures of these compounds were confirmed by
1
compound 5 were added dropwise. The solution was refluxed using elemental analysis and spectral (FTIR and H NMR)
for 5 h, and after cooling the mixture was poured into ice data. These analyses are good evidence, which corresponds
water. The precipitate was filtered and washed several times to the structures of the suggested compounds. The appear-
with water and ethanol then dried.
ance of bands around 3430 and 3285 cm¡1 in FTIR spectra
O
C
O
- HI
CH3
C
CH2I
X
+
I2
X
+
H2C
C
S
C
S
SH
C
NH
NH2
H2N
C
NH2
H2N
X
O
NH
H
HC
C
S
C
HC
S
C
- H2O
NH2
C
NH2
X
X
N
N
OH
X = Cl , Br , OH
Sch. 2. The cyclization mechanism of compounds 1–3.

608
Tomi et al.
Fig. 2. 1H NMR spectrum of compound 5.
and peaks near 7.00 ppm in 1H NMR spectra (Figure 1) that
The aminothiadiazoles 4 and 5 (Scheme 3) were synthe-
is assigned to the amino group on thiazole derivatives are sized by thioetherification reaction between the compound
good evidence for the structures given to the products. Also (X) with 1,2-dibromo ethane and 1,3-dibromo propane in
the band near 1620 cm¡1 in FTIR spectra was utilized to con- ethanolic KOH solution to product the compounds 4 and 5
firm that cyclization reaction was occurring.
respectively. The compound (X) was synthesized according
to the procedure described in the reference.[19] Yield 88%,
mp: 232ꢀC; lit. mp: 232ꢀC.[19]
The bands near 3300 and 3100 cm¡1 in FTIR spectra and
peaks near 7.30 ppm in 1H NMR spectra (Figure 2) that are
assigned to the NH2 group are consistent with their proposed
structures.
N
N
SH
H2N
S
(X)
The microanalytical data of carbon, hydrogen, nitrogen
and sulfur for compounds 1–5 were formed to be satisfactory
and within the permissible limit error.
N
N
N
N
NH2
S
S
C
C
H2N
H2
H2
S
S
N
(4)
Weight Loss Measurement
Table 1 presents the values of percentage inhibition efficiency
(%IE) and corrosion rate obtained from weight loss method
at different concentrations of inhibitors at 30ꢀC for 3 h. It
has been found that all of these compounds inhibit the corro-
sion of copper in 1M HNO3 solution, at all concentrations
used in this study (i.e., 50–250 ppm), thus decreasing the
weight loss of copper metal (Figure 3). The variation of
N
N
N
NH2
S
S
C
C
C
H2N
H2
H2
H2
S
S
(5)
Sch. 3. The chemical structures of compounds 4 and 5.

Synthesis of Thiadiazole and Thiazole
609
Adsorption Isotherm
Table 1. Corrosion parameters for Cu in 1M HNO3 solution in
absence and presence of different concentrations of various
inhibitors from weight loss measurements at 30ꢀC for 3 h.
In order to obtain a better understanding of corrosion inhi-
bition of the metal surface, adsorption isotherms at 30ꢀC
were drawn. The degree of surface coverage (u) for differ-
ent inhibitor concentrations was evaluated from weight
loss data. Data were tested graphically by fitting to various
isotherms. A straight line was obtained by plotting log
(u/1¡u) versus log C (Figure 5) suggesting that the adsorp-
tion of the all organic compounds 1–5 from HNO3 on
copper surface follows Langmuir’s adsorption isotherm
Inhibitor
conc. (ppm)
Weight
loss (mg)
Rcorr. £ 10¡5
%IE
(mg / cm2. s)
(1M) HNO3
4.4821
—
4.15
1) C9H7ClN2S
50
100
150
200
1.9744
1.8861
1.7135
1.6118
1.5015
55.95
57.92
61.77
64.04
66.50
1.83
1.75
1.59
1.49
1.39
(Eq. 5)[20,21]
:
250
logðu=1 ¡ uÞ D logK C logC
(5)
2) C9H7BrN2S
50
100
150
200
250
1.9515
1.8771
1.6659
1.5244
1.4204
56.46
58.12
62.83
65.99
68.31
1.81
1.74
1.54
1.41
1.32
Where, K and C are the adsorptive equilibrium constant and
the concentration of inhibitor, respectively.
3) C9H8N2OS
50
100
150
200
250
4) C6H8N6S4
50
100
150
200
250
5) C7H8N6S4
50
100
150
200
250
1.6919
1.4140
1.1958
0.9479
0.7947
62.25
68.45
73.32
78.85
82.27
1.57
1.31
1.11
0.88
0.74
Effect of the Temperature
The effect of rising temperature on the inhibition efficiency
and the corrosion rate of Cu in 1M HNO3 solution in the
absence and presence of 250 ppm of the selected thiazole
and thiadiazole compounds were studied of weight loss
measurements over a temperature range from 30–60ꢀC for
3 h. From Table 2 and Figure 6 it is clear that the corro-
sion inhibition decreases as the temperature as increases.
This indicates that the corrosion inhibition takes place by
adsorption of the inhibitors at the electrode solution
interface.[22,23]
0.8942
0.6929
0.5526
0.4294
0.2030
80.05
84.54
87.67
90.42
95.47
0.83
0.64
0.51
0.40
0.19
0.8552
0.6356
0.4912
0.3245
0.1135
80.92
85.82
89.04
92.76
97.46
0.79
0.59
0.45
0.30
0.11
The activation energy (Ea) of the corrosion process was
calculated using the Arrhenius equation[24]
:
Rcorr: D A e¡ Ea=RT
(6)
(7)
And logarithmic form
inhibition efficiency to increase in inhibitor concentrations is
shown in Figure 4. It has been indicated that the %IE for all
of these compounds increases with the increase in concentra-
tion of inhibitor.
logRcorr: D logA ¡ Ea=2:303RT
Where A is Arrhenius constant, R is the general gas constant,
and the T value is absolute temperature.
Figure 7 shows Arrhenius plots (log Rcorr vs. 1/T) for
uninhibited Cu in 1M HNO3 and in the presence of the com-
pounds 1–5 (Table 3). The values of Ea can be obtained from
the slope of the straight lines. Ea found to be 98.82, 105.04,
114.56, 128.9, and 130.40 KJ/mol for compounds 1–5,
respectively, and for copper in 1M HNO3 without the inhibi-
tor is equal 76.18 KJ/mol, which is accordance with litera-
ture values.[22]
It is clear that the values of Ea increase in the presence of
the inhibitors. This result is in accordance with the strength
of adsorption on the copper surface[25] and indicates that the
formation of the adsorption film occurs by a physical mecha-
nism.[26] This was attributed to an appreciable decrease in the
adsorption process of the inhibitor on the metal with increase
of temperature and corresponding increase in the reaction
Fig. 3. Weight loss curves for copper in 1M HNO3 in presence
different concentrations of inhibitors (1–5) at 30ꢀC for 3 h.

610
Tomi et al.
Fig. 4. Percentage inhibition efficiency (%IE) curves for copper in 1M HNO3 in presence different concentrations of inhibitors (1–5)
at 30ꢀC for 3 h.
Fig. 5. Log(u/1¡u) vs. log C curves for copper in 1M HNO3 in presence different concentrations of inhibitors (1–5) at 30ꢀC for 3 h.

Synthesis of Thiadiazole and Thiazole
611
Table 2. Inhibition efficiency at 250 ppm of compounds (1–5) for Table 3. Variations of log rate without and with the presence of
the corrosion of Cu in 1M HNO3 after 3h immersion at different inhibitors verses reciprocal of temperature.
temperature.
Log Rcoor.
Inhibition efficiency (IE)
1/T, 10¡3 K¡1 Copper
1
2
3
4
5
Tꢀ/C
1
2
3
4
5
3.300
3.195
3.096
3.003
¡4.38 ¡4.86 ¡4.88 ¡5.13 ¡5.74 ¡5.98
¡3.92 ¡4.18 ¡4.20 ¡4.28 ¡4.30 ¡4.31
¡3.52 ¡3.51 ¡3.62 ¡3.71 ¡3.74 ¡3.76
¡3.15 ¡3.13 ¡3.18 ¡3.22 ¡3.24 ¡3.25
30
40
50
60
66.50
45.01
18.72
5.69
68.31
51.03
20.57
2.28
82.27
55.94
35.43
14.18
95.47
57.54
39.18
18.72
97.46
58.89
41.19
19.8
In this study, we compared the value of%IE at the limiting
rate because of the greater area of the metal that is exposed to value and the corresponding inhibitor concentration. We
HNO3 solution.[27]
concluded that the relative strength of these heterocycles
compounds as inhibitors increases in the following order: 1<
2 < 3< 4< 5.
The derivatives 1–5 have either electron-donating
groups such as OH group in the compound 3, or electron
withdrawing group such as Cl and Br in compounds 1
and 2. The above order of %IE may be originated from
the changing the substituents in the ring. It is clear from
the above sequence that compounds containing electron
donating groups are more efficient inhibitors than those
containing electron withdrawing groups. While the com-
pounds 4 and 5 give further improvement in the inhibition
efficiency due to an increase in the number of active cen-
ters as well as the surface area. Both of inhibitors have
four S and six N atoms as active centers.
Mechanism of Inhibition
The inhibition efficiency of thiazole and thiadiazole deriva-
tives toward the corrosion of copper in 1M HNO3 can be
explained on the basis of the number of adsorption sites, their
charge density, molecular size, mode of interaction with
metal surface, and the ability to form metallic complexes.[27]
It is apparent from the molecular structures that these com-
pounds are able to get adsorbed on the metal surface through
p-electrons of aromatic ring and lone pair of electrons on the
N and S atoms, and as a protonated species such as
amines.[20]
Fig. 6. Percentage inhibition efficiency (%IE) curves for copper in 1M HNO3 in presence different concentrations of inhibitors (1–5)
at varying temperatures for 3 h.

612
Tomi et al.
Fig. 7. Arrhenius plots of copper in 1M HNO3 with and without different inhibitors (1–5).
10. Fouda, A.; Al-Sarawy, A.; Al-Katori, E. Thiazole derivatives as
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12. Singh, A. K.; Quraishi, M. A. The effect of some bis-thiadiazole
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