Synthesis and theoretical study of new barbituric acid derivatives as corrosion inhibitors for mild steel

Article abstract of DOI:10.14233/ajchem.2018.21595

Two barbiturates namely, 5-(4-nitrobenzylidene)pyrimidine-2,4,6-Trione [N1] and 5-Amino-2-[4-((2,4,6-Trioxotetrahydropyrimidin-5-ylidene)methyl)phenoxy]benzoic acid [N2] were synthesized. The molecular structure, electronic construction and efficiency of

Full text of DOI:10.14233/ajchem.2018.21595

Asian Journal of Chemistry; Vol. 30, No. 12 (2018), 2761-2764
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2018.21595
Synthesis and Theoretical Study of New Barbituric
Acid Derivatives as Corrosion Inhibitors for Mild Steel
1
1
2,*
NOOR RAED HADI , HAYDER M. ABDULJALIL and MOHANAD MOUSA KAREEM
1
2
Department of Physics, College of Science, University of Babylon, Hilla, Iraq
Department of Chemistry, College of Science, University of Babylon, Hilla, Iraq
*
Corresponding author: E-mail: mohanad_1972@yahoo.com
Received: 19 July 2018; Accepted: 20 September 2018;
Published online: 31 October 2018;
AJC-19144
Two barbiturates namely, 5-(4-nitrobenzylidene)pyrimidine-2,4,6-trione [N1] and 5-amino-2-[4-((2,4,6-trioxotetrahydropyrimidin-5-
ylidene)methyl)phenoxy]benzoic acid [N2] were synthesized. The molecular structure, electronic construction and efficiency of inhibition
studied using density functional theory (DFT) was achieved by B3LYP/6-31G. The quantum chemical characteristics such as EHOMO,
ELUMO, Egap, negative charge density, total energy, and differences of bond length and angles. Corrosion inhibition potentials was
studied varying with different concentration, temperature and time. In order to determine the reactivity, the available sites attacked by
nucleophile or electrophile was analyzed. The correlation and theoretical results agreed with the experimental data. The prepared compounds
1
13
structure were confirmed by TLC, FTIR, UV-visible and H, C NMR techniques.
Keywords: Barbiturates, Quantum chemical properties, Corrosion inhibition, Density functional theory.
and oxygen atoms in their structure are attracted the interest of
INTRODUCTION
the scientist in the scope of corrosion and industrial chemistry
[14]. Organic compounds are the most efficient inhibitors due
to including some affected factors such as electronegativity, and
conjugation. Physical and chemical properties of the molecule
like size, donor-acceptor atoms, orbital p character,electronic
structure, and types of functional group are affected on the adsor-
ption on the surface of the metal [15]. Donor-acceptor organic
compounds considered excellent corrosion inhibitors due to their
important rule in moving the electrons to unoccupied d orbital
of metal surface forming the coordinating covalent bonds. Also,
they accepted electrons from surface ofmetal to form another
bonds [16,17]. However, barbituric acid is considered to be the
main substance that enters the formation of inhibitory substances.
Barbituric acid is suitable for condensation reaction with cyclic
amide and active methylene group and converted into acid in
aqueous medium to produce barbiturates [18,19].
The industrial fields suffered numerous losses due to corro-
sion and the protection process is the best technique against the
corrosion. Inhibitor of corrosion among the various ways used
to protect the metal surface from the degradation and destruc-
tion, it is considered the best protection methods in industry.
These methods were used because it is cheap and considered
as traditional method [1-4]. The theoretical and experimental
experiments have been conducted to calculate the properties
of inhibitory substance. Due to their anti-corrosive properties,
inhibitors used in different industries, but some of them appeared
affect in the environment. Therefore, researchers have focussed
on preparing the friendly environmentally inhibitors, such as
organic inhibitors [5-12].
Mild steel is an alloy made by combining two or more
metallic elements and the iron is present in higher percentage, to
give the greater resistance to corrosion in acidic or basic medium
The geometry of molecule structure effected on adsorption
on the metal surface where planar molecules are trending to
absorb the metal surface better than those molecules having
less planar. Quantum calculations are found suitable tool for
the elucidate the mechanism of corrosion inhibition [20-22].
[
13]. The chemical inhibitor methods stay the best effective and
practical method among different methods used in treating corro-
sion problems. For this reason, evolution the types of inhibitors for
corrosion based organic compounds includes sulphur, nitrogen,
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(

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762 Hadi et al.
Asian J. Chem.
and continued to stir for another 9 h. The reaction mixture was
cooled to room temperature and washed by 1 N HCl followed
by distilled water (Scheme-I). The solid brown colour product
EXPERIMENTAL
Quantum chemical calculations: B3LYP level will be used
to study the quantum physical calculations. This includes studying
the relation between the structure of molecules and the efficiency
of corrosion inhibition of molecules that create a correlation
between structural and electronic characteristics of molecules
and experimental data. Density functional theory (DFT) used
to optimize the molecules geometry by Becke's three parameter
interchange functional along with Lee-Yang-Parr correlation
functional (B3LYP) [23].
This study includes the calculation of theoretical physical
and chemical parameters like energy of the lowest unoccupied
molecular orbital (ELUMO), highest occupied molecular orbital
HOMO), energy gap (∆E), electron affinity (A), ionization
potential (I), softness (S), global hardness (η), electronegativity
(
N2) in 81% yield and m.p. > 250 ºC was obtained. The reaction
was monitored by TLC (acetone:chloroform 3:2, R = 0.54).
),3300(-NH), 3300-2700(-COOH),
040 (C-H arom.), 3118 (C=C-H), 1709 (C=O carboxyl), 1680
C=O amide), 1581 (C=C alkene), 1507,1462 (C=C arom.),
f
-1
IR (KBr,νmax, cm ): 3400(-NH
3
(
2
1
396 (C-NH
2
1
), 1346 (C-NH), 1019 (Ar-O-Ar), 850 (C=C arom.
ring bend.). H NMR (ppm): δ 10.17 (s, H, COOH), 10.14 (s,
2
H, NH), 8.44 (s, 2H, NH
2
), 8.18-8.44 (d, 4H, Ar-H), 7.29-
13
7.26 (d, 3H,Ar-H), 6.04 (s, 1H, HC=). C NMR ( ppm): δ170.61
(
C, COOH), 164.12 (2C, C=O), 152.69 (C, Ar-O), 151.53 (C,
C=C), 148.07 (C, C=O), 142.58 (C, Ar-O), 138.30 (C, Ar-N),
28.83 (C, C-Ar), 126.17 (2C, C-Ar), 123.92 (2C, C-Ar), 122.49
2C, C-Ar), 120.55 (C, H-C=), 116.64 (2C, C-Ar). Anal. calcd.
found) % for C18 : C, 58.85 (58.92); H, 3.54 (3.62);
(
E
1
(
(
(
χ) and chemical potential (K) in eV [24,25].
H
13
N O
3 6
Melting points were conducted in Stuart 30 apparatus and
N, 11.44 (11.38).
are uncorrected. The FTIR spectral analysis is conducted using
Bruker spectrometer device. UV spectra recorded with double
1
beam Spectrophotometer PG CECIL- CE7200 device. H and
13
C NMR spectra recorded on a Bruker AC 400 NMR device
in CDCl -d and DMSO-d with TMS as a reference. Elemental
analyses were done on CHN-Elemental analysis, Euro EA
106. Starting chemical compounds were obtained from Fluka
or Aldrich.
Mild steel composition (wt %): C: 0.370 %; Si: 0.230
; Mn: 0.680 %, S: 0.016 %, Ni: 0.059 %, Co: 0.009 %, Cu:
.160 % and Fe as balance. The mild steel surface was abraded
3
6
1
%
0
and polished with 360 to 1600 grade of emery paper. The dimen-
sions of the steel for this work in the form of a rectangle (10
cm × 2 cm × 0.5 cm) shape.
Synthesis of 5-(4-nitrobenzylidene)pyrimidine-2,4,6-
trione [N1]: Barbituric acid (0.015 mol, 2 g), 4-nitrobenzal-
dehyde (0.015 mol, 2.26 g) and sodium acetate (0.015 mol,
Scheme-I: Synthesis of barbituric acid derivatives
RESULTS AND DISCUSSION
The geometry of a molecule determines many of its physical
and chemical properties. It is necessary to find the relaxation
of molecule, in which the optimized structure of molecule is
the structure in minimum energy which were obtained with
DFT method by three-parameter hybrid-functional of Becke's
(B3LYP), these forms are shown in Fig. 1 by using B3LYP/6-
31G level, which is selected because it has a lower total energy
as shown in Table-1. The results of the parameters of geomet-
rical optimization of [N1] and [N2] compared with experimental
1
.23 g) were mixed in the mortar. The mixture were finely
grounded at room temperature and then the mixture was dissolved
in 10 mL of DMSO, and finally the solution was poured in
cold water (Scheme-I). The product was washed with boiling
water and ethanol which afforded solid yellow product in 73 %
yield, m.p. decomp. > 300 ºC). The reaction was monitored by
-1
TLC (acetone:chloroform::3:2, R
326 (N-H), 3117 (C-H arom.), 3120 (-C=C-H), 1692 (C=O
amide), 1615 (C=C alkene), 1617 (C=C arom.), 1514, 1488
NO ), 1396 (C-NO ), 1346 (C-NH), 850 (C=C alkene bend.),
75 (C=C arom. ring bend.). H NMR (ppm): δ 8.84 (s, 2H,
NH), 8.34-8.41 (d, 2H, Ar-H), 7.88 (d, H, Ar-H), 7.35 (d, H,
f
= 0.67). IR (KBr, νmax, cm ):
1
13
3
results and proved that FT-IR, H NMR and C NMR data are
identical.
(
7
2
2
1
TABLE-1
EHOMO AND ELUMO OF BARBITURIC ACID (N), N1
AND N2 BY BASIS SET 6-31G AT B3LYP
13
Ar-H), 6.69 (s, 1H, HC=). C NMR (ppm): δ 192.32 (C, C=O),
54.34 (C, C=O), 150.59 (C, C=C), 144.91 (C, C=O), 130.61 (C,
C-NO ), 127.82 (C, C-Ar), 124.24 (C, C-Ar), 122.78 (C, C-
Ar), 90.42 (C, H-C=), 40.30-38.64 (C, DMSO solvent). Anal.
calcd. (found) % for C11 : C, 50.57 (50.73); H, 2.68
2.65); N, 16.09 (16.22).
Synthesis of 5-amino-2-(4-((2,4,6-trioxotetrahydro-
pyrimidin-5(2H)-ylidene)methyl)phenoxy)benzoic acid
N2): A mixture compound N1 (0.015 mol, 3.91 g), 5-amino
salicylic acid (0.015 mol, 2.29 g) and K CO (0.015 mol, 2.07 g)
in DMF (10 mL) was heated at 70 ºC and stirred for 9 h under
nitrogen atmosphere, then K CO (0.015 mol, 2.07 g) added
Molecular
EHOMO (eV)
-6.89309
-7.70153
-5.97227
ELUMO (eV)
-1.06096
-3.28818
-2.60273
1
Barbituric acid (N)
2
N1
N2
H
7
N
O
3 5
(
It seems that the electron transfer of reacting species
happened because the interaction between LUMO and HOMO.
The tendency of electron donation from molecule indicated
by measures the energy of HOMO (EHOMO) which promoting
the adsorption of inhibitor molecules on the surface of mild
steel with good inhibition efficiency. While the ability of
(
2
3
2
3

Vol. 30, No. 12 (2018)
Study of New Barbituric Acid Derivatives as Corrosion Inhibitors for Mild Steel 2763
(c)
(b)
(a)
Fig. 1. (a) Optimized geometry for barbituric acid at the B3LYP/ 6-31G basis set, (b) Optimized geometry for N1 at the B3LYP/ 6-31G basis
set, (c) Optimized geometry for N2 at the B3LYP/ 6-31G basis set
molecule to acceptance of electrons indicates by ELUMO. The
ability of inhibitor to bind on the metal surface increased with
increasing of HOMO energy and decreased of LUMO energy.
The physical and chemical reactivity of molecules proved by
the frontier molecular orbital theory (FMO) [26,27].
3.0
2
.5
.0
2
N2 N1
N
1.5
The ∆E gap is a function of inhibitor reactivity on behalf of
the adsorption on metal surface. The % IE (inhibition efficiency)
value of molecule depends on ∆E value, where ∆E decreases
resulting to increase the % IE value. In addition, good inhibition
efficiency depends on lower values of energy differences, due
to that energy which need to remove the electron from the
orbital are low [28]. Therefore, the rigid molecules have high
1
.0
.5
0
0
200
250
300
350
Wavelength (nm)
Fig. 2. UV-visible spectra of compounds N2 (blue line), N1 (red line) and
400
450
500
550
600
-4
N (green line) recorded in DMSO (1 × 10 M)
∆
E gap [29], so soft basis inhibitors are the most effective for
metals than hard molecules (Tables 2 and 3) [30].
peaks correspond to nitrobenzaldehyde entity observed at λmax
=
306 nm while compound N2 displayed a absorption peak
TABLE-2
maxima λmax = 417 nm reflecting the effective of conjugation
to nitrobenzaldehyde and 5-amino salicylic acid units. It is
interesting to note that the onset wavelength of these com-
pounds N, N1 and N2, corresponds to an optically determined
band gap energy Egap = 2.75, 3.90 and 4.60 eV, respectively,
which is close to the theoretical value (Table-2).
ENERGY OF THE BARBITURIC ACID (N), N1
AND N2 MOLECULES BY BASIS SET 6-31G AT B3LYP
Total energy of Total energy of
molecules (a.u) each atom (a.u) gap (eV)
Energy
Molecules
Barbituric acid (N)
-489.880
-963.382
-1309.012
-486.916
-957.223
-1299.599
5.832134
4.413352
3.369538
N1
N2
The weight loss of mild steel in 1, 3 and 5 N of H
2
SO in
4
absence and existence of inhibitor at 25, 35 and 45 ºC, respec-
tively and time are shown in Table-4. The weight loss of mild
The UV-visible spectra of compounds barbituric acid (N),
N1 and N2 in DMSO displayed broad CT bands at end absorp-
tions reaching into 417 nm (Fig. 2). Compound N has an absorp-
tion peak at 263 nm, compound N1 has additional absorption
steel in H
temperature. Also, the results explained that the rate of corro-
sion for mild steel in H SO solutions increasing with increase
2
SO
4
solutions increased with increasing the time and
2
4
TABLE-3
QUANTUM PARAMETERS FOR BARBITURIC ACID (N), N1 AND N2 MOLECULES BY BASIS SET 6-31G AT B3LYP
Molecular
η (eV)
S (eV)
K (eV)
IP (eV)
6.89309
7.70153
5.97227
EA(eV)
1.06096
3.28818
2.60273
Barbituric acid (N)
6.362612
6.057441
4.670904
0.078584
0.082543
0.107046
-5.832134
-4.413352
-3.369538
N1
N2
TABLE-4
RATE OF CORROSION FOR MILD STEEL WITH AND WITHOUT INHIBITOR
Corrosion rate
Without inhibitor
35 °C
With inhibitor (N2)
Conc. of H SO
2
2
4
(
g/h cm )
2
5 °C
45 °C
3.5524 × 10
2.41304 × 10
0.000249375
7.1122 × 10
4.7442 × 10
0.000116979
3.91785 × 10
7.49174 × 10
0.00021017
25 °C
35 °C
4.49486 × 10
45 °C
–
–
–
–
–
–
–
–
–
6
5
5
6
6
5
6
6
5
–5
–5
–5
–6
–6
–6
–6
–6
–6
–6
–6
–6
–5
–6
–6
1
3
5
1
3
5
1
3
5
N
N
N
N
N
N
N
N
N
5.59441 × 10
2.92161 × 10
1.14619 × 10
4.28322 × 10
9.16667 × 10
1.08333 × 10
3.94231 × 10
8.08051 × 10
1.00508 × 10
3.20848 × 10
1.53039 × 10
7.32682 × 10
1.42045 × 10
5.76484 × 10
4.74393 × 10
1.58810 × 10
9.99144 × 10
5.60391 × 10
1.88374 × 10
1.0274 × 10
7.1714 × 10
1.0708 × 10
6.90053 × 10
4.02469 × 10
1.23834 × 10
9.54885 × 10
4.97432 × 10
9.58042 × 10
–5
–5
–6
1 h
3 h
5 h
2.76755 × 10
2.7087 × 10
1.18007 × 10
5.70678 × 10
1.52041 × 10
7.43735 × 10
5.76865 × 10
–5
–6
–5
–5
–6
–5
3.31957 × 10
–5
–6
–5
–5
–6
–5
–5
–6
1.47546 × 10
–5
–5
3.13213 × 10
–5
7.14493 × 10
–6
–5
7.64555 × 10
–6
–5
–6
6.07877 × 10
7.3514 × 10
–5
–6
6.54435 × 10
6.03596 × 10

2
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CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.
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