Synthesis of Betti base derivatives catalyzed by nano-CuO-ionic liquid and experimental and quantum chemical studies on corrosion inhibition performance of them

Article abstract of DOI:10.1007/s11164-018-3287-2

In this research, for the first time, aminonaphthol derivatives were introduced as efficient corrosion inhibitors. A linear polarization method was employed to investigate the corrosion inhibitory effect of the synthesized aminonaphthols at a concentratio

Full text of DOI:10.1007/s11164-018-3287-2

Res Chem Intermed
https://doi.org/10.1007/s11164-018-3287-2
Synthesis of Betti base derivatives catalyzed
by nano‑CuO‑ionic liquid and experimental
and quantum chemical studies on corrosion inhibition
performance of them
1
2
1
Reza Teimuri‑Mofrad · Iraj Ahadzadeh · Mahdi Gholamhosseini‑Nazari ·
1
1
Somayeh Esmati · Aziz Shahrisa
Received: 29 September 2017 / Accepted: 11 January 2018
Springer Science+Business Media B.V., part of Springer Nature 2018
©
Abstract In this research, for the ꢀrst time, aminonaphthol derivatives were intro-
duced as eꢁcient corrosion inhibitors. A linear polarization method was employed
to investigate the corrosion inhibitory eꢂect of the synthesized aminonaphthols at a
concentration of 200 ppm for mild steel acid pickling in 1 M HCl and 0.5 M H SO
2
4
solutions. The results showed that, even in such strongly corrosive media, all of the
synthesized aminonaphthol derivatives exhibit good inhibitory eꢂects toward mild
steel corrosion with inhibition eꢁciencies in the range of 84–95%. A facile, eꢁ-
cient and environmentally friendly method has been introduced for the synthesis
of aminonaphthol derivatives by nano-CuO in ionic liquid as a novel catalytic sys-
tem. Mild, one-pot, operational simplicity and reusability of the catalyst make this
protocol highly signiꢀcant. Experiments showed that these compounds can be used
as eꢂective corrosion inhibitors for mild steel acid pickling. The semi-emperical
B3LYP method was used for the theoretical calculations. The results of quantum
chemical studies conꢀrmed the experimental ꢀndings.
Keywords Betti bases · Nano-CuO · Ionic liquid · Corrosion inhibitor · Linear
polarization · DFT calculations
Electronic supplementary material The online version of this article (https://doi.org/10.1007/
s11164-018-3287-2) contains supplementary material, which is available to authorized users.
*
Reza Teimuri-Mofrad
teymouri@tabrizu.ac.ir
1
2
Laboratory of Organic Synthesis Research, Department of Organic and Biochemistry, Faculty
of Chemistry, University of Tabriz, Tabriz 5166614766, Iran
Research Laboratory for Electrochemical Instrumentation and Energy Systems, Department
of Physical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz 5166614766, Iran
1
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R. Teimuri-Mofrad et al.
Introduction
Compounds with nitrogen- and oxygen-containing functional groups are an
important structural motif of the various biologically active natural products and
drugs [1–4]. A series of these types of compounds are the aminonaphthols, so-
called ‘Betti bases’, [5] which exhibit interesting biological activities [6–8]. Vari-
ous publications have reported the use of the Betti reaction to prepare interme-
diates of drug-like compounds [9, 10]. The hydroxyl and amino groups in the
structure of aminonaphthols make them potent ligands to chelate with organo-
metallic reagents, and they can be used as catalysts for asymmetric induction
reactions [11, 12]. Reaction of aminonaphthols with aldehydes causes the forma-
tion of 1,3-oxazine derivatives which are biologically active scaꢂolds [13–15].
Recently, the synthesis of aminonaphthols has attracted growing interest owing to
the above-mentioned uses [16–19].
In recent years, nanocrystalline metal oxides have been considered as one of
the most promising catalysts in place of traditional catalysts [20, 21]. In modern
organic synthesis, copper (II) oxide nanoparticles (NPs) have been widely used as
catalysts due to their good stability and commercial availability [22–24]. These
nanoparticles are widely used to catalyze various useful chemical transformations
such as carbon–carbon and carbon–heteroatom (C–N, C–O and C–S) bond forma-
tion [25–27]. Studies have shown that the use of nanosized copper catalysts in
combination with ionic liquids provides more eꢂective processes and has more
advantages compared with traditional methods [28].
On the other hand, employing corrosion inhibitors is very essential for the corro-
sion control of metals and alloys in industrial systems. Corrosion inhibitors reduce
the rate of corrosion through one or more of the following mechanisms: decreas-
ing the rate of anodic or cathodic reactions, decreasing the rate of diꢂusion reac-
tants to the metal surface, and increasing the electrical resistance of the surface of
metals through the formation of a surface passive metal oxide or insoluble complex
[29–34]. Synthetic organic compounds with N, O and S atoms in their structures
exhibit good corrosion inhibition and therefore are being widely studied and used
for industrial corrosion protection applications [35–38]. Development of cheap,
eꢂective and environmentally safe corrosion inhibitors has always been a global
industrial and environmental concern [39–46]. As a part of our interest in the devel-
opment and optimization of multi-component reactions, we have recently reported
eꢁcient methods for the synthesis of aminonaphtol derivatives [47–52]. Here, we
wish to introduce CuO NPs in ionic liquid as an ideal catalytic system for the syn-
thesis of aminophenol derivatives via the one-pot three-component condensation of
amines, aromatic aldehydes and β-naphthol (Scheme 1). Betti bases synthesized by
this new route were applied as eꢁcient corrosion inhibitors for mild steel acid pick-
ling in 1 M HCl and 0.5 M H SO solutions. We used a linear polarization (LP)
2
4
method to investigate the corrosion inhibitory eꢁciency of the synthesized Betti
bases at a concentration of 200 ppm. Finally, theoretical calculations using the semi-
emperical B3LYP/6-31G method were performed. The results of quantum chemical
studies conꢀrmed the experimental ꢀndings.
1
3

Synthesis of Betti base derivatives catalyzed by nano‑CuO‑ionic…
Scheme 1 Synthesis of aminonaphthol derivatives
Experimental
Materials and methods
Melting points were determined on a MEL-TEMP model 1202D and are uncor-
rected. FT-IR spectra were recorded on a Bruker Tensor 27 spectrometer as KBr
1
disks. The H NMR spectra were recorded on a Bruker Spectrospin Avance 400
1
3
spectrometer using CDCl3 as the solvent. C NMR spectra were determined on
the same instrument at 100 MHz. All chemical shifts are reported as d (ppm) and
coupling constants (J) are given in Hz. A ꢀeld emission scanning electron micro-
scope (FE-SEM) instrument (Tescan MIRA3) was used. The chemical reagents
used the syntheses were purchased from Merck and Sigma-Aldrich and used
without any further puriꢀcation. All the quantum calculations were performed
using the DFT method at B3LYP/6-31G (d) level in gas phase with the Gaussian
0
9 W software package [58, 59].
General procedure for the synthesis of aminonaphthols 4a–g
To a mixture of aldehyde (1 mmol), amine (1.2 mmol) and β-naphthol (1 mmol)
in [BMIM][OH], nano-CuO (12.5 mg) was added. The reaction mixture was
stirred at 60 °C on a preheated oil bath. After completion of the reaction (pro-
gress of the reaction was checked by TLC), hot ethanol (10 ml) was added and
the solution was ꢀltered for the separation of the catalyst. Then, the mixture was
cooled to room temperature, and the product was precipitated and collected by
ꢀ
ltration. The residue was puriꢀed by recrystallization from (EtOH/acetone, 4:1)
to give the desired aminonaphthols as a pure solid.
Selected spectral data for synthesized compounds
1
‑(Phenyl (pipyridin‑1‑yl) methyl) naphthalen‑2‑ol (4a) White solid; M.p: 192–
−
1 1
1
94 °C; FT-IR (KBr) ν 3423, 3062, 3019, 2948, 1635, 1478, 1041 cm ; H NMR
(
400 MHz, CDCl ): δ 1.21–1.65 (m, 6H, CH2), 1.89–2.07 (m, 2H, –NCH), 2.65 (m,
3
1
3

R. Teimuri-Mofrad et al.
1
7
7
H, –NCH), 3.29 (m, 1H, –NCH), 5.06 (s, 1H, methine-H), 7.14–7.25 (m, 5H, Ar–H),
.34 (t, 1H, J = 7.6 Hz, Ar–H), 7.54 (m, 2H, Ar–H), 7.64 (d, J = 8.8 Hz, 1H, Ar–H),
.67 (d, J = 8.8 Hz, 1H, Ar–H), 7.82 (d, J = 8.4 Hz, 1H, Ar–H), 14.06 (bs, 1H, OH)
1
3
ppm; C NMR (100 MHz, CDCl ): δ 23.1, 25.0, 50.8, 53.7, 71.0, 115.1, 118.9,
3
1
1
19.9, 121.2, 122.1, 125.3, 126.6, 126.8, 127.5, 127.8, 128.1, 128.3, 131.3, 138.6,
54.4 ppm;
1
1
1
2
‑[(2‑Bromophenyl)(piperidin‑1‑yl)methyl]naphthalen‑2‑ol (4k) White solid; M.p:
71–173 °C; FT-IR (KBr) ν 3411, 3053, 2930, 2854, 1561, 1515, 1459, 1248, 1079,
−
1 1
025 cm ; H NMR (400 MHz, CDCl ): δ 1.25–1.77 (m, 6H, CH2), 2.32–2.45 (m,
3
H, –NCH), 2.59–2.62 (m, 1H, –NCH), 3.30–3.34 (m, 1H, –NCH), 5.81 (s, 1H,
methine-H), 7.02–7.06 (m, 1H, Ar–H), 7.13–7.24 (m, 3H, Ar–H), 7.37 (t, J 7.5, 1H,
Ar–H), 7.56–7.61 (m, 2H, Ar–H), 7.66–7.69 (m, 2H, Ar–H), 7.83 (d, J = 8.6 Hz, 1H,
1
3
Ar–H), 14.38 (s, 1H, OH) ppm; C NMR (100 MHz, CDCl ): δ 22.9, 24.9, 25.4,
3
4
1
8.3, 53.8, 68.0, 115.0, 119.1, 120.5, 121.4, 124.6, 125.6, 127.5, 127.6, 127.7, 128.5,
28.6, 130.2, 131.7, 131.8, 137.5, 155.6 ppm.
Electrodes and corrosion tests
Working electrodes (1 cm × 1 cm square) were cut from a mild steel plate with com-
position (in wt%) C 0.01, Si 0.35, P 0.018, Cr 0.04, Mo 0.03, Ni 0.017, Cu 0.02, Al
0
.06, and Fe balance. The samples were polished to mirror ꢀnish, using emery-type
papers. Then, the electrodes were mounted in polyester resin so that only one side
of them was in direct contact with the solution. Th hydrochloric and sulfuric acid
used were of analytical reagent grade (Merck) and double-distilled water was used
throughout for solution preparation and rinsing.
For the electrochemical measurements, a laboratory-made electrochemical setup
consisting of a potentiostat logged to a personal computer was used. In the con-
ventional three-electrode assembly, a graphite plate electrode and a saturated calo-
mel reference electrode (SCE) were used. After immersion of the specimens, prior
to electrochemical measurements, a stabilization period of 30 min was observed,
which proved to be suꢁcient for the open circuit potential (OCP) to attain a sta-
ble value. To be conꢀdent of the reproducibility, each measurement was performed
two or three times with nominally identical electrodes in the same conditions and
the arithmetic average of the results was chosen. Linear polarization was performed
−
1
within the potential range ± 20 mV versus OCP at a scan rate of 1 mV s . Potential
sweep was performed from the cathodic to the anodic direction. All potentials were
reported versus SCE.
Results and discussion
Initially, the reaction of β-naphthol (1a), benzaldehyde (2a) and morpholine (3a)
was chosen as a model reaction. To explore the feasibility, a series of Cu-based cata-
lysts were used in the model reaction under solvent-free conditions at 40 °C.
1
3

Synthesis of Betti base derivatives catalyzed by nano‑CuO‑ionic…
As shown in Table 1, diꢂerent copper salts produced smaller yields (< 17%,
entries 1–6), and when CuO used, the yield relativity increased (23% yield, entry 7).
Nano-CuO gave a promising result in a shorter time (38% yield, entry 8).
For optimizing the reaction conditions, the model reaction was tested in a variety
of solvents, diꢂerent amounts of the catalyst and diꢂerent temperatures (Table 2).
At ꢀrst, a variety of conventional organic solvents and ionic liquids were screened
for the model reaction at 40 °C with the use of 20 mol % of nano-CuO (entries 1–9).
The use of solvents such as EtOH, CHCl and CH Cl aꢂorded the desired prod-
3
2
2
uct in low yields (20–28% entries 1–4), and conventional ionic liquids aꢂorded
the related product in moderate yields (32–53% entries 4–9). Interestingly the best
results were achieved in [BMIM][OH] (53% yield, entry 7).
The model reaction was then performed with the use of diꢂerent quantities of
nano-CuO (7.5, 10, 12.5 and 15 mol%) (entries 10–13) and at various temperatures
(
entries 14–18). As Table 2 shows, the use of 10 mol% of nano-CuO at 60 °C pro-
duced the best result (87% yield, entry 16). To develop the scope and generality
of the procedure, the reaction of β-naphthol with diꢂerent aldehydes and amines
was performed with the use of nano-CuO in [BMIM][OH] (10 mol%) at 60 °C. As
shown in Table 3, in all cases the desired products (4a-q) were obtained in a short
period of time (40–60 min) in good yields (81–90%).
Table 1 Screening of the catalytic activity of various Cu-based catalysts in the model reactiona
Entry
Catalyst (20 mg)
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
CuI
CuBr
CuCl
Cu (CH COO)
Cu (NO3)2
CuSO4
CuO
90
90
90
90
90
90
90
60
< 10
< 10
< 10
15
14
16
3
2
23
38
nano-CuO
a
Reaction conditions: β-naphthol/benzaldehyde/morpholine = 1:1:1.2 at 40 °C under solvent-free condi-
tions
b
Isolated yield
1
3

R. Teimuri-Mofrad et al.
Table 2 Optimization of temperature, solvent and amount of nano-CuO in the model reactiona
Entry
Catalyst amount Solvent
mg)
Temperature
Time (min)
Yield (%)b
o
(
( C)
1
2
3
4
5
6
7
8
9
20
20
20
20
20
20
20
20
20
15
12.5
10
7.5
10
10
10
10
10
EtOH
40
40
40
40
40
40
40
40
40
40
40
40
40
25
50
60
70
80
90
90
90
90
75
75
75
75
75
75
75
75
75
75
60
50
50
50
28
24
21
20
39
44
53
32
33
53
52
53
41
34
79
89
88
84
CHCl3
CH Cl
2
2
H2O
[BMIM] [Cl]
[BMIM] [Br]
[BMIM] [OH]
[BMIM] [BF4]
[BMIM] [PF6]
[BMIM] [OH]
[BMIM] [OH]
[BMIM] [OH]
[BMIM] [OH]
[BMIM] [OH]
[BMIM] [OH]
[BMIM] [OH]
[BMIM] [OH]
[BMIM] [OH]
10
11
12
13
14
15
16
17
18
a
Reaction conditions:β-naphthol/benzaldehyde/morpholine = 1:1:1.2
Isolated yield
b
The recyclability of the catalyst was next investigated using the model reaction in the
presence of nano-CuO in [BMIM][OH] (10 mol%) at 60 °C. After work-up and separa-
tion of the catalyst, the obtained nanocatalyst was washed with diethyl ether (3×5 mL),
and dried under vacuum for reuse in subsequent reactions. The recovered catalyst was
reused for 3 runs without any loss in activity. As evident from the FE-SEM images of
the nano-CuO before and after three cycles, the morphology of the catalyst remained
unchanged (Fig. 1).
A plausible mechanism for the nano-CuO-catalyzed reaction is proposed in
Scheme 2. The interaction between the catalyst and the carbonyl group of the aldehyde
leads to the increase of the electrophilicity of the carbonyl. The amine then reacts with
the activated aldehyde and, after dehydration, iminium ions are generated. Finally, the
nucleophilic attack of the β-naphthol to the iminium ions produces the desired product.
Then, the application of aminonaphthol as a corrosion inhibitor was investigated for
the ꢀrst time. Table 4 shows the linear polaraization resistance (LPR) and OCP values
of the mild steel electrodes in corrosive media in the presence of 200 ppm of the syn-
thesized aminonaphthols.
Equation (1) was used for the calculation of Inhibition eꢁciencies (%η):
ꢀ
ꢀ ꢀ
ꢀ
% = [(1 R ) − (1∕R)] (1 R )
(1)
0
0
1
3

Synthesis of Betti base derivatives catalyzed by nano‑CuO‑ionic…
Table 3 The synthesis of aminonaphthols with nano-CuOa
R
1
R
2
R
3
, R
4
Time
(min)
Yield
mp
Entry
Product
b
o
(Aldehyde)
(amine)
(%)
( C)
1
H
H
H
Benzaldehyde
Piperidine
60
50
40
86
85
90
192–194
151–153
178–179
2
-Chloro
2
3
Piperidine
Piperidine
benzaldehyde
4-Nitrobenz
aldehyde
3-Nitrobenz
aldehyde
4
H
Piperidine
50
88
170–172
2
40°C
5
6
H
H
2-Naphtaldehyde
Benzaldehyde
Morpholine
Morpholine
60
50
87
89
(
dec.)
174–175
1
3

R. Teimuri-Mofrad et al.
Table 3 (continued)
R
R
2
R
3
, R
4
Time
(min)
Yield
mp
Entry
Product
(%)b
o
1
(Aldehyde)
(amine)
( C)
2
-Chloro
7
8
H
Morpholine
55
86
86
163–164
161–163
benzaldehyde
3
-Chloro
H
H
Morpholine
Morpholine
60
benzaldehyde
4
-Chloro
9
50
90
156–157
benzaldehyde
4
-(N,N-
1
0
H
Dimethylamino)
benzaldehyde
Morpholine
60
81
134–136
2
-Bromo
11
12
13
H
H
H
Piperidine
Morpholine
Piperidine
55
55
50
85
86
87
171–173
163–165
159–161
benzaldehyde
2
-Bromo
benzaldehyde
2
-Bromo-5-Fluoro
benzaldehyde
1
3

Synthesis of Betti base derivatives catalyzed by nano‑CuO‑ionic…
Table 3 (continued)
R
R
2
R
3
, R
4
Time
(min)
Yield
mp
Entry
Product
(%)b
o
1
(Aldehyde)
(amine)
( C)
2
-Bromo
1
4
5
Br
Piperidine
50
50
84
86
181–183
180–182
benzaldehyde
2-Bromo
1
Br
Morpholine
benzaldehyde
2
-Bromo-5-Fluoro
1
6
7
Br
Br
Morpholine
Pyrolidine
50
45
86
83
164–165
177–179
benzaldehyde
2-Bromo
benzaldehyde
1
a
Reaction conditions: β-naphthol/Aldehyde amine = 1:1:1.2 and nano-CuO (10 mg) at 60 °C in [BMIM]
[
OH]
b
Isolated yield
2
where R and R are the values of the LPR (in Ω.cm ) observed in the absence
0
(
Blank) and presence of the inhibitors, respectively. Corrosion inhibition parameters
are reported in Table 4, from which it is clear that LPR values and hence corrosion
inhibition eꢁciencies increase signiꢀcantly in the presence of the aminonaphthols.
The corrosion potential also changes markedly in a rather non-uniform fashion.
Comparison of LPR values and calculated inhibition eꢁciencies of diꢂerent
derivatives of aminonaphthol clearly show some interesting points:
1
. LPR values and calculated inhibition of eꢁciencies aminonaphthol derivatives
with piperidine moiety are higher than aminonaphthol derivatives with morpho-
line moiety (entries 1, 6; 2, 7, 11, 12).
2
. The nitro group in the ortho position of aldehyde increases the inhibition eꢁcien-
cies and LPR values, The nitro group substituted in the para position of aldehyde
decreased these values (entries 1, 3, 4).
1
3

R. Teimuri-Mofrad et al.
Fig. 1 FE-SEM images of a fresh nano-CuO and b nano-CuO after three cycles
3
4
5
. The additional aromatic ring in the structure of aminonaphthol signiꢀcantly
increases the inhibition eꢁciency and LPR values (entries 1, 5).
. The ꢃuoro substituent in the structure of aminonaphthol causes an increase in the
inhibition eꢁciency and LPR values (entries 11, 13, 15, 16).
. The chloro group in the ortho position of the aldehyde has a negligible eꢂect on
the inhibition eꢁciency and LPR values (entries 1, 2, 6, 7) and the existence of
this substituent in the meta and para positions of the aldehyde slightly increases
the inhibition eꢁciency (entries 6, 8). However, the bromo group in the ortho
position of the aldehyde signiꢀcantly decreases the Inhibition eꢁciency and LPR
values (entries 1, 6, 11, 12).
6
7
. The existence of the bromo substituent in the structure of β-naphthol signiꢀcantly
increases the inhibition eꢁciency and LPR values (entries 11, 14).
. The aminonaphthol derivative with the 4-(N,N-dimethylamino) substituent has
the highest inhibition eꢁciency and LPR values (entry 10).
Next, the quantum chemical parameters were calculated using the semi-empirical
B3LYP/6-31G (d) method for the comparison of the experimental and theoretical
inhibition eꢁciencies of the synthesized aminonaphthols. The optimized structure
and calculated HOMO and LUMO molecular orbitals of compound 4j are shown in
Fig. 2.
The amount of the energy of the highest occupied molecular orbital (E
) and
HOMO
the energy of the lowest unoccupied molecular orbital (E
) are related to the
LUMO
reactivity of a compound. The E
shows the ability of electron donating of a
HOMO
molecule. It has been demonstrated that the inhibition eꢁciency increases with the
increase of E values. A compound with a high E value has a tendency to
HOMO
HOMO
donate electrons to a compound with a low E
value. A compound with lower
LUMO
E
could easily accept electrons from a donor compound [53, 54]. ΔE is also a
LUMO
1
3

Synthesis of Betti base derivatives catalyzed by nano‑CuO‑ionic…
δ+
Scheme 2 Proposed mechanisms for the nano-CuO-catalyzed synthesis of aminonaphthols via in a one-
pot, three-component reaction
parameter related to the reactivity of the molecules, as ΔE decreases, the reactiv-
ity and inhibition eꢁciency of the molecules increases [55]. Equations (2–5) were
used for the calculation of the quantum chemical parameters such as E
, E
,
HOMO
LUMO
energy gap (ΔE = E
− E
), the dipole moment (µ), absolute electronagativ-
LUMO
HOMO
ity (χ), global hardness (η) and softness (σ), [56–58] and the results are summarized
in Table 5.
ELUMO + EHOMO
ꢀ
= −
(2)
2
ELUMO − EHOMO
ꢀ
=
(3)
2
1
3

R. Teimuri-Mofrad et al.
Table 4 Corrosion inhibition parameters of the synthesized aminonaphthols as determined from LPR
studies
Entry Compounds LPR (Ω.cm2)
Inhibition eꢁciencies
%η)
Corrosion Potential (mV
vs. SCE)
(
1
M HCl 0.5 M H SO 1 M HCl 0.5 M H SO4 1 M HCl 0.5 M H SO4
2 4 2 2
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
4a
4b
4c
4d
4e
4f
4 g
4 h
4i
4j
4k
4l
4m
4n
4o
4p
4q
128.2
123.9
78.3
142.8
158.2
93.1
110.2
114.8
118.2
122.6
135.6
93.1
93.6
93.4
89.5
94.3
94.6
91.2
91.4
91.8
92.6
94.8
90.0
84.6
93.2
94.2
93.7
94.2
93.7
86.0
86.6
87.0
87.4
88.6
83.5
81.9
87.5
87.1
91.3
91.1
84.7
88.4
89.7
88.6
91.1
89.9
− 320
− 202
− 52
− 430
− 185
− 153
− 176
− 123
− 153
− 630
− 385
− 258
− 166
− 122
− 254
− 330
− 105
− 183
− 186
− 173
− 285
− 435
− 254
− 350
− 222
− 352
− 385
− 435
− 285
− 323
− 212
− 157
− 295
− 335
95.1
85.2
100.0
110.3
158.8
82.1
123.6
119.2
174.2
172.4
100.8
132.8
150.2
135.1
172.4
152.6
0
1
2
3
4
5
6
7
53.4
120.8
140.2
130.2
140.8
130.2
2
2
LPR values for Blank 1 M HCl = 8.2 Ω cm and for 0.5 M H SO = 15.4 Ω cm
2
4
Fig. 2 a The optimized structure, b HOMO and c LUMO distribution for compound 4j
As illustrated at Eq. (4) the softness, σ, is the inverse of global hardness:
1
ꢀ
=
(4)
ꢁ
The hardness and softness amounts could be a factor in the stability and reac-
tivity of the molecules. Soft molecules which have small energy gaps are more
1
3

Synthesis of Betti base derivatives catalyzed by nano‑CuO‑ionic…
Table 5 Quantum chemical parameters of compounds 4a–q
Entry Compounds EHOMO (eV) ELUMO (eV) ∆E (eV) µ (D) χ (eV) η (eV) σ (eV−1
) ∆N (e)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
4a
4b
4c
4d
4e
4f
4 g
4 h
4i
4j
4k
4l
4m
4n
4o
4p
4q
− 5.3198
− 5.2882
− 5.6815
− 5.6273
− 5.3302
− 5.4488
− 5.4306
− 5.5946
− 5.5919
− 4.8256
− 5.2488
− 5.3737
− 5.3312
− 5.3772
− 5.5010
− 5.5190
− 5.5100
− 0.9861
− 1.0044
− 2.1187
− 2.1072
− 1.0493
− 1.0563
− 1.0686
− 1.1608
− 1.1799
− 0.9241
− 1.0035
− 1.0637
− 1.0699
− 1.2762
− 1.3325
− 1.3753
− 1.2629
4.3337 1.7681 3.1529 2.1668 0.4615 0.8877
4.2838 2.8434 3.1463 2.1419 0.4669 0.8996
3.5628 6.4937 3.9001 1.7814 0.5613 0.8701
3.5201 5.8998 3.8672 1.7600 0.5682 0.8899
4.2809 1.9201 3.1897 2.1404 0.4672 0.8901
4.3925 2.1155 3.2525 2.1962 0.4553 0.8531
4.3620 2.5754 3.2496 2.1810 0.4585 0.8598
4.4338 2.5792 3.3777 2.2169 0.4511 0.8169
4.4120 3.3893 3.3859 2.2060 0.4533 0.8191
3.9015 2.5271 2.8748 1.9507 0.5126 1.0573
4.2453 2.7133 3.1261 2.1226 0.4711 0.9125
4.4100 2.5661 3.2187 2.1550 0.4640 0.8574
4.2613 1.8689 3.2005 2.1306 0.4693 0.8916
4.1010 3.8322 3.3267 2.0505 0.4877 0.8957
4.1685 2.8556 3.4167 2.0842 0.4798 0.8596
4.1437 3.6225 3.4471 2.0718 0.4827 0.8574
4.2471 3.8533 3.3864 2.1235 0.4709 0.8508
0
1
2
3
4
5
6
7
reactive than hard molecules because the electron from a soft molecule could be
easily moved to an acceptor [56]. The Pearson electronegativity scale was used
for the calculation of the fraction of transferred electrons (ΔN) from the corro-
sion inhibitor to the metal atoms, according to Eq. (5) [58]:
ꢀFe − ꢀinh
ΔN = ꢀ2(ꢁ
ꢁ]
(5)
Fe
+ ꢁinh
In this equation, χ and χ demonstrate the absolute electronegativity of the
Fe
inh
iron and inhibitor, respectively, η and η demonstrate the absolute hardness of
Fe
inh
the iron and inhibitor molecule, respectively. According to previous literature,
the theoretical values of χ = 7.0 eV and η = 0 were used [56].
Fe
Fe
Quantum chemical calculations showed that the highest value of E
HOMO
(
− 4.8256 eV) and lowest value of ΔE (3.9015 eV) are related to compound 4j.
This compound also has the highest value of σ (0.5126 eV). These data show
that compound 4j has the highest corrosion inhibition eꢁciency which is in good
agreement with the obtained experimental data. The value of ΔN also shows that
the inhibition eꢁciency is highest in compound 4j. The results show that replac-
ing a hydrogen atom with an electron-donating substituent (N,N-dimethylamino)
improves the corrosion inhibition eꢁciency.
1
3

R. Teimuri-Mofrad et al.
Conclusions
In summary, we have developed the application of aminonaphthols as a corrosion
inhibitor for the ꢀrst time. We also introduced the nano-CuO/ionic liquid as a new
and eꢁcient catalytic system for the synthesis of aminonaphthols via the three-com-
ponent reaction of aldehydes, amines and β-naphthol. The mild reaction conditions,
simplicity of workup and short reaction times make this method very attractive.
All synthesized aminonaphthol derivatives were applied as highly eꢁcient corro-
sion inhibitors for mild steel corrosion prevention in hydrochloric and sulfuric acid
solutions. The results showed that, even in such strongly corrosive media, all of the
synthesized aminonaphthols exhibits good inhibitory eꢂects toward mild steel cor-
rosion with inhibition eꢁciencies in the range of about 81–95%. Therefore, these
compounds can be practically used as eꢂective corrosion inhibitors for acid pickling
applications. The quantum chemical properties, such as the E
, E
, energy
LUMO
HOMO
gap (ΔE), the dipole moment (µ), absolute electronagativity (χ), global hardness (η)
and softness (σ) were calculated at the B3LYP/6-31G (d) level with Gaussian 09 W
software. According to the theoretical studies, compound 4j has the highest corro-
sion inhibition eꢁciency which corroborates well with the experimental ꢀndings.
Acknowledgements The authors would like to acknowledge the ꢀnancial support from the Iran
National Science Foundation (INSF) and the University of Tabriz.
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