N. Sait, N. Aliouane, L. Toukal et al.
Journal of Molecular Liquids 326 (2021) 115316
4-(2-{[ethoxy (hydroxy) phosphonyl] (3-nitrophenyl) methyl} hydra-
zinyl) benzoic acid on the corrosion of carbon steel. They found that
the inhibitory adsorption of this phosphonate followed Langmuir
isotherm.
Metal surface modification with self-assembled phosphonic acid
layers has also investigated [29,30]. It is found that the protective
layer was spontaneously formed on metal surface and efficiently pre-
vents the metal from corrosion in sodium chloride solution. However,
X.T. Le [31] found that, the self-assembled benzylphosphonic acid layers
are instable in sulfuric acid due to excess of protons.
Table 1 shows the results of previous studies [24,32–35]. Optimal in-
hibition efficiency greater than 90% can be achieved with phosphonate
in aggressive environments. Furthermore, inhibitory action is due to
the existence of heteroatoms (N, P and O), conjugate bonds and aro-
matic rings in molecular structure which are served as centers of inter-
action between phosphonates and metallic surfaces.
In the present work, the corrosion inhibition efficiency of new phos-
phonic acid, ethylene bis [(2-hydroxy-5,1,3-phenylene) bis methylene]
tetraphosphonic acid (ETPA), which have four phosphonic acid func-
tions and many binding molecules on the corrosion of carbon steel in
3% NaCl solution was studied using potentiodynamic polarization
(PDP) and electrochemical impedance spectroscopy (EIS). Some ther-
modynamic values were deduced from adsorption isotherms. Finally
DFT was employed to find the quantum parameters to estimate the ad-
sorption behavior and describes the mechanism of corrosion inhibition.
round-bottom flask, equipped with a reflux condenser. The mixture
was heated at 150 °C for 6 h. The excess of triethylphosphite was evap-
orated under reduced pressure with diethyl ether. The diethyl 4-
methoxybenzyl phosphonate 3 was then analyzed by 1HNMR. Yield:
(1,5 g, 50%). 1HNMR (CDCl3, δ ppm): 1,29 (t, 14,2 Hz, 2 × CH3, 6H),
3.05 (d,
J = 20.9 Hz, 2H), 3.83 (s, OCH3, 3H), 4.01(q, J =
10.6 Hz,2 × CH2,4H), 6.80 (d, J = 8.1 Hz, arom-H, 2H), 7.17 (d, J =
10.6 Hz, arom-H, 2H).
2.1.3. Synthesis of 1-(1′-methoxy-4′-phenylvinyl)-4-methoxybenzene 4
Compound 4 was prepared according to a published procedure [36]
with some modification as follow: 250 mL reaction vessel equipped
with a magnetic stirrer and reflux condenser. The flask was charged
with (0.100 g, 2.1 mol) of diethyl 4-methoxybenzyl phosphonate and
(0.100 g, 2.1 mol) 4-methoxybenzaldehyde. After stirring for 1 h,
(0.035 g, 2.5 mol) of sodium ethylate in dry DMF (600 mL) was
added. The mixture was stirred for 1 h at 0 °C then at room temperature
for 24 h. The yellow precipitate which was formed was recrystallized by
ice water (yield 80%). 1HNMR (DMSO‑d6, δ ppm): 4.21 (s, 6H, O-CH3),
7.34(d, J = 8.85 Hz, 4H, arom-H), 7.44 (s, 2H, HC_CH), 7.91 (d, J =
10.1 Hz, 4H, arom-H).
2.1.4. Synthesis of 1,2-Bis (4-methoxyphenyl) ethane 5
The reaction vessel is a stainless-steel Parr-Hydrogenator (Parr–
4842) that can stand pressures up to 10 bar. The reaction mixture
which was prepared by adding 0.100 g of 4 and 0.050 g of Pd/C and
4 mL of methanol was stirred for 3 h under H2 atmosphere. The mixture
was diluted with 10 mL EtOH then filtered through celite. The filtrate
was evaporated under vacuum and the remaining residue was washed
with chloroform and dried under vacuum to give 0.098 g (98% yields).
1HNMR (CDCl3, δ ppm): 2.83 (s, 4H, H2C-CH2), 3.79 (s, 6H, O-CH3),
6.83 (d, 4H, arom-H), 7.09 (s, 4H, arom-H).
2. Experimental and theoretical calculation
NMR spectra were recorded with a JeolGX. Purification of the phos-
phonate derivative was performed with a Hewlett-Packard 1100 HPLC
system using C18 column.
2.1. Synthesis of ETPA
2.1.5. Synthesis of Bis (4-hydroxyphenyl)ethane) 6
The novel polyphosphonate (ETPA) was synthesized through a
multi-step process as shown in Scheme 1 (Section 3.1).
Compound 6 was prepared according to the literature [37] with
some modification as follow: (0.1 g, 0.037 mol) of bis-(4-
methoxyphenyl)-ethane was dissolved in dry CH2Cl2 (1.7 mL) and
under nitrogen in a 150 mL Erlenmeyer flask, fitted with a septum.
The solution was cooled to −70 °C in dry ice/2-propanol bath. Boron
tribromide (0.9 mL, 0.078 mol) was added through the septum. The re-
action mixture was stirred at room temperature overnight and then
poured into ice-cold water. After neutralization with an excess of so-
dium acetate (10 mol/L), the resulting suspension was filtered. The pre-
cipitate was washed twice with H2O (20 mL) and air-dried overnight to
give a white crude product. Finally, (0.095 g, 0.035 mol) of white solid
was taken up in methanol (100 mL), filtered and evaporated (yield:
95%). 1HNMR (CD3OD, δ ppm): 2.70 (s, 2 × CH2), 6.65 (d, J = 8.2 Hz,
4 × arom-H), 6.90 (d, J = 8.2 Hz, 4 x arom-H).
2.1.1. Synthesis of 4-methoxybenzyl chlorate 2
2 mol of SiO2, 0.18 mol of trimethylsilyl chloride (TMSCl)) and
1.25 mL of CCl4 were added to 100 mL round-bottom flask. The mixture
was stirred at room temperature for a few minutes and 92.5 mmol of 4-
methoxybenzyl alcohol (2.88 mL) was added drop wise. The mixture
was stirred for 2 h at room temperature. The solvent was evaporated
at 117–118 °C and under 10 mmHg with hexamethyl disiloxane to
give the expected chloride 2 with excellent purity and a 50% yield. Com-
pound 2 can be stabilized by addition anhydrous potassium carbonate
and stored under nitrogen. 1HNMR (CDCl3, δ ppm): 3.19 (s, OCH3, 3H),
3.98 (s, 2H), 6.32 (d, J = 8.2 Hz, 2H), 6.70 (d, J = 8.2 Hz, 2H). 13CNMR
(67.5 MHz, CD3Cl): δ = 46.3 (CH2-Cl), 55.23 (O-CH3), 114.1 (2 × CH),
129.85(2 × CH), 134.1 (C-CH2Cl), 152.8 (C-OCH3).
2.1.6. Synthesis of 4,4-ethylenebis[2,6-bis(hydroxymethyl)phenol] 7
Compound 7 was synthesized according to published procedure
[38], the product 7 is obtained with a yield of (1,4 g, 70%). 1HNMR
(CD3OD, δ ppm): 3.78 (s, 4H, 2 × CH2), 4.65 (s, 8H, 4 × CH2-OH), 6.98
(s, 4H, arom-H).
2.1.2. Synthesis of diethyl4-methoxybenzylphosphonate 3
(2.1 g, 0.21 mol) of 4-methoxybenzyl chloride 2 and (0.26 mol,
1.91 mL) of triethylphosphite were added into a two-neck 100 mL
Table 1
Studies of phosphonates as inhibitors for metals in different corrosive environments.
Compounds
Metal
Aggressive environment
IE (%)
Optimum concentration
Ref
Diethyl(phenyl(phenylamino)methyl)phosphonate (DEPAMP)
[hydroxy(phenyl)methyl] phosphonate Acid (HPMPA)
Phosphatidylcholine
α-aminophosphonates
2-hydroxy-5-[4-hydroxy-3,5-bis(phosphonomethyl)
benzyl]-3-(phosphonomethyl) benzylphosphonic acid,
CS
CS
Cu
CS
CS
1 M HCl
1 M HCl
1 M HCl
92
91
96
94.3
88
10−3 mol/L.
0.4 mM
10%
[32]
[33]
[34]
[35]
[24]
250 g/m3СО2 and 200 g/m3Н2S
50 mg/ml
3% NaCl
10−3
M
2