′-((2-methoxy-naphthalene-1-yl)methylene) pyrimidine-5-carbohydrazide (H5) and

Abstract
Corrosion of carbon steel is a major problem that destroys assists of industries and world steel installations; the importance of this work is to introduce new heterocyclic compounds as effective and low-cost corrosion inhibitors. Three compounds of carbohydrazide derivatives, namely: 5-amino-N′-((2-methoxynaphthalen-1-yl)methylene)isoxazole-4-carbohydrazide (H4), 2,4-diamino-N′-((2-methoxy-naphthalene-1-yl)methylene) pyrimidine-5-carbohydrazide (H5) and N′-((2-methoxynaphthalen-1-yl)methylene)-7,7-dimethyl-2,5-dioxo-4a,5,6,7,8,8a-hexahydro-2H-chromene-3-carbohydrazide (H6) were used to examine the efficacy of corrosion of carbon steel in 1 M hydrochloric acid solution. This corrosion efficacy was detected by utilizing various methods including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), weight loss measurements (WL), surface morphology analyses by atomic force microscopy (AFM), quantum chemical computations based on density functional theory (DFT) and molecular dynamics (MD) simulation. The results indicated that these compounds act as mixed type inhibitors i.e. reduce the corrosion rate of carbon steel due to the formation of a stable protective film on the metal surface and reduce the cathodic hydrogen evolution reaction. As confirmed from impedance, carbohydrazide derivatives molecules are adsorbed physically on metal surface with higher corrosion efficacy reached to (81.5–95.2%) at 20 × 10⁻⁶ M concentration at room temperature. Temkin isotherm model is the most acceptable one to describe the carbohydrazide derivative molecules adsorption on the surface of carbon steel. Protection mechanism was supported by quantum chemical analyses and Monte Carlo modeling techniques. The theoretical calculations support the experimental results obtained. This proves the use of carbohydrazide derivatives as a very effective inhibitors against the corrosion of carbon steel in acidic media.
1 Introduction
Carbon steel is an essential material for many applications such as factories structures and petroleum pipelines. These structures may be contacted with various solvents that can affect their consistency and durability through aggressive behavior, which ultimately lead to carbon steel corrosion and destruction, especially in acidic media. The cost of corrosion has been estimated at $276 billion per year in the United States.¹ Heterocyclic organic compounds which contain multiple bonds and heteroatoms, such as O, N or S are excellent corrosion inhibitors because it could be adsorbed on the metal surface through these heteroatoms.² The adsorbance of such compounds on the metal surface blocks active sites and reduces the rate of corrosion. However, the effectiveness of the inhibitor depends on the physical and chemical properties of the inhibitor structure, due to the existence of specific functional groups, aromaticity, electronic density, kind of corrosive solution and the structure of the inhibitor.^3–8 Because of its use in numerous industries, the study of organic corrosion inhibitors is a fruitful area of science. The most important result of corrosion inhibition is the control of risks that can arise from decreasing in metal thickness in tanks and pipelines which results in a material leakage and severe consequences as fires and explosions. In other words, the corrosion inhibition increases safety and environmental protection issues.⁹ Many researches have been approved that many heterocyclic compounds such as hydrazide derivatives have a better inhibition role on carbon steel in acidic medium.¹⁰ The hydrazide derivatives have various applications in medicine and engineering fields. Hydrazides derivatives have been elucidated their effectiveness as anticancer, antibacterial, anti-inflammatory, analgesic and antioxidant factors.¹¹ Furthermore, they are also used as effective inhibitors for mitigation of corrosion for various metals as carbon steel. Many scientists as Fouda et al.¹² and Agarwal et al.¹³ has studied various hydrazide derivatives and proved their effective corrosion inhibition efficacy, some of the investigated compounds were followed Temkin isotherm and the others were followed Langmuir isotherm.^14–16 In continuation to our previous study,¹⁷ the objective of this research is to examine the effectiveness of three newly synthesized hydrazide derivatives as carbon steel corrosion inhibitors by introducing various electron donating atoms such as N and O atoms or donating group such as (CH₃) and (OH) in these compounds. The investigated compounds are similar in the structure in the hydrazide nucleus but differ in the substituents that affect the compounds inhibition abilities. The corrosion inhibition of the investigated compounds was further deduced using quantum chemical calculations and Monte Carol simulations techniques.