Three Monohalogenated Aminopyrazines as Effective Corrosion Inhibitors for Carbon Steel in Acid Medium

A series of aminopyrazine derivatives were designed and synthesized for the development of effective inhibitors for Q235 steel corrosion in 1.0 M HCl solution, in which the monohalogenated aminopyrazine showed good inhibitive performance. The corrosion protection properties of the monohalogenated aminopyrazine, including 2-amino-5-chloropyrazine (ACP), 2-amino-5-bromopyrazine (ABP), and 2-amino-5-iodopyrazine (AIP), were further investigated using weight-loss test and electrochemical techniques. The results indicated the halogen-substituted aminopyrazine have excellent inhibition performance, and these aminopyrazine derivatives act as mixed type inhibitors with predominant cathodic effectiveness. Adsorption of halogen-substituted aminopyrazine on steel surface obeyed the Langmuir adsorption isotherm. The adsorption of the inhibitor molecules on steel surface was further supported by scanning electron microscope (SEM). The inhibition mechanism of the investigated monohalogenated aminopyrazine was derived using density functional theory (DFT) based quantum chemical calculations for their neutral as well as protonated forms. Both experimental and DFT studies suggested that the inhibition efficiency of three halogen-substituted aminopyrazine followed the order of eta(AIP)>eta(ABP)>eta(ACP).