Abstract: Three kinds of Mannich base corrosion inhibitors BK1, BK2 and BK3 (collectively referred to as BK group corrosion inhibitors) were synthesized by reacting hexylamine, phenylmethylamine and cyclohexylamine with acetone and formaldehyde, respectively. Three kinds of Mannich base corrosion inhibitors (collectively referred to as PA group corrosion inhibitors) were synthesized by reacting hexylamine, phenylmethylamine and cyclohexylamine with acetone and formaldehyde, respectively. In addition, double-Mannich base corrosion inhibitor D1 was synthesized by reacting BK2 with acetone and formaldehyde as a precursor. Double-mannich base corrosion inhibitor D2 was synthesized by reacting PA1 with cyclohexylmethanone and formaldehyde as precursor. The corrosion inhibition of N80 specimens in acidic media was investigated with the eight corrosion inhibitors mentioned above. The quantum chemical parameters of the Mannich base molecules were calculated using density functional theory. The results of grey correlation analysis show that the energy of the lowest unoccupied molecular orbital (E_LUMO)，the energy gap(ΔE)，dipole moment(μ)，isotropic average polarizability(α) and negative electrostatic potential of van der Waals surface area (A_S-) had the good correlation with the inhibition rate of Mannich base. The grey correlation degrees ranged from 0.736 to 0.891 and the linear determination coefficients ranged from 0.556 to 0.968. It was concluded that some quantum parameters，such as ELUMO and ΔE of the BK series were lower than those of the PA series，while their μ，α and A_S- were higher than those of the PA series. Compared to the hexyl group of the BK1 and the cyclohexyl group of BK3，the phenylmethyl group of the BK2 increased the polarizability and the area of the negative electrostatic potential，resulting in α and A_S- BK2 > BK1 > BK3. The E_LUMO and ΔE of D1 and D2，due to the second β-carbonyl group，were lower than those of BK2 and PA1. The best corrosion inhibition efficiency was obtained for BK2 in the BK series，and the corrosion inhibition increased with further synthesis to obtain double Mannich base D1. The corrosion inhibition effect was further increased from 99.2 %to 99.4% for N80 specimens under the same conditions.

Key words: corrosion inhibition performance, Mannich base, quantum chemistry, structure-activity relationship