•Benzothiazole derivatives BTC6T and BTC8T were synthesized.•Their corrosion inhibiting effect against steel in a 1 M HCl solution was studied.•EIS, potentiodynamic polarization, and weight loss methods were used for analysis.•These inhibitors were adsorbed onto surfaces by both physical and chemical means.•Both inhibitors offered enhanced stability and inhibition efficiencies.Two benzothiazole derivatives, namely 2-(n-hexylamino)-4-(3′-N,N-dimethylamino-propyl)amino-6-(benzothiazol-2-yl)thio-1,3,5-s-triazine (BTC6T) and 2-(n-octylamino)-4-(3′-N,N-dimethylamino-propyl)amino-6-(benzothiazol-2-yl)thio-1,3,5-s-triazine (BTC8T), were synthesized to study their corrosion inhibiting effect against steel in a 1 M HCl solution. The corrosion inhibition efficiency was measured using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and weight loss methods. Both inhibitors offered extra stability and higher inhibition efficiencies again steel corrosion than previously reported benzothiazole family inhibitors. These inhibitors can be adsorbed onto surfaces by both physical and chemical means. Finally, quantum chemical parameters were calculated using the density functional theory method (DFT) and the correlation between the theoretical and experimental results are discussed.

Four chiral l-lysine-based gemini surfactants with different spacers were synthesized, namely, disodium (18R,23R)-12,20,21,29-tetraoxo-13,19,22,28-tetraazatetracontane-18,23-dicarboxylate([C12-2-C12]Na2), disodium (18R,25R)-12,20,23,31-tetraoxo-13,19,24,30-tetraazadotetracontane-18,25-dicarboxylate([C12-4-C12]Na2), disodium(18R,27R)-12,20,25,33-tetraoxo-13,19,26,32-tetraazatetratetracontane-18,27-dicarboxylate([C12-6-C12]Na2), disodium(2R,2′R)- 2,2′-(6-chloro-1,3,5-triazine-2,4-diyl)bis(azanediyl)bis(6-dodecanamidohexanoate) ([C12-T-C12]Na2). The chemical structures of the prepared compounds were confirmed by 1H-NMR, ESI–MS and IR spectra. Further, the critical micelle concentration (CMC) of these surfactants in aqueous solutions was determined by surface tension and conductometry methods at 25 °C. Moreover, the adsorption and micellization behaviors of these surfactants were estimated by pC20, the minimum average area per surfactant molecule (Amin), and standard free energy for micellization and adsorption (\( \Updelta G_{\text{mic}}^{^\circ } \) and \( \Updelta G_{\text{ads}}^{^\circ } \)). The results show that the four gemini surfactants have low CMC values and significantly low surface tension. Furthermore, the surfactants show strong adsorption at the air–water interface. The CMC and Amin values of the surfactants were found to be in the order of [C12-2-C12]Na2 < [C12-4-C12]Na2 < [C12-6-C12]Na2 < [C12-T-C12]Na2, which were in agreement with the sequence of \( \Updelta G_{\text{mic}}^{^\circ } \) and \( \Updelta G_{\text{ads}}^{^\circ } \). The circular dichroism of the surfactants indicated the formation of chiral aggregates above the CMC values.

Three novel quaternary ammonium salt cationic gemini surfactants (QAS Cn–2–Cn where n represents the hydrocarbon chain lengths of aliphatic amine, i.e., 6, 8, 12) were synthesized from 2,4,6–trichloro–1,3,5–triazine, ethylenediamine, N,N–dimethylpropane–1, 3–diamine and benzyl chloride. 1H-NMR, 13C-NMR, ESI–MS spectra and elemental analysis were used to confirm the chemical structures of the prepared compounds. Their critical micelle concentrations (CMC) in the aqueous solutions were determined by surface–tension, electrical conductivity and steady–state fluorescence methods respectively. With the increasing length of the hydrophobic chain, the values of their CMC decreased. The values of CMC, γCMC, pC20, Гmax, and Amin were derived from surface tension measurements, while the thermodynamic parameters of micellization (∆Gmic° and ∆Gads°) were determined by electrical conductivity. These properties are significantly influenced by the hydrophobic chain length.

A series of X-type alkyl sulfonate Gemini surfactants (XCn, n = 6, 8, 10) was synthesized by a simple method. The chemical structures of the prepared compounds were confirmed by 1H NMR, 13C NMR, ESI–MS and Elementary analysis. The surface activity and thermodynamic properties of micellization of the X-type alkyl sulfonate Gemini surfactants were compared with sodium dodecylsulfate by means of surface tension. The properties of XCn are superior to those of SDS such as the γCMC and CMC of XC10 are 26.3 mN/m and 0.2 mmol/L respectively. The adsorption isotherms for XCn were established by fitting the pre-CMC surface tension data with a quadratic function. The thermodynamic parameters of micellization (\( \Updelta G_{m}^{ \circ } \), \( \Updelta H_{m}^{ \circ } \), \( \Updelta S_{m}^{ \circ } \)) derived from electrical conductivity indicate that the micellization of XCn is entropy-driven.

A series of novel alkylbetaine zwitterionic gemini surfactants (ZS Cn-2-Cn where n represents the hydrocarbon chain length of aliphatic amine, the values of n are 6, 8, 12, 14) were synthesized from cyanuric chloride, aliphatic amine, N,N-dimethylpropane-1,3-diamine and sodium chloroacetate. The chemical structures of the prepared compounds were confirmed by 1H NMR, 13C NMR, ESI-MS, IR spectra and elemental analysis. Their critical micelle concentrations (CMC) in the aqueous solutions were determined by surface-tension and steady-state fluorescence methods at 30 °C. A relationship between a logarithm of CMC and hydrophobic chain length showed a linear decrease upon increasing of chain length and then a departure from linearity at n = 12. The surface-tension measurements of ZS Cn-2-Cn determined that there is a low CMC, a great efficiency in lowering the surface tension. In addition, adsorption and micellization behavior of ZS Cn-2-Cn were estimated from pC20 and the minimum average area per surfactant molecule (Amin).Graphical abstractResearch highlights▶ The surfactants ZS Cn-2-Cn are novel alkylbetaine zwitterionic gemini surfactants. ▶ The three chlorines of the cyanuric chloride react with –NH2 step by step at high yield, so the synthesis is quite simple and easily controllable. ▶ The novel alkylbetaine zwitterionic gemini surfactants ZS Cn-2-Cn have a low CMC, a great efficiency in lowering the surface tension.

A series of novel dialkyl disulfonate gemini surfactants (2Cn-SCT where n is the carbon number of the hydrophobic chain) were synthesized from cyanuric chloride, aliphatic amine and taurine. The chemical structures of the prepared compounds were confirmed by 1H NMR, 13C NMR, IR spectra, and ESI–MS. Their critical micelle concentrations (CMC) in the aqueous solutions at 25 °C were determined by surface tension and electrical conductivity methods. With the increasing length of the carbon chain, the values of their CMC initially decreased, and then increased with an alkyl chain length of 14. The surface tension measurements of 2Cn-SCT (except for n = 14) determined that there is a low CMC, a great efficiency in lowering the surface tension, and a strong adsorption at the air–water interface. In addition, adsorption and micellization behavior of 2Cn-SCT were estimated from pC20, the minimum average area per surfactant molecule (Amin), and standard free energy micellization and adsorption (\( \Updelta G_{\text{mic}}^{^\circ } \,{\text{and}}\,\Updelta G_{\text{ads}}^{^\circ } \)). These properties are significantly influenced by the chain length n, and the adsorption is promoted more than the micellization.

A series of cleavable aryl sulfonate anionic surfactants were synthesized from cyanuric chloride, aliphatic amine and H-acid mono sodium salt. Their structures were identified by 1H NMR, Infrared Spectrum (IR) and Elementary Analysis (EA). Their critical micelle concentrations (CMC) in aqueous solutions at 25 °C were determined by a steady-state fluorescence probe method and a surface-tension method. With the increasing length of the carbon chain, the value of their CMCs and surface tensions under CMC (γCMC) initially decreased and then reached a minimum (respectively 2.63 × 10−5 mol L−1 and 28.29 mN m−1) when the carbon number was 10. The CMC and γCMC then increased when the carbon number was increased to 12. The results showed that, compared with sodium dodecyl benzene sulfonate (SDBS), such kinds of surfactants have much lower surface adsorption amounts and greater molecular areas on the aqueous surface.