## 4 Discussion
The corrosion rate and inhibition efficiency values obtained by us for the essential oil of fennel fruits also differ from the data for other \"green inhibitors\", under the same experimental conditions; examples include the following:* Spearmint (_Mentha spicata_ L.) essential oil [6]: at concentration 1.00 g/L, corrosion rate 0.051 mg/(cm\({}^{2}\).h) and inhibition efficiency 81%; at concentration 1.50 g/L, corrosion rate 0.023 mg/(cm\({}^{2}\).h) and inhibition efficiency 88%; at concentration 2.00 g/L, corrosion rate 0.015 mg/(cm\({}^{2}\).h) and inhibition efficiency 93%; steel plate composition: 0.09% P; 0.38% Si; 0.01% Al; 0.05% Mn; 0.21% C; and 0.05% S, with the remaining % being Fe. * Immortella (_Helichrysum italicum_ subsp. _italicum_ essential) essential oil [3]: at concentration 1.00 g/L, corrosion rate 0.082 mg/(cm\({}^{2}\).h) and inhibition efficiency 78.4%; at concentration 1.50 g/L, corrosion rate 0.070 mg/(cm\({}^{2}\).h) and inhibition efficiency 81.7%; at concentration 2.0 g/L, corrosion rate 0.067 mg/(cm\({}^{2}\).h) and inhibition efficiency 83.7018% at concentration 2.0 g/L, corrosion rate 0.185 mg/(cm\({}^{2}\).h) and inhibition efficiency 82.3%; steel plate composition: 0.09% P; 0.38% Si; 0.01% Al; 0.05% Mn; 0.21% C; and 0.05% S, with the remaining % being Fe. * Anise (_Pimpinella anisum_ L.) essential oil [7]: at concentration 1.00 g/L, corrosion rate 0.338 mg/(cm\({}^{2}\).h) and inhibition efficiency 70.22%; at concentration 2.0 g/L, corrosion rate 0.185 mg/(cm\({}^{2}\).h) and inhibition efficiency 83.70%; steel plate composition: 0.370% C; 0.230% Si; 0.680% Mn; 0.016% S; 0.077% Cr; 0.011% Ti; 0.059% Ni; 0.009% Co; and 0.160% Cu, with the remaining % being Fe. According to the authors, the inhibition efficiency is highest (92%) at a concentration of oil of 4 g/L
* African juniper (_Tetractlins articulata_ [PERSON]) essential oil [8]: at concentration 1.00 g/L, corrosion rate 0.187 mg/(cm\({}^{2}\).h) and inhibition efficiency 64%; at concentration 2.0 g/L, corrosion rate 0.100 mg/(cm\({}^{2}\).h) and inhibition efficiency 80%; steel plate composition: 0.21% C; 0.38% Si; 0.09% P; 0.01% Al; 0.005% Mn; and 0.005% S, with the remaining % being Fe. * African juniper (_T. articulata_ [PERSON]) extract [8]: at concentration 1.00 g/L, corrosion rate 0.110 mg/(cm\({}^{2}\).h) and inhibition efficiency 78%; at concentration 2.0 g/L, corrosion rate 2.0 g/L, corrosion rate 0.05% S, with the remaining % being Fe. * African juniper (_T. articulata_ [PERSON]) extract [8]: at concentration 1.00 g/L, corrosion rate 0.110 mg/(cm\({}^{2}\).h) and inhibition efficiency 78%; at concentration 2.0 g/L, corrosion rate 2.0 g/L, corrosion rate 2.0 g/L, corrosion rate 2.0 g/L, corrosion rate 0.1237 mg/(cm\({}^{2}\).h) and inhibition efficiency 90.18%; steel plate composition: 0.370% C; 0.230% Si; 0.680% Mn; 0.016% S; 0.077% Cr; 0.011% Ti; 0.059% Ni; 0.009% Co; and 0.160% Cu, with the remaining % being Fe  
These differences, in our opinion, may be due to the different composition of the described \"green\" inhibitors and the steel plates used. The results for the inhibitor anethole (Figure 4) show that at an anethole concentration of 1.0 mL/L, the inhibition efficiency is 50.02%, at 1.5 mL/L, its value is preserved, and at 2.0 mL/L, the value decreases to 45.86%. As the anethole concentration increased from 1.0 to 2.0 mL/L, the corrosion rate increased from 0.102 to 0.111 mg/(cm\({}^{2}\).h). This decrease in inhibition efficiency is most likely due to structural changes in the anethole molecule, with the ether group being unstable in the presence of strong acids. In aromatic ethers, in which anethole is included, the alkyl-oxygen bond is always broken, not the aryl-oxygen. Initially, a salt is formed whose anion is a good nucleophile, and upon heating, nucleophilic substitution takes place at the saturated carbon atom (S\({}_{\text{N}}\)) as shown on Figure 8 [35]. Figure 8: Alteration in the ether group of anethole in the presence of strong acids.