## 3 Results and Discussion  
Isolation of SCC by DMSO-CdCl\({}_{2}\), CoCl\({}_{2}\), CuCl\({}_{2}\), MnCl\({}_{2}\), CrCl\({}_{3}\), Co(TFA)\({}_{2}\), Mn(TPA)\({}_{2}\), Cu(TFA)\({}_{2}\) Extraction Systems  
The organic solvent as the main component of the extraction system (ES) must satisfy following requirements: to be immiscible with the hydrocarbon phase and dissolve metal chlorides and metal trifluoroacetates. Dissolution of inorganic salts in organic solvents is due to the effects of solvation and coordination. The effect of solvation is provided by \(\eta\)-donating solvents, whose heteroatoms have a lone electron pair. These solvents, DMF and DMSO, were used in our experiment. Data on the extraction of the SCC fraction boiling in the temperature range of 200-350 \({}^{\circ}\)C with solutions of metal chlorides in DMF are given in Table 1.  
According to the data presented in Table 1, the treatment of diesel fuel with DMF allows reducing the total sulfur content to 0.12%. However, SCC removal using the 'DMF-chlorides, metal trifluoroacetates' extraction systems is more efficient. We can make some assumptions about the dependence of the rate of SCC extraction with extraction systems (ES) on the type of metal cations. According to the results presented in Table 1, a general trend is observed: After introduction of metal \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Metal Salts**} & **Concentration** & \multirow{2}{*}{**S(t)\%. \%**} & **Degree of Extraction of Sulfur Compounds, \% (First Extraction)** & **Degree of Extraction of Sulfur Compounds, \% (Second Extraction)** & **Deference of Extraction of Sulfur Compounds, \% (Second Extraction)** & **Deference of Extraction Systems, \% (Second Extraction)** \\ \hline CdCl\({}_{2}\) & 0.12 & 0.110 & 38.8 & 0.06 & 66.5 & 1.4571 \\ CoCl\({}_{2}\) & 0.50 & 0.055 & 69.4 & 0.05 & 72.2 & 1.4571 \\ CuCl\({}_{2}\) & 1.76 & 0.060 & 66.5 & 0.05 & 72.2 & 1.4569 \\ MnCl\({}_{2}\) & 2.50 & 0.050 & 72.2 & traces & - & 1.4569 \\ CrCl\({}_{2}\) & 2.75 & 0.050 & 72.2 & traces & - & 1.4569 \\ Co(TFA) & 0.11 & 0.035 & 80.5 & traces & - & 1.4566 \\ Mn(TFA)\({}_{2}\) & 0.11 & 0.030 & 83.3 & traces & - & 1.4565 \\ Cu(TFA)\({}_{2}\) & 0.11 & 0.04 & 77.7 & traces & - & 1.4568 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Results of extraction of sulfur compounds from the diesel oil fraction (200–350 \({}^{\circ}\)C) with solutions of chlorides and TFA metals in DMF. The total sulfur content (St) in the initial sample is 0.22%, \(n_{4}\)[20] (DT) = 1.4655. S\({}_{\text{tot}}\) content in the initial sample after treatment with DMF is 0.12%. The extraction time is 30 min. The temperature is 25 \({}^{\circ}\)C.  
sults into DMF its extraction capacity relative to sulfur-containing compounds of diesel fuels increases as compared to DMF without metal salts. Only trace amounts of sulfur-containing compounds remain in diesel fuels after two extractions. A comparison of the results obtained with those of other investigations has shown that the value of degree of removal of sulfur-containing compounds approaches or even exceeds the known values for the removal of SCC obtained with the use of other extraction systems. The data on the extraction of SCC from diesel fuels using one of the most effective extractants, \(N\)-methyl-2-pyrrolidone, are reported in [11]. The efficiency of ES in the case of use of chlorides and metal trifluoroacetates can be explained on basis of Pearson hard-soft acid-base theory (HSAB) [15]. According to this concept, the interaction of a soft (hard) acid with a soft (hard) base proceeds more quickly or results in a more favorable equilibrium position. In our case, among the used metal chlorides, cadmium chloride can be identified as a mild Lewis acid, while cobalt, nickel and copper chlorides as Lewis intermediate acids. Manganese and chromium chloride are identified as hard acids.