## 3 Results and Discussion
If we consider the process of dissolving metal chlorides in an organic solvent as an acid-base Lewis interaction, then manganese chloride and chromium chloride react with DMF as a hard base and a hard acid and, according to the HSAB concept, form the most stable compounds. According to the data in Table 1, the highest yield in sulfur is given by ES, when the interaction of a hard acid-hard base (MnCl\({}_{2}\) or CrCl\({}_{3}\)-DMF) occurs. To the contrary, the lower yield for sulfur is given by ES when the hard base-mild acid (CdCl\({}_{2}\)-DMF) interaction is observed. Study of Intermolecular Interactions in the 'DMF-Metal Salt-Model Compound' System by the Method of PMR Spectroscopy  
To study intermolecular interactions in the DMF-metal salt system, the PMR method was chosen, whose high sensitivity allows us to register weak intermolecular interactions. The PMR method was used to study interactions in the organic solvent--metal chloride--model compound system. Dihexylsulfide and dibenzothiophene were used as model compounds. Figure 1 shows a graphical representation of PMR spectra of I--DMF and II--DMF with CoCl\({}_{2}\). According to the spectra, when the cobalt chloride is added to the DMF solution, the proton signals are shifted to the weak-field region. This fact indicates that in the presence of metal chloride a solvent molecule behaves like an electron donor [12]. It can be assumed that the metal cation is coordinated to the carbonyl group of solvent through its oxygen atom, which results in an enhancement of the properties of the acceptor center localized on the nitrogen atom and leads to a more complete extraction of sulfur compounds from diesel fuels using ES. Table 2 shows the PMR spectra of solutions of model compounds in DMF. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Compounds, Molecular Ratio**} & \multicolumn{6}{c}{**Chemical Shifts, ppm**} \\ \cline{2-9}  & \multicolumn{3}{c}{**DMF**} & \multicolumn{3}{c}{**Aliphatic Protons and Protons in Aromatic Rings**} \\ \cline{2-9}  & **CH\({}_{3}\)\({}^{\text{a}}\)** & **CH\({}_{3}\)\({}^{\text{b}}\)** & **H\({}^{\text{c}}\)** & **CH\({}_{2}\)\(\sigma\)** & **CH\({}_{2}\)\(\bar{\rho}\)** & **CH\({}_{3}\)\(\gamma\)** & **Ring** \\ \hline \(N\)_-_dimethylformamide_ & 2.83 & 2.95 & 7.83 & - & - & - & - & - \\ \hline Dihexylsulfide (DHS) & - & - & - & 2.42 & 1.76–1.1(8 ft) & 0.92 & - \\ \hline DH5 DMF = 1:1 & 2.76 & 2.91 & 7.91 & 2.46 & 1.76–1.1 & 0.89 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Data of the PMR spectra of model compounds in carbon tetrachloride (0.2 mol/dm\({}^{3}\)). Figure 1: Graphic presentation of PMR spectra of dimethylformamide and the complex ’Dimethylformamide-cobalt chloride’. I—DMF, II—DMF with CoCl\({}_{2}\). In all cases, the signals of all protons of DMF are shifted to a strong field, while those of protons of model compounds are shifted to a weak field, i.e., a DMF molecule behaves like an acceptor, while a molecule of the model compound acts as an electron donor. The highest absolute values of proton shifts of DMF methyl groups are observed for dibenzothiophene, while the lowest ones for dipropylsulfide. This suggests a weak interaction between DMF and sulphide and a stronger one with aromatic compounds. In the practice of DMF extracting this should be manifested in the preferred extraction of aromatic compounds. If it is assumed that the interaction of metal salts, as electron-accepting compounds, with DMF is due to the coordination of the metal cation through the oxygen atom of the carbonyl group of negatively charged solvent. The result of this interaction is the redistribution of the electron density in the dimethylformamide molecule and the enhancement of the properties of the acceptor center localized on the nitrogen atom. Hence, sulfur compounds of a diesel fuel represented mainly by sulfides and thiophene derivatives having an excess electron density on the sulfur atom will easier interact with the DMF-metal salt systems than with DMF.