## 3 Results and Discussion
### Preparation of Magnetically Separable Heterogeneous Base Catalysts  
The magnetically separable heterogeneous base catalysts were prepared using a sol-gel process. Thus, the process of preparation (Scheme 2) was based on copolymerization of either 1-(2-(dimethylamino)ethyl)-3-(3-(trimethoxysil)propyl)urea or _N_-[3-(trimethoxysil)propyl]-ethylenediamine with tetraethoxysilane (TEOS) in the presence of magnetite nanoparticles supported with ionic liquid groups (**MNP-IL-C4**) that were prepared by reacting Fe\({}_{3}\)O\({}_{4}\) nanoparticles with 1-butyl-3-(3-trimethoxysilpropyl)-1\(H\)-imidazol-3-ium chloride in ethanol. **MNP-IL-C4** was utilized in this process as it is highly dispersible in methanol, which was used as a medium for preparing the silica sol-gel matrices. TEOS was first hydrolyzed using acid catalyst, and then the silane monomers functionalized with amine groups were added. Since the hydrolysis of the silane monomers containing amine groups is much faster than with TEOS, we decided to first hydrolyze TEOS under acidic conditions in order to bring on the end of the process to homogeneous distribution of the amine groups on the formed silica sol-gel backbone. After the copolymerization process was completed, black wet gels were obtained that were then dried to give black xerogels that could be strongly attracted to an  
Figure 4: Infrared (FT-IR) spectrum of the catalysts **(a)** **MNP-NMe2** and **(b)** **MNP-NH2**. external magnetic field. By this way of preparation, two types of magnetically separable heterogeneous base catalysts were synthesized: the first catalyst contains secondary and primary amine groups (**SG-MNP-NH2**) while the second catalyst contains tertiary amine groups (**SG-MNP-NMe2**). **Scheme 2. ** Preparation of magnetically separable heterogeneous base catalysts. \[ \begin{array}{ccccc}\text{Si(OEt)}_{4}&+&\text{(MeO)}_{3}\text{Si}&\text{N}& \text{NH}_{2}&\text{MNP-IL-C}_{4}\\ \text{Si(OEt)}_{4}&+&\text{(MeO)}_{3}\text{Si}&\text{H}&\text{H}&\text{MeOH/H }_{2}\text{O}\end{array} \]  
The two heterogeneous base catalysts, **SG-MNP-NH2** and **SG-MNP-NMe2**, were characterized by TEM, TGA-DTA and XRD methods. According to TEM analysis (Figure 5), it can be seen for both heterogeneous catalysts that the magnetic nanoparticles supported with ionic liquid groups (**MNP-IL-C4**) are embedded in the silica sol-gel matrices. It seems that the distribution of the magnetic nanoparticles in the silica sol-gel matrices is homogeneous in the case of **SG-MNP-NH2** while it is not uniform in the case of **SG-MNP-NMe2**. XRD analysis (Figure 6) confirmed the presence of magnetic nanoparticles in the silica sol-gel matrices. Thus, the XPD patterns of **SG-MNP-NH2** (Figure 6 (b)) and **SG-MNP-NMe2** (Figure 6 (a)) contain the characteristic peaks of the magnetite nanoparticles in addition to the broad peaks between 2\(\theta\) = 12\({}^{\circ}\) and 2\(\theta\) = 33\({}^{\circ}\) that correspond to amorphous silica produced by the sol-gel process. Figure 5: TEM micrographs of magnetically separable heterogeneous base catalysts: (**a) SG-MNP-NH2**, scale bar 50 nm; (**b) SG-MNP-NMe2**, scale bar 50 nm. Figure 6: Powder XRD patterns of magnetically separable heterogeneous base catalysts: (**a**) **SG-MNP-NMe2** and (**b**) **SG-MNP-NH2**. Figure 7: TGA-DTA curves of (**a**) **SG-MNP-NH2** catalyst and (**b**) **SG-MNP-NMe2** catalyst. In addition, TGA-DTA techniques were utilized to determine the thermal behavior of the catalysts **SG-MNP-NH2** and **SG-MNP-NMe2**. The representative thermograms are shown in Figure 7. The DTA results of the catalyst **SG-MNP-NH2** (Figure 7(a)) show a broad endothermic peak centered at 125 \({}^{\circ}\)C which can be attributed to the removal of physical adsorbed organic volatiles and water. The mass loss after this desorption process is about 6%. In addition, the strong exothermic peak at 266 \({}^{\circ}\)C and the weak exothermic peak at 425 \({}^{\circ}\)C are accompanied by a mass loss of 12%.