## 3 Results and Discussion
### Catalytic Studies of the Quasi-Homogeneous and Heterogeneous Base Catalysts  
Our catalytic studies were initiated by testing the activity of the _quasi_-homogeneous base catalysts **MNP-NH2** and **MNP-NMe2** in a Knoevenagel reaction. Thus, malononitrile and benzaldehyde were reacted at 80 \({}^{\circ}\)C in the presence of 2 mol of the base catalysts dispersed in different solvents: DMSO, DMF, ethanol and water. We chose to use these polar solvents as a medium for the condensation reaction because the catalysts were more dispersible in them than in non-polar solvents like toluene, cyclohexane and heptane. After 1 h, the two catalysts gave quantitative yields of the condensation product in all of these experiments and no significant influence was observed for the type of the solvent used in these reactions. The activity of the two catalysts in the Knoevenagel condensation was similar to magnetically separable systems reported before [55; 56; 57; 58; 59]. In the second stage of our study, we investigated the reactivity of the catalysts **MNP-NH2** and **MNP-NMe2** in nitroaldol reaction. Thus, nitroethane and _p_-anisaldehyde were reacted at 80 \({}^{\circ}\)C for 16 h and in the presence of one of the two _quasi_-homogeneous catalysts dispersed in different solvents. In these experiments, the type of the solvent and the type of the catalyst utilized in the nitroaldol reaction could significantly affect the catalytic performance. When the reaction was performed in DMSO using **MNP-NH2** as a catalyst, only 25% of the desired product, (_E_)-1-methoxy-4-(2-nitropropylene-1-enyl)benzene, was obtained. The use of the same catalyst dispersed in ethanol led to the formation of the desired product in a yield of 68%. The condensation reaction catalyzed by **MNP-NH2** in toluene, cyclohexane and heptane did not yield any product. It is worth mentioning that the catalyst was not dispersible in these solvents and in fact worked as a heterogeneous catalytic system. It seems that the strong aggregation of the catalyst **MNP-NH2** in non-polar solvents lead to a limited accessibility to the active sites of the catalyst. When **MNP-NMe2** was utilized as a catalyst for the nitroaldol condensation in different solvents, no products were detected. The nitroaldol reaction of nitroethane with _p_-anisaldehyde was also investigated using **SG-MNP-NH2** and **SG-MNP-NMe2** as magnetically separable heterogeneous base catalysts. The heterogeneous condensation reaction was optimized using different organic solvents. The results are summarized in Table 1. The results clearly show that non-polar solvents are preferable as a medium for the condensation reaction to polar solvents. The highest yield of the product (_E_)-1-methoxy-4-(2-nitroprop-1-en-1-yl)benzene was obtained when cyclohexane was applied as solvent. The heterogeneous catalyst **SG-MNP-NMe2** led to the formation of 1-(4-methoxyphenyl)-2-nitropropan-1-ol as main product. In this case, it was also found that non-polars solvent are preferable to polar solvent as the product was produced a higher yield. The heterogeneous nitroaldol reaction using the catalyst **SG-MNP-NH2** was then tested in the condensation of several aromatic aldehydes with nitroethane. The condensation reactions were performed at 80 \({}^{\circ}\)C and cyclohexane was applied as a solvent for these reactions. The results of these reactions are presented in Table 2. The results show that the steric effect in this heterogeneous condensation reaction is negligible. Thus, when 2-methoxybenzaldehyde or 2-chlorobenzaldehyde is utilized as a substrate, high yields of the desired products are obtained. Aromatic aldehydes substituted with strong electron withdrawing groups lead to the formation of the condensation products in moderate yield. On the other hand, aromatic aldehydes containing electron-donating groups such as isopropyl give excellent yields of the condensation products.