Mechanism of 2,3-dihydroquinazolin-4(1H)-ones synthesis catalyzed by the TPMS (1)
A reasonable mechanism for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones catalyzed by the TPMS (1) is demonstrated in (Scheme 2). Firstly, isatoic anhydride is activated by TPMS; therefore, the carbonyl group of isatoic anhydride is able to be protonated to form intermediate (I), after that, the amine attacks on the carbonyl to afford intermediate (II). By emission of CO2, intermediate (III) is obtained. Thereafter, the reaction between (III) and TPMS activates the aldehyde, resulting in intermediate (IV). An intramolecular nucleophilic attack from the nitrogen of amid group to the active carbon of the imine moiety, followed by losing one molecule of H2O, affords cyclized intermediate (V) which is converted to product (VI) via an intramolecular cyclization.
EDX analysis of TP and TPMS nanocatalyst (1)
Through EDX analysis, the rough percentage of elements in the structures can be determined. The presence of C, O, and N elements confirms the formation of TA / PEI catalyst (Fig. 3a), and the observation of C, O, N, Fe, and S elements in (Fig. 3b) showed that the TMPS scaffold is prepared. By comparison between the two analyzes and by considering the existence of S and Fe elements, it can be implied that the TPMS nanocatalyst (1) has been synthesized.
FESEM analysis of TPMS nanocatalyst (1)
To determine the surface morphology and particle size distribution, FESEM analysis is used. As it is clear from the images in (Fig. 4), the scattering of particle size between 17 nm and 27 nm is clearly observed. Having a porous surface and regular dispersion of particles on the surface has confirmed the bonding of two polymers and the immobilization of iron particles and SO3H groups on the surface.
TGA analysis of TPMS nanocatalyst (1)
TGA analysis shows the behavior of material against heat. The main base of the catalyst is TA and PEI polymers, on the other hand, organic compounds are generally decomposed at about 400 oC. As shown in (Fig. 5), about 23% of the mass is lost between 100 to 400 oC, and a sharp drop from 400 to 450 oC is seen due to the complete decomposition of organic compounds. The strong connection between two polymers with the linker causes a dramatic rise at the decomposition temperature. After 450°C, the curve has a gentle slope, and at 600°C, the slope is almost zero, which indicates the stability of the magnetic material.
FTIR analysis of (a) TA (b) TPMS (c) TP.
The FTIR spectrum of TA molecules indicates some characteristic bands of phenolic –OH, between 3000 and 3600 cm-1, and the C=O group depicted at 1697 cm-1, the stretching mode of aromatic groups located at 1612, 1521, and 1426 cm-1. furthermore, the FT-IR spectrum of TA/PEI polyplex particles indicates both peaks from initial TA molecules and branched PEI polymer, for instance, the stretching C-H bands at 2950 from branched PEI chains, the C=O peaks at 1702 cm-1from TA molecules, and the bending N-H band at 1600 cm-1 from branched PEI chains. The characteristic peak at 580 cm-1 of TPMS could be ascribed to the lattice absorption of the Fe3O4 nanoparticles. The characteristic absorption bands at 1190–1200 cm-1 and 1020–1130 cm-1 can be ascribed to the asymmetric and symmetric stretching modes of O=S=O, moreover, the absorption band at 573–629 cm-1 can be attributed to the stretching mode of S–O. The combination of mentioned spectrums is illustrated in (Fig. 6).
XRD pattern of TPMS nanocatalyst (1)
XRD is a non-destructive method that provides detailed information on the crystallographic structure, chemical composition, and physical properties of materials. XRD pattern for TPMS is illustrated in (Fig. 7). The bifurcated peak at 2θ = 30˚ was the peak index of tannic acid and 2θ = 57.4˚ was the PEI. The peak is located at 2θ = 63˚, 57˚, 43˚, 36˚, 30˚, which indicates that it is magnetic. Overlap is observed in some peaks, which makes them look sharper. According to the registered index card for Fe3O4 (card no. JCPDS, 01-088-0315)[111], tannic acid and PEI and the conformity with the provided XRD broad spectrum at 2θ = (20-30), the formation of supramolecular nanomagnetic catalyst has proved. Other observed sharp bands belong to PEI and Fe moiety.
VSM spectrum of TPMS nanocatalyst (1)
The vibrating sample magnetometry (VSM), was the final analysis for the characterization of the catalyst, which has performed at room temperature. VSM has indicated the magnetic feature of TPMS nanocatalyst (1), by using this technique, the saturation magnetization of the catalyst was found to be 29.94 emu/g (Fig. 8). The S shape of the VSM curve has shown the magnetic properties of the catalyst.
The optimization of the reaction conditions has been performed by various changes in different parameters including solvent, catalyst loading, catalyst, temperature and time for the model reaction (Tables 1). The application of the TPMS catalyst (1) for the synthesis of desired products has been investigated as well in (Table 2).
To evaluate the best catalyst, all three catalysts have been placed in the same conditions and the same reaction that can be seen in the first three rows in (Table 1), which according to the obtained results; TPMS had the shortest reaction time and maximum efficiency (Entry 3). Moreover, in other rows, the optimization of the model reaction by employing TPMS, as catalyst, in different solvents, reaction time and various amounts of the catalyst has been performed. The best situation was observed in (Entry 10)
After determining the superior catalyst and the best reaction conditions in the model reaction, other 2,3-dihydroquinazoline-4 (1H) -one derivatives were synthesized by using ammonium acetate and various types of aldehydes and the results are illustrated in (Table 2), which indicates the high compatibility of the catalyst whit the reaction.
Selected spectral data of representative compounds
1-(4-(dimethylamine) phenyl)-2,3-dihydroquinazolin- 4(1)-one (5h):
White solid: m.p. 229-230 °C. 1H NMR (500 MHz, DMSO-d6): δ (ppm) 8.07 (s, 1H), 7.61 (d, J = 8.0 Hz, 1H), 7.30 (d, J = 12.0 Hz, 1H) 7.25-7.23 (m, 2H), 7.21 (d, J = 8.0 Hz, 1H) 6.92 (d, J = 8.0 Hz, 2H) 6.74-6.72 (m, 1H), 6.68 (s, 1H), 6.65 (s, 1H), 5.64 (s, 3H). FT-IR (KBr): νmax/cm-1; 3440 (NH), 1639 (CO), 1400-1500 (C=C), 2927 (C-H).
2-(5-Bromo-2-hydroxyphenyl)-3-phenyl-2,3-dihydroquinazolin-4(1H)-one (5b):
White solid: m.p. 210-217 °C; 1H NMR (500 MHz, DMSO-d6): δ (ppm) 5.97 (s, 1H, CH), 6.78 - 6.71 (m, 3H, Ph), 7.26 -7.24 (m, 8H, Ph), 7.64 (dd, J = 7.8 Hz, J = 1.2 Hz, 1H, Ph), 10.24 (1H, s, OH); FT-IR (KBr): νmax / cm-1; 3400 (NH), 1636 (CO), 1400-1500 (C=C), 2926 (C-H)