12‐Tungstosilicic Acid H₄[W₁₂SiO₄₀] Over Natural Bentonite as a Heterogeneous Catalyst for the Synthesis of 3,4‐dihydropyrimidin‐2(1H)‐Ones

Abstract

Regionally available bentonite was modified by using heteropolyacid 12‐tungstosilicic acid H4[W12SiO40] (TSA). The prepared 10–30 % TSA/bent catalysts were characterized by XRD, FTIR, FeSEM and EDS. The catalytic activity of all three samples was studied on classical Biginelli reaction. Among all, 30 % TSA/bent displayed high catalytic activity and reusability. The effect of solvent was also undertaken to find the best media for the reaction. This protocol was extended to various aldehydes for the synthesis of different dihydropyrimidones (DHPMs) in high yields in ethanol.

Fe(III)/Bentonite as a Heterogeneous Catalyst for the Synthesis of 3,4‐dihydropyrimidin‐2‐(1H)‐ones

“…The intensity of this peak decreased in all three samples and almost vanished in 30 % Fe(III)/bent. It showed that crystallinity of SiO 2 turned to amorphous nature [88,96,102] as similar observation made by us in our previous work [93,94] . Other diffraction peaks of bentonite observe at 2θ=19.9 ° , 26.6 ° , 28.58 ° , 36.0 ° , 42.5 ° and 61.7 ° [103–106] .…”

“…The low intensity peak at 61.7 ° reveals about octahedral sheet in bentonite [105] which remains intact in all three samples. It indicates that no distraction occurred in octahedral sheet after supporting of Fe(III) while in our reported work, this peak almost disappeared as percentage TSA & TPA increased in bentonite which could led to some distraction in octahedral sheet [93,94] . A new peaks 30.81 ° , 38.67 ° , 44.54 ° , 67.07 ° , 67.47 ° and 80.53 can be assigned to Fe(III) over bentonite and some peaks such as 38.67 ° , 67.07 ° , 67.47 ° and 80.53 ° are not detected at higher loading (20 & 30 % Fe(III)/bent).…”

“…The yield of product was 95, 88, 60 and 90 % in acetonitrile, DMF, methanol and solvent‐free conditions respectively as represented in Table 2 (entry 7–10). Catalyst 30 % Fe(III)/bent required to high loading (0.15 g) than our reported work on 30 %TSA/bent and 30 %TPA/bent (0.09 g) catalysts [93,94] . Various DHPMs are prepared using 0.15 g of catalyst in acetonitrile for 7 h of reaction time as shown in Table 3.The DHPMs are obtained in good to high yield of products.…”

“…FeCl 3 /bentonite for the synthesis of (E)‐1‐(2,4‐dimethylthiazol‐5‐yl)‐3‐phenylprop‐2‐en‐1‐ones under solvent‐free conditions, Cu‐bentonite for the synthesis of benzimidazoles, benzoxazoles and benzothiazoles, vanadium‐chromium‐bentonite used as catalyst for epoxidation of cyclohexene, H 2 SO 4 activated bentonite, bentonite functionalized by propyl sulfonic acid and ionic liquid 8B@bentonite for esterification reaction, montmorillonite KSF for pyrano and furanoquinolines and CTMAB‐bentonite for synthesis of 3,4‐dihydropyrano[c]chromene derivatives [77–84] . In the literature, a very few examples available on bentonite based catalyst for Biginelli reaction which include montmorillonite KSF catalyst, bentonite clay, montmorillonite KSF assisted by microwave, activated montmorrilonite, bentonite‐PS‐SO 3 H, Fe(III)‐montmorillonite K10, TiO 2 ‐pillared montmorillonite, Co@imine‐Na + ‐MMT, ionic liquid@bentonite and including our reported work on H 4 [W 12 SiO 40 ]/bent & H 3 [PW 12 SiO 40 ]/bent [85–95] . In this work, we developed Fe(III)/bent as a heterogeneous catalyst for synthesis of 3,4‐dihydropyrimidin‐2‐(1H)‐ones.…”

Quaternary Vanado‐Molybdotungstophosphoric Acid [H5PW6Mo4V2O40] Over Natural Montmorillonite as a Heterogeneous Catalyst for the Synthesis 4H‐Pyran and Polyhydroquinoline Derivatives

“…and its effectiveness as an catalyst has been explored in various organic transformations. [30][31][32][33] Therefore, we synthesized Keggin type quaternary vanadomolybdotungstophosphoric heteropoly acid H 5 PW 6 Mo 4 V 2 O 40 .14H 2 O (abbreviated as VMWP). It looks that the substitution of vanadium into the Keggin framework increasing the thermal stability and catalysis ability also increases.…”