Increased SBA-15-SO3H Catalytic Activity through Hydrophilic/Hydrophobic Fluoroalkyl-Chained Alcohols (RFOH/SBA-15–Pr-SO3H)

Abstract

A superior catalytic activity for the SBA-15-functionalized sulfonic acid containing fluoroalkyl chain alcohols (R F OH/SBA-15-Pr-SO 3 H adduct) is presented for the synthesis of highly substituted imidazoles. The advantages of this method include low catalyst loading, simple procedure, excellent yields, recyclability of catalyst, and short reaction times.Key words fluoroalkyl chain alcohols, TFE/SBA-15-Pr-SO 3 H, imidazole, multicomponent reaction Solid Brønsted acid catalysts have received a great deal of attention for applications in green and recyclable protocols and their versatility has been demonstrated in the various processes. 1-4 Mesoporous silica materials (MSM), such as SBA-15, offer high surface area, good thermal stability, and potential for tunability 5,6 by which it is possible to modify the surface activity and nature of of the MSM. 7-9 One approach is to functionalize with mercaptopropyltrialkoxysilane when a subsequent oxidation process provides a surface sulfonic acid functionality. 10,11 One of the major concerns in the area of sulfonated MSM is catalyst poisoning with water, and several groups have addressed this problem (Figure 1). 12-16 Karimi et al. developed an efficient catalytic system by immobilizing a hydrophobic ionic liquid onto SBA-15. 14,17 Co-functionalization of a hydrophobic functionality such as a phenyl group or alkyl chain with a Brønsted acid function is another approach to increase the hydrophobicity. 16,18 Unfortunately, this method results in pore-size restriction. Wilson et al. prepared a monolayer of MPTS which produced a highly functionalized SO 3 H inside the MSM-type material. 13 This method was efficient in the fabrication of highly acidic MSM-SO 3 H. To prevent pore-size decrease, phenylene-and ethylene-bridged periodic mesoporous organosilicas (PMO) have been investigated, 19,20 but these were most suitable for the hydrophobic compounds. Therefore, development of a MSM-SO 3 H catalyst resistant to poisoning by water while maintaining the suitable hydrophilicity remains a target. Figure 1 Silica/SO 3 H catalyst poisoning with waterFluorous compounds have the unusual property of being both hydrophobic and lipophilic and thus can cause an increase in the acid strength and decrease catalyst poisoning as a result of water-repellency of the surface. [21][22][23] We have demonstrated that confining fluoroalkyl-chain alcohols (R F OH) inside SBA-15 (R F OH/SBA-15) produces an efficient catalytic system by increasing mass transfer and water repellency. [24][25][26] and that such catalytic systems can be applied to the synthesis of 1,2,4,5-tetrasubstituted imidazoles by multicomponent reaction. Imidazoles are key structures in biological systems and an active moiety in several drugs. [27][28][29][30] There are many approaches for the synthesis of substituted imidazoles. 31-35 However, these molecules are usually polar compounds; therefore, an increase in the surface hydrophobicity of the catalyst may lower the diffusibility and mass transfer into the mesochannels and, as ...

Current advances in the utility of functionalized SBA mesoporous silica for developing encapsulated nanocatalysts: state of the art

“…37). 159 Various amines and aldehydes could be successfully used in his protocol to furnish the corresponding imidazoles aer 50 min in high yields (88-95%). The simplicity of the process, reusability of the catalyst and low amount of catalyst were the merits of this protocol.…”

Cu(II) immobilized on guanidinated epibromohydrin‐functionalized γ‐Fe2O3@TiO2 (γ‐Fe2O3@TiO2‐EG‐Cu(II)): A highly efficient magnetically separable heterogeneous nanocatalyst for one‐pot synthesis of highly substituted imidazoles

“…Accordingly, the optimal molar ratio of benzaldehyde:benzil:ammonium acetate was selected as 1:1:2.5. To investigate the effect of solvent, the model reaction was carried out in H 2 O, EtOH and CH 3 CN (Table 1, entries [15][16][17]. It was found that conducting the reaction under solvent-free condition generates the desired product in excellent yield within a short reaction time, in comparison with the use of solvent (compare entry 5 with entries 15-17).…”

The first urea‐based ionic liquid‐stabilized magnetic nanoparticles: an efficient catalyst for the synthesis of bis(indolyl)methanes and pyrano[2,3‐d]pyrimidinone derivatives

“…A possible mechanism for the synthesis of pyrano[2,3-d] pyrimidinones (6) is depicted in Scheme 3. [37] Firstly, the MNP catalyst activates the carbonyl group of the aromatic aldehyde to afford intermediate 7 and malononitrile 5 is tautomerized to 12.…”

“…Subsequently, 1,3-dimethylbarbituric acid (4) is tautomerized to 14 and undergoes nucleophilic attack by 13, providing the Michael adduct 15. Adduct 15 is tautomerized using the MNP catalyst to produce intermediate 16 which cyclizes to give compound 17 and which afterwards is tautomerized to give the fully aromatized pyrano [2,3-d]pyrimidinones (6).…”

“…[5] These mixed organic-inorganic catalysts have been used with numerous support materials, including porous inorganic oxides, for example MCM, zeolites and SBA-type silicas, due to their high surface areas and excellent defined structures. [6,7] Nanoparticles have received increasing consideration as alternative supports for catalysis. As the diameter of the particle decreases to the nanometre scale, abundant extrinsic surface becomes available for surface modifications.…”