Synthesis of Superacid‐Functionalized Mesoporous Nanocages with Tunable Pore Diameters and Their Application in the Synthesis of Coumarins

Abstract

Here we demonstrate for the first time the preparation of a triflic acid (TFA)-functionalized mesoporous nanocage with tunable pore diameters by the wet impregnation method. The obtained materials have been unambiguously characterized by XRD, N(2) adsorption, FTIR spectroscopy, and NH(3) temperature-programmed desorption (TPD). From the characterization results, it has been found that the TFA molecules are firmly anchored on the surface of the mesoporous supports without affecting their acidity. We also demonstrate the effect of the pore and cage diameter of the KIT-5 supports on the loading of TFA molecules inside the pore channels. It has been found that the total acidity of the materials increases with an increase in the TFA loading on the support, whereas the acidity of the materials decreases with an increase in the pore diameter of the support. The acidity of the TFA-functionalized mesoporous nanocages is much higher than that of the zeolites and metal-substituted mesoporous acidic catalysts. The TFA-functionalized materials have also been employed as the catalysts for the synthesis of 7-hydroxy-4-methylcoumarin by means of the Pechmann reaction under solvent-free conditions. It has been found that the catalytic activity of the TFA-functionalized KIT-5 is much higher than that of zeolites and metal-substituted mesoporous catalytic materials in the synthesis of coumarin derivatives. The stability of the catalyst is extremely good and can be reused several times without much loss of activity in the above reaction.

Catalytic performance of Metal-Organic-Frameworks vs. extra-large pore zeolite UTL in condensation reactions

“…It should be noted that catalytic activity of and FeBTC is comparable with periodic mesoporous silica chloride (the yield of target product 75% at 130°C and 180 min of TOS),(Karimi and Behzadnia, 2011) and SBA-15-Ph-Pr-SO 3 H (the yield of target product 65% at 130°C and 240 min of TOS) (Kalita et al, 2010), which were shown to be one of the most promising catalysts for Pechmann condensation of 1-naphthol.…”

“…Pechmann reaction was carried out in the presence of concentrated H 2 SO 4 (Russell and Frye, 1955), CF 3 COOH (Woods and Sapp, 1962), P 2 O 5 (Canter et al, 1931), AlCl 3 (Das Gupta et al, 1969). During the last decade, zeolites (Hoefnagel et al, 1995), amberlyst (Sabou et al, 2005), montmorillonite K 10 (Li et al, 1998), heteropolyacids (Torviso et al, 2008), functionalized mesoporous silica [e.g., Zr-TMS (Torviso et al, 2008), Al-MCM-41 (Sudha et al, 2008), SBA-15-Ph-Pr-SO 3 H (Karimi and Zareyee, 2008)], metal oxides (e.g., sulfated zirconia) (Tyagi et al, 2007), inorganic ion exchangers (Sabou et al, 2005), and superacid-functionalized mesoporous materials (Kalita et al, 2010) have also been employed to catalyze Pechmann condensation.…”

Ordered organo-inorganic hybrid mesoporous solid acid catalysts (Zr–TMS–TFA) for Michael addition of indoles with α,β-unsaturated carbonyl compounds under environmentally benign solvent free conditions

“…Moreover, Ji et al found that indolylketones could be expeditiously synthesized by p-toluenesulfonic acid (PTSA) using ultrasonic irradiation [54]. Very recently, Kalita et al [55,56] reported the triflic acid functionalized over Zr-TMS and cage like three dimensional mesoporous materials and found very promising catalyst for the synthesis of 7-hydroxy 4-methylcoumarin via Pechmann reaction. Besides, various authors have reported acid functionalized mesoporous materials for different organic transformation [57,58].…”

Cage Like Al-KIT-5 Mesoporous Materials for C–C Bond Formation Reactions Under Solvent Free Conditions

“…Very recently, we observed excellent results for aza-Michael reaction catalysed over the same Al-KIT-5 mesoporous materials under solvent free condition [12]. Moreover, Kalita et al reported the functionalization of mesoporous KIT-5 materials using super acid like triflic acid and found very good catalytic activities for the synthesis of coumarin via Pechmann reaction of resorcinol and ethyl acetoacetate under solvent free system [13].…”