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

Kalita, Pranjal; Kumar, Rajiv

doi:10.1016/j.micromeso.2012.08.015

Cited by 8 publications

(5 citation statements)

References 67 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This simple functionalization process could convert the homogeneous nature of TFA or sulfonic acids into a heterogeneous catalytic system that would offer environmentally benign reaction conditions, and a green catalyst that can be recovered and reused several times, which would significantly minimize the waste of superacids during reaction. Porous materials that can offer high surface area, large pore volume, and uniform pore size distribution have been used as supports for the functionalization and have been employed as catalysts for various acid‐catalyzed reactions . SPA‐functionalized porous catalysts have been investigated as heterogeneous catalysts for the synthesis of coumarin by the Pechmann reaction .…”

Section: Introductionsupporting

confidence: 93%

“…This small decrease in conversion and selectivity is due to a slight loss of loosely bound TFA molecules from the surface of the SBA‐15 mesoporous network. The loss of C and S content in the catalyst was also observed in our previous report, an effect that was determined by elemental analysis . However, the reduction in the activity of the catalyst is quite minimal, even after three repeated cycles.…”

Section: Resultsmentioning

confidence: 99%

“…Very recently, Kalita et al. reported the functionalization of TFA onto the surface of KIT‐5 and Zr‐TMS mesoporous materials and demonstrated their catalytic activity in the synthesis of coumarin through the Pechmann reaction of resorcinol and ethyl acetoacetate in a solvent‐free system and for the Michael addition of indole to enone . Moreover, various authors have reported superacid‐functionalized mesoporous materials for different organic transformations .…”

Section: Introductionmentioning

confidence: 95%

See 2 more Smart Citations

Preparation of Highly Active Triflic Acid Functionalized SBA‐15 Catalysts for the Synthesis of Coumarin under Solvent‐Free Conditions

et al. 2015

Self Cite

View full text Add to dashboard Cite

Highly acidic SBA‐15 with different pore diameters has been prepared by functionalizing the mesoporous walls with different amounts of triflic acid (TFA). The structure of the SBA‐15 before and after the functionalization with TFA was investigated by powder X‐ray diffraction and nitrogen adsorption isotherms. The interaction of TFA with the surface silanol groups of SBA‐15 and the acidity of the materials have been investigated by FTIR spectroscopy and temperature‐programmed desorption of ammonia, respectively. The characterization results reveal that the mesoporous structure of the SBA‐15 is retained even after the loading of TFA in the mesochannels and that the TFA molecules are bonded with the surface silanol groups of the SBA‐15 supports. The acidity of the materials increases with increasing amount of TFA from 5 to 20 wt %. These functionalized, highly acidic materials are found to be highly active in the synthesis of coumarin and the catalytic efficiency was found to correlate with the total acidity or the amount of TFA in the porous channels of the SBA‐15 catalysts. It has also been found that the activity of the TFA‐functionalized SBA‐15 in the synthesis of coumarin is much higher than that of different zeolites, pure mesoporous silica SBA‐15, and other mesoporous catalysts used in this study.

show abstract

Section: Introductionsupporting

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

See 1 more Smart Citation

Preparation of Highly Active Triflic Acid Functionalized SBA‐15 Catalysts for the Synthesis of Coumarin under Solvent‐Free Conditions

et al. 2015

Self Cite

View full text Add to dashboard Cite

show abstract

“…[10] The recycling of TfOH is thus significant from an economic ande nvironmental perspective. So far, homogeneous catalysts have been recycled by heterogenisation, [11] the use of biphasic conditions [12] and scavenging. [13] Particularly,t he heterogenisation of TfOH is used widely.…”

Section: Introductionmentioning

confidence: 99%

“…[13] Particularly,t he heterogenisation of TfOH is used widely. [11] Attempts have been made to make all supported acids ites accessiblef or reaction( to allow rates and selectivities comparable to those obtained with homogeneous TfOH), but only sites on the surfacew ere available for catalysis. [14] Biphasic conditions have been used as as ophisticatedw ay to recycle per-A" release and catch" methodw as developed by utilising the scavenging effect of af luorousz witterion on ah omogeneous triflic acid (TfOH) catalysti nM ichael addition and Rupe rearrangement.…”

Section: Introductionmentioning

confidence: 99%

“Release and Catch” Effect of Perfluoroalkylsulfonylimide‐Functionalized Imidazole/Pyridine on Brønsted Acids in Organic Systems

et al. 2016

View full text Add to dashboard Cite

A “release and catch” method was developed by utilising the scavenging effect of a fluorous zwitterion on a homogeneous triflic acid (TfOH) catalyst in Michael addition and Rupe rearrangement. Both TfOH and the zwitterion were recycled with >90 % recovery using toluene. The zwitterions were designed by functionalising imidazole/pyridine with the perfluoroalkylsulfonylimide group. The “caught” TfOH was delivered to ethyl acetate and re‐used. The smooth delivery was primarily because of the fluorous tail of the zwitterion, the hydrophobicity of which probably weakened the ability of the zwitterion to form H bonds, so that retro‐ion‐exchange occurred towards the formation of the acid and zwitterion. The method was universal for other strong Brønsted acids such as H2SO4 and p‐MeC6H4SO3H. The method combined the significant advantages of homogeneous catalysis and heterogeneous isolation. Based on the H0 acidity function and the 31P NMR chemical shift of Et3P=O adducts, it is reasonable to deduce that the decrease of the acid strength of the formed composites of Brønsted acids and the zwitterion drove the scavenging effect.

show abstract

Room Temperature Ring Opening of Epoxides Over Triflic Acid Functionalized Cage Like Mesoporous Materials

2016

View full text Add to dashboard Cite

Here, we have synthesized triflic acid functionalized three dimensional cage like KIT‐5 mesoporous materials for ring opening of epoxides with alcohols to produce β‐alkoxyalcohols. The mesoporosity and structure of the materials are retained, which is confirmed from characterization data of the catalysts. These data suggested the presence of triflic acid in the channel of mesoporous materials. Excellent to very good yield of the desired products were obtained using our methodology, which is due to the higher acidity of the triflic acid functionalized catalyst used. Present studies suggested that triflic acid functionalized mesoporous catalyst possessed higher catalytic activity than that of zeolites and other metal substituted mesoporous materials. The stability of the catalyst was also found to be excellent and used for three consecutive cycles without any significant lose in yield.

show abstract

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

Cited by 8 publications

References 67 publications

Preparation of Highly Active Triflic Acid Functionalized SBA‐15 Catalysts for the Synthesis of Coumarin under Solvent‐Free Conditions

Preparation of Highly Active Triflic Acid Functionalized SBA‐15 Catalysts for the Synthesis of Coumarin under Solvent‐Free Conditions

“Release and Catch” Effect of Perfluoroalkylsulfonylimide‐Functionalized Imidazole/Pyridine on Brønsted Acids in Organic Systems

Room Temperature Ring Opening of Epoxides Over Triflic Acid Functionalized Cage Like Mesoporous Materials

Contact Info

Product

Resources

About