Investigating the role of SBA-15 silica on the activity of quaternary ammonium halides in the coupling of epoxides and CO2

Abstract

Keywords:CO 2 valorization cyclic carbonates tetrabutylammonium halide salts organocatalysis ordered mesoporous silica A B S T R A C T The conversion of CO 2 into cyclic carbonates in the presence of epoxides is one of the most promising methods to valorize this important C 1 building block. Tetrabutylammonium halide salts are known to catalyze this reaction with moderate activity, and often a co-catalyst is added to increase efficiency. Herein, the influence of the addition of ultra-large pore SBA-15 silica on the catalytic activity of tetrabutylammonium halide salts for this reaction has been investigated in detail. Whereas a negative effect of silica was observed for the NBu 4 Cl catalyst, surface silanols were shown to strongly improve the yield of the reaction when NBu 4 Br and NBu 4 I were used as catalysts. The catalytic activity of the NBu 4 I salt could be increased by a factor of ten when a relevant amount of mesoporous silica was added. This latter catalytic system leads to high yields and selectivity for a wide variety of substrates under mild condition (80°C). Measurement of the activation parameters demonstrated that the rate enhancement is entropically driven: the pre-organization of the reactants and catalyst on the surface leads to a marked decrease of the activation energy of the reaction. A direct comparison between yield improvement induced by the addition of either an amorphous or a mesostructured silica highlights the crucial role played by the shape and concavity of the support.

The role of Zn in the sustainable one-pot synthesis of dimethyl carbonate from carbon dioxide, methanol and propylene oxide

“…At the same time, Zn 2+ and Brdissociate from the product and dissolve into the reaction solution. The Zn surface might contribute to the activation of the epoxide via Zn(II) atoms but also via Zn-OH groups acting as hydrogen bond donors (Lagarde et al, 2019). Following this mechanism, it would be expected that the addition of Zn powder would have little effect on PC formation, in line with the experimental results presented in Figure 1.…”

Recent developments in state-of-the-art silica-modified catalysts for the fixation of CO2 in epoxides to form organic carbonates

“…This catalytic system showed 76% yield and 100 of selectivity towards cyclic carbonate products for a wide variety of substrates under mild conditions using tetrabutylammonium iodide (TBAI) as the co-catalyst at 80 °C, under 10 bar of CO 2 pressure and 6 h reaction time [Table 3, entry 17]. 179…”

Structure-Property Relationship for Different Mesoporous Silica Nanoparticles and its Drug Delivery Applications: A Review

“…After removal of the surfactant, the organosilanes can be attached to the silanol channels using trichloro organosilanes or trialkoxy organosilanes ( Barczak, 2019 ). A series of organosilanes including amine ( Aguado et al, 2009 ), thiol ( Li et al, 2011 ), chloride ( Han et al, 2003 ), cyano ( Prouzet et al, 1999 ), ester ( Prouzet et al, 1999 ), aldehyde ( Yin et al, 2020 ), epoxy ( Yeganeh et al, 2019 ), anhydride ( Park et al, 2019 ), isocyanate ( Ratirotjanakul et al, 2019 ), phosphor ( Yamada et al, 2019 ), imidazole ( Nuri et al, 2019 ), ammonium ( Lagarde et al, 2019 ), acryl ( Xiao Song et al, 2019 ), alkyl ( Nuntang et al, 2019 ), and phenyl ( Gao et al, 2019 ) are available for application in the grafting procedure. The grafting is done by silicification so that the reaction is carried out on free (Si-OH) and attached silanol (HO-Si-OH) groups ( Barczak, 2019 ).…”