Synthesis of a family of peracid-silica materials and their use as alkene epoxidation reagents

Abstract

Alkene epoxidation is an important process for the production of resin monomers and other chemical intermediates. The challenges of and high costs associated with purifying these reactive intermediates motivates the search for new reagents that can afford epoxides in high yields and selectivity with no soluble byproducts. Here, we synthesize a family of silica-supported peracids with variations in the peracid surface density and surface chemistry and describe their use as epoxidation reagents. Materials in this study were synthesized from either sol-gel co-condensation with cyanoalkylsilanes or by grafting of silyl esters to pre-formed silica, giving titrated peracid loadings from 0.3 to 1.5 mmol/g. At constant peracid:alkene ratios, epoxide yields increased monotonically with increasing surface density, up to 1.0 mmol/g for the highest loading materials. Mixed silica surfaces possessing both alkyl and peracid moieties gave, at similar peracid surface densities, 2-3-fold greater olefin conversion, and doubled epoxide selectivity from 45 to >95%, as compared to materials with peracids alone. Hydrophobic, mixed silanesupported peracids give unusual, high selectivity to dioxide syntheses from dienes even at low conversion, suggesting strong adsorption of reactive intermediates, which is not possible for soluble peracids.These experiments suggest tunable parameters that lead to improvements in selectivity and yields in epoxidation with these easily-handled, immobilized peracids.

Hybrid Approach for Selective Sulfoxidation via Bioelectrochemically Derived Hydrogen Peroxide over a Niobium(V)–Silica Catalyst

“…17,51 Substitution of "greener" solvents has benefits in terms of cost as well as environmental and human health. 57 This overall scheme could be tuned to other reactions such as dihydroxylation of alkenes and/or epoxidation, 18 as well as other H 2 O 2 -dependent catalytic processes. Building on the success of this proof-ofconcept system for green chemistry using MPPC-derived H 2 O 2 , performance could likely be improved by more tightly coupling the catalyst and MPPC design, including electrode construction, buffer choice, and catalyst architecture.…”

“…17 Thus, sulfoxidation of a thioanisole derivative over a similarly formulated niobium(V)−silica catalyst was chosen as a model reaction system for proof-of-concept testing of the direct use of bioelectrochemically derived H 2 O 2 for selective oxidation in an aqueous buffer (rather than in acetonitrile or other organic solvents). This approach could be adapted to the epoxidation and/or dihydroxylation of alkenes, 18 the oxidative depolymerization of lignin macromolecules, 19 or other H 2 O 2 -dependent catalytic processes. H 2 O 2 can be generated for these applications via electrocatalytic oxygen reduction.…”

Simple Sol‐Gel Protein Stabilization toward Rainbow and White Lighting Devices

“…[8,9] Nowadays, there are only a handful number of protein stabilization methods, which can be broadly classified into two categories: i) genetically encoded modifications, consisting in a meaningful alteration of the amino acidic sequence to achieve desired effects, such as higher superficial charge, increased aromaticity, oligomerization, etc. [10][11][12][13] and ii) post-translational modifications, including a variety of chemical strategies such as encapsulation with heteropolymeric systems, [14][15][16][17][18] surface grafting, [19,20] reverse micelles, [21][22][23][24] and sol-gel chemistry [3,25,26] to shield the proteins from the surroundings. Among them, the sol-gel method stands out, since the bio-functionality of hybrid proteins@SiO 2 nanomaterials has been preserved over exceptionally long periods of time spanning from months to years under dry ambient storage, suspension in organic solvents, harsh temperatures/irradiations, and metabolic degradation compared to their non-encapsulated counterparts.…”

Orientation of 1,1′-Bi-2-naphthol Grafted onto TiO2

“…Modification of oxide surfaces and particles by organic ligands has numerous applications, such as in selective separations, chemical sensing, selective catalysis, and drug delivery. − A common feature of these applications is a dependence on chemical and physical interactions between an analyte and a recognition site, referred to as the “molecular recognition event”. The molecular recognition event is sensitive to the chemical composition, local structure, and, where relevant, chirality of the organic modifier. ,− Therefore, it is of great importance to understand the properties of organic modifiers when immobilized onto surfaces.…”