Modified Ti/MCM-41 catalysts for enantioselective epoxidation of styrene

Abstract

Ti sites grafted on MCM-41, pretreated at different temperatures, have been modified with chiral tartrates, leading to different species. Those solids are active catalyst for the epoxidation of styrene with tert-butyl hydroperoxide, although their efficiency is not optimal, mainly due to the subsequent epoxide rearrangement to phenyl acetaldehyde and further oxidation of it. Styrene oxide is obtained with moderate enantioselectivity, in the range of 55-62% e.e., and the best overall results correspond to the use of MCM-41 calcined at the lowest temperature (550ºC). These results are much better with regard to styrene oxide selectivity than those obtained in homogeneous phase under the same conditions, whereas enantioselectivity is similar. The heterogeneous catalysts are recoverable, but only partially due to a loss in activity, although enantioselectivity is kept at similar levels, demonstrating the stability of the supported Ti-tartrate species.

Recent Developments in Heterogeneous Catalyzed Epoxidation of Styrene to Styrene Oxide

“…Fadhli et al. carried out epoxidation of styrene over Ti grafted on MCM41 and modified with chiral tartrates as catalyst and tert‐butyl hydroperoxide as an oxidant (Scheme ) and obtained styrene oxide with moderate enantioselectivity, 55–62% e.e …”

Excellent alkene epoxidation catalytic activity of macrocyclic‐based complex of dioxo‐Mo(VI) on supermagnetic separable nanocatalyst

“…[15][16][17][18] A main idea for supporting of metal complexes is to anchor the metal complexes onto large-surface-area inorganic materials such as zeolites and metal oxides. [16,[19][20][21][22][23][24][25] Nowadays, magnetite nanoparticles are of particular interest because of their unique properties including high surface area, low toxicity, ability to be separated and biocompatibility. [16,[26][27][28][29][30] Magnetic separation renders the recycling of catalysts from solution using external magnetic fields much easier than filtration and centrifugation.…”

Functionalized Ordered Mesoporous Silicas (MCM-41): Synthesis and Applications in Catalysis

“…Then, diethyl L-tartrate or diisopropyl L-tartrate (0.4 mmol) was added to the MCM-41. The resulting suspension was refluxed in toluene for 12 h to yield the desired catalyst Fadhli-Fraile et al [44] also used Ti/MCM-41, titanium grafted on the silica surface through the formation of Si-O-Ti bonds, for use in the epoxidation of styrene with tert-butyl hydroperoxide (THP). The catalyst was synthetized by pre-treatment of the surface of the scaffold with Ti(Oi-Pr) 4 as titanium precursor.…”