91819-58-8Relevant articles and documents
Organocatalytic epoxidation and allylic oxidation of alkenes by molecular oxygen
Orfanidou, Maria,Petsi, Marina,Zografos, Alexandros L.
supporting information, p. 9172 - 9178 (2021/11/30)
Pyrrole-proline diketopiperazine (DKP) acts as an efficient mediator for the reduction of dioxygen by Hantzsch ester under mild conditions to allow the aerobic metal-free epoxidation of electron-rich alkenes. Mechanistic crossovers are underlined, explaining the dual role of Hantzsch ester as a reductant/promoter of the DKP catalyst and a simultaneous competitor for the epoxidation of alkenes when HFIP is used as a solvent. Expansion of this protocol to the synthesis of allylic alcohols was achieved by adding a catalytic amount of selenium dioxide as an additive, revealing a superior method to the classical application of t-BuOOH as a selenium dioxide oxidant.
Development of rapid and selective epoxidation of α-pinene using single-step addition of H2O2in an organic solvent-free process
Eze, Valentine C.,Harvey, Adam P.,López Fernández, Ana María,Mukhtar Gunam Resul, Mohamad Faiz,Rehman, Abdul
, p. 33027 - 33035 (2021/12/07)
This study reports substantial improvement in the process for oxidising α-pinene, using environmentally friendly H2O2 at high atom economy (～93%) and selectivity to α-pinene oxide (100%). The epoxidation of α-pinene with H2O2 was catalysed by tungsten-based polyoxometalates without any solvent. The variables in the screening parameters were temperatures (30-70 °C), oxidant amount (100-200 mol%), acid concentrations (0.02-0.09 M) and solvent types (i.e., 1,2-dichloroethane, toluene, p-cymene and acetonitrile). Screening the process parameters revealed that almost 100% selective epoxidation of α-pinene to α-pinene oxide was possible with negligible side product formation within a short reaction time (～20 min), using process conditions of a 50 °C temperature in the absence of solvent and α-pinene/H2O2/catalyst molar ratio of 5?:?1?:?0.01. A kinetic investigation showed that the reaction was first-order for α-pinene and catalyst concentration, and a fractional order (～0.5) for H2O2 concentration. The activation energy (Ea) for the epoxidation of α-pinene was ～35 kJ mol-1. The advantages of the epoxidation reported here are that the reaction could be performed isothermally in an organic solvent-free environment to enhance the reaction rate, achieving nearly 100% selectivity to α-pinene oxide.
Engineering a Highly Defective Stable UiO-66 with Tunable Lewis-Br?nsted Acidity: The Role of the Hemilabile Linker
De Geyter, Nathalie,De Vos, Dirk E.,Feng, Xiao,Hajek, Julianna,Hoffman, Alexander E. J.,Jena, Himanshu Sekhar,Leus, Karen,Leyssens, Karen,Marquez, Carlos,Meynen, Vera,Morent, Rino,Van Der Voort, Pascal,Van Speybroeck, Veronique,Veerapandian, Savita K. P.,Wang, Guangbo
, p. 3174 - 3183 (2020/03/10)
The stability of metal-organic frameworks (MOFs) typically decreases with an increasing number of defects, limiting the number of defects that can be created and limiting catalytic and other applications. Herein, we use a hemilabile (Hl) linker to create up to a maximum of six defects per cluster in UiO-66. We synthesized hemilabile UiO-66 (Hl-UiO-66) using benzene dicarboxylate (BDC) as linker and 4-sulfonatobenzoate (PSBA) as the hemilabile linker. The PSBA acts not only as a modulator to create defects but also as a coligand that enhances the stability of the resulting defective framework. Furthermore, upon a postsynthetic treatment in H2SO4, the average number of defects increases to the optimum of six missing BDC linkers per cluster (three per formula unit), leaving the Zr-nodes on average sixfold coordinated. Remarkably, the thermal stability of the materials further increases upon this treatment. Periodic density functional theory calculations confirm that the hemilabile ligands strengthen this highly defective structure by several stabilizing interactions. Finally, the catalytic activity of the obtained materials is evaluated in the acid-catalyzed isomerization of α-pinene oxide. This reaction is particularly sensitive to the Br?nsted or Lewis acid sites in the catalyst. In comparison to the pristine UiO-66, which mainly possesses Br?nsted acid sites, the Hl-UiO-66 and the postsynthetically treated Hl-UiO-66 structures exhibited a higher Lewis acidity and an enhanced activity and selectivity. This is further explored by CD3CN spectroscopic sorption experiments. We have shown that by tuning the number of defects in UiO-66 using PSBA as the hemilabile linker, one can achieve highly defective and stable MOFs and easily control the Br?nsted to Lewis acid ratio in the materials and thus their catalytic activity and selectivity.
