Study on the epoxidation of olefins with H_(2)O_(2)catalyzed by biquaternary ammonium phosphotungstic acid

Selective epoxidation of olefins is an important field in chemical industry.In this work,we developed a new phosphotungstic acid catalyst{[(C_8H_(17))(CH_(3))_(2)N]_(2)(CH_(2))_(3)}_(1.5){PO_(4)[WO(O_(2))_(2)]_(4)}with long carbon chain and biquaternary ammonium cation.Cyclohexene could be epoxidized to cyclohexene oxide in 96.3%conversion and 98.2%selectivity.The catalyst type,solvent type,catalyst loading,initial molar ratio,temperature,cycle performance and substrate extensibility were studied and optimized,the kinetic parameters about overall reaction and unit reaction were also calculated.Dynamic light scattering analysis was carried out to explain the different catalytic performance between catalysts with different carbon chain length.This novel catalyst and the corresponding dynamics and mechanism study could probably help the industrial application on the epoxidation of cyclohexene with H_(2)O_(2).

Catalytic epoxidation of olefin over supramolecular compounds of molybdenum oxide clusters and a copper complex

The catalytic epoxidation of olefin was investigated on two copper complex-modified molybdenum oxides with a 3D supramolecular structure, [Cu（bipy）]4[Mo15O47].2H2O （1） and [Cu1（bix）][（Cu1bix） （δ-MoVl8O26）0.5] （2） （bipy = 4,4＇-bipyridine, bix = 1,4-bis（imidazole-1-ylmethyl）benzene）. Both compounds were catalytically active and stable for the epoxidation of cyclooctene, 1-octene, and styrene with tert-butyl hydroperoxide （t-BuOOH） as oxidant. The excellent catalytic performance was attributed to the presence of stable coordination bonds between the molybdenum oxide and copper complex, which resulted in the formation of easily accessible Mo species with high electropositivity. In addition, the copper complex also acted as an active site for the activation of t-BuOOH, thus im- proving these copper complex-modified polyoxometalates.

Engineering Ru(N^N)_(3)-modified covalent organic framework for photocatalytic olefin epoxidation

Photocatalytic olefin oxidation using air as an oxidant is an environmentally friendly method for producing epoxides. Covalent organic frameworks(COFs) have emerged as promising photocatalysts in various organic synthesis reactions. The combination of tri-(2-pyridinal aldehyde)-containing precursor with 4,4’,4’’-(1,3,5-triazine-2,4,6-triyl)trianiline generated(N^N)-I-COF. Via imine-to-quinoline transformation and coordination anchorage of Ru(N^N)_(3)unit, Ru(N^N)_(3)@Q-COF was obtained with improved chemical stability, skeleton conjugation, and novel photochemical characteristics, and demonstrated excellent photocatalytic activity in olefin epoxidation with a wide range of substrates. The presence of H_(2)O played a crucial role in the formation of reactive oxygen species(ROSs), which in turn influenced the olefin oxidation process. The hydrophilicity of Ru(N^N)_(3) facilitated the approach of H_(2)O and O_(2) to the photogenerated charges, thereby promoting ROSs generation. The lipophilicity of Q-COF allowed for the absorption of olefin substrates, and its nano-channels increased encountering possibility between olefins and ROSs. Consequently, Ru(N^N)_(3)@Q-COF provided an intriguing platform for olefin photooxidation and could be recycled multiple times without any degradation in performance. This report revealed that the conversion of classical ROSs into less potent oxidants with rapid kinetic rates played a crucial role in achieving highly efficient and selective epoxidation of terminal olefins.

Theoretical and experimental investigations of the enantioselective epoxidation of olefins catalyzed by manganese complexes

The enantioselective epoxidation of olefin by Mn^(II)(R,R-PMCP)(OTf)2, H_(2)O_(2) and H_(2)SO_(4) was explored by DFT calculations and experiments. Theoretical results suggest that [Mn^(V)(O)(R,R-PMCP)(SO_(4))]^(+) species with a triplet ground spin state serves as the active species for the olefin epoxidation. It can be generated by the H_(2)SO_(4) assisted O-O heterolysis of Mn^(III)(OOH) species. Mn^(III)-persulfate is also involved in this system, but it cannot promote the olefin epoxidation directly, preferring instead to transform into Mn^(V)(O). Actually, the asymmetric epoxidation reactions with H_(2)O_(2)/H_(2)SO_(4) or Oxone provide similar enantioselectivity in the presence of manganese catalyst. These observations further support the transformation of Mn^(III)-persulfate to Mn^(V)(O) species.

Synthesis and Properties of Nonatungstotricobaltosilicate Isomers

Introduction Recently substituted-type of heteropolyanions has received much attention from the point of view of their catalysis. Hill, Finke, Neumann reported respectively that transition metal mono-substituted heteropolyanions PW;M, P;W;M and SiW;Ru have an ability to catalyze the epoxidation of olefin. We discovered that trisubstituted Keggin heteropolyanions have this property too. This paper describes the synthesis, properties of α- and β-[SiW;O;Co;（H;O）;];and its catalysis for the epoxidation of olefin by PhIO.

Synthesis of a Magnetic Core-shell Fe_(3)O_(4)@Cu_(3)(BTC)_(2) Catalyst and Its Application in Aerobic Olefin Epoxidation

Olefin epoxidation is a fundamental reaction in organic chemistry.Herein,a novel magnetic core-shell Fe_(3)O_(4)@Cu_(3)(BTC)_(2) metal-organic framework(MOF)heterogeneous catalyst was synthesized for the use in olefin epoxidation.Additionally,the size selectivity of the Fe_(3)O_(4)@Cu_(3)(BTC)_(2) catalyst in olefin epoxidation was investigated.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)results indicated that Fe_(3)O_(4)@Cu_(3)(BTC)_(2) presented a microsphere morphology,and Cu_(3)(BTC)_(2) MOFs were well dispersed on the Fe_(3)O_(4)(PAA)surface after 10 cycles of the synthesis process.The synthesized magnetic core-shell Fe_(3)O_(4)@Cu_(3)(BTC)_(2) heterogeneous catalyst could facilitate efficient aerobic olefin epoxidation.Furthermore,the catalyst was used in the aerobic oxidation of alcohols and was found to exhibit excellent activity for primary alcohols.

A new reagent pair sodium percarbonateacetic anhydride for epoxidation of olefins

A new convenient method for epoxidation of olefins by sodium percarbonate-acetic anhydride is reported.It is found that the epoxides in 60—80% yields can be obtained in 18—24 h without ultrasonication.However,higher yields(some nearly quantitative)can be reached only within 1—3 h under ultrasonication.A comparison between the ultrasonicated epoxidations by use of sodium percarbonate and sodium perborate is also made.The experimental results have revealed that ultrasonication plays a main role in accelerating the interaction of both sodium percarbonate and sodium perborate with acetic anhydride,but it does not alter the mechanism of these two epoxidations.

Solar-driven green synthesis of epoxides

Epoxides are one of the most important intermediates used in the production of valuable chemicals. Traditional preparation methods often rely on hazardous oxidants or extensive fossil fuel-powered thermal catalytic systems, resulting in significant waste production and CO_(2) emissions. Solar-driven photo(electro)chemistry is an emerging option for achieving the environmentally-friendly synthesis of epoxides. In this review, we firstly summarize the fundamental understanding of epoxidation reactions among various systems, including molecular catalysis, heterogeneous thermal catalysis and electrocatalysis. Then, we focus on the recent advances in the synthesis of epoxides achieved by photo(electro)chemical approaches. This review is concluded by the rational design of photoelectrochemical systems towards efficient epoxide synthesis.

Design and synthesis of hybrid solids based on the tetravanadate core toward improved catalytic properties

Five inorganic-organic hybrid vanadates based on tetravanadate cores, transition metals and N-donor ligands have been designed and synthesized under hydrothermal conditions, namely, [Zn（elM）312V4O12 （1）, [Zn（plM）3]2V4O12.H2O （2）, [Zn（iplM）3]2V4O12 （3）, [Co（eIM）3]2V4O12.H2o （4）, [Cu（eIM）2（H20）]2V4O12 （5） （eIM = 1-ethylimidazole, plM = 1-propylimidazole, ipIM = isopropylimidazole）. All compounds were fully characterized by single-crystal XRD, powder XRD, elemental analysis, TGA, and FT-IR spectroscopy. The hybrid zinc vanadates （1-3） and cobalt vanadate （4） exhibit interesting 2D folded structures and the hybrid copper vanadate （5） presents a 1D chain configuration. All compounds can catalyze olefin epoxidation reactions when using TBHP （TBHP = tert-butyl hydroperoxide） as an oxidant in acetonitrile. The introduction of transition metal ions into tetravanadate cores not only improved the catalytic activity but also fulfilled the heterogeneous catalytic behavior. 1-5 all exhibit extraordinary efficiency in converting olefins to the corresponding epoxides with high conversion and selectivity （particularly, cony. up to 97.1%, sele. up to 100% for 1 ）. Leaching test was also carried out to prove the heterogeneous behavior.