Epoxidation Of Cyclic Alkenes Research Articles

Pore size-tunable titanosilicates post-synthesized from germanosilicate by structural reorganization and H2TiF6-assisted isomorphous substitution

Titanosilicates with large porosities are highly desirable for the selective liquid-phase epoxidation of alkenes in particular requiring open reaction spaces. Structural collapse and healing took place readily in one-pot when calcined and as-synthesized UTL-type germanosilicates both were subject to severe acid treatment, benefiting from the structural instability and modifiability of Ge-rich double four ring (D4R) units. Several structural derivatives with continuously tunable pore sizes were obtained by precisely controlling the acid treatment process. Isomorphous incorporation of Ti active centers and structural reorganization were then simultaneously realized via solid-liquid phase treatment using aqueous hexafluorotitanic acid (H2TiF6) solution, giving rise to three titanosilicates of Ti-ECNU-14 (OKO), Ti-ECNU-15 and Ti-UTL with different pore sizes varying form medium pores (10-ring) to extra-large pores (14-ring). The obtained titanosilicates with high content of tertrahedrally coordinated Ti ions in framework performed unique catalytic performance in the epoxidation of cyclic alkenes using hydrogen peroxide or anhydrous tert-butyl hydroperoxide as an oxidant.

Highly Efficient Epoxidation of Cyclic Alkenes Catalyzed by Ruthenium Complex.

The epoxidation of cyclic alkenes with molecular oxygen was efficiently completed in excellent epoxide yield using a novel ruthenium complex as catalyst under mild reaction conditions.

Highly efficient epoxidation of cyclic alkenes catalyzed by ruthenium complex.

The epoxidation of cyclic alkenes with molecular oxygen was efficiently completed in excellent epoxide yield using a novel ruthenium complex as catalyst under mild reaction conditions.

Epoxidation of cyclic alkenes with hydrogen peroxide and tert-butyl hydroperoxide on Na-containing Tiβ zeolites

The liquid-phase epoxidation of a series of cyclic alkenes with H2O2 and TBHP over Na–Tiβ zeolites without undergoing further acid-treatment has been carefully investigated. Many factors such as the time, the conversion, the solvent, the Si/Na ratio, the Si/Ti ratio and the Ti/Na ratio, have been found to take effects on the conversion of cyclohexene and H2O2 as well as the selectivity to epoxide. Lower conversion (about 6.2mol%) of cyclohexene has shown an improvement for the selectivity to epoxide (about 90%). The solvent having bigger dielectric constant is very helpful to enhance the reactivity of substrate, particularly MeCN is an optimal choice for improving the selectivity to epoxide (up to 59%). The reactivity of cyclic alkenes decreases with increasing carbon number from C6 to C12, the selectivity to corresponding cyclic epoxides is C12≈C8(100%)>C7(71%)>C5(20%)>C6(1.2%), where the exception of C5 is related to its low dissolubility and steric conformations of reactant and products molecules. Linear alkene shows the higher reactivity and the lower selectivity to epoxide than cyclic alkene with the same carbon number. TBHP as the oxidant significantly retards the reactivity of C6, C7 and C12, and shows more beneficial to the selective production of epoxide than H2O2.

Pernitrated metalloporphyrins as catalysts in oxidation with magnesium monoperoxophthalate: I. Epoxidation of cyclic olefins

Metalloporphyrins with several nitro groups in β-positions were used in the epoxidation of cyclic olefins with magnesium monoperoxyphthalate (MMPP) as an oxygen atom donor, under mild conditions. Iron- and manganese-pernitrated complexes are able to promote the epoxidation of alkenes without requiring the addition of any nitrogen base. Cobalt porphyrins showed low activity, but addition of the cocatalyst raised it.

Aerobic epoxidation of cyclic alkenes catalyzed by poly(vinylbenzyl)acetylacetonato cobalt(II complex

Poly(vinylbenzyl)acetylacetonato complex of cobalt is an effective and stable catalyst for the epoxidation of cycloalkenes with molecular oxygen under 25°C with i-butyraldehyde as the sacrificial reductant. The acetylacetone ligand/Co mole ratio, the reaction time, and the strain and electronic nature of cycloalkenes all affect the conversions of alkenes and selectivities to the corresponding epoxides. The catalyst can be recycled at least seven times without loss of its activity.

Oxidation of alkenes using the RuCl 3/PhIO system

The RuCl 3 catalysed epoxidation of olefins gave more than 10% of epoxide. Pyridine addition increased the yield and selectivity of the epoxide. Epoxidation of norbornene gave exo- and endo-epoxide. The effect of surfactants supports the involvement of carbocation intermediates. The epoxidation of cyclic olefins follows the reactivity order cyclo-octene > norbornene > cyclopentene > cycloheptene > cyclohexene. Spectral studies suggest that oxo ruthenium (V) is the active oxidizing species.

Epoxidation of cyclic alkenes by bis(acetonitrile)chloronitropalladium(II): on the role of heterometallacyclopentanes and .beta.-hydrogen elimination in the catalytic oxidation of alkenes

Reaction of the palladium complex with norbornene in acetone leads to the quantitative formation of the metallacycle, which can be isolated as a yellow solid. Decomposition of this metallatricycle under nitrogen in toluene solution produces exo-epoxynorbornene (ca 90% yield) at an initial rate of 3%/h. Part of this stability and change in product selectivity is attributed to the allycyclic bridgeheads. Intrametallacyclic ..beta..-hydrogen is restricted by the rotational rigidity of the bicyclic norbornane skeleton and by the attendant reintroduction of ring strain. 1 table.