Oxidants urea/H2O2 peroxide

The effect of structural variation and the use of different caboxylate salts as cocatalysts was investigated by Pietikainen . The epoxidation reactions were performed with the chiral Mn(III)-salen complexes 173 depicted in Scheme 93 using H2O2 or urea hydrogen peroxide as oxidants and unfunctionalized alkenes as substrates. With several soluble carboxylate salts as additives, like ammonium acetate, ammonium formate, sodium acetate and sodium benzoate, good yields (62-73%) and moderate enantioselectivities (ee 61-69%) were obtained in the asymmetric epoxidation of 1,2-dihydronaphthalene. The results were better than with Ai-heterocycles like Ai-methylimidazole, ferf-butylpyridine. 

V-methylmorpholine 7V-oxide or 4-phenylpyridine TV-oxide as cocatalysts. The yields and enantioselectivities obtained with H2O2 or urea hydrogen peroxide were comparable, with slightly better yields for the epoxidation with H2O2 (73% versus 68% for the epoxide of 1,2-dihydronaphthalene in the presence of NH4OAC). 

Since its discovery in 1991, methyltrioxorhenium (MTO, 80) has attracted much interest as one of the most versatile catalysts for oxidation.When it is associated with a stoichiometric amount of H2O2, the system can efficiently transform alkene to epoxide, although formation of undesired diol can occur. Alternatively, water-free conditions, using urea hydrogen peroxide (UHP), allow the formation of the desired epoxide without byproducts. A maj or drawback of the MTO/UHP system is its insolubility in organic solvents, leading to a kinetically slow heterogeneous system. 

So, when conducting the reaction at 65-85 °C in water, alcohol, ester, acetonitrile, the polyketone particles of size 0.01-100 micrometers transform the polyesters by the oxidation under the peroxide agents per-oxybenzoic, m-chloroperoxybenzoic, peroxyacetic, trifloumperoxyacetic, monoperox rphthalic, monoperox5rmaleine acids, combinations of H2O2 and urea or arsenic acid [405, 406],... 

H2O2 converts carboxylic acids (RCOOH) into peroxy acids (RCOOOH), which are themselves used as oxidizing agents. Hydrogen peroxide reacts with acetone to form acetone peroxide, and it interacts with ozone to form hydrogen trioxide, also known as trioxidane. Reaction with urea produces carbamide peroxide, used for whitening teeth. 

Recently, Katsuki and Saito reported that di-g-oxo titanium complexes of chiral salen ligands serve as efficient catalysts for asymmetric oxidation of various sulfides using H2O2 or the urea-hydrogen peroxide adduct as oxidants [108]. Enantioselectiv-... 

Torisawa [17] developed an alternative oxidative amidation of aldehydes using palladium chloride (PdCl2)-xantphos complex as a catalyst. The use of hydrogen peroxide (H2O2)-urea complex as oxidant prevents the formation of imine from the carbinolamine intermediate and minimizes the level of benzoic acid side... 

Chromogenic detection of horseradish peroxidase POase is widely used in enzyme immunoassays (EIA) and many suitable chromogens (which are oxidized by the enzyme in the presence of the peroxide or urea peroxide substrates) have been developed. Peroxide is the usual substrate, particularly on solid phases since its reduction results in the formation of inert water near the solid phase (Fig. 7.9). It should be realized that POase has a very pronounced optimum concentration of H2O2 substrate (Tijssen et al., 1982). Activity is low at low substrate concentrations, but inhibition is considerable at high substrate concentrations. The universally used POase, C isozyme, has an optimum in solution of 0.003% peroxide but higher concentrations are usually required on a solid phase. 

Several other MOFs have also been used as oxidation catalysts. Kim and coworkers used [Zn2(BDC)(L-Lac)(DMF)] (DMF) as a heterogeneous catalyst for the oxidation of thioethers to sulfoxides by urea hydroperoxide (UHP) or hydrogen peroxide (H2O2) [26]. Its size selectivity was illustrated by the higher conversion of smaller sulfides over larger ones. Snejko and coworkers reported the use of ln2(OH)3(BDC)i,5 [27] and [Sc2(BDC)3] [28] as active catalysts for the oxidation of alkylphenylsulfides. 

---