H2O2 as Oxidant

This was also accomplished with BaRu(0)2(OH)3. The same type of conversion, with lower yields (20-30%), has been achieved with the Gif system There are several variations. One consists of pyridine-acetic acid, with H2O2 as oxidizing agent and tris(picolinato)iron(III) as catalyst. Other Gif systems use O2 as oxidizing agent and zinc as a reductant. The selectivity of the Gif systems toward alkyl carbons is CH2 > CH > CH3, which is unusual, and shows that a simple free-radical mechanism (see p. 899) is not involved. ° Another reagent that can oxidize the CH2 of an alkane is methyl(trifluoromethyl)dioxirane, but this produces CH—OH more often than C=0 (see 14-4). ... 

As an example heme-models have been reported to catalyze the epoxidation of olefins to the corresponding epoxides in good yield [16, 17]. In particular, [Fe TPP)Cl] (TPP = 5,10,15,20-meso-tetraphenylporphyrin) was reported to oxidize naturally occurring propenylbenzenes to the corresponding epoxides up to 98% selectivity (conversion 98%) using H2O2 as oxidant [16]. The major drawback... 

A practical method of modification of polysaccharides by clean oxidation using H2O2 as oxidant and cheap iron phthalocyanine as catalyst has been developed. Since no acids, bases or buffers and no chlorinated compounds were used, a pure product can be recovered without additional treatment. Importantly, this flexible method provides materials with a wide range of DScho and DScooh just by an appropriate choice of the reaction conditions. Oxidized polysaccharides thus obtained possess various, tailormade hydrophihc/hydrophobic properties which have been tested successfully in cosmetic and other apphcations. 

An overview of the pubhshed known results of tungsten-catalyzed epoxidation of unfunctionahzed olefins with H2O2 as oxidant is given in Table 23. 

SCHEME 96. MTO-catalyzed epoxidation of various olefins using H2O2 as oxidant in the presence of different cocatalysts... 

In 1998, Begue and coworkers reported on a very selective conversion of sulfides to sulfoxides in hexafluoro-2-propanol (HFIP) as solvent using 30% H2O2 as oxidant without the need for a catalyst (equation 54) . A variety of differently substituted acyclic sulfides and also a cyclic one could be cleanly oxidized to the sulfoxides in very good yields ranging from 82 to 99% and no sulfone formation was observed. C=C double bonds in the substrate are tolerated without being epoxidized. This excellent reactivity is explained... 

Taylor and Flood could show that polystyrene-bound phenylselenic acid in the presence of TBHP can catalyze the oxidation of benzylic alcohols to ketones or aldehydes in a biphasic system (polymer-TBHP/alcohol in CCI4) in good yields (69-100%) (Scheme 117) °. No overoxidation of aldehydes to carboxylic acids was observed and unactivated allylic alcohols or aliphatic alcohols were unreactive under these conditions. In 1999, Berkessel and Sklorz presented a manganese-catalyzed method for the oxidation of primary and secondary alcohols to the corresponding carboxylic acids and ketones (Scheme 118). The authors employed the Mn-tmtacn complex (Mn/168a) in the presence of sodium ascorbate as very efficient cocatalyst and 30% H2O2 as oxidant to oxidize 1-butanol to butyric acid and 2-pentanol to 2-pentanone in yields of 90% and 97%, respectively. This catalytic system shows very good catalytic activity, as can be seen from the fact that for the oxidation of 2-pentanol as little as 0.03% of the catalyst is necessary to obtain the ketone in excellent yield. 

SCHEME 153. MTO-catalyzed -oxidation reactions with H2O2 as oxidant... 

In 2003, Kulkarni and coworkers presented a method for the -selective oxybromi-nation of a variety of substituted phenols employing a novel heterogeneous catalytic system, the CrZSM-5 as catalyst, H2O2 as oxidant and KBr as bromine source ". Next to CrZSM-5 also other zeolites have been tested as catalysts, but although MoZSM-5 showed the highest conversion after 5 hours (89%), para-selectivity was lower (para 36% ortho 31% dibromination 22%) than observed with the CrZSM-5 material (83%... 

Titanium containing pure-silica ZSM-5 (TS-1) materials are synthesized using different methods. The activity of the titanium containing catalysts for the oxidation of alkanes, alkenes and phenol at temperatures below 100 °C using aqueous H2O2 as oxidant is reported. The relationships between the physicochemical and catalytic properties of these titanium silicates are discussed. The effects of added duminum and sodium on the catalytic activity of TS-1 are described. The addition of sodium during the synthesis of TS-1 is detrimental to the catalytic activity while sodium incorporation into preformed TS-1 is not. The framework substitution of aluminum for silicon appears to decrease the amount of framework titanium. 

The salen-Cu complex 5a was shown to oxidize a selected number of secondary alcohols (e.g. l-phenylethanol) to the corresponding ketones, with a wider range of primary alcohols being further oxidized to the analogous carboxylic acids, in the presence of 5-15 equiv. of H2O2 as oxidant, while molecular oxygen proved inefficient as oxidant [152], The derivative 5b has been reported to catalyze the electrochemical oxidation of primary alcohols (but not secondary alcohols) into the corresponding aldehydes, with turnovers > 30 [153]. 

Table 9.4 presents results of different sulfides that underwent asymmetric oxidation using catalytic WO3 in the presence of cinchona alkaloids such as hydroquinidine 2,5-diphenyl-4,6-pyrimidinediyl diether [(DHQD)2-PYR] with 30 % H2O2 as oxidant. 

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