Other selected oxidants

Complexes of iridiumfO), rutihenium(O), palladiumfO) and platinum(O) are oxidized by tetrachloro-l,2-benzoquinone or tetrabromo-l,2-benzoquinone.2 A mixture of AlQa and CH2Q2 has been used as an oxidant O but the mechanism and nature of the by-products are not known. In dichloromethane AIQ3 will oxidize lMo(00)2(l py)2]- The dimer. 

N-halosucdnimides (chloro-, bromo-, and iodo-) are useful reagents for oxidations in organic chemistry and for the oxidative halogenation of metal complexes. For example, the reaction of the rhenium hydride, trans-(H,Br)-[Re(Bt)(FO(CO)(PMe Cp l with N-hromosucdnimide in THF at 0 C 

Both TCNE and TCNQ are poor ligands for most metals. However, upon electron uptake by back-donation or by complete reduction, they bind to metal fragments via the C=C 7i-system or by the nitrogen atoms of the ON groups and a wide variety of di-, tri-, and tetranudear metal complexes are 

Organic disulphides can oxidize metal carbonyls is by a photochemical redox reaction, Eq. 8.60  

The mechanisms involve the formation of extremely reactive metal carbonyl radicals as a result of photolysis. The radicals are oxidized in a dark reaction by the organic disulphide, accompanied by formation of thiolate 

---

See also page 1234, Section 18 for some other selective oxidations of diols. 

A more long term goal is to explore the use of OMS and OL systems for other selective oxidations. Conventional manganese oxide reagents are typically used as oxidizing agents for stoichiometric oxidations on a laboratory scale. 51 Specific examples include oxidation of primary and secondary alcohols,10 transformation of vitamin A to retinene, l02 overoxidation of aldehydes to acids and esters, 03 etc. Radical intermediates and specific stereochemistries are important in these systems. We expect that these reactions can be carried out catalyticaiiy using our OMS and OL materials. 

Partly because gold catalysts are active under mild conditions, they have been investigated for other selective oxidation and for selective hydrogenation reactions. Details are given in Sect. 6.2.4. 

Among the many other selective oxidation catalysts, those based on... 

Having explored the potential of hydrotalcites for selective hydroxylation of phenol to dihydroxy benzenes, efforts are been continually made for exploiting these materials for other selective oxidation reactions. Functionalization of C-H in benzene to C-OH as phenol is one of the challenging reaction, which has been attempted over these catalysts. Encouraging conversion with good selectivity towards phenol is noted. Carpentier et ai [117J have studied... 

A review of the experimental results reported in the literature (up to November 2014) reveals that all the results reported seem to obey an empirical correlation given by C2 selectivity-F CH4 conversion <1 (see Figure 33.23). This strongly indicates that improved yields can only be achieved with novel reactor concepts. An important aspect of the oxidative coupling reaction (and many other selective oxidation reactions) that can be exploited to maximize the total C2 product yield is that the O2 reaction order of the preferred OCM reaction is lower than the O2 reaction order of the unselective (total) oxidation reactions. 

The reaction is carried out either over bulk Fe2(Mo04)3-Mo03 or over silver catalysts with very high selectivity. Over different catalysts other selective oxidation products or total oxidation can be obtained. Some years ago we focused our attention on vanadia-titania catalysts, where methyl formate can be obtained with high yields. ... 

Other Selective Oxidation Reactions 22.4.1. Selective oxidation of amines... 

Table 27.4. Membrane reactors using dense ceramic membranes for the oxidative dehydrogenation (ODH) of alkanes and other selective oxidations.

The oxidation of CH3OH to HCHO is considered as a probe reaction for other selective oxidation reactions such as butane to maleic anhydride, o-xylene to phthalic anhydride, and ODH of alkanes to alkenes. Consequently, the concepts developed for the selective oxidation of methanol over vanadium oxide catalysts can be easily transferred to other catalytic reactions. Weckhuysen and Keller [82] carried out methanol oxidation as a probe reaction over various V2O5/S oxides (S = HO2, Zr02, Nb205, Ce02, and AI2O3). The relative independence of turnover frequency (TOP) to vanadia loading on amorphous oxide supports indicated that the reaction was first order with respect to surface vanadium oxide site. 

Acetylsucrose [63648-81-7] has been prepared in 40% yield by direct acetylation of sucrose using acetic anhydride in pyridine at 40° C (36). The 6-ester has subsequently been obtained in greater than 90% yield, by way of 4,6-cycHc orthoacetate. Other selective methods for the 6-acylated derivatives include the use of alkyl tin reagents such as dibutyl tin oxide (37) and of dibutyl stannolane derivatives (38). Selective acetylation of sucrose by an enzymic process has also been described. Treatment of sucrose with isopropenyl acetate in pyridine in the presence of Lipase P Amano gave, after chromatography, 6-0-acetylsucrose (33%) and 4/6-di-O-acetylsucrose (8%). The latter compound has been obtained in 47% yield by the prolonged treatment (39). 

The selective oxidation is catalyzed by silver, which is the only good catalyst. Other olefins are not converted selectively to the epoxides in the presence of silver. However, propylene epoxidation is appHed commercially the catalysts are either molybdenum complexes in solution or soHd Ti02—Si02 (see... 

Dibenz[yellow-green colour (due to other pentacyclic impurities) has been removed by crystn from benzene or by selective oxidation with lead tetraacetate in acetic acid [Moriconi et al. J Am Chem Soc 82 3441 7960]. 

When used at room temperature in the presence of an active platinum catalyst in an inert solvent, e.g., acetone or ethyl acetate, oxygen will oxidize nonhindered, saturated hydroxyl groups and exposed allylic alcohols. This reagent has found extensive use in sugar chemistry and is particularly suited for the selective oxidation of either 3a- or 3j -alcohols of steroids. Other hydroxyl groups on the steroid skeleton are much less sensitive to oxidation. As a result, this reaction has been used extensively in research on polyhydroxy cardiac-active principles, e.g., the cardenolides and bufadienolides, where the 3-hydroxyl group is easily oxidized without extensive oxidation or dehydration of other hydroxyl groups. The ordinarily difficult selective oxidation of the... 

The reactions of olefins with peracids to form epoxides allows for the selective oxidation of carbon-carbon double bonds in the presence of other functional groups which may be subject to oxidation (for example, hydroxyl groups). The epoxides that result are easily cleaved by strong acids to diols or half-esters of diols and are therefore useful intermediates in the synthesis of polyfunctional compounds. 

Epoxyfarnesol was first prepared by van Tamelen, Stomi, Hessler, and Schwartz 4 using essentially this procedure. It is based on the findings of van Tamelen and Curphey5 that N-bromosuccinimide in a polar solvent was a considerably more selective oxidant than others they tried. This method has been applied to produce terminally epoxidized mono-, sesqui-, di-, and triterpene systems for biosynthetic studies and bioorganic synthesis.6 It has also been applied successfully in a simple synthesis of tritium-labeled squalene [2,6,10,14,18,22-Tetracosahexaene, 2,6,10,15,19,23-hexamethyl-, (all-E)-] and squalene-2,3-oxide [Oxirane, 2,2-dimethyl-3-(3,7,12,16,20-pentamethyl-3,7,ll,-15,19-heneicosapentaenyl)-, (all-E)-],7 and in the synthesis of Cecropia juvenile hormone.8... 

In the case of tertiary N-ethylamine derivatives the N-ethyl group is first selectively oxidized by p-chloranil to an enamino group which then condenses with excess p-chloranil to a blue aminovinylquinone derivative [7]. Secondary N-ethyl derivatives do not yield blue aminovinylquinone derivatives they probably react directly with chloranil by nucleophihc attack at one of the four chlorine atoms to yield aminoquinones of other colors [7], It has also been suggested that some classes of substances react to yield charge transfer complexes [1, 5, 8, 12],... 

---