Ruthenium , catalytic oxidation

There is little data available to quantify these factors. The loss of catalyst surface area with high temperatures is well-known (136). One hundred hours of dry heat at 900°C are usually sufficient to reduce alumina surface area from 120 to 40 m2/g. Platinum crystallites can grow from 30 A to 600 A in diameter, and metal surface area declines from 20 m2/g to 1 m2/g. Crystal growth and microstructure changes are thermodynamically favored (137). Alumina can react with copper oxide and nickel oxide to form aluminates, with great loss of surface area and catalytic activity. The loss of metals by carbonyl formation and the loss of ruthenium by oxide formation have been mentioned before. 

Epimerization of 50 at C-3 furnished carba-a-DL-allopyranose (60). Stepwise, 0-isopropylidenation of 50 with 2,2-dimethoxypropane afforded compound 56. Ruthenium tetraoxide oxidation of 56 gave the 3-oxo derivative 57, and catalytic hydrogenation over Raney nickel converted 57 into the 3-epimer 58 exclusively. Hydrolysis of 58, and acetylation, provided the pentaacetate 59, which was converted into 60 on hydrolysis. ... 

FIGURE 11.5 Chromatograms at 450nm of the reaction mixture at 6h of catalytic oxidation of 13-carotene by dioxygen catalyzed by ruthenium mesitylporphyrin. 

Similar acetic acid conversions and higher acid yield distributions using ruthenium(IV) oxide in combination with methyl iodide, ethyl iodide and hydrogen iodide as the added iodide promoter under comparable conditions. This is consistent with these different starting materials ultimately forming the same catalytically active species. 

It was also found that the specific catalytic activity (TOF) could be maintained at a high value over a wide range (0.5-9% wt) of ruthenium loading. The independence of activity from catalyst loading was attributed to the high dispersion of deposited ruthenium-hydrated oxide in the catalysts with high loading, which was confirmed by the microscopy studies. 

Catalytic oxidant.1 In combination with N-methylmorpholine N-oxide (7,244) as the stoichiometric oxidant, this ruthenium compound can be used as a catalytic oxidant for oxidation of alcohols to aldehydes or ketones in high yield in CH2C12 at 25°. Addition of 4A molecular sieves is generally beneficial. Racemization is not a problem in oxidation of alcohols with an adjacent chiral center. Tetrabutylammonium perruthenate can also be used as a catalytic oxidant, but the preparation is less convenient. 

Exposure of 144 to catalytic quantities of ruthenium tetroxide, generated in situ from ruthenium trichloride and sodium periodate, produces the symmetrical lactones 145 <2000JA9558>. It is proposed that the products form as a result of the ruthenium-catalyzed oxidative cleavage of the a-diketones to produce intermediate glycols (Equation 49). 

The use of cyclic sulfates in synthetic applications has been limited in the past because, although cyclic sulfites are easily prepared from diols, a convenient method for oxidation of the cyclic sulfites to cyclic sulfates had not been developed. The experiments of Denmark [70] and of Lowe and co-workers [71 ] with stoichiometric ruthenium tetroxide oxidations and of Brandes and Katzenellenbogen [72a] and Gao and Sharpless [68] with catalytic ruthenium tetroxide and sodium periodate as cooxidant have led to an efficient method for this oxidation step. Examples of the conversion of several diols (67) to cyclic sulfites (68) followed by oxidation to cyclic sulfates (69) are listed in Table 6D.7. The cyclic sulfite/cyclic sulfate sequence has been applied to 1,2-, 1,3-, and 1,4-diols with equal success. Cyclic sulfates, like epoxides, are excellent electrophiles and, as a consequence of their stereoelectronic makeup, are less susceptible to the elimination reactions that usually accompany attack by nucleophiles at a secondary carbon. With the development of convenient methods for their syntheses, the reactions of cyclic sulfates have been explored, Most of the reactions have been nucleophilic displacements with opening of the cyclic sulfate ring. The variety of nucleophiles used in this way is already extensive and includes H [68], [68,73-76], F" [68,72,74], PhCOCT [68,73,74], NOJ [68], SCN [68],... 

Although the preceding catalase biomimetic reactions are important, the true biological role of the OEC is to evolve 02 from H20. Only a few complexes evolve 02 from H20 and even fewer contain Mn (see complex 67). Perhaps the best known case is the catalytic oxidation of water by the dinuclear ruthenium complex [(bpy)2(H20)Ru0Ru(H20)(bpy)2]4+ 68, which has been well documented [9,160] and will not be discussed here. 

Keywords Ruthenium Ruthenium tetroxide Catalytic oxidation Alcohols Ethers... 

Fig. 4.34 A catalytic cycle for ruthenium-catalyzed oxidative cleavage of olefins.

Oxidation of allylic alcohols. Ruthenium(IV) oxide, particularly the hydrate, is more efficient than MnO, for oxidation of allylic alcohols to the corresponding aldehydes. Only catalytic amounts are required if the oxidation is conducted under oxygen. An antioxidant is also required to prevent further oxidation. Either system oxidizes primary allylic alcohols in high yield (76-98%) yields arc lower in oxidations of secondary allylic alcohols. 

Pintar A., Besson M., Gallezot R, Catalytic oxidation of Kraft bleaching plant effluents in the presence of titania and zirconia supported ruthenium, Appl. Catal B Environ., 30 (2001) pp. 123-139. ... 

Aqua(phosphine)ruthenium(II) complexes [121] are useful for activation of molecular oxygen, and catalytic oxidation of cyclohexene can be carried out with 1 atm of O2 [121a,bj. The ruthenium catalyst bearing perfluorinated 1,3-diketone ligands catalyzes the aerobic epoxidation of alkenes in a perfluorinated solvent in the presence of i-PrCHO [122]. Asymmetric epoxidations of styrene and stilbene proceed with 56-80% e.e. with ruthenium complexes 38-40 (Figure 3.2) and oxidants such as PhI(OAc)2, PhIO, 2,6-dichloropyridine N-oxide, and molecular oxygen [123-125]. 

As shown in Scheme 3.8, the catalytic oxidation reactions can be rationalized by assuming the formation of oxo-ruthenium species by the reaction of low-valent ruthenium complexes with peroxides. The C-H activation at the a-position of amines and the subsequent electron transfer gives iminium ion ruthenium complex 55. Trapping 55 with f-BuOOH would afford the corresponding a-ferf-butylhydroxy-amines, water, and low-valent ruthenium complex to complete the catalytic cyde. 

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