Selective aerobic

Figure 1.16 Schematic and comparative illustrative of grafting (a) an amorphous silica gel and (b) an ordered MCM-41 silica materials. Entrapment of oxidation catalyst perruthenate inside the channels of MCM-41 silica (below) results in a shape-selective aerobic catalyst, which may not be desirable from the viewpoint of catalyst versatality (Reproduced from ref. 39, with permission.)...

Similarly, a water-soluble palladium complex of a sulfonated phenanthroline ligand catalyzed the highly selective aerobic oxidation of primary and secondary alcohols in an aqueous biphasic system in the absence of any organic solvent (Figure 1.8) [40]. The liquid product could be recovered by simple phase separation, and the aqueous phase, containing the catalyst, used with a fresh batch of alcohol substrate, affording a truly green method for the oxidation of alcohols. 

It is appropriate and very instructive to briefly discuss a relatively new and very successful approach, namely, the development of catalysts with designed and atomically engineered active centers. Thomas and coworkers used micro- and meso-porous solids and carried out delicate structural and compositional variations to prepare specific catalysts capable of promoting regioselective, shape-selective, and enantioselective conversions.183-185 This strategy resulted in the development of framework-substituted CoALPO-18 and MnALPO-18 molecular sieves for the selective aerobic oxidation of linear alkanes to the corresponding monocarboxylic acids,186 and that of hexane to adipic acid.187 Framework-substituted MALPO-36... 

In this context, Leitner et al. have developed a novel catalytic system for selective aerobic oxidation of alcohols based on highly dispersed Pd nanoparticles in a PEG matrix with scC02 as the substrate and product phase (Scheme 3.2) [13]. 

Recently two heterogeneous TPAP catalysts were developed which could be recycled successfully and displayed no leaching In the first example the tetraalkylammonium perruthenate was tethered to the internal surface of mesoporous silica (MCM-41) and was shown [ 101] to catalyse the selective aerobic oxidation of primary and secondary allylic and benzylic alcohols (Fig. 17). Surprisingly, both cyclohexanol and cyclohexenol were unreactive although these substrates can easily be accommodated in the pores of MCM-41. No mechanistic interpretation for this surprising observation was offered by the authors. 

Another improvement is the use of a Ru/TEMPO catalyst combination for the selective aerobic oxidations of primary and secondary alcohols to the corresponding aldehydes and ketones, respectively (Fig. 1.22) [72]. The method is effective (>99% selectivity) with a broad range of primary and secondary aliphatic, allylic and benzylic alcohols. The overoxidation of aldehydes to the corresponding carboxylic acids is suppressed by the TEMPO which acts as a radical scavenger in preventing autoxidation. 

Recently, an alternative to the catalytic system described above was reported [204]. The new catalytic procedure for the selective aerobic oxidation of primary alcohols to aldehydes was based on a CunBr2(Bpy)-TEMPO system (Bpy=2,2 -bipyridine). The reactions were carried out under air at room temperature and were catalyzed by a [copper11 (bipyridine ligand)] complex and TEMPO and base (KOtBu) as co-catalysts (Fig. 4.70). 

Dijksman, A., Marino-Gonzalez, A., Payeras, A.M., Arends, W., and Sheldon, R.A. 2001. Efficient and selective aerobic oxidation of alcohols into aldehydes and ketones using Ruthenium/TEMPO as the catalytic system. Journal of the American Chemical Society, 123 6826-33. 

Nanoparticlulated gold supported by nanocrystalline or mesostruc-tured nanocrystalline ceria catalysts represents an alternative to catalysts for selective aerobic oxidation of aliphatic and aromatic aldehydes which is much better than the gold supported by the precipitated ceria (Corma and Domine, 2005). The ceria or yttria supported Au are also active and extremely selective for the homocoupling of arylboronic acids, and the activity is directly correlated with Au(lll) (Carrettin et al., 2005). 

A number of systems consist of a palladium salt, typically PdCb or Pd(OAc)2, with abase. For example, PdCb-NaOAc catalyzes the aerobic oxidation of secondary alcohols in ethylene carbonate under nuld conditions. Sheldon has carried out mechanistic investigations on a number of related Pd systems and shown that water-soluble complexes of Pd(II) with phenanthrohnes are stable, recyclable catalysts for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic liquid liquid system. The active catalyst is a dihydroxy-bridged palladium dimer. 

Oxidation of primary alcohols. Selective aerobic oxidation of RCH OH to... 

F. Minisci, C. Gambarotti, M. Pierini, O. Porta, C. Punta, F. Recupero, M. Lucarini, V. Mugnaini, Molecule-induced homolysis of N-hydroxyphthalimide (NHPI) by peracids and dioxirane. A new, simple, selective aerobic radical epoxidation of alkanes. Tetrahedron Lett. (2006) 1421. 

A selective aerobic oxidation of alcohols to the corresponding aldehydes or ketones was reported by Jiang et al. using a two-component system VOCacacJ /DABCO in the ionic liquid [bmim][PF ] [32] (Scheme 14.36). 

Shen et al. used HPW/MCM-41 system for the photocatalytic selective aerobic oxidation of alcohols to aldehydes and ketones in ionic hquids [49]. Based on the property of this photocatalytic reaction, many variables such as the amount of HPW, irradiation energy and time, snbstrates, reaction media, etc., that may affect the... 

Jiang N, Ragauskas AJ (2007) Vanadium-catalyzed selective aerobic alcohol oxidation in ionic hquid [bmim][PFJ. Tetrahedron Lett 48 273-276... 

Jiang N, Ragauskas AJ (2007) Selective aerobic oxidation of activated alcohols into acids or aldehydes in ionic hquids. J Org Chem 72 7030-7033... 

Shen HY, Mao HL, Ying LY, Xia QH (2007) Photocatalytic selective aerobic oxidation of alcohols to aldehydes and ketones by HPW/MCM-41 in ionic liquids. J Mol Catal A Chem 276 73-79... 

Shen HY, Ying LY, Jiang HL, Zaher MAJ (2007) Efficient copper-bisisoquinoline-based catalysts for selective aerobic oxidation of alcohols to aldehydes and ketones. Int J Mol Sci 8 505-512... 

Newmann R, Levin M (1991) Selective aerobic oxidative dehydrogenation of alcohols and amines catalyzed by a supported molybdenum-vanadium heteiopolyanion salt. J Oig Chem 56 5707-5710... 

Selective Aerobic Epoxidation of Olefins over NaY and NaZSM-5 Zeolites Containing Transition Metal Ions... 

Luobeznova I, Raizman M, Goldberg I, Gross Z (2006) Synthesis and full characterization of molybdenum and antimony corroles and utilization of the latter complexes as very efficient catalysts for highly selective aerobic oxygenation reactions. Inorg Chem 45 386-394... 

Scheme IX, 10. Selective aerobic photochemical alkane hydroperoxidation catalyzed by the system quincme-copper n) acetate .

The selective aerobic oxidation of primary alcohols to aldehydes, but not secondary alcohols to ketones, is reminiscient of the chemistry catalyzed by the Cu-dependent enzyme, galactose oxidase (39). Similarly, the Cu-binding P-amyloid protein relevant to Alzheimer s disease promotes aerobic oxidation of cholesterol, a primary alcohol (cholesterol oxidase activity) (40). The Cu-dependent amine oxidases catalyze the aerobic oxidation of amines to aldehydes (41), the hydration products of imines. Each of these enzymes that promotes aerobic oxidation of primary alcohols and amines to the same products as Ni(TRISOX) catalyze the net reaction in Equation 1. If the net reactions... 

Recently, an alternative to the catalytic system described above was reported by Gamez et al. (9,103) The new catalytic procedure for the selective aerobic oxidation of primary alcohols to aldehydes was based on... 

Once the oxygen is depleted in the soil, selected aerobic bacteria assumes a facultative role and functions like anaerobic bacteria. During this process, these bacteria use other electron acceptors... 

The following sections provide more information about the chemistry and process technology related to the AO process. This content is followed by a discussion of recent academic developments highlighting emerging opportunities for the use of quinone catalysts in selective aerobic oxidation of organic molecules. 

Future Developments Selective Aerobic Oxidation Reactions Catalyzed by Quinones 229... 

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