Selective oxidation of organic molecules

Abstract Palladium-catalyzed oxidation reactions are among the most diverse methods available for the selective oxidation of organic molecules, and benzoquinone is one of the most widely used terminal oxidants for these reactions. Over the past decade, however, numerous reactions have been reported that utilize molecular oxygen as the sole oxidant. This chapter outlines the fundamental reactivity of benzoquinone and molecular oxygen with palladium(O) and their catalyst reoxidation mechanisms. The chemical similarities... 

The usefulness of bimetallic systems in catalytic studies was mentioned in Section 1.6, and their preparation is surveyed in Sections 3.2.3 and 4.6 their beneficial application to selective oxidation of organic molecules is particularly stressed in Sections 8.3-8.5. 

The selective oxidation of organic molecules is one of the most important processes used in the chemical industry. Its reactions fall into two broad categories (i) gas-phase oxidation of hydrocarbons (alkanes, alkenes) to oxygenated products and (ii) further oxidation of molecules containing one or more oxygen atoms (mainly in the liquid phase). 

Osmium and ruthenium polypyridine complexes initially received much attention from Dwyer and coworkers because the M(II), M(III), and M(IV) oxidation states are substitution inert.Interest in them has been renewed because of their photochemical reactions and the role they play in the study of reactions of coordinated ligands " and of mixed valence ions and in the preparation of electroactive polymer films. The aqua complexes " also have important potential applications in the selective oxidation of organic molecules and water. We found that trifluoromethanesulfonato (triflato) complexes are convenient synthetic intermediates in the preparation of aqua and oxo species, " and we describe the syntheses of the cii-bis(2,2 -bipyridine) complexes here. 

An important feature of both manganese oxides and the Mo-V oxide is that they are redox active. Therefore, applications as catalysts, conductive materials, and electrode materials have been investigated. For example, both the manganese oxides and the Mo-V oxide have excellent catalytic activity for selective oxidation of organic molecules. However, catalytic activity characteristic of ordered porosity has not yet been reported, because pores are so small that only very small organic molecules can enter the pores. 

Oxidation by dioxygen has a fundamental difficulty. The molecule has a diatomic structure, while in most cases only one atom is needed for selective oxidation of organic compounds. Even in the case of more complex reactions, the stoichiometry of which requires several (and sometimes many) oxygen atoms, the oxidation process on a catalyst surface is likely to proceed step by step, involving consecutively one oxygen atom after another. 

Since the discovery in the early 80 s of the remarkable catalytic activity of Ti-modified silicalite-1 (TS-1) in the selective oxidation of organic substrates by dilute H2O2, the field of transition metal modified zeolites grew tremendously as shown in a number of recent reviews [156,235,236]. In addition to its hydrophobicity, the major role of the zeolite matrix is the stabilization of isolated redox centers. However, the limited accessibility of these sites precluded the use of large substrate molecules. The discovery of crystalline mesoporous silicate was immediately perceived as an ideal solution to these limitations. 

Ti, V and Sn-modified mesoporous silicates were reported to be active in a number of liquid phase oxidation reactions. Ti-containing samples were used for the selective oxidation of large organic molecules in the presence of te/t-butyl hydroperoxide (TBHP) or dilute H2O2 [71,136,137,139-141,147,186,237]. Typical data shown in Table 5 indicate that both Ti-MCM-41 and Ti-HMS are efficient cat ysts for the epoxidation of bulky olefins such as a-terpineol and norbomene in the presence of TBHP or H2O2. Comparison with H-B indicates that the accessibility of active sites plays a critical role in the liquid phase oxidation of organic molecules. Mesoporous titanosilicates also exhibited remarkable activity in the hydroxylation of 2,6-di-rerr-butyl phenol (2,6 DTBP) [142,147] and the oxidation of cyclododecanol [147], naphthol [147] aniline [237] and chloroaniline [186]. However, they were disappointingly poor catalysts for the liquid phase oxidation of n-hexane and aliphatic primary amines, as well as the ammoximation of cyclohexanone [147,238]. 

Selective oxidation is used in the activation of raw materials to provide useful products and chemical intermediates. Catalytic methods for the oxidation of organic molecules of this type are of growing interest with regard to eco-sustainable chemical processes [18,356]. Heterogeneous catalysts may be used under mild conditions with gaseous oxygen or air in aqueous dispersion to promote these transformations effectively. 

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. 

Isopropyl 2-iodoxybenzoate is a useful reagent for the clean, selective oxidation of organic sulfides to sulfoxides [1127]. This reaction proceeds without overoxidation to sulfones and is compatible with the presence of the hydroxy group, double bond, phenol ether, benzylic carbon and various substituted phenyl rings in the molecule of organic sulfide. Duschek and Kirsch have reported that isopropyl 2-iodoxybenzoate in the presence of trifiuoroacetic anhydride can be used for the a-hydroxylation of p-keto esters at room temperature in THF [1128]. 

Development of an efficient catalyst for selective oxygenation is an important objective in synthetic organic chemistry. However, the asymmetric C—H bond oxidation reactions by metal oxo species are still challenging due to the over oxidation of the newly formed C—O bonds. Metalloenzymes always accomplish highly efficient and selective oxygenation of organic molecules under mild conditions. To mimic these systems, a few artificial catalysts have been developed for this process. 

The structural sensitivity of electrode reactions such as oxygen reduction and oxidation of organic molecules is well known. This is brought about by the particle size dependence of various physico-chemical factors such as heats of adsorption, Fermi level density of states, electron binding energies in the catalyst, and selective surface segregation in the case of multi-component catalysts [224-229]. 

The AIREs have a higher surface selectivity and sensitivity thus, the interface/surface reactions can be selectively monitored with less interference from the bulk solution. Generally, in situ FTIRS studies are concerned with the dissociative adsorption and oxidation of organic molecules, the formation, adsorption and oxidation of intermediates, the nature of adsorbed species and their interaction with catalysts, the determination of reaction selectivity, and also effects of catalyst composition, size, and morphology. The dual-path mechanism and active/poisoning intermediates in the electrooxidation of small organic molecules (SOMs) have been well characterized by in situ FTIRS methods. ... 

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