Oxidation of organic molecules

Free-radical chain oxidation of organic molecules by molecular oxygen is often referred to as autoxidation (see Section 12.2.1). The general mechanism is outlined below. 

It is not within the scope of this review to deal with products of oxidation of organic molecules in cases other than those for which a kinetic analysis has also been attempted. However, much insight into the modes of reactivity of Cr(VI) and Mn(VII) is to be gained from such information and the reader is referred to the recent excellent reviews of Wiberg on Cr(VI) and Stewart on Mn(VIII). 

The biochemical oxidation of organic molecules is accomplished by enzymes known as oxidases. Specific oxidases exist for the oxidation of each... 

In addition, the rate of Oz reduction, forming 02 by electron, is of importance in preventing carrier recombination during photocatalytic processes utilizing semiconductor particles. 02 formation may be the slowest step in the reaction sequence for the oxidation of organic molecules by OH radicals or directly by positive holes. Cluster deposition of noble metals such as Pt, Pd, and Ag on semiconductor surfaces has been demonstrated to accelerate their formation because the noble metal clusters of appropriate loading or size can effectively trap the photoinduced electrons [200]. Therefore, the addition of a noble metal to a semiconductor is considered as an effective method of semiconductor surface modification to improve the separation efficiency of photoinduced electron and hole pairs. 

H. Gerischer, A. Heller, Photocatalytic oxidation of organic molecules at Ti02 particles by sunlight in aerated water,... 

Mn-dependent peroxidase differs from lignin peroxidase in that it utilizes Mn (II) as the main substrate (74). The oxidized manganese ion, Mn (III), carries out the oxidation of organic molecules. Compound I of Mn-dependent peroxidase is able to oxidize Mn (II) to Mn (III) as well as some phenolic compounds the compound II can only oxidize Mn (II) (14) ... 

Chapter 6, by Clennan, on oxygenation in zeolites critically summarizes the results on oxidation of organic molecules within zeolites by singlet oxygen and superoxide anion. This chapter complements Chapter 6, Volume 5 by Va-senko and Frei. In addition to Chapter 6, Chapter 7 in this volume and Chapters 3, 4, and 5 in Volume 5 are exceptional resources in the area of excited-state behavior of organic molecules within zeolites. 

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... 

Table I. Effect of Aliphatic Amines on Gas-Phase Oxidation of Organic Molecules...

The catalytic role of copper complexes in the oxidation of organic molecules is not restricted to solution, but can also occur at surfaces, particularly involving ion exchange1173 on silica gel,1174 Lind molecular sieves1175 or ion exchange resins.1176 The ion exchange of the [Cu(OH2)6]2+ cation has been most studied,1177 both at room temperature and after thermal... 

Two-electron redox phenomena are rare for Cu, and therefore Cu is not a suitable catalyst for epoxidations, for example. However, Cu is useful for free radical reactions such as deep oxidation of organic molecules in waste streams and ring or side chain oxidation of aromatic compounds. 

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). 

Dissolved metals affect the concentration of atmospheric trace gases, such as ozone, organics and sulfur compounds. Ozone is formed in the troposphere through a complex series of homogeneous reactions as shown schematically in Fig. 4. The chain represented in the figure by thick arrows involves the cooperative oxidation of organic molecules and NO with the intermediacy of HO, formed by subsequent photolysis of NO2 and O3, and HO2 radicals. 

Another important type of electro-organic process is that in which reaction takes place at a bulk phase oxide layer on metallic electrode surfaces. Such oxide layers can mediate the oxidation of organic molecules, as in the case of alcohols and amines at oxidized Ni [529], and passage of current may be regarded as serving to maintain the oxide layer. 

They play very diverse and important roles such as 02 transport and storage (hemoglobin and myoglobin), catalytic dehydrogenation or oxidation of organic molecules... 

Since photocatalysis was discovered in the early 1970s, more than 6,200 papers related to this process have been published. Most of the work on this subject has focused on showing that organic molecules can be oxidized in PC reactors. So far, more than 800 organic molecules have been tested for oxidation in PC reactions (Blake, 2001). In most cases, the tested organic molecules were converted to CO2, water, and mineral acids. Therefore, it can be definitely concluded that photocatalysis works for oxidation of organic molecules. The rate of oxidation depends on several factors that will be addressed in the upcoming section. 

It was also found that there exists a s mergic effect in the organic oxidation and inorganic reduction. Some studies show that the presence of some metal ions can affect the rate of oxidation of organic molecules. For instance, the rate of oxidation of phenol can be affected by the presence of silver (Huang et al., 1996) and silver can also affect the oxidation of textile dyes (Sokmen and Ozkan, 2002). The presence of Cr(VI) affects the rate of oxidation of salicylic acid (Colon et al., 2001). 

Oxidation of organic molecules with O2 (flameless) is referred to as autoxidation. The synthesis of cumene hydroperoxide from cumene is initiated by catalytic amounts of 2.36 as the radical initiator, which generates the cumyl radical A. The cumyl radical A reacts with O2 to give the radical B in the first propagation step and regenerated in the second propagation step, in which cumene hydroperoxide (2.62) is also formed (Scheme 2.48). 

The importance of bismuth oxide species in oxidation of organic molecules is illustrated in Scheme 1, which shows a... 

In turn, this made it possible for the newly evolved aerobes to leave the marine environment and establish terrestrial life, and the subsequent evolutionary development of higher forms of life. Aerobic life had to develop and make effective use of dioxygen as an energy source through oxidation of organic molecules. This required the biosynthesis of a series of metalloproteins to facilitate the transport and the... 

Several transition metal phosphate systems are found to catalyze mild oxidations of organic molecules. Catalytic activity is due to transition metal redox couples see Oxidation Catalysis by Transition Metal Complexes and Oxide Catalysts in Solid-state Chemistry), but the phosphate groups are important in determining the underlying and surface structures. 

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