Oxidation reactions arenes

L = P(CH3)3 or CO, oxidatively add arene and alkane carbon—hydrogen bonds (181,182). Catalytic dehydrogenation of alkanes (183) and carbonylation of bensene (184) has also been observed. Iridium compounds have also been shown to catalyse hydrogenation (185) and isomerisation of unsaturated alkanes (186), hydrogen-transfer reactions, and enantioselective hydrogenation of ketones (187) and imines (188). 

Trifluoroacetic acid is a useful medium for a number of oxidation reactions It IS highly resistant to strong oxidants, even to permanganates and chromates For instance, various alkanes, cycloalkanes, and arenes can be oxidized degradatively by potassium permanganate in trifluoroacetic acid under mild conditions [28]... 

The reductive transformation of arene carboxylates to the corresponding aldehydes under aerobic conditions has already been noted. In addition, aromatic aldehydes may undergo both reductive and oxidative reactions, with the possibility of decarboxylation of the carboxylic acid formed ... 

The direct oxidation of arenes to quinones is a reaction with a limited scope [41], Only substrates that form stable quinones give good yields. For example, oxidation of anthracene to stable 9,10-anthraquinone with chromic acid is practiced on industrial scale. Such oxidations are believed to proceed through a series of one-electron oxidation/solvolysis steps. Yields and selectivity may be improved by using a strong one-electron oxidant such as cerium ammonium nitrate (CAN), as in the oxidation of phenanthrene to phenanthrenequinones (Eq. 9) [42]. 

In the presence of oxygen, the formation of biaryls by Pd(II) oxidation of arenes can be made to be catalytic in palladium.576 For example, toluene with Pd(OAc)2 and 02 at 150°C for 16 hr afforded bitolyls in 20,600% yield based on palladium. It was concluded that biaryl formation in these systems occurs via free aryl radicals.576 The role of homolytic processes in these reactions is not clear, and further clarification of the mechanism is desirable. 

There is a wider general interest in understanding the oxidation of cysteine thiolates in proteins since they are involved in redox-sensing reactions [99], Therefore, such oxidation reactions of thiols induced by Ru coordination may also play a more general role in the pharmacological activity of Ru-arene complexes by coupling Ru coordinative binding to redox processes both outside and inside cells. 

In addition to the NIH shift, the zwittcrionie species may nndergo direct loss of D to generate 4-hydroxyanisolc. in which there is no retention of deuterium (Fig. 4-6). The alternative pathway (direct loss of D ) may be more favorable than the NIH shift in some aromatic oxidation reactions. Therefore, depending on the substituent group on the arene.. some aromatic hydroxylation reactions do not di.splay any NIH. shift. 

Besides toluenes, ethyl- or isopropyl-substituted arenes can also be oxidized selectively to acetyl-substituted systems which may be transformed further into the corresponding carboxylic acids. Even f-butyl groups, as in 4,4 -bis(r-butyl)biphe-nyl, can be oxidized to the corresponding carboxyl groups [7], Due to the strong interest in the commercial production of 2,6- and 1,4-dicarboxynaphthalenes, there are many patents concerning the oxidation of methyl-, ethyl-, or isopropyl-substituted arenes to the aromatic di-acids [8], Also, toluenes or xylenes connected by spacer groups like -0-, -S-, isopropyl or hexafluoroisopropyl are of practical interest for applications in air oxidation reactions (see Section 2.4.5.2.V). 

See [6]. The following reaction types have been listed (a) Geometric isomerization of alkenes (b) Allylic [1,3] hydrogen shift (c) Cycloaddition of alkenes. Dimerization, Tri-merization. Polymerization (d) Skeletal rearrangments of alkenes and methathesis (e) Hydrogenation of alkenes (f) Additions to alkenes (g) Additions to C = X (h) Aliphatic substitutions (i) Aromatic substitution (j) Vinyl substitution (k) Oxidation of alkenes (1) Oxidation of alcohols (m) Oxidation of arenes (n) Oxidative decarboxylation (o) Oxidation of amines (p) Oxidation of vinylsilanes and sulfides (q) Oxidation of benzal-dehyde (r) Dehydrogenations. 

There are several classic examples of the use of FTIR spectroelectrochemistry in elucidating the EC reactions of oxidized carbonyl complexes. These include the isomerization of 17e complexes for example, the isomerization of m-[Mo(CO)2(P-P)2]+ to the trans-isomer.139 Similarly, the cis-isomer of [Re(CO)2(P P)2]+ or [Re(CO)(P—P)2X] will isomerize on oxidation as monitored in a reflection IR cell.140 One-electron oxidation of [IrH(CO)(PPh3)3] is reversible, but further oxidation to the dication induces hydride oxidation and the appearance of bands due to the 16e complex [Ir(CO)(PPh3)3]+.141 Oxidation of arene tricarbonyls of Group 6 metals is frequently irreversible, especially in coordinating solvents at ambient temperature. However, the mesitylene tungsten tricarbonyl complex is oxidized by two electrons with the reversible take up of MeCN.142... 

Dr. Fred Guengerich at Vanderbilt University has published mechanistic schemata for cytochrome P450 involvement in an extensive array of both common and uncommon oxidative reactions and reductive reactions. Some of those are exhibited later in this chapter in a brief consideration of reductive reactions. Mechanisms for carbon hydroxylation, heteroatom oxygenation, N-dealkylation, O-dealkylation, alcohol oxidation, arene epoxidation, phenol formation, oxidation of olefins and acetylenes, reduction of nitro compounds, reductive dehalogenation, and azo reduction, to name a few, are provided. 

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