Cyclic peroxides oxidation

Photochemical synthesis of sulphoxides was reported for the first time by Foote and Peters111 in 1971. They found that dialkyl sulphides undergo smoothly dye-photosensitized oxidation to give sulphoxides (equation 32). This oxidation reaction has been postulated to proceed through an intermediate adduct 63, which could be a zwitterionic peroxide, a diradical or cyclic peroxide, which then reacts with a second molecule of sulphide to give the sulphoxide (equation 33). 

Haszeldine, R. N. et al., J. Chem. Soc., 1959, 1085-1086 1,1,1-Trichloroethane exploded after heating under oxygen at 54 bar and 100°C for 3 h [1], Trichloroethylene, remaining in a pipe after cleaning operations, exploded under 27 bar pressure of oxygen at ambient temperature. It was later found possible to explode stoicheiometric mixtures [2], Chlorotrifluoroethylene and bromotriflu-oroethylene each react explosively with oxygen at ambient temperature [3], but controlled oxidation of the former produces an explosive cyclic peroxide, 4.5-dichloro-3,3,4,5,6,6-hexafluoro-1,2-dioxane [4]. 

As mentioned earlier (see p. 122) the previously postulated dioxetane intermediate in firefly bioluminescence has been challenged as no 180 is in-corporated in the carbon dioxide released during oxidation of firefly luciferin with 18C>2. In view of the crucial significance of the 180. experiments De Luca and Dempsey 202> rigorously examined the reliability of their tracer method. They conclude from their experiments that all available evidence is in favour of a linear, not a cyclic peroxide intermediate — in contrast to Cypridina bioluminescence where at least part of the reaction proceeds via a cyclic peroxide (dioxetane) as concluded from the incorporation of 180 into the carbon dioxide evolved 202,203). However, the dioxetane intermediate is not absolutely excluded as there is the possibility of a non-chemiluminescent hydrolytic cleavage of the four-membered ring 204>. 

Some of the investigations carried out in the first half of the twentieth century were related to CL associated with thermal decomposition of aromatic cyclic peroxides [75, 76] and the extremely low-level ultraviolet emission produced in different reaction systems such as neutralization and redox reactions involving oxidants (permanganate, halogens, and chromic acid in combination with oxalates, glucose, or bisulfite) [77], In this period some papers appeared in which the bright luminescence emitted when alkali metals were exposed to oxygen was reported. The phenomenon was described for derivatives of zinc [78], boron [79], and sodium, potassium, and aluminum [80]. 

The brilliant emissions resulting from the oxidation of certain oxalic acid derivatives, especially in the presence of a variety of fluorophores, are the bases of the most active area of current interest in CL. This group of chemiluminescent reactions has been classified as peroxyoxalate chemistry because it derives from the excited states formed by the decomposition of cyclic peroxides of oxalic acid derivatives called dioxetanes, dioxetanones, and dioxetanediones. 

The oxidation of naphthalic acid (1,8-naphthalenedicarboxylic acid) by peroxide, rather surprisingly, does not proceed by formation of a cyclic peroxide but rather via a dioxirane [53] (a three-membered ring containing a carbon atom and a peroxide group). CL is observed from this reaction. 

Hydrocarbons with conjugated double bonds are oxidized with the formation of cyclic peroxides [46,80,82], for example ... 

Polynuclear aromatic hydrocarbons can be oxidized photolytically with the formation of cyclic peroxide. For example, anthracene is photooxidized to peroxide with the quantum yield 0 = 1.0 [205], The introduction of quenchers lowers the peroxide yield. 

The anodic oxidation of 1,3-diketones in the presence of olefins in an oxygen atmosphere gave the extremely stable cyclic peroxides 80 in good yield [101,102] (Scheme 40). A catalytic amount of electricity was sufiicient for the reaction and an electro-intiated radical chain mechanism was suggested. 

In 1998, Strukul and coworkers presented a diphosphine-palladium complex, with which the Baeyer-Villiger oxidation of cyclic and for the first time also acyclic ketones could be catalyzed in the presence of various peroxidic oxidants (H2O2, TBHP, KHSO5, carbamide peroxide) (Scheme 158)4 . pj-om these oxidants H2O2 turned out to be the most efficient one, whereas almost no conversion was obtained (<1% after several days) with TBHP. The authors could show that an increase in the bite angle of the diphosphine caused... 

Although the parent formaldehyde-derived dioxirane (H2CO2) was the first of this intriguing class of cyclic peroxides to be prepared and spectrally characterized in 1976, the conversion of aldehydes into the corresponding dioxiranes by treatment with Caroate was deemed difficult because of the expectedly facile Baeyer-Villiger oxidation of the aldehydes to their carboxylic acids. Most gratifyingly, however, is that it was recently demonstrated that optically active aldehydes may also serve as promising catalysts for asymmetric epoxidations. For example, ee values up to 94% were obtained with the aldehyde 14 as dioxirane precursor. 

This sequel on contemporary dioxirane chemistry should leave little if any doubt in the interested reader s mind that these fascinating and entertaining three-membered-ring cyclic peroxides are very popular oxidants and stUl in much demand, as witnessed by the current intensive research activities. Since the last Patai volume on Organic Peroxides some twenty years ago , which could have hardly featured a chapter on this subject since it was then in its infancy, dioxirane chemistry has literally exploded and become established as a prominent field in peroxide chemistry, as manifested by the now well over a thousand publications on this subject. ... 

The synthetic value of this unusual class of cyclic peroxides in selective oxyfunction-alizations is undisputable, the mechanistic complexity of the oxygen transfer a formidable challenge, and the intricate structural and electronic features a theoretical delight. While we know already much about the reactivity and selectivity of this powerful oxidant, there is conspicuous demand in solving the following problems ... 

The oxidation of organic substances by cyclic peroxides has been intensively studied over the last decades , from both the synthetic and mechanistic points of view. The earliest mechanistic studies have been carried out with cyclic peroxides such as phthaloyl peroxide , and more recently with a-methylene S-peroxy lactones and 1,2-dioxetanes . During the last 20 years, the dioxiranes (remarkable three-membered-ring cyclic peroxides) have acquired invaluable importance as powerful and mild oxidants, especially the epoxidation of electron-rich as well as electron-poor alkenes, heteroatom oxidation and CH insertions into alkanes (cf. the chapter by Adam and Zhao in this volume). The broad scope and general applicability of dioxiranes has rendered them as indispensable oxidizing agents in synthetic chemistry this is amply manifested by their intensive use, most prominently in the oxyfunctionalization of olefinic substrates. 

In the presence of hydrogen peroxide and base, acridinium salts lead to chemiluminescence emission. Acridans, in their reduced forms, are able to react directly with oxygen in aprotic solvents with 4>cl up to 10% . Scheme 31 shows the proposed mechanism for chemiluminescence of 9-cyano-lO-methylacridan and 9-cyano-lO-methylacridinium salt in the presence of oxidant and base, which postulates the cyclic peroxidic intermediate 44. 

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