Peroxidic intermediates

Butane-Naphtha Catalytic Liquid-Phase Oxidation. Direct Hquid-phase oxidation ofbutane and/or naphtha [8030-30-6] was once the most favored worldwide route to acetic acid because of the low cost of these hydrocarbons. Butane [106-97-8] in the presence of metallic ions, eg, cobalt, chromium, or manganese, undergoes simple air oxidation in acetic acid solvent (48). The peroxidic intermediates are decomposed by high temperature, by mechanical agitation, and by action of the metallic catalysts, to form acetic acid and a comparatively small suite of other compounds (49). Ethyl acetate and butanone are produced, and the process can be altered to provide larger quantities of these valuable materials. Ethanol is thought to be an important intermediate (50) acetone forms through a minor pathway from isobutane present in the hydrocarbon feed. Formic acid, propionic acid, and minor quantities of butyric acid are also formed. 

Mercury-sensitized irradiation of 1,2,3-triphenylisoindole (65) in the presence of oxygen gives a peroxide (103). This peroxide is relatively stable compared with the peroxide (104) derived from similar oxidation of 1,3-diphenylisobenzofuran and can be reconverted to the isoindole (65) by pyrolysis or by treatment with zinc and acetic acid. Reduction of 103 under mild conditions affords o-dibenzoylbenzene (46) and aniline. Aerial oxidation of 47 gives 46 and methylamine, presumably via a peroxide intermediate similar to 103. °... 

Fig. 1.12 Mechanism of the bioluminescence reaction of firefly luciferin catalyzed by firefly luciferase. Luciferin is probably in the dianion form when bound to luciferase. Luciferase-bound luciferin is converted into an adenylate in the presence of ATP and Mg2+, splitting off pyrophosphate (PP). The adenylate is oxygenated in the presence of oxygen (air) forming a peroxide intermediate A, which forms a dioxetanone intermediate B by splitting off AMP. The decomposition of intermediate B produces the excited state of oxyluciferin monoanion (Cl) or dianion (C2). When the energy levels of the excited states fall to the ground states, Cl and C2 emit red light (Amax 615 nm) and yellow-green light (Amax 560 nm), respectively.

The beauty of bromide-mediated oxidations is that they combine mechanistic complexity with practical simplicity and, hence, utility. They involve an intricate array of electron transfer steps in which bromine atoms function as go-betweens in transfering the oxidizing power of peroxidic intermediates, via redox metal ions, to the substrate. Because the finer mechanistic details of these elegant processes have often not been fully appreciated we feel that their full synthetic potential has not yet been realized. Hence, we envision further practical applications in the future. 

Secondary anti-oxidants. These compounds react with the hydroperoxide and peroxide intermediates. They are usually di-valent sulfur or tri-valent phosphorous compounds ... 

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>. 

Another well-known CL amplifier, which is also frequently used for superoxide detection in biological systems, is luminol (5-amino-2,3-dihydro- 1,4-phthalazinedione). It has been proposed that luminol semiquinone reacts with superoxide to form the peroxide intermediate, whose decomposition is accompanied by chemiluminescence [62]. 

Polyethylene glycols Peroxide intermediates Formaldehyde Formic acid Ethylene... 

DR. HENRY TAUBE (Stanford University) Another interesting point about Collman s complex should be noted. Let us presume that a peroxide intermediate is generated in his case. In all of Dr. Endicott s examples, the remarkable observation is that it is very difficult to reduce the 0-0 bond kinetically in the binuclear p-peroxo complexes. In Collman s case, this reduction... 

Figure 24. Typical power curve for a fuel cell. The voltage drops quickly from the OCV due to the formation of the peroxide intermediate. Operation of the fuel cell at the knee of the curve where concentration is limiting performance can damage the electrodes and lead to rapid deterioration of cell operation.

The AFC is one of the oldest fuel cell types. The cell reactions are as follows (the existence of the peroxide intermediate H02 has been already discussed) ... 

The ferric peroxide intermediate could undergo either heterolytic or homolytic cleavage to give either a ferryl or diferryl oxene. In the path shown in Fig. 14, the organic radical is generated by reaction with the Fe center after heterolytic 0—0 bond cleavage. For RNRB2 this is the... 

Since its discovery by Chandross and to this day, peroxy-oxalate chemiluminescence has been controversial because of its enormous complexity in view of the many alternative steps involved in this process. The principal mechanistic feature of the peroxy-oxalate chemiluminescence pertains to the base-catalyzed (commonly imidazole) reaction of an activated aryl oxalate with hydrogen peroxide in the presence of a chemiluminescent activator, usually a highly fluorescent aromatic hydrocarbon with a low oxidation potential . A variety of putative high-energy peroxide intermediates have been proposed for the generation of the excited states . In the context of the present chapter, it is of import to mention that recent work provides experimental evidence for the intervention of the 1,2-dioxetanedione 18 (Scheme 11) as the high-energy species responsible for the chemiexcitation. Furthermore, clear-cut experimental data favor the CIEEL mechanism as a rationalization of the peroxy-oxalate chemiluminescence . 

Intramolecular electron transfer initiated peroxide decomposition. . 1236 HIGH-EFFICIENCY ORGANIC CHEMILUMINESCENT REACTIONS INVOLVING PEROXIDE INTERMEDIATES. 1238... 

VI. HIGH-EFFICIENCY ORGANIC CHEMILUMINESCENT REACTIONS INVOLVING PEROXIDE INTERMEDIATES... 

In this part of the chapter we will give a more detailed description of some highly efficient organic chemiluminescence systems, which occur with the involvement of peroxide intermediates. We have chosen to begin the subject with the well-known and widely applied luminol oxidation and will show that, even though this reaction has been exhaustively studied, several critical points in its mechanism remain unclear and are still the subject of... 

In aprotic media, only molecular oxygen and a strong base are needed to produce chemiluminescence from luminol. In such media, an important intermediate in the reaction is the dianion of luminol, which can be oxidized by oxygen, resulting in the formation of the diazaquinone 27 and deprotonated hydrogen peroxide. The subsequent nucleophilic attack by hydrogen peroxide dianion to one of the diazaquinone carbonyls gives rise to the formation of a metastable peroxidic intermediate that, by several steps, results in chemiexcited 3-aminophthalate (Scheme 16)123,174, iso ... 

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. 

Since di-te/7-butylsulfide delivers the sulfoxide in the photosensitized reaction and no a-hydroxysulfides were observed from the other sulfides of Table XIV, the photosensitized oxidation of sulfides (and probably also that of sulfoxides) takes another course than in the thermal reaction. It was suggested that singlet oxygen (formulated as the sensitizer-oxygen adduct -Sens-CV278,280) reacts with a sulfide to give a highly reactive sulfo-peroxide intermediate, 431, which immediately reacts with another sulfide molecule to yield two stable sulfoxide molecules. 

Compound 213 rearranges into 215 on treatment with alkaline peroxide intermediate 214 is probably formed by ring opening of 213 in alkali... 

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