Peroxy anion

The salts of alkyl xanthates, A/,A/ -di-substituted dithio-carbamates and dialkyidithiophosphates [26] are effective peroxide decomposers. Since no active hydrogen is present in these compounds, an electron-transfer mechanism was suggested. The peroxide radical is capable of abstracting an electron from the electron-rich sulfur atom and is converted into a peroxy anion as illustrated below for zinc dialkyl dithiocarbamate [27] ... 

The usual oxidizing agents transfer oxygen (or halogens and related species with subsequent hydrolysis) stepwise to the sulfur of thioethers Rates of step A compared with those of step B are faster with electrophilic oxidation agents (peroxy acids) inversely, rates of step B compared with those of step A are faster with nucleophilic oxidation agents (peroxy anions)339-341. 

Ph0)2P0.0C6H4N02-(4) + OH-, ro2 CTABr, CTAC1 + NaOH and peroxy-anions. Rate comparisons and quantitative rate analysis Bunton et al., 1984... 

In order to model the oxygenation of vitamin K in its hydroquinone form, a naph-thohydroquinone derivative with a 1-hydroxy group and 4-ethyl ether was prepared and its alkoxide subjected to oxidation with molecular oxygen. Products consistent with two possible mechanisms were isolated, the epoxy-quinone which must derive from a peroxy anion intermediate at the 4-position, and a 2-hydroxy product which... 

It has now been more than a decade since Beckman and his collaborators first disclosed their observations that the combination of two relatively unreactive, yet biologically relevant free radicals, superoxide anion and nitric oxide, would produce a new highly reactive physiologically important reagent. The interaction of these two presumably innocuous species appears to be diffusion controlled and produces a thermally stable peroxy anion, peroxynitrite (equation 1). ... 

The effect might be caused by the dielectric constant, which is 10 for 1-octanol and 2 for n-decane, or a hydrogen bonding to the peroxy anion may be involved. 

Si and Fe3+---0 -Si centers in quartz. However, they may also form without attendant ionizing radiation. One possiblity is the redox conversion of OH or Si-OH pairs into molecular H2 plus peroxy. Such OH or Si-OH pairs derive from traces of dissolved "water . Peroxy anions, 022 , or peroxy entities, X/°° Y (X, Y=Si, Al,Fe3+...) are equivalent to self-trapped positive hole pairs. 

O dimers may appropriately be called peroxy anions, 022 . In a silicate matrix they appear to occur as peroxy links or, more generally, peroxy entities, X/00 Y where X,Y = Si4+,A13+, Fe3+... Chemically a peroxy entity represents an extra oxygen it may be called an interstitial oxygen atom though this does not correctly convey the covalent binding in the 0-0 bond. 

Peroxy anions or entities cannot be detected by any currently known technique unless the 0-0 bond is activated. One method is ionizing radiation. In the case of high purity fused silica irradiating with y- and x-rays led to peroxy radicals ( ) and dangling bonds at the three-fold coordinated silicon which were fully characterized using EPR (16.17) ... 

The Weitz-Scheffer reaction, the epoxidation of a,(3-unsaturated carbonyls, is valuable transformation in organic chemistry.75 The accepted two-step mechanism involves the addition of peroxy anion and formation of peroxyenolate, which undergoes a ring-closing intramolecular nucleophilic substitution of C2 carbon atom. 

The predicted isotope effects for the addition transition states are of about 1.030 at C3 and 1.008 at C2 and small KIEs for remaining carbons, as can be expected for a major bonding change at C3 and minor at C2. Predicted isotope effects for the ring-closure step are 1.012 at C2 near unity at C3. The value of 1.012 is near the low end of primary 13C KIEs, but consistent with relatively low isotope effects observed in other epoxidation reactions (vide infra). Overall, KIEs support the addition of a peroxy anion to the enone as the rate-limiting step. 

The peroxy-anion transfer reaction of Equation 45 has been established (51). This finding was intriguing because we had shown previously that FlEt- reacts with molecular oxygen to provide 4a-FlEtOO" (Equation 37). Combination of Equations 37 and 45 yields Equation 46, establishing that the dihydroflavin anion is a catalyst for the reaction of oxygen with the phenolate ion. 

The advantage of using peracids is their ability to oxidize sulfoxides selectively over sulfides at high pH using the nucleophilic anion (Figure 3.95) since sulfoxide oxidation is nucleophilic, whereas sulfide oxidation is electrophilic. This behaviour is due to the formation of peroxidic intermediates by the addition of peroxy anion to the sulfoxide.378... 

Solutions of KO2 and l8-crown-6 in DMSO cause oxidation of the solvent to die sulfone. The phosphorus-containing peroxy anion (EtO)2P03" obtained on reaction of KO2 widi diefiiyl chlorophosphate [(EtO)2POCl] in acetonitrile has been used to prepare sulfones from sulfoxides at 20 C. Similarly, various sulfoxides are readily oxidized chemoselectively to the sulfones in high yields by 2-nitrobenzene peroxysulfur intermediate (26) generated in situ from 2-nitrobenzenesulfonyl chloride and KO2 (Scheme 8 Ar = 2-N02C6H4). ... 

Br > OTs > Cl, are observed, as are the expected stereoselectivity and inversion at the carbon center. In DMF, the final product is the dialkyl peroxide. The peroxy radical (ROO-), which is produced in the primary step and has been detected by spin trapping, is an oxidant that is readily reduced by 02 - to form the peroxy anion (R00 ). Because the latter can oxygenate Me2SO to its sulfone, the main product in this solvent is the alcohol (ROH) rather than the diaUcyl peroxide. 

A proposed mechanism for the above carboxylation creates such a base from vitamin K. " Vitamin K is reduced to its hydroquinone form (vitamin KH ). Molecular oxygen is incorporated into the conjugate acid form of vitamin KH to form a peroxy anion, which subsequently forms a dioxe-tane intermediate. The peroxy bond is cleaved by the adjacent cnolatc anion to produce an intermediate sufficiently basic to deprotonatc the a-carbon. 

Manganese and cobalt compounds are particularly effective in decomposing hydroperoxides (eqs. (17) and (19)) and hence are frequently used as oxidation catalysts [47]. In spite of their similar abilities in this regard, the results of their use in a given instance can be quite different. Manganous ions are reported to have a pronounced ability to reduce peroxy radicals directly to peroxy anions (eq. (20)) [50] ... 

These peroxy anions need only pick up a proton to become hydroperoxides. 

Upon wanning, the epoxy-p-quinols 3 were obtained. Interestingly, when the p-hy-droperoxide was dissolved in DMF containing t-BuOK, most of 2 reverted instantaneously to 1 with the liberation of oxygen. This indicates the reversibility of the dioxygen addition and the inherent instability of the peroxy anions in absence of suitable solvation. 

JE Mclsaac, LR Subbaraman, HA Mulahusen, and EJ Behrman. The nucleophilic reactivity of peroxy anions. J. Org. Chem. 37 1037-1041,1972. 

At present, the alternative mechanisms of electron transfer to 02 and of peroxy anion formation have not been resolved. 

---