Oxidation of anions

Carbanions have been oxidized under phase transfer conditions in the presence of both crown ethers and cryptates. The substrate which has been most studied is fluorene which undergoes phase transfer catalyzed air oxidation to yield fluorenone in high yield according to equation 11.11 [10, 18]. Crown complexed f-butoxide in 

Work examining the factors directing the termination step has been reported by the Jahn group [212], 

Den s et al. reported an interesting example of a radical tandem 1,4-addition/carbocyclization reaction initiated by oxidation of dialkylzinc by dissolved oxygen in the solvent [213]. Reduction of the final radical with dialkylzinc through a radical/polar crossover reaction afforded a new organo-zinc derivative that could be further fimctionahzed. 

---

In the oxidation of anionized 1,3-dicarbonyl compounds (Table 8, numbers 1-7) at potentials between 0.6 and 1.4 V (see) and in the presence of butadiene, mainly the additive dimer (24) is obtained in the presence of ethyl vinyl ether chiefly the disubstituted monomers (28) or (29) arise. 

Radicals prepared by anodic oxidation of anions or by the Kolbe reactions can couple with other radicals or add to double bonds. For instance in Scheme 2 [4, 5], the... 

Electrochemical oxidations of anions lead to radicals that may add to the carbon-carbon double bonds. In this way, the oxidation of anions of dimethyl malonate or methyl acetylacetate in the presence of olefines gives di- or tetrahy-drofurans derivatives in moderate yields (Scheme 43) [60]. 

Sodium methylate acting on 2-chloroanthraquinone substitutes the methoxy group for chlorine and produces anion-radicals of the substrate (Shternshis et al. 1973). The study of kinetics has demonstrated that the amount of substrate anion-radical hrst increases and then sharply decreases. The inhibitor (p-BQ) decelerates the formation of anion-radicals. The rate of formation of 2-methoxy-anthraquinone also decreases. If anion-radicals are produced on the side pathway, the rate of formation of the end product on introduction of the inhibitor should not have decreased. Moreover, it should even rise because oxidation of anion-radicals regenerates uncharged molecules of the substrate. Hence, the anion-radical mechanism controls this reaction. 

Reactions involving electron transfer. Reaction of free ion radicals, oxidation of anion radicals of aromatic and heteroaromatic hydrocarbons. Usually an energy acceptor is required to be present... 

II. EXPERIMENTAL METHODS OF ACHIEVING EMISSION A. Oxidation of Anions... 

Emission resulting from chemical oxidation of anion radicals has now been obtained under a variety of conditions. A summary of the conditions and a qualitative characterization of the reported results can be found in Table I. Several reported failures to observe emission have been included in the table where these results may have special significance. That the oxidizing power of the oxidant influences the emission can be seen by the finding that chlorine and bromine, but not iodine, act on the anion radical of 9,10-diphenylanthracene to produce emission. 

Oxidation of Anionic Polymers In the Solid State The ability of the macroradical and of the macroions to diffuse In the mixture, and to interreact Is responsible for the secondary products formation coupling reaction and alcoholate synthesis. To prevent the diffusion phenomenon, we have carried out the deactivation In the solid state. The living polymers have been prepared In benzene, with or without a solvating agent (THF or TMEDA) and the solution has been freeze dried before the oxygen introduction. The experimental results are collected in Table VII. 

Kido, T. Soda, K. (1984) Oxidation of anionic nitroalkanes by flavoenzymes, and participation... 

Radical ions are typically formed as the primary intermediate when the substrate is a neutral compound of the n-electron type. In contrast, the electron transfer to or from a saturated organic compound is usually associated with bond breaking. This has led to the term dissociative electron transfer and is observed, for example, during the reduction of alkyl halides (Equation 6.4) where it is seen that the primary organic intermediate in such cases is a neutral radical (R ) [31]. Radicals are also formed by the oxidation of anions or by the reduction of cations ... 

Platinum. Photolysis of some Pt(IV) complexes in aqueous solutions or in a frozen matrix results in the outer-sphere oxidation of anions and reduction of platinum to Pt(II)311-314, probably via a Pt(III) intermediate. 

A great variety of substituted radicals for dimerization can be generated by anodic oxidation of anionic species r5"Me5+, e.g., sodium salts of 1,3-dicarbonyl compounds, aliphatic nitro compounds, phenols, oximes, alkynes, thio-lates or organometallics (Eq. (157) ). 

The oxidation of anionic a-complexes of 1,3,5-trinitrobenzene with an oxidative CuBr/CCl4 system led to the formation of 3-organyl-4,6-dinitroanthranyls (2,1-ben-zisoxazoles) the structure of which was proved by PMR, IR spectroscopy, and mass spectrometry [745],... 

Simple two-electron oxidation of anionic HNCC has been shown to proceed with or without concomitant addition of CO. For example, while oxidation of [OSs(CO)i5] with FeClj under CO gives Os5(CO)ie (383), Os6(CO)i8 is the product of the oxidation of [Os6(CO)ig] under the same... 

Indirect electroinitiation occurs by electrolysis of the supporting electrolyte in the presence of monomer when conditions for direct initiation are not fulfilled. Cerrai et al. [311] electrolyzed R4N + P and R4N + I3 in 1,2-dich-loroethane in the presence of isobutyl vinyl ether. They found iodine formed by the oxidation of anions... 

The anodic limiting potential of RTILs is basically determined by the oxidation of anions. However, the anodic limiting potential of EMI and DMABP is determined not by the oxidation of the anions, but by the cation, since the anodic limiting potential of the EMI and DMABP system is independent of the anions. 

Although generally dimerization is one of the typical reactions of radical qiecies, the yields of the dimers are not always hi Thus the anodic oxidation of anions of monoalkylated malonic esters in acetonitrile gives the corre nding dimers in 20-55% yield. However, Giignard reagents give satisfactory results in anodic dimerization (equation 53). ... 

Homoleptic amido compounds of U, U(NR2)5, have been synthesized by oxidation of anionic tetravalent complexes, [U(NR2)5]. A unique hexakisamido U complex has been isolated using 2,3 5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene. The [U(dbabh)] anion can be oxidized to form a species both of which have a near-perfect octahedral geometry with the six antido ligands. ... 

An interesting class of pentavalent complexes supported by the cyclooctatetraenyl ligand has been developed. Oxidation of anionic U(IV) mono-ring amide complexes with TlBPh4 or AgBPli4 generates the corresponding pentavalent amide... 

Jahn et al. reported an elegant new domino process based on the combination of anionic and radical reactions relying on a key oxidation of anion 249 followed by a radical cyclization leading to 250 (Scheme 74) [207]. Radical 250 can be trapped by TEMPO to yield functionaUzed pyrrolidine 251 in high yield and acceptable stereoselectivity the 2-3 cis relationship was controlled in the initial anionic addition, but the relative configurations at C3 and C4 were largely non-controlled. All-carbon cyclopentanes [208], in particular prostanes [209] could also be prepared through this method. More recently, Jahn and Rudakov reported its extension to nitroalkenes [210]. 

At very positive potentials the oxidation of anions of the background electrolyte may also limit the range of available potentials. Therefore, MBF4 or MPFg should be used in work at such potentials [5], These electrolytes are generally preferred to perchlorates, as the preparation of water-free perchlorates can be dangerous because of their oxidative properties. Another advantage is that they are relatively soluble in various solvents and it is quite easy to prepare these salts in pure form. 

Lyne and O Neil [117] reported the in vivo detection of dopamine using stearate-modified carbon-Nujol paste electrodes. Prior to their work, the detection of dopamine by voltammetric techniques was hindered primarily due to the coexisting ascorbic acid in the extracellular fluid of the mammalian brain. Ascorbic acid oxidizes at electric potentials similar to that of dopamine on many electrode materials. These authors found that the use of stearate-modified carbon-Nujol paste electrodes retards the electro-oxidation of anionic species (such as ascorbate) to such an extent that the cationic dopamine species could be detected in their presence. 

Radicals generated by oxidation of anions can either dimerize [Eq. (2), path a] or add to double bonds to yield additive monomers or dimers [Eq. (2), path b] ... 

Satisfactory to good yields of adducts have been found for styrenes [Eq. (21a), Y = phenyl], conjugated dienes (Y = vinyl), enamines (Y = NR2), and enol ethers (Y = alkoxy), particularly if they are unsubstituted at the 6-carbon atom to Y. Nonactivated alkenes react less satisfactorily. In the oxidation of anionized 1,3-dicarbonyl compounds (Table 11, numbers 1-8) at potentials between 0.6 and 1.4 V (SCE) and in the presence of butadiene, only the additive dimer LXII is obtained in the presence of ethyl vinyl ether only the disubstituted monomers LXVI or LXVII arise, but with styrene both types of products LXII and LXVI are formed. This result indicates that the primary adduct LXIII is oxidized rapidly between 0.6 to 1.4 V to the carbenium ion in the case of an ethoxymethyl radical (Y = OEt), and slowly in the case of an allyl radical (Y = vinyl). 

---