Phenoxazines reduction

Starting from phenoxazine, the leuco 47 is obtained through a multistep reaction involving nitration, reduction, and acylation.6... 

Among the more recent approaches to phenoxazines and phenothiazines the reductive cyclization of 2-nitrodiphenyl ethers and sulfides with trialkyl phosphites is the most interesting. Here too a spiro intermediate is involved, produced by attack of an initially formed aryl nitrene on the second aromatic ring. The sulfide (252), for example, reacts with triethyl phosphite to yield 1-methylphenothiazine (253) and it is clear that in this case ring opening of the spiro intermediate also proceeds with a rearrangement of the Smiles type (Scheme 113) (75JCS(P1)2396). 

Oxidation of oxalic acid with dimethyl-V,V-dichlorohydantoin and dichloroisocya-nuric acid is of first order with respect to the oxidant. The order with respect to the reductant is fractional. The reactions are catalysed by Mn(II). Suitable mechanisms are proposed.129 A mechanism involving synchronous oxidative decarboxylation has been suggested for the oxidation of a-amino acids with l,3-dichloro-5,5-dimethylhydantoin.130 Kinetic parameters have been determined and a mechanism has been proposed for the oxidation of thiadiazole and oxadiazole with trichloroiso-cyanuric acid.131 Oxidation of two phenoxazine dyes, Nile Blue and Meldola Blue, with acidic chlorite and hypochlorous acid is of first order with respect to each of the reductant and chlorite anion. The rate constants and activation parameters for the oxidation have been determined.132... 

An approach that has been used for the synthesis of unsubstituted phenoxazine in 32% yield involves the condensation of o-nitrochloro-benzene with o-nitrophenol, followed by reduction and ring closure of the 2,2 -diaminodiphenyl ether (8).28,29... 

A number of ESR spectra of semiquinone radicals, formed as intermediate reduction products of phenoxazine dyestuffs, have been investigated by Heineken and Bruin in acid and in alkaline solution.49,50... 

Reductive acetylation of various 3//-phenoxazin-3-ones has been shown to yield the corresponding 3-acetoxyphenoxazines.40... 

The change in color from various shades of red to yellow, which accompanies the reduction of substituted 3iZ-phenoxazin-3-ones, has made them suitable as bromometric and stannometric redox indicators111-113 RuziCka114 reported also the microdetermination of compounds containing SH groups with such derivatives. Phenoxazine has been described as a stabilizer for polymerizable vinylpyridines115... 

Substituted cation and neutral radicals have been obtained by reduction of phenoxazine and phenothiazine dyes. ESR spectra were obtained, but not analyzed in detail, by Heineken et In alkaline media the... 

There have been reports of various phenothiazine and phenoxazine anion-radicals which are species which correspond to structure 244 and its substituted derivatives. Thus, reduction of phenothiazin-3-one in... 

The phenoxazine can then participate in reversible oxidation-reduction reactions, and moreover by transamination and cyclization of one side chain, in a manner analogous to xanthurenic acid formation discussed below, can give a pyridinophenoxazine derivative which equally undergoes reversible oxidation-reduction, and which, being a derivative of 8-hydroxy-quinoline, would bind metals strongly (see also 122a). 

This method was applied to assemble integrated electrically-contacted NAD(P)-dcpcndcnt enzyme electrodes. The direct electrochemical reduction of NAD(l ) cofactors or the electrochemical oxidation of NAD(P)H cofactors are kineticaUy unfavored. Different diffusional redox mediators such as quinones, phenazine, phenoxazine, ferrocene or Os-complexes were employed as electrocatalysts for the oxidation of NAD(P)H cofactors An effective electrocatalyst for the oxidation of the NAD(P)H is pyrroloquinoline quinone, PQQ, (7), and its immobilization on electrode surfaces led to efficient electrocatalytic interfaces (particularly in the presence of Ca ions) for the oxidation of the NAD(P)H cofactors. This observation led to the organization of integrated electrically contacted enzyme-electrodes as depicted in Fig. 3-20 for the organization of a lactate dehydrogenase electrode. 

There have been reports of various phenothiazine and phenoxazine anion-radicals which are species which correspond to structure 244 and its substituted derivatives. Thus, reduction of phenothiazin-3-one in DMF gives 259 for which hyperfine splittings are indicated in gauss. The assignment of splittings was made following study of halogenated derivatives of 259 and McLachlan MO calculations. Similar anions from phenoxazin-... 

The irradiation of the phenoxazin-3-one dye, resazurin (21), in the presence of tertiary amines results in its efficient deoxygenation via the triplet state, forming the dye resorufin (22). The radiolysis/photolysis of aqueous solutions of pyrimidines produces radicals which are the result, in general, of 1-electron reduction involving hydrated electrons. The structures of the radicals were assigned on the basis of their by EPR spectra. The study included 2-hydroxypyrimidine... 

Phenoxazines and phenothiazines 32 and 33 are also made by reductive cyclization of o-nitrodiphenyl ethers or o-nitrodiphenyl sulfides, respectively, with triethyl phosphite. 

A new, fairly general, route to 3//-phenoxazin-3-ones (396) consists of the condensation of resorcinols with substituted o-nitrochlorobenzenes, followed by reductive cyclization of the resulting nitro-ethers (Scheme 152). Under the... 

There is information from other studies which probe the question of delineation of the electronic spectra and kinetic stability of organic radical intermediates produced by Ce(IV) oxidations. For example, Kemp et al. (1980) determined such spectra for the radical-cation and neutral radical produced in the first two kinetic steps when phenothiazine and phenoxazine are the reductants. The combination of stopped-flow and rapid-scan spectrophotometry were used to evaluate kinetic parameters for these steps. 

The actual number of protons taking part in the reduction and oxidation of the mediator depends on the structural elements of the phenoxazine. ... 

Cavill, G.W.K., P.S. Clezy, and F.B. Whitfield The Chemistry of Mould Metabolites IV. Reductive Acetylation and Reoxidation of Some Phenoxazin-3-ones. Tetrahedron 12, 139 (1961). 

Selective reduction with and without simultaneous hydrolysis s. 14, 43 3-Imino- from 3-nifro-phenoxazines s. U, 44... 

---