Diazo cation radicals

Principally the same, but chemically simpler, sequence was used to prepare arylnitro anion-radicals from arylamines, in high yields. For instance, aqueous sodium nitrite solution was added to a mixture of ascorbic acid and sodium 3,5-dibromo-4-aminobenzenesulfonate in water. After addition of aqueous sodium hydroxide solution, the cation-radical of sodium 3,5-dibromo-4-nitro-benzenesulfonate was formed in the solution. The latter was completely characterized by its ESR spectrum. Double functions of the nitrite and ascorbic acid in the reaction should be underlined. Nitrite takes part in diazotization of the starting amine and trapping of the phenyl a-radical formed after one-electron reduction of the intermediary diazo compound. Ascorbic acid produces acidity to the reaction solution (needed for diazotization) and plays the role of a reductant when the medium becomes alkaline. The method described was proposed for ESR analytical determination of nitrite ions in water solutions (Lagercrantz 1998). 

In summary, the copper ion transfers an electron from the unsaturated substrate to the diazo-nium cation, and the newly formed diazonium radical quickly loses nitrogen. The aryl radical formed attacks the ethylenic bond within the active complexes that originated from aryldiazo-nium tetrachlorocuprate(II)-olefin or initial arydiazonium salt-catalyst-olefln associates and yields >C(Ar)-C < radical. The latter was detected by the spin-trap ESR spectroscopy. The formation of both the cation-radical [>C=C<] and radical >C(Ar)-C < as intermediates indicates that the reaction involves two catalytic cycles. In the other case, radical >C(Ar)-C < will not be formed, being consumed in the following reaction ... 

The phenomena enumerated in Section 2.4 do not, of course, fully describe all the differences between chemical and electrode processes of ion radical formation. From time to time, effects are found that cannot be clearly interpreted and categorized. For instance, one paper should be mentioned. It bears the symbolic title ir- and a-Diazo Radical Cations Electronic and Molecular Structure of a Chemical Chameleon (Bally et al. 1999). In this work, diphenyldiazomethane and its 15N2, 13C, and Di0 isotopomers, as well as the CH2-CH2 bridged derivative, 5-diazo-10,ll-dihydro-5H-dibenzo[a,d]cycloheptene, were ionized via one-electron electrolytic or chemical oxidation. Both reactions were performed in the same solvent (dichloromethane). Tetra-n-butylammonium tetrafluoroborate served as the supporting salt in the electrolysis. The chemical oxidation was carried out with tris(4-bromophenyl)-or tris(2,4-dibromophenyl)ammoniumyl hexachloroantimonates. Two distinct cation radicals that corresponded to it- and a-types were observed in both types of one-electron oxidation. These electromers are depicted in Scheme 2-28 for the case of diphenyldiazomethane. 

The reaction of diazo cation with phenolate yielding the azo dye may proceed through the formation of the diazo ether. Kekule came to this conclusion in 1870. Zollinger (1958), considering this conclusion, proposed and explained the mechanism by which the diazo ethers convert into the C-diazo compounds, that is, into the hydroxyazo dyes. The diazo ether preliminarily dissociates into the phenolate ion and the diazonium ion i.e., a two-stage intermolecular reaction takes place. The CIDNP effect suggests that the diazo ether may reversibly convert into the radical pair ... 

The kinetics of the formation of diazo and carbene cation radicals were also studied by Parker, Bethell and coworkers (Parker and Bethell, 1987 Bakke et al., 1987). They used diazodiphenylmethane and its 2,2 -bridged derivatives 9.58 and 9.59. In... 

In this section, we discussed radicals generated by one-electron transfer to or from diazo compounds, i. e., redox reactions. We will add here a reaction of diazo compounds with stable organic n cation radicals, although this process is neither a reduction nor an oxidation. 

Abstract Diazonium salts have been previously used to cleave DNA via generation of carbon centered radicals and cations. Efforts have been made in the past decade or so to develop diazo compounds and a-diazoketones for physiologically relevant DNA cleavage. These efforts, coupled with their relevance to the mechanism of action of kinamycin and lomaiviticin antibiotics and other naturally occurring diazo compounds, will be discussed. 

Small changes in the solvent or in the conditions of oxidation can lead to changes in the electronic and molecular structure of aryldiazo radical cations, from a linear allylic 7T- to a bent a-radical state. Both states have been observed in the radical cations of diphenyldiazomethane (49) and 5-diazo-10,ll-dihydro-5//-dibenzo[a, /]cycloheptene... 

The carbon dioxide anion-radical was used for one-electron reductions of nitrobenzene diazo-nium cations, nitrobenzene itself, quinones, aliphatic nitro compounds, acetaldehyde, acetone and other carbonyl compounds, maleimide, riboflavin, and certain dyes (Morkovnik and Okhlobystin 1979). The double bonds in maleate and fumarate are reduced by CO2. The reduced products, on being protonated, give rise to succinate (Schutz and Meyerstein 2006). The carbon dioxide anion-radical reduces organic complexes of Co and Ru into appropriate complexes of the metals(II) (Morkovnik and Okhlobystin 1979). In particular, after the electron transfer from this anion radical to the pentammino-p-nitrobenzoato-cobalt(III) complex, the Co(III) complex with thep-nitrophenyl anion-radical fragment is initially formed. The intermediate complex transforms into the final Co(II) complex with the p-nitrobenzoate ligand. 

Reactions arising via photo-oxidation of diazo-compounds are thought to involve carbonyl oxide intermediates, and stilbene derivatives are formed via aryldiazomethane radical-cations on dicyanoanthracene-sensitized irradiation of aryldiazomethanes. " A 1,4-biradical is formed by stepwise cleavage on photolysis of l,12-bis(diazo)-l,12-dihydroindeno[2,3-a]fluorene. ... 

With 1 as catalyst, alkene bonds which have oxidation potentials less than 1.6 V (vs standard calomel electrode) are considered potentially susceptible to this transformation. With the stronger oxidant 2, the scope of the reaction can be extended to include, for example, tetraalkyl-substituted double bonds, but obviously not disubstituted alkenes such as cyclohexene. On the other hand, electron-rich alkenes such as enol ethers and vinyl sulfides cannot be cyclo-propanated by this method. In order to suppress cyclodimer formation from the alkene and its radical cation, the diazo ester is sometimes applied in a four- to fivefold amount with respect to the alkene. 

We use the term diazo compounds not only to name specific structures according to lUPAC rules (e. g., diazomethane, see below), but also as a class name (as meant in the title of this book and in chapter headings), including neutral, cationic, anionic, and radical compounds with the group — N2 or — N2 —, but excluding azo compounds, i.e., compounds in which the — N2— group is bound on both sides to C-atoms. 

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