Complex formation of verdazyl radicals with verdazilium salts

Russian Journal of General Chemistry -     

Autocatalysis in oxidation reactions of verdazyl radicals with hydroperoxides

The reaction of 2,4,6-triphenyl- and 2,3,4,6-tetraphenylverdazyl with tert-butyl hydroperoxide in acetonitrile solution and acetonitrile-water mixture was studied. This reaction was shown to be autocatalytic owing to verdazylium hydroxide formation in the course of the reaction. The main kinetic parameters were determined for the catalytic and non-catalytic reactions.     

Allylation and vinylation of aryl radicals generated from diazonium salts

Allylation and vinylation of aryl radicals generated from aryl diazonium salts provides rapid and efficient access to chlorinated and brominated derivatives of styrene and allylbenzene. Allyl chlorides were found to be better substrates than bromides due to decreased halogen transfer. Donor- and acceptor-substituted diazonium salts are well tolerated. The products represent important precursors for numerous further transformations.     

Azocoupling reactions of enaminocarbonyl derivatives of 1,2,3,4-tetrahydroisoquinoline with diazonium salts

It has been shown that enamino amide and enamino ketone derivatives of 1,2,3,4-tetrahydroisoquinoline react with diazonium salts to form azo compounds. Depending on the enamine structure they can exist just as azo dyes or as azohydrazone tautomers. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1382–1387, September, 2006.     

Kinetics and mechanism of reactions between aromatic olefins and hydroxyl radicals

The rates of the reactions of hydroxyl radicals (OH) with styrene, α-methylstyrene, and β-methylstyrene have been measured by irradiating mixtures of these aromatic olefins and NO in an environmental chamber at 298 K. Experimental conditions were used whereby the competition of ozone with OH in oxidizing the hydrocarbons could be considered negligible. The rate constant values, obtained by a relative method using isooctane as reference hydrocarbon, are: styrene (5.3 ± 0.5) × 10^?11 cm³/molec·s, α-methylstyrene (5.3 ± 0.6) × 10^?11 cm³/molec·s, and β-methylstyrene (6.0 ± 0.6) × 10^?11 cm³/molec·s. A simplified kinetic treatment of the experimental data shows that styrene and β-methylstyrene are stoichiometrically converted to benzaldehyde, suggesting that OH attack occurs only on the aliphatic moiety of the aromatic olefins. Benzaldehyde was observed to undergo consecutive oxidation by OH, and its maximum formation yield was about 60%. A reaction mechanism is proposed where the primary rate-determining OH attack leads to the formation of 1-hydroxy-2-phenyl-2-ethenyl radicals, from which benzaldehyde is formed through fast intermediate reactions.     

CIDNP as the proof of a radical mechanism of the reactions of Grignard reagents with diazonium salts

The PMR spectrum recorded during the reaction of tert-butylmagnesium chloride with p-chlorophenyl diazonium tetrafluoborate shows the CIDNP effect in the spectra of the the reaction products. Enhanced absorption and emission (the multiplet effect) has been observed for the protons of the vinyl group of isobutylene and the methyl protons of isobutane. The reaction of these diazonium salts with benzylmagnesium chloride results in only one polarised product, chlorobenzene. Such a polarisation proves the radical mechanism of the reaction which started with one-electron transfer from the Grignard reagent to the diazonium salt.     

The copper-catalyzed cross-coupling reactions of aryl diazonium salts and isocyanides

The copper-catalyzed cross-coupling reaction of aryl diazonium salts and isocyanides has been performed. This is a successful example of preparation of arylcarboxyamides with moderate to good yield under mild conditions.     

Electrochemical studies of verdazyl radicals

The redox properties of verdazyl radicals are presented using cyclic voltammetry techniques. These radicals can be reversibly reduced as well as oxidized. Electron-donating and -withdrawing substituents have significant effects on the oxidation and reduction potentials as well as the cell potential (E(cell) = | E(ox) degrees - E(red) degrees |) for these radicals; a correlation between the electron spin distribution and redox properties is developed.     

Kinetics and mechanism of redox reactions of radical cations of the triphenylamine series with neutral free radicals

Theoretical and Experimental Chemistry -     

Reaction of 5-alkylidenerhodanines with diazonium salts

In the action of diazonium salts on 5-alkylidenerhodanines, azo compounds are formed by the replacement of one or two hydrogen atoms in the methyl group. In the case of 5-ethylidenerhodanines, the formation of an azorhodanine through the replacement of the alkylidene residue by an arylazo group takes place simultaneously. In the formazyl derivatives the long-wave absorption maximum is displaced hypsochromically by 15–20 nm as compared with the dyes having a single azo group.     

Pd-catalyzed arylation reactions with phenol diazonium salts: application in the synthesis of diarylheptanoids

The first total synthesis of the natural product (3S,7R)-5,6-dehydro-de-O-methyl centrolobine and various analogues is reported, using a highly regio- and diastereoselective Mizoroki-Heck reaction of phenol diazonium salts and enantiopure dihydropyrans. The assigned relative configuration was confirmed by single-crystal X-ray structure analysis, but a revision of the absolute configuration is proposed based on polarimetric measurement.     

Reaction of heterocyclic diazonium salts with hydrazones

Depending on the nature of the heteroring and the hydrazone, a formazan or a heterylazophenylhydrazone are formed in the reaction of an aryl hydrazone with the diazonium salt obtained from a heterocyclic amine. Disproportionate to form a triphenylformazan is also possible.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1062–1064, August, 1972