Mechanism of the electrochemical reduction of 2-halo-5-nitrothiophenes in dimethylformamide

The reduction of 2-bromo-5-nitrothiophene and 2-iodo-5-nitrothiophene in dimethylformamide (DMF) was studied by means of classical and commutated polarography, EPR spectroscopy, a rotating platinum disk electrode with a ring, and preparative electrolysis. It was established that, depending on the nature of the halogen, their anion radicals may undergo further reduction to 2-nitrothiophene anion radicals or decomposition with splitting out of a halide anion and conversion to nitrothienyl radicals, which were identified on the ring electrode. The latter are capable of undergoing dimerization to 2,2-dinitro-5,5-dithienyl. The spectra of the anion radicals of 2-nitrothiophene and 2,2-dinitro-5,5-dithienyl were recorded by means of EPR. A mechanism for the reduction of halonitrothiophenes is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 195–198, February, 1981.     

Role of electron transfer in reactions involving substitution of halogen in 2-halo-5-nitrofurans

The replacement of the halogen in 2-halo-5-nitrofurans (Hal=C1, Br, I) in dimethylformamide (DMF) under the influence of tetra-n-butylammonium hydroxide to give 2-hydroxy-5-nitrofuran salts was studied. The intermediate anion radicals of the halonitrofurans were recorded by EPR spectroscopy; bromo- and iodonitrofurans can give 5,5-dinitro-2,2-difuryl anion radicals under the influence of Bu₄NOH. The polarographic reduction of halonitrofurans in the presence of hydrogen peroxide also leads to 2-hydroxy-5-nitrofuran. A mechanism for the transformation is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1604–1607, December, 1979Original article submitted March 17, 1977; revision submitted October 30, 1978.     

EPR spectra and π-electronic structures of anion radicals of a nitro-substituted indoline spiropyran

Electrochemical generation was used to obtain anion radicals of 1,3,3-trimethyl-5-nitrospiro (indoline-2,2-[2H]chromene), and their EPR spectra in acetonitrile, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) were recorded. On the basis of an analysis of the hyperfine structure (hfs) of the EPR spectra it was concluded that, as a consequence of the relatively weak interaction of the -systems of the indoline and benzopyran fragments, cleavage of the bond between the spiro carbon atom and the oxygen atom in the pyran ring does not occur in the formation of the anion radical, and the additional unpaired electron is delocalized in the -system of the indoline fragment of the molecule.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1477–1481, November, 1984.     

ESR spectra of electrochemically generated free anion radicals of hetaryl-substituted trichloro-1,4-benzoquinones

The ESR method was used to confirm the formation of free anion radicals in the source of electrochemical reduction of 5-thiazolul-substituted 1,4-benzoquinones and related compounds, as well as the ability of the unpaired electron to become delocalized over the system of electrons not only of the benzoquinone nucleus but also of the hetaryl substituent added to it.Latvian Institute of Organic Synthesis, Riga, LV-1006. Riga Technical University, Riga, LV-1048. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 258–261, February, 1995. Original article submitted December 30, 1994.     

Electrochemical reduction of prostanoid syntone 7α-hydroxy-6Β-3′-oxo-4′-(m-chlorophenoxy)-1′e-butenyl-cis-2-oxabicyclo[3.3.0]octan-3-one

The reactivity of the prostanoid syntone 7-hydroxy-6-3-oxo-4-(m-chlorophenoxy)-1E-butenyl-cis-2-oxabicyclo[3.3.0]octan-3-one is determined by the presence of an enone fragment in the molecule. The electrochemical reduction of this enone in DMF proceeds in two stages. In the first stage the single-electron reduction is accompanied by the dimerization of the originally formed anion radicals. The further reduction of the anion radical is also complicated by the subsequent reactions. The four-stage reduction of the investigated enone in 50% aqueous ethanol reflects the influence of the protogenic medium on its electrochemical behavior. The formation of a diketone at the first and of a saturated ketone at the second stage has been explained by the dimerization of the originally formed anion radical and its further reduction. At the potentials of the third and fourth stages the original diketone is reduced to the corresponding ketoalcohol, which catalyzes the discharge of hydrogen in the potential region of the fourth wave.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1012–1017, May, 1991.     

Influence of the chemical nature of deposited metal ions on their catalytic properties in oxidation of methane by nitrous oxide

The catalytic properties of deposited metal ions in the reaction between methane and nitrous oxide were studied. On the basis of a previously proposed mechanism for the heterogeneous-catalytic reaction, an interpretation was given for the observed activity and selectivity series with respect to the formation of methanol, carbon monoxide and dioxide. The determining factor regulating the catalytic properties in this system is the bond energy of metal ions with the adsorbed oxygen anion radicals O.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 455–461, July–August, 1988.The authors wish to express their gratitude to V. M. Lukyanchuk for providing samples of the catalysts, and to A. N. Korol' for his assistance in carrying out the chromotographic analysis.     

Effect of the heteroatom on the one-electron reduction of α-nitro derivatives of five-membered heterorings

The potentials of the first polarographic half waves of the electrical reduction in dimethylformamide (DMF) of -nitro derivatives of furan, thiophene, selenophene, and their analogs in the benzene series and the hfs constants of the EPR spectra of the electrochemically generated anion radicals of these compounds are presented. It was established that these parameters in the series of examined heterorings regularly follow the electron affinities of the heteroatoms in their s²p²pp valence state. The relative conductivity of the electronic effects of substituents is higher (1.08) in the level of the unpaired electron of the furan ring, while the conductivities in the thiophene (0.95) and selenophene (0.94) ring are lower, than in the case of the benzene ring. The conductivity through the heterorings in the molecular state is higher by a factor of 1.2 than in the level of the unpaired electron.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1606–1612, December, 1980     

Comparing Positively and Negatively Charged Distonic Radical Ions in Phenylperoxyl Forming Reactions

In the gas phase, arylperoxyl forming reactions play a significant role in low-temperature combustion and atmospheric processing of volatile organic compounds. We have previously demonstrated the application of charge-tagged phenyl radicals to explore the outcomes of these reactions using ion trap mass spectrometry. Here, we present a side-by-side comparison of rates and product distributions from the reaction of positively and negatively charge tagged phenyl radicals with dioxygen. The negatively charged distonic radical ions are found to react with significantly greater efficiency than their positively charged analogues. The product distributions of the anion reactions favor products of phenylperoxyl radical decomposition (e.g., phenoxyl radicals and cyclopentadienone), while the comparable fixed-charge cations yield the stabilized phenylperoxyl radical. Electronic structure calculations rationalize these differences as arising from the influence of the charged moiety on the energetics of rate-determining transition states and reaction intermediates within the phenylperoxyl reaction manifold and predict that this influence could extend to intra-molecular charge-radical separations of up to 14.5 Å. Experimental observations of reactions of the novel 4-(1-carboxylatoadamantyl)phenyl radical anion confirm that the influence of the charge on both rate and product distribution can be modulated by increasing the rigidly imposed separation between charge and radical sites. These findings provide a generalizable framework for predicting the influence of charged groups on polarizable radicals in gas phase distonic radical ions.

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Allyl sulfonium salt as a novel initiator for active cationic polymerization of epoxide by shooting with radicals species

A rapid cationic polymerization of cyclohexene oxide that completed within a few minutes was achieved by a new initiation system that involves (1) a copper‐catalyzed reduction of benzoyl peroxide by an ascorbic acid derivative that generates free radicals and (2) capture of the radicals by allyl sulfonium salt having hexafluoroantimonate (SbF) as a counter anion, followed by fragmentation of sulfonium radical cation, from which a super acid HSbF₆ was produced to initiate the rapid polymerization. The key factor in designing an efficient allyl sulfonium salt was attachment of an electron withdrawing ester group at the allyl group, of which ability to stabilize the formed radical can enhance the efficiency in trapping radicals by the allylic salt. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4178–4183, 2010     

π-Electron structure of the nitrofuran system

Distribution of the unpaired electron in the first free MO, the partial bond orders created by this electron, and the energy level corresponding to it in anion radicals of the nitrofuran series have been examined on the basis of quantum-chemical calculations by the MOH method of the -electron system of 5-nitrofuran and its 2-substituted derivatives. Distribution of the spin density of the electrons in the anion radicals has also been calculated by McLachlan's method. The parameters of the first free MO obtained by calculation agree satisfactorily with the physicochemical characteristics of the corresponding particulars measured experimentally (HFS constants in the EPR spectra and polarographic half-wave potentials).     

Mechano-ions produced by mechanical fracture of solid polymers

It is said that the free radical caused by C-C-bond scission, homogeneous scission, is produced by mechanical degradation. In addition to free radicals, ionic species are produced due to the mechanical destruction of the polymers. Studies in our group concerning this problem are summarized. When the polymers were ground with tetracyanoethylene (TCNE) powder in a vibration glass ball mill in vacuum in the dark at 77 K, the TCNE anion radical (TCNE$ \bar . $) was detected by electron spin resonance (ESR) method. The TCNE$ \bar . $ is formed by the abstraction of electrons by TCNE from the anion produced by a heterogeneous bond scission of carboncarbon bonds in the polymer main chain. The identification of TCNE$ \bar . $ was carried out by the spectral simulation on the basis of an anisotropic hyperfine tensor including a forbidden transition term. Several polymers were examined; polyethylene, polypropylene, poly(tetrafluoroethylene) and poly(vinylidene fluoride). The ratio of ionic species and free radicals is discussed.     

EPR recording of fatty aromatic radicals during chlorarylation

Reaction of aryldiazonium chlorides with unsaturated compounds in the presence of copper dichloride leads to chlorarylation products having a multiple bond. In the initial stage an aryldiazonium salt is formed with a complex tetrachlorocuprate anion (ArN₂)₂ ²⁺CuCl₄ ^2–. This salt reacts with styrene or acrylonitrile to give radicals of the type ArCH₂HX (Ar=p-MeOC₆H₄, X=Ph, CN), which were recorded from the corresponding EPR spectra in the form of spin adducts of nitrosodurol.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1214–1216, May, 1991.     

Direct formation of excited singlet states in the electrogenerated chemiluminescence of mixed systems involving N-aryl-2-pyrazolines

The direct formation of the excited singlet states ¹P^* in the electron transfer reaction between the cation radicals

of certain N-aryl-2-pyrazolines and the anion radicals

of some polycyclic aromatic hydrocarbons, and aryl-substituted oxazoles and oxadiazoles is observed in electrogenerated chemiluminescence studies using measurements of the relative emission intensities and investigations in a magnetic field.     

EPR study of rearrangement of ω-carbalkoxyalkyl radicals using spin traps

Conclusions The rearrangement of the radicals CH₂(CH₂)_nCH₂CO₂R to CH₃(CH₂)_nCHCO₂R (n=1-4) was studied by the EPR method at room temperature, with a recording of the intermediate radicals as the spin-adducts with nitrosodurene. The ratio of the yields of the rearranged radicals with the 1,6-, 1,5-, 1.4-, and 1,3-migration, of hydrogen was, respectively, equal to 0.251 0.10 0.03.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2628–2631, November, 1977.     

EPR spectra of free radicals formed during electrochemical reduction of 5-substituted 2-furaldehydes and 2-thiophenaldehydes

Using EPR we have found that during electrochemical reduction of 5-substituted 2-furaldehydes and 2-thiophenaldehydes, carbon-centered free radicals (products of protonation of radical anions) may form, along with radicals of a different structure, and also -type radical anions of different conjugated dimers. We have determined the hyperfine structure and measured the values of the constants for the EPR spectra of some of these radicals.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1051–1060, August, 1997.     

Mechanisms of processes involving β-substituted cyclopropyl radicals. Ring expansion in the reaction with CO

The reaction of -substituted cyclopropyl radicals with CO was studied by ESR. Tile acyl radical resulting from the addition of CO to the cyclopropyl radical was detected. At temperatures near 270 K, an intramolecular rearrangement of the acyl radical affords substituted 2-oxocyclobutyl radicals (ring expansion reaction). Mechanisms for the free-radical transformations studied were suggested.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 497–499, February, 1996.     

Long-wave light absorption and photochemical decomposition of peroxide radicals

Photochemical decomposition of alkylperoxide radicals in glassy matrices at 77 K was experimentally studied. Irradiation with light up to 405 nm leads to the photodecomposition of peroxide radicals. The quantum yield of the reaction was estimated to be 10^–2. A light-induced angular dependence of the ESR spectra of peroxide radicals resulting from photoselection was detected. The photoselection found proves that the photodecomposition is induced by the absorption of light in the inherent absorption band of RO₂.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1074–1077, June, 1995.The work was carried out with the financial support of the Russian Foundation for Basic Research (Project No. 95-03-08505) and the International Science Foundation (Grants NBU 000 and NBU 300).     

Synthesis of 5-nitro-N,N-diphenylhydrazinopyrimidines and investigation of their free radicals

A number of 5-nitro-N,N-diphenylhydrazinopyrimidines were synthesized. Free radicals were obtained by oxidation of these compounds with PbO₂. The stabilities of 5-nitro-4-pyrimidinylhydrazyl radicals are close to the stability of the ,-diphenyl--2,4-dinitrophenylhydrazyl radical. The structures of the compounds obtained were confirmed by the UV, IR, PMR, and EPR spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1545–1549, November, 1980.     

Radical decomposition of <Emphasis Type="Italic">N,N</Emphasis>-bis-(3-chloro-1,4-naphthoquinon-2-yl) amine in basic conditions followed by EPR

EPR spectroscopy was used to assess the radicals produced upon basic decomposition of N,N-bis-(3-chloro-1,4-naphthoquinon-2-yl) amine (BClNQA). Three radicals have been trapped and identified: N-bis(3-chloro-1,4-naphthoquinone) hydrazine radical (6), 2-hydroxy-3-chloro-1,4-naphthoquinone anion radical (9) and 2-amino-3-chloro-1,4-naphthoquinone radical (8). The probable reaction mechanism, the structure of intermediates as well as the reaction profile are discussed.