Pulse radiolysis investigations of one-electron reduction of terephthalonitrile in aqueous solutions

Pulse radiolysis of aqueous solutions of terephthalonitrile (TPN) was carried out to study the redox properties of anions of TPN, by determining the rate constants for the reaction of TPN with specific one-electron reducing species formed on reaction of OH radicals with methyl,ethyl,isopropyl alcohols,tetrahydrofuran and cytosine. Formation of anions of TPN, which absorb at wavelength 340 nm, was followed. From the graph of rate constants and maximum absorbance vs reduction potential of reducing species, reduction potential of TPN was found out to be —0.85 V vs NHE. Reduction of thionine (TH⁺) and methyl viologen (MV²⁺) with the help of radical anions of TPN was carried out to establish its high reduction potential.     

Alternating copolymerizations of styrene and acrylic monomers initiated with carbanions in the presence of ZnCl2

On electrochemical initiation of alternating copolymerizations of styrene–acrylonitrile (AN) and styrene–diethyl fumarate (DEF) in the presence of ZnCl₂, radical anions of AN–ZnCl₂ and DEF–ZnCl₂ complexes produced at the cathode were assumed to initiate copolymerization. In analogy with the cathode-initiated copolymerization, the radical anions of AN–ZnCl₂ and DEF–ZnCl₂, generated with the carbanions such as sodium naphthalene, disodium α-methylstyrene tetramer dianion, and butyllithium, were also found to produce alternating copolymers of styrene–AN and styrene–DEF. On the contrary, no polymers were obtained from methyl methacrylate (MMA)–styrene and methacrylonitrile (MAN)–styrene in the presence of ZnCl₂ either with carbanions or by electrochemical reduction. Styrene–MAN–ZnCl₂ yielded an alternating copolymer with carbanions upon introduction of oxygen.     

Reaction of thiobenzophenones with the manganese pentacarbonyl anion

The first study of the reactions of thioketones with metal carbonyl anions is described. Reaction of thiobenzophenones with the manganese pentacarbonyl anion and methyl iodide or benzyl bromide in methanol affords the complexes [Ar₂CHSMn(CO)₄]₂, identified on the basis of analytical and ir, as well as nmr (¹H, ¹³C) spectral data. The reaction is proposed to occur via charge-transfer and radical intermediates.     

Theoretical and Experimental Investigation of Functionalized Cyanopyridines Yield an Anolyte with an Extremely Low Reduction Potential for Nonaqueous Redox Flow Batteries

Cyanopyridines and cyanophenylpyridines were investigated as anolytes for nonaqueous redox flow batteries (RFBs). The three isomers of cyanopyridine are reduced at potentials of −2.2 V or lower vs. ferrocene^+/0 (Fc^+/0), but the 3-CNPy⋅⁻ radical anion forms a sigma-dimer that is re-oxidized at E≈−1.1 V, which would lead to poor voltaic efficiency in a RFB. Bulk electrochemical charge-discharge cycling of the cyanopyridines in acetonitrile and 0.50 M [NBu₄][PF₆] shows that 2-CNPy and 4-CNPy lose capacity quickly under these conditions, due to irreversible chemical reaction/decomposition of the radical anions. Density-functional theory (DFT) calculations indicated that adding a phenyl group to the cyanopyridines would, for some isomers, limit dimerization and improve the stability of the radical anions, while shifting their E_1/2 only about +0.10 V relative to the parent cyanopyridines. Among the cyanophenylpyridines, 3-CN-6-PhPy and 3-CN-4-PhPy are the most promising as anolytes. They exhibit reversible reductions at E_1/2=−2.19 and −2.22 V vs. ferrocene^+/0, respectively, and retain about half of their capacity after 30 bulk charge-discharge cycles. An improved version of 3-CN-6-PhPy with three methyl groups (3-cyano-4-methyl-6-(3,5-dimethylphenyl)pyridine) has an extremely low reduction potential of −2.50 V vs. Fc^+/0 (the lowest reported for a nonaqueous RFB anolyte) and loses only 0.21 % of capacity per cycle during charge-discharge cycling in acetonitrile.     

Reactivity of O2 − radical anions on hydrated ZrO2 surface

The concentration of O₂ ^? radical anions generated on the surface of hydrated ZrO₂ in an H₂O₂ solution was found to depend on H₂O₂ concentration. It was shown that this method can be used for detecting H₂O₂ in solutions at concentration as low as 0.01 wt%. The radical anions were found to react with organic molecules, even at room temperature. The decomposition kinetics of O₂ ^? radical anions was double-exponential with two reaction rate constants. The existence of two distinct rate constants suggests that two types of O₂ ^? radical anions with similar spectroscopic properties but different reactivity are present on the surface of hydrated ZrO₂. It is highly likely that different arrangements of hydroxyl groups near the radical anions account for the presence of the two types of O₂ ^? with different reactivity. The rate constants obtained in the presence of the organic compounds studied were found to conform with the expected order of reactivity: toluene > benzene ? hexane.     

Dimerization and protonation reactions of nitrosonitrobenzenes radical anions

The electrochemical behavior of 2-, 3-, and 4-nitrosonitrobenzenes (NNB) in DMF (with Bu₄NClO₄ suppoting salt) in the presence and in the absence of different proton donors (water, phenol, benzoic, acetic, chloroacetic, and sulfuric acids) is studied by the methods of cyclic voltammetry, chronoamperometry and also by electrolysis at the controlled potential. The electrochemical reduction of these compounds is shown to preferentially afford either monomeric (N-nitrophenylhydroxylamines) or dimeric (azoxy compounds) products, which is determined by the interplay between reactions of protonation and dimerization of NNB radical anions. The dimerization reactions proceed fast and reversibly to afford the corresponding dimeric dianions with the basicity much higher as compared with NNB radical anions as the result of which the monomeric products are formed in the presence of “strong” proton donors and the dimeric products form in the presence of “weak” proton donors. Like the effective rate of formation of dimeric products, the basicity of radical anions increases in the row 4- < 3- < 2-NNB.     

Chemistry of polyfluorocarbanions 1. Nucleophilic iodofluorination of perfluoroalkyl vinyl ethers

Nucleophilic iodofluorination of perfluorovinyl methyl (I) and perfluorovinyl propyl (II) ethers by iodine chloride in nitrobenzene or sulfolan afforded 1-iodoperfluoro-1-methoxyethane (III) and 1-iodoperfluoro-l-propoxyethane in yields of 65 and 77%, respectively. In addition to compound (III), the reaction of perfluorovinyl methyl ether afforded two side products: l-iodo-2-chloroperfluoro-1-methoxyethane and 2-iodo-l-chloroperfluoro-1-methoxyethane. The latter products are formed via a radical reaction, which takes place under drastic conditions. On the basis of quantum chemical calculations of (I), (II), and the two anions formed from (I), CF₃OCFCF₃ (VI) and CF₃OCF₂CF₂ (VII), it is proposed that nucleophilic iodofluorination of perfluoroalkyl vinyl ethers involves the formation of thermodynamically more stable anions. The higher reactivity of (I) compared with (II) is in accord with the energy of the lowest unoccupied molecular orbitals and the charge density on the CF₂ carbon atoms.¹⁹F NMR spectra of the synthesized products are shown.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 669–672, March, 1991.     

[2+2]-Cycloadditionen und -Cycloreversionen in Radikalanionen. Eine ESR.-spektroskopische Beschreibung am Beispiel 2,2′-disubstituierter Biphenyle

[2+2]-Cycloadditions and -cycloreversions in radical anions. An ESR. spectroscopic study for 2,2′-disubstituted diphenyl derivatives The radical anions derived from the polycyclic olefins 1, 2 and 3 are shown by ESR. spectroscopy to undergo [_π2+_π2]-cycloaddition reactions even at low temperatures. Similarly, facile cleavage by [_σ2+_σ2]-cycloreversion processes is observed for the radical anions of the corresponding cyclobutane species. This reactivity, which is in marked contrast with the thermal stability of the neutral parent compounds, is discussed taking into account the molecular geometry and the spin density distribution.     

Effect of ortho substitution on the charge localization of dinitrobenzene radical anions

Optical and electron paramagnetic resonance spectroscopies were used to study the radical anions of several m-dinitrobenzenes and p-dinitrobenzenes with substituents on ortho positions relative to the nitro groups. 1,4-Dinitrobenzene, 1,4-dimethyl-2,5-dinitrobenzene, and 2,5-dinitrobenzene-1,4-diamine radical anions are delocalized (class III) mixed valence species, but in the dinitrodurene radical anion the nitro groups are forced out of the ring plane due to the steric hindrance, which results in localization of the charge. The radical anions m-dinitrobenzene, 2,6-dinitrotoluene, and dinitromesitylene are all localized (class II) mixed valence species, as is common for m-dinitrobenzenes, and the rate of intramolecular electron transfer reaction strongly decreases with the number of methyl substituents. The same mechanism of rotation of the nitro groups out of the ring plane due to steric hindrance caused by neighboring methyl groups is also responsible for slowing the reaction. However, 2,6-dinitroaniline radical anion and 2,6-dinitrophenoxide radical dianion are charge-delocalized because the strong electron releasing amino and oxido groups increase the conjugation between the two charge-bearing units.     

ESR.-Messungen an Radikal-Anionen Trimethylsilyl-substituierter Hetero-π-Systeme

The ESR. spectra of the radical anions of trimethylsilyl-substituted derivatives of p-benzoquinone, phenylketone, diimine, p-benzoquinone-diimide, aniline and p-phenylenediamine are reported. In most cases the coupling constants of ²⁹Si isotopes in natural abundance have been measured. The comparison of the ESR. data for the radical anions of the trimethylsilyl derivatives with those for the radical anions of the corresponding parent hydrocarbons and/or alkyl-substituted compounds provide additional evidence for the overall electron withdrawing effect of the trimethylsilyl substituent (Si←C_π and Si←n_π delocalization).     

The Radical Ions of Indolizino [6,5,4,3-aij]quinoline and Some of its Derivatives

Indolizino [6,5,4,3-aij]quinoline (1) and its 3,9-dimethyl- (2) , di-tert-butyl- (3) and diphenyl- (4) derivatives yield persistent radical cations which have been studied by ESR and ENDOR spectroscopy. The corresponding radical anions have also been prepared, but only that of 3 was amenable to a complete characterization by hyperfine data. The π-spin populations in the radical anions are essentially localized on the 13-membered C-perimeter, and thus both the HOMO and LUMO of 1 exhibit an ‘annulenyl character’. The radical anions of 1 and 2 have gradually been converted into those of the corresponding 3,4-dihydro derivatives ( 1 -H₂ and 2 -H₂) which have been unambiguously identified by a combination of preparative and spectroscopic methods.     

Photochemical reactions of disulphide radical anions in Frozen water-salt matrix

Photochemical reactions of disulphide radical anions CH₃SSCH ₃ ^– induced by light with =436, 405 and 365 nm in a watersalt matrix of 6M LiCl at 77 K have been studied. It has been shown that upon excitation disulphide radical anions may enter into electron photodetachment reaction and the S–S bond is cleft. Kinetical nonequivalence of disulphide radical anions in photochemical reactions has been shown to manifest itself in different mechanisms of their transformations.     

Photochemistry of the IrCl<Subscript>6</Subscript><Superscript>2−</Superscript> complex in aqueous solutions in the presence of the bromide anions

Laser flash photolysis (308 nm) was applied to study photochemistry of the IrCl₆ ²⁻ complex in aqueous solutions in the presence of the Br⁻ anions. The formation of the Br₂ ^·− radical anions in the reaction between the Br⁻ ion and secondary radical pair formed after the photon absorption by the initial complex was observed. The Br₂ ^·− radical anions decay both in recombination and in the reaction with the initial IrCl₆ ²⁻ complex.     

Application of the pulse radiolysis technique to reactions of organic radical ions

The nanosecond pulse radiolysis technique has been applied to study the rate constants for charge transfer and substitution reactions of radical ions. Electron transfer from biphenyl anion to styrene derivatives shows a correlation with the reduction potential of the acceptors expected from the Marcus theory. The positive charge transfer from biphenyl cation to the same acceptors shows a much larger rate constant, suggesting a considerable shift of the free energy relationship to the positive side of G^o. The substitution reaction of fluorenone anion with organic halides shows an S_N2 character, while that of diethyl fumarate shows electron transfer nature. The dimerization of radical anions has been proven for benzophenone and fluorenone, when their lifetime of the parent anions are prolonged by countercations.     

EPR Spectra and Spin Density Distribution of O,S-Dimethyl 4,4-Dithioterephthalate Radical Anions

Abstract

The preparation of O-methyl S-trideuteromethyl 4,4-dithioterephthalate and S-methyl O-trideuteromethyl 4,4-dithioterephthalate is described. The EPR spectra of the corresponding radical anions are measured. Comparison with the spectrum of O,S-dimethyl 4,4-dithioterephthalate radical anions allows the unequivocal assignment of the proton hyperfine structure (proton “hfs”) coupling constants in the above asymmetric species. Assignment of the arene proton hfs coupling constants is achieved by PM6 and density functional theory MO calculations of the spin density distribution and application of McConnell's relationship a^H _μ = ?2.4·ρ^π _μ. The spin density distribution in the asymmetric title compound is compared with those in the radical anions of dimethyl terephthalate and the corresponding symmetric sulfur analogs.     

Solvation Dependences of Isotropic Hyperfine Interaction Constants and out-of-Plane Distortions of ortho-Substituted Nitrobenzene Radical Anions

For a number of ortho-substituted nitrobenzene radical anions (RAs) generated in DMF and its binary mixtures with water, it is shown that for radical anions with a substituent of minor effective volume in one ortho position to the nitro group, the dependences of the isotropic hyperfine interaction (ihfi) constants on the mole fraction of water are S-like and dictated by the medium composition and the concerted out-of-plane rotational and pyramidal distortions of the nitro group of the radical anion. The S-like shape of the solvation dependences of the ihfi constants is dictated by the dominant rotational distortions of the nitro group. For most radical anions with two ortho substituents or with one ortho substituent with a large effective volume, the S-like dependences are not observed, and the values of the nitrogen ihfi constants depend on the dominant pyramidal distortion of the nitro group. For the 2-tert-butylnitrobenzene radical anion in water, the nitrogen ihfi constant is a_N=25.62 G, which is typical of nitroaliphatic radical anions. This effect is explained based on the pyramidal structure of the nitro group in the case of its large rotation angles.     

Kinetic study of bleaching of photoinduced forms of o-methylnitrobenzothiazoles

Photochromic properties of benzothiazole derivatives containing nitro and methyl groups in the ortho positions with respect to each other were studied by flash photolysis. The rate constant of bleaching of the corresponding photoinduced nitronic acids and their anions increases as the CH₃C-CNO₂ bond becomes longer. The application of the thermodynamic approach to predict the kinetic stability of nitronic acids is limited owing to specific intramolecular interactions. The lifetime of photoinduced nitronic acid anions tends to increase with rise in the chemical shift of the methyl protons.     

Generation and characterization of distonic dehydrophenoxide radical anions under electrospray and atmospheric pressure chemical ionizations

We have explored the possibilities of generating radical anions under electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) conditions. By using different sets of ortho-, meta-, and para-isomers of nitrobenzoic acids, methylphenols, and nitrophenols, and m-, and p-isomers of hydroxybenzaldehydes and hydroxyacetophenones as the precursor molecules, we have successfully generated the isomeric distonic dehydrophenoxide radical anions (m/z 92) using the ESI process by applying relatively high capillary voltages, the in-source dissociation (ISD) condition. Under the same conditions, the o-hydroxybenzaldehyde and the o-hydroxyacetophenone yielded the even-electron dehydrophenoxide anion (m/z 93) due to the well-known ortho-effect. The distonic phenoxide radical anions at m/z 92 were also generated under APCI-ISD conditions by using m- and p-isomers of nitrobenzaldehydes and nitroacetophenones. While the o-nitrobenzaldehyde and the o-nitroacetophenone mainly yielded the phenoxide anion at m/z 93, due to the ortho-effect. The collision-induced dissociation (CID) experiments of all the anionic precursor molecules formed from either ESI or APCI produced comparable mass spectra as those observed in the ESI-ISD or the APCI-ISD experiments. The radical anions at m/z 92 reacted with CO₂ and O₂ to form the CO₂ adduct and the oxygen atom abstraction product, respectively, revealing the dual-character of the distonic radical anions, the phenide ion and the phenyl radical. Computational studies support the results of the ion-molecule reactions.     

Molecular ions of 3,3′-bi(2-R-5,5-dimethyl-4-oxopyrrolinylidene) 1,1′-dioxides

The electrochemical reduction of 3,3′-bi(2-R-5,5-dimethyl-4-oxopyrrolinylidene) 1,1′-dioxides (R = CF₃, Me, Ph, Bu^t), which are cyclic dinitrons with conjugated C=C bond, in acetonitrile is an EE process producing stable radical anions and dianions, whereas the electrochemical oxidation is an EEC (R = Me, Ph) or EE process (R = Bu^t) with formation of radical cations (except for the case of R = CF₃) and dications (R = Bu^t) stable under standard conditions. Radical cations of the dioxides with R = Me, Ph, and Bu^t and radical anions of the whole series of the compounds studied, including R = CF₃, were characterized by ESR spectroscopy combined with electrochemical measurements and quantum-chemical calculations. The electrochemical behavior of the Bu^t-substituted dinitron is unique: the EE processes in the region of negative and positive potentials with formation of the dianion, radical anion, radical cation, and dication stable at T = 298 K were observed for the first time within one cycle of potential sweep in the CV curve measured in MeCN. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1148–1154, May, 2005.     

Application of vegetable oils for electrocatalytic synthesis of hydrocarbons

Conditions of Kolbe cross-electrosynthesis of 10-undecylenic and acetic acids are studied on different catalyst anodes. It is shown that the key anodic process stages are the stages of formation of vinyl radicals from anions of unsaturated and methyl radicals under electrosynthesis of acetate anions. As dependent on the conditions of the process, the main product formed on the anode of the Pt-10% Ir alloy is either hydrocarbon CH₃CH₂CH(CH₃)(CH₂)7CH₂CH₃ (58 wt %) being the product of addition of three methyl radicals to a vinyl radicals or olefin CH₂=CH(CH₂)₇CH₂CH₃ (57 wt %) being the product of dimerization of vinyl and methyl radicals.