Free radicals from electrochemical reduction of hexahydroquinolones and hexahydroisoquinolones

Electrochemical reduction of 3,5-diethoxycarbonyl- and 3,5-diacetyl-2,6-dimethyl-1,4-dihydropyrdine, hexahydroquinol-5-one, and hexahydroisoquinol-8-one, which contain dihydropyridine moieties, produces free radicals detectable by EPR only for the most easily reduced hexahydroisoquinol-8-ones. The hyperfine structure of the EPR spectra is determined and is consistent with that for the 4,5-dihydropyridine moiety.Latvian Institute of Organic Synthesis, Riga LV-1006, Latvia; Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 924–928, July, 1999.     

Free radicals in the electrochemical reduction of 1,2-dihydro-3-nitropyridine derivatives

The formation of primary radical anions of N-substituted 1, 2-dihydro-3-nitropyridines was confirmed by the ESR method under conditions of electrochemical generation of free radicals, and their structure was established. The causes of the different ability of 1,2- and 1,4-dihydro-3-nitropyridines to form free radicals during electrochemical reduction that are stable enough to be studied by the ESR method are examined.Latvian Institute of Organic Synthesis, Riga LV-1006.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1222–1227, September, 1996. Original article submitted May 20, 1996.     

Reaction of sterically hindered gem-dialkylcyclohexadienones with acid agents

Conclusions A study was made of the reactions of six sterically hindered gem-dialkylcyclohexadienones with hydrogen chloride, aluminum bromide, acetic acid, and solutions of sulfuric acid in acetic acid and in acetic anhydride.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 178–180, January, 1972.     

Free radicals in the electrochemical reduction of derivatives of 3,5-dinitro-1,2-dihydropyridine

The characteristics (potentials, limiting currents, reversibility) of the electrochemical reduction of 3,5-dinitro-1,2-dihydropyridines were determined by cyclic voltammetry and polarography. It was established by ESR that the free radicals formed in these processes have a radical-dianion structure in the case of both the N-unsubstituted and the N-substituted dihydropyridines. The hyperfine coupling constants of the interaction between the unpaired electron and the nuclei of the atoms at various positions of the heterocycle were determined.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 212–218, February, 1997.     

Free radicals in the electrochemical reduction of certain mononitro and dinitro derivatives of pyridine

In the primary process of electrochemical reduction of substituted 3-nitropyridines in dimethylformamide, their anion radicals are formed. This also takes place in the reduction of 3,5-dinitropyridines and 3-nitropyridines with a nitrophenyl substituent at position 2 or 4. For these dinitro derivatives, however, secondary free radicals are formed as well; in a basic medium, these are the products of reduction of the corresponding Meisenheimer complexes. Serving as the reaction center for electroreduction is the nitro group on the pyridine ring, not the group on the phenyl ring. For the mononitropyridines and dinitropyridines that were studied, free radicals of the nitropyridine type are formed as the primary species. The structure of the primary and secondary free radicals was established by analysis of the hyperfine structure of their ESR spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1079–1087, August, 1993.     

Free radicals of electrochemical reduction of derivatives of 3-nitro-1,4-dihydropyridines

By means of ESR, under conditions of eletrochemical generation of particles, the formation of four types of secondary free radicals has been confirmed in the process of electrochemical reduction of molecules of N-unsubstituted derivatives of 3-nitro-1,4-dihydropyridine in dimthylformamide — specifically, a dianion radical of the molecule of the original compound; an anion radical of the corresponding isomeric 4,5-dihydropyridine; a radical of the nitroalkane type; and in addition, for the compound substituted with a nitrobenzene group; a free radical with the nitrobenzene structure. Methods for synthesis of the individual compounds are described, and a scheme is presented for the mechanism of their electrochemical conversion.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 355–364, March, 1995. Original article submitted February 21, 1995.     

Free radicals in the perimidine series. 2-Tert-butylperimidyl radicals

Electrochemical and EPR methods have been applied to a study of perimidyl free radicals containing a bulky tert-butyl substituent in the 2-position. A stepwise mechanism is proposed for the dehydrogenation of 1,3-dimethyl-2-tert-butyl-2,3-dihydroperimidine; the mechanism involves formation of a cation-radical from the substrate in the first step. Shielding of the nitrogen atoms seems to be an important factor in increasing the stability of free perimidyl radicals.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 970–972, July, 1986.     

Free radicals in the reactions of organic cations

By using the ESR and CIDNP methods the formation of free radicals in the reaction of nucleophilic and electrophilic substitution is proved. The role of free radicals in the mechanism of these reactions is discussed.     

An electron spin resonance study of radicals from chloramine-t-1 : Spin trapping of radicals produced in acid media

Under acid conditions aqueous solutions of chloramine-T form nitrogen-centred radicals via loss of the chlorine atom. The nitrogen radicals produced have been studied by ESR spectroscopy using the spintrapping method. Adducts of the spin trap phenyl-t-butyl nitrone are oxidized by chloramine-T in acid media to give a paramagnetic product in which the unpaired electron interacts with two inequivalent nitrogen atoms. The spin trap 5,5-dimethyl-2-pyrrolidine-1 -oxide is oxidized rapidly to 5,5-dimethyl-2-pyrrolidone-1-oxyl by chloramine-T under acid onditions. The water soluble trap α-4-pyridyl-1-oxide-N-t-butyl nitrone forms a stable nitroxide adduct with a nitrogen radical of chloramine-T in acid solution. Identical results were obtained with chloramine-B (sodium salt of N-chlorobenzene sulfonamide), indicating the involvement of the N-chloramine group in radical formation.     

Free radicals produced by the oxidation of gallic acid: An electron paramagnetic resonance study

Background  

Gallic acid (3,4,5-trihydroxybenzoic acid) is found in a wide variety of plants; it is extensively used in tanning, ink dyes, as well as in the manufacturing of paper. The gallate moiety is a key component of many functional phytochemicals. In this work electron paramagnetic spectroscopy (EPR) was used to detect the free radicals generated by the air-oxidation of gallic acid.     

Free radicals as host molecules

Perchlorotriphenylmethyl radical (1) and some of its radical derivatives form inclusion compounds with cyclic molecules. Thermal stabilities and crystal studies of some clatrates of1 are presented and discussed.     

Free azoxy radicals from benzoquinolines

Conclusions The 5,6- and 7,8-benzo derivatives of 4-methyl-2-spirocyclohexyl-3,4 3,2-tetrahydrofurano-1,2,3,4-tetrahydroquinoline and their paramagnetic N-oxides were synthesized. A study was made of the paramagnetic absorption spectra of the free radicals, which are bezoquinoline derivatives.     

Electrochemical oxygen reduction on nitrogen doped graphene sheets in acid media

Nitrogen doped graphene were prepared via exfoliated graphite oxide. This graphene exhibited significantly high oxygen reduction activity. High electric conductivity, high surface area, large amount of edge sites and pyridinic N site in rGS (reduced graphene sheets) contribute to the high ORR (oxygen reduction reaction) activity. The rGS showed a potential to replace expensive Pt for oxygen reduction reaction in PEMFC.     

Free radicals in electrochemical reduction of 1-(nitrophenyl)-3,5-dicarbethoxy-4-phenyl-1,4-dihydropyridines

In the primary electrochemical reduction of 1-(nitrophenyl)-3,5-dicarbethoxy-4-phenyl-1,4-dihydropyridine in DMF, free radicals of nitrophenyl type are formed; these are the products of a one-electron reduction of cathode-protonated molecules of the original compound. In alkaline DMF, where cathodic protonation of the initial compound is retarded, union-radicals of the starting material are generated in addition, together with p-nitrophenol free radicals.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1498–1505, November, 1992.     

Free radicals promote electrocatalytic nitrogen oxidation

In this work, we introduce hydroxyl radicals into the electrocatalytic nitrogen oxidation reaction (NOR) for the first time. Cobalt tetroxide (Co₃O₄) acts not only as an electrocatalyst, but also as a nanozyme (in combination with hydrogen peroxide producing ˙OH), and can be used as a high-efficiency nitrogen oxidation reaction (NOR) electrocatalyst for environmental nitrate synthesis. Co₃O₄ + ˙OH shows an excellent nitrogen oxidation reaction (NOR) performance among Co₃O₄ catalysts in 0.1 M Na₂SO₄ solution. At an applied potential of 1.7 V vs. RHE, the HNO₃ yield of Co₃O₄ + ˙OH reaches 89.35 μg h⁻¹ mg_cat⁻¹, which is up to 7 times higher than that of Co₃O₄ (12.8 μg h⁻¹ mg_cat⁻¹) and the corresponding FE is 20.4%. The TOF of Co₃O₄ + ˙OH at 1.7 V vs. RHE reaches 0.58 h⁻¹, which is higher than that of Co₃O₄ (0.083 h⁻¹), demonstrating that free radicals greatly enhance the intrinsic activity. Density functional theory (DFT) demonstrates that ˙OH not only can drive nitrogen adsorption, but also can decrease the energy barrier (rate-determining step) of N₂ to N₂OH*, thus producing great NOR activity.

In this work, we introduce hydroxyl radicals into the electrocatalytic nitrogen oxidation reaction (NOR) for the first time. Co₃O₄ + ˙OH shows an excellent NOR performance among Co₃O₄ catalysts in 0.1 M Na₂SO₄ solution.     

Rhenium deposition onto platinum surface by reduction of perrhenic acid with methanol in hydrochloric acid media

It has been demonstrated that rhenium deposition onto Pt surface in hydrochloric acid media can also be carried out by reduction of perrhenic acid with methanol. Above 0.5 M Cl⁻ ion concentration, however, it is practical to combine the use of methanol with hydrogen.