Stable nitroxide radicals from 2-substituted quinoline-N-oxides with organometallic compounds

Stable nitroxide radicals were obtained by the oxidation of 1-hydroxy-2,2-diphenylquinolines prepared by allowing the PhMgBr to act upon a number of 2-phenylquinoline-N-oxides in THF. Methyl-, ethyl- and benzyl-magnesium compounds gave rise to other nitroxides which were identified from their ESR spectra, but not isolated in the solid state. t-Butyl-magnesium chloride reacted with quinoline-N-oxides giving only the deoxidation products. The ESR spectra of numerous nitroxide radicals were interperted and discussed.     

Stable nitroxide radicals from phenylisatogen and arylimino-derivatives with organo-metallic compounds

Stable nitroxide radicals were obtained by the oxidation of 1-hydroxyindolines prepared by allowing the organo-metallic compounds to act upon 2-phenylisatogen and arylimino-derivatives. In both cases nitroxides are obtained with a ^N of approximately 9 gauss, in agreement with similar known compounds. The ESR spectra of numerous nitroxide radicals are discussed and a number of cases of magnetic non-equivalence of methylenic protons adjacent to asymmetric carbon are brought to light.     

Quinoline nitroxide radicals. Ipso-attack in the reaction between 2-methoxy and 2-cyanoquinoline N-oxide,and phenylmagnesium bromide

2-Methoxy and 2-cyanoquinoline N-oxide, when treated with phenylmagnesium bromide, undergo a nucleophilic ipso-attack at C-2, yielding, by elimination of methoxymagnesium bromide or cyanomagnesium bromide, the corresponding 2-phenylquinoline N-oxides, which react with the excess of Grignard reagents forming 2,2-diphenylquinoline 1-oxyls. Even when the methoxy and cyano groups are in position 4, the attack by the Grignard reagent takes place at C-2 giving 2-phenylquinolines and 2-phenylquinoline N-oxides by elimination of hydroxymagnesium bromide and bromomagnesium hydride, respectively; the formation of 2,2-diphenylquinoline l-oxyls in these reactions is discussed.     

Studies on the interaction of peroxy radicals with transition metals complexes: I. Effect of 2-cyano-2-propyl and 2-cyano-2-propyl peroxy radicals on cobaloximes

Reactions of CH₃Co(DH)₂py (1) and [Co(DH)₂py]₂ (2) with (CH₃)₂(CN)C (r) and (CH₃)₂(CN)COO (rO₂) radicals were investigated. At 60°C, reaction or r with (1) results in non-homogeneous ligand decomposition, whereas for 2, complex (CH₃)₂CNCCo(DH)₂py (6) and a precipitate are formed. Ligand decomposition also took place at 60°C when the reaction of rO₂ radicals with 1 and 2 was investigated. However, the same reaction with rO₂ radicals at −10°C, yielded two complexes, CH₃OOCo(DH)₂py (3) and Co(DH)₂py (4) with 1, and complex 6 for the reaction of rO₂ with 2.     

The trifluoroacetic anhydride-sodium iodide system as a reagent for determination and microdetermination of nitroxide radicals

A trifluoroacetic anhydride-sodium iodide mixture (TFAA-I) reacts with nitroxide radicals with liberation of iodine. Since stoichiometric amounts of iodine are formed from nitroxides, the TFAA-I reagent can be applied to their analytical determination. Two procedures for the determination of nitroxides (titrimetric on mumol and spectrometric on nmol levels) are described.     

The constitution of the grignard reagent : VIII. The structure of complexes between ethylmagnesium bromide and 1-ethoxy-2-methylbutane

From measurements of the degree of association and of the optical rotation of solutions of ethylmagnesium bromide in (+)(S)-1-ethoxy-2-methylbutane [(+)-(S)-L] and benzene it is concluded that these solutions contain the species EtMgBr·2L (I), (EtMgBr)₂·3L (III) and (EtMgBr·L)₂ (II) which have molecular rotations [M]²⁵_D of 3.79°, 5.92° and 4.26° respectively. Equilibrium constants of 103 mole/l and 1.41 mole/l at 25° were calculated for the equilibria between these species.     

Reaction rates between water and the Karl Fischer reagent

Reaction rates between water and the Karl Fischer reagent have been determined by potentiometric measurement for various compositions of the Karl Fischer reagent. The study has been made with an iodine complex concentration of 0.3-1.2 mM and sulphur dioxide complex at 0.01-0.5M. The concentration of excess of pyridine had no measurable effect on the rate of the main reaction. The reaction was found to be first-order with respect to iodine complex, to sulphur dioxide complex, and to water. The rate constant was (1.2+/-0.2) x 10(3) 1(2). mole(-2). sec(-1). In an ordinary titration it is therefore essential to keep the sulphur dioxide concentration high for the reaction to go to completion within a reasonable time. The extent of side-reactions was found to be independent of the iodine concentration at low concentrations. The side-reactions increased somewhat with increasing sulphur dioxide pyridine concentrations and decreased to about 60% when the temperature was lowered from 24 degrees to 7 degrees.     

Quenching of cascade reaction between triplet and photochrome probes with nitroxide radicals

We proposed a new method for the study of molecular dynamics and fluidity of the living and model biomembranes and surface systems. The method is based on the measurements of the sensitized photoisomerization kinetics of a photochrome probe. The cascade triplet cis-trans photoisomerization of the excited stilbene derivative sensitized with the excited triplet Erythrosin B has been studied in a model liposome membrane. The photoisomerization reaction is depressed with nitroxide radicals quenching the excited triplet state of the sensitizer. The enhanced fluorescence polarization of the stilbene probe incorporated into liposome membranes indicates that the stilbene molecules are squeezed in a relatively viscous media of the phospholipids. Calibration of the "triple" cascade system is based on a previously proposed method that allows the measurement of the product of the quenching rate constant and the sensitizer's triplet lifetime, as well as the quantitative detection of the nitroxide radicals in the vicinity of the membrane surface. The experiment was conducted using the constant-illumination fluorescence technique. Sensitivity of the method using a standard commercial spectrofluorimeter is about 10(-12) mol of fluorescence molecules per sample and can be improved using an advanced fluorescence technique. The minimal local concentration of nitroxide radicals or any other quenchers being detected is about 10(-5) M. This method enables the investigation of any chemical and biological surface processes of microscopic scale when the minimal volume is about 10(-3) microL or less.     

Quinoxaline N-oxide ion radicals. 2. Structures of anion radicals of N-oxides of hydroxymethyl derivatives of quinoxaline and products of their electrochemical reduction

The redox properties of 1,4-dioxides of hydroxymethyl and formyl derivatives of quinoxaline were studied by means of EPR spectroscopy and polarography. The electrochemical reduction of the 1,4-dioxides proceeds in several steps with successive deoxidation and the formation of dianions of substituted quinoxalines and is also accompanied by an intramolecular redox process. The experimentally observed hfs constants in the EPR spectra of the anion radicals formed in the reduction are in agreement with the corresponding values calculated by the INDO method.See [1] for communication 1.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1412–1416, October, 1985.The authors thank I. A. Abronin for his assistance in performing the quantum-chemical calculations.     

Reaction of 4-acylaminomethylpyridine N-oxides with phenylbutazone in the presence of acetic anhydride

Reaction of 4-acylaminomethylpyridine N-oxides with phenylbutazone in the presence of acetic anhydride is described. In the pharmacological screening one compound shows an interesting anticonvulsant activity.     

Mechanism of grignard reagent formation. Further evidence for the surface nature of the reaction

The use of Rieke magnesium permits one to obtain reaction with (S)-(+)-1-bromo-1-methyl-2,2-diphenylcyclopropane (1) at −65°C to yield a chiral Grignard reagent that is 33–43% optically pure.     

Electronic spectra and structure of 2-bromopicolines, their N-oxides, and 2-bromo-4-nitropicoline N-oxides

The UV spectra of 2-bromopicolines, their N-oxides, and 2-bromo-4-nitropicoline N-oxides are presented and the influence of substituents onλ _max andε _max of spectral bands are discussed. The electronic spectra were calculated using the modified INDO method. Transition energies, intensities, and assignments were compared with UV spectra. The degree of intramolecular CT in 2-bromopicoline N-oxides is greater than those in 2-bromopicolines and smaller than those in 2-bromo-4-nitropicoline N-oxides. The differences of the HOMO-LUMO energies indicate that the susceptibilities in the photochemical reaction lie in the order: 2-bromo-4-nitropicoline N-oxides>2-bromopicoline N-oxides>2-bromopicolines. Department of Organic Chemistry, University of Economics, PL-53 342 Wroclaw, Poland. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 197–207, February, 1998.