A novel general method for the synthesis of nitrones by reaction of nitroso compounds with anions of aliphatic nitro compounds

Anions of aliphatic nitro compounds R¹R²C=NO₂ ^– react with nitroso compounds RNO to give nitrones R¹R₂C=N(O)R. Salts of nitro compounds with metals and Et₃N, as well as trimethylsilyl nitronates in the presence of F^–, can serve as the sources of the anions. The structure of the nitrones was established by NMR spectroscopy. 1,3-Dipolar cycloaddition of a series of the nitrones obtained to olefins was investigated.For a brief communication see Ref. 1Translated from IzvestiyaAkademii Nauk. Seriya Khimicheskaya, No. 4, pp. 901–907, April, 1996.     

Electrochemical generation of anion radicals of nitroso and nitro compounds from substituted 2,6-dinitroanisoles

Conclusions In the electrochemical reduction of 2,6-dinitro-4R-anisole (R = COO^–, OCH₃, H, Cl) in DMSO-CH₃OH, the formation of anion radicals of the initial anisoles and AR of the corresponding 2-nitroso-4R-6-nitroanisoles was demonstrated. The structure was established, and a mechanism was proposed for the formation of anion radicals of these nitroso compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3,pp. 520–526, March, 1976.     

Reactions of 1-hydroxy-1-methylethyl radicals with NO2-: time-resolved electron spin resonance

The reaction of the alpha-hydroxyalkyl radical of 2-propanol (1-hydroxy-1-methylethyl radical) with nitrite ions was characterized. A product of the reaction was assigned as the adduct nitro radical anion, [HO-C(CH(3))(2)NO(2)](*-). This radical was identified using time-resolved electron spin resonance (TRESR). The radical's magnetic parameters, the nitrogen hyperfine coupling constant (a(N) = 26.39 G), and its g-factor (2.0052) were the same as those of the nitro radical anion previously discovered in (*)OH spin-trapping experiments with the aci-anion of (CH(3))(2)CHNO(2). Production of [HO-C(CH(3))(2)NO(2)](*-) was determined to be 38% +/- 4% of the reaction of (CH(3))(2)C(*)-OH with nitrite. The reason why this fraction was less than 100% was rationalized by invoking the competitive addition at oxygen, which forms [HO-C(CH(3))(2)ONO](*-), followed by a rapid loss of (*)NO. Furthermore, by taking this mechanism into account, the bimolecular rate constant for the total reaction of (CH(3))(2)C(*)-OH with nitrite at reaction pH 7 was determined to be 1.6 x 10(6) M(-1) s(-1), using both decay traces of (CH(3))(2)C(*)-OH and growth traces of [HO-C(CH(3))(2)NO(2)](*-). This correspondence further confirms the nature of the reaction. The reaction mechanism is discussed with guidance by computations using density functional theory.     

Investigation of short lived radicals in aromatic nucleophilic substitution by use of nitroso compounds as scavengers

Radical intermediates formed in reaction of substituted nitrobenzene compounds with nucleophilic reagents have been trapped by t-nitrosobutane to yield nitroxide radicals which have been characterized in situ by ESR. The formation of short-lived radicals originating from reagents and solvents has been shown.     

Evaluation of thermal hazards based on thermokinetic parameters of 2-(1-cyano-1-methylethyl)azocarboxamide by ARC and DSC

Journal of Thermal Analysis and Calorimetry - Azo compounds (azos) are widely used as radical initiators in the polymerization industry. Nonetheless, due to the azo group molecular structure, azos...     

Activation barriers in the homolytic cleavage of radicals and ion radicals

As revealed by several experimental examples, radicals and ion radicals may, in contrast with closed-shell molecules, undergo exothermic homolytic cleavages (.A..B --> A: +.B) with substantial activation barriers. A two-state semiclassical model is proposed for explaining the existence of the barrier and estimating its magnitude. It is based on the intersection of the potential energy surfaces characterizing the dissociation of a bonding state, .A..B -->.A. +.B, on one hand, and the approach to bonding distance of a repulsive state, A: +.B --> A therefore B, on the other. After inclusion of the bond cleavage and formation as Morse curves in the normal-mode analysis, a simple activation driving force relationship is obtained, the two main ingredients of the intrinsic barrier being the triplet excitation energy of the A moiety and the pi*--> sigma* excitation energy in .A-B. The model is then tested by quantum chemical calculations, first on a simplified system to evaluate the calculation techniques and then on a real system. A comparison of the model predictions with experiment is finally performed using the rate data recently gathered for the cleavage of 4-cyanophenyl alkyl ether anion radicals, which cover a respectable range of driving forces, showing satisfactory agreement between theoretical predictions and experimental data.     

The hetero Diels-Alder reactions of masked o-benzoquinones with nitroso compounds

The first examples of hetero Diels-Alder reaction of masked o-benzoquinones with nitroso dienophiles leading to novel and highly functionalized heterocycles, which are potential intermediates for nitrogenous natural products are reported.     

Rotational mobility of nitroxyl radicals in polyesters

Rotational mobility of nitroxyl radicals in polyester films was investigated at temperatures from ?180 to +240°C by ESR spin-probe techniques. Evidence obtained indicated that mobility of radicals was related to polymer structure and reflected increased volume made available to the probe molecule by the polymer matrix. A single correlation time, which followed the form τ_C = τ₀ exp {E_a/RT}, was calculated for the temperature range of rapid reorientation (～10⁹ Hz) of nitroxyl radicals. E_a ranged from 5 to 25 kcal/mole for various systems. Uniaxially oriented semicrystalline polymer matrix restricted radical mobility to a greater extent than a semicrystalline biaxially oriented sample. Effective local viscosity encountered by a nitroxyl radical in several polymers was calculated as 9–13 poise.     

Reactivities of superoxide and hydroperoxyl radicals with disubstituted cyclic nitrones: a DFT study

The unique ability of nitrone spin traps to detect and characterize transient free radicals by electron paramagnetic resonance (EPR) spectroscopy has fueled the development of new spin traps with improved properties. Among a variety of free radicals in chemical and biological systems, superoxide radical anion (O(2)(?-)) plays a critical role as a precursor to other more oxidizing species such as hydroxyl radical (HO(?)), peroxynitrite (ONOO(-)), and hypochlorous acid (HOCl), and therefore the direct detection of O(2)(?-) is important. To overcome the limitations of conventional cyclic nitrones, that is, poor reactivity with O(2)(?-), instability of the O(2)(?-) adduct, and poor cellular target specificity, synthesis of disubstituted nitrones has become attractive. Disubstituted nitrones offer advantages over the monosubstituted ones because they allow bifunctionalization of spin traps, therefore accommodating all the desired spin trap properties in one molecular design. However, because of the high number of possible disubstituted analogues as candidate, a systematic computational study is needed to find leads for the optimal spin trap design for biconjugation. In this paper, calculation of the energetics of O(2)(?-) and HO(2)(?) adduct formation from various disubstituted nitrones at PCM/B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) level of theory was performed to determine the most favorable disubstituted nitrones for this reaction. In addition, our results provided general trends of radical reactivity that is dependent upon but not exclusive to the charge densities of nitronyl-C, the position of substituents including stereoselectivities, and the presence of intramolecular H-bonding interaction. Unusually high exoergic ΔG(298K,aq)'s for O(2)(?-) and HO(2)(?) adduct formation were predicted for (3S,5S)-5-methyl-3,5-bis(methylcarbamoyl)-1-pyrroline N-oxide (11-cis) and (4S,5S)-5-dimethoxyphosphoryl-5-methyl-4-ethoxycarbonyl-1-pyrroline N-oxide (29-trans) with ΔG(298K,aq) = -3.3 and -9.4 kcal/mol, respectively, which are the most exoergic ΔG(298K,aq) observed thus far for any nitrone at the level of theory employed in this study.     

The determination of organic nitro,nitroso and azo compounds with copper

An indirect gravimetric method for the determination of organic nitro, nitroso and azo compounds has been investigated. The amount of nitro, nitroso, and azo compound present is calculated from the loss in weight of copper metal during the reduction of the compound to the amine. Interferences are discussed in detail. No standard solutions are required and only commonly available equipment is used Accuracy is of the order of ± 0 5%     

Assay of nitro and nitroso compounds by solution thermochemistry

Some nitro and nitroso compounds have been determined by direct reduction with Ti(III) chloride without the necessity for degassing the analyte solutions. Methods have been developed for the determination of some binary mixtures by both enthalpimetry and catalytic thermometric titrimetry. The accuracy at the 0.1 mMole level is±1%, and the time taken for a single titration is less than 2 minutes.

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Zusammenfassung Einige Nitro- und Nitrosoverbindungen wurden durch direkte Reduktion mit Ti(III)-chlorid bestimmt, ohne dass die Notwendigkeit der Verdampfung der Analysenlösung besteht. Es wurden Methoden zur Bestimmung einiger binärer Gemische durch Enthalpimetrie und katalytische thermometrische entwickelt. Die Genauigkeit beträgt im Bereich von 0.1 mMol±1%, und eine Titration erfordert weniger als 2 Minuten.

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- . . 0,1 ± 1%, , 2 .

     

Bulky alkyls and amides of main group 5 elements II. Rotational barriers in phosphorus compounds containing bulky groups

The group [(CH₃)₃Si]₂CH is effectively bulkier than the (CH₃)₃C group in inhibiting rotation about the PC bond in R₂PCI compounds. In phosphonamidous chlorides, RP(CI)NR₂′, increasing the bulk of the groups at nitrogen, e.g., from CH₃ to (CH₃)₂CH to (CH₃)₃Si, increases the rotational barriers about the PN bond; however, changing R from (CH₃)₃C to [(CH₃)₃Si]₂CH increases the barrier, which is a reversal of the trend earlier observed. It is suggested that these very bulky silylated groups represent limiting cases of steric interference.     

One-pot synthesis of 7-bromo-1-[4-(1-cyano-1-methylethyl)]-phenyl-[1,2,4]-triazole-[4,3-a]-quinoxalin

[1,2,4]-Triazole-[4,3-a]-quinoxaline is an important component of many drugs. The yield of the reported methods for triazole cyclization step was usually as low as 20%. In this article, the triazole cyclization step was successfully done by using microwave method with a high yield of 75% for the first time.     

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.     

Reaction of di-t-butyliminoxy radicals with organometallic compounds

Reactions of the title iminoxy radical 1 with Grignard and organolithium reagents RM yield initially di-t-butyl ketoxime 2 (in salt form) together with the radical R-. This radical R- can combine with unreacted iminoxy radical on oxygen to give the oxime ether 3. For steric reasons attack on nitrogen is difficult and therefore nitrone 6 is not formed, or in trace amounts only. The even more hindered attack on carbon is never observed, i.e. there is no formation of (intermediary) nitroso compounds. The relatively reactive methyl and phenyl radicals can abstract hydrogen from the solvent (diethyl ether). In this way α-ethoxyethyl radicals are formed, which can combine with the iminoxy radical on oxygen, yielding the acetal-like oxime ether 7.