On the dimerization process of nitroso compounds

Summary Many organic C-nitroso compounds R-NO form stable dimers with a covalent NN bond. To gain insight into the dimerization reaction 2 R-NO (R-NO)₂ a theoretical study of the dimerization to atrans-form was performed using HNO as a model compound. Complete geometry optimizations were carried out at the HF, MP2 and QCISD levels using a 6–31G* basis. In the stationary points energies were calculated at the MP4(SDTQ) and QCISD(T) levels. For the equilibrium structure of the monomer and dimers stable RHF solutions were found, whereas for the TS UHF and UMPn calculations were applied. Extensive spin contamination was found in the UHF wavefunction, and projections up tos+4 were invoked. Relative energies were corrected for differences in ZPE. Calculations were made (a) for the least-motion path (C _2h symmetry) and (b) for a path with complete relaxation of all internal coordinates. Along the latter path a TS having virtuallyC _i symmetry was found. Along path (a) an activation energy of around 150 kcal/mol was predicted, in conformity with a symmetry forbidden reaction. On the relaxed path (b) the barrier to dimerization was estimated to be 10.7 kcal/mol at the MP4(SDTQ)//MP2 level, and 10.9 kcal/mol at the QCISD(T)//QCISD level. Unscaled ZPE corrections, calculated at the SCF level, changed these values to 12.7 and 12.9 kcal/mol, respectively. The reaction energy for the dimerization process is predicted to be – 17.2 kcal/mol at the MP4(SDTQ)//MP2 level corrected for ZPE. Calculations at the G1 level gave a corresponding value of – 16.4 kcal/mol. The equilibrium constant for the association to thetrans dimer is estimated to beK _p =259 atm, indicating that the dimer should be an observable species in the gas phase.     

Rearrangement of nitrocarbenes to acyl nitroso compounds

Acyl nitroso compounds may be trapped as eneophiles and Diels-Alder adducts under thermal and transition metal catalyst conditions using nitrodiazomethane, ethyl nitrodiazoacetate and trifluoromethylnitrodiazomethane.     

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 .

     

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.     

The ene reactions of nitroso compounds involve polarized diradical intermediates

The ene reactions of nitroso compounds were studied with B3LYP/6-31G* geometry optimizations and energy calculations, along with single point energy evaluations using CASPT2/6-31G** and UCCSD(T)/6-311+G* methods. Reactions of HNO with propene and of MeNO and p-NO2C6H4NO with propene or substituted alkenes were also studied. The reaction mechanism is stepwise and involves a polarized diradical intermediate. The electronic structure of this intermediate is between that of a closed shell polar species and that of a pure diradical, and it is stabilized by polar solvents. A weak C-N bonding interaction combined with a CH-O hydrogen bond leads to heightened barriers to rotation about formally single bonds compared to conventional diradicals. Consequently, rotation is slower than hydrogen abstraction and cyclization to form an aziridine N-oxide. This aziridine N-oxide does not lead to ene products without subsequent ring opening but provides a mechanism for the RNO moiety to translate from one end of the alkene to the other. B3LYP calculations are also able to reproduce kinetic isotope effects and regioselectivity.     

Hydrolysis of acyloxy nitroso compounds yields nitroxyl (HNO)

Nitroxyl (HNO/NO(-)), the reduced form of nitric oxide, has gained attention based on its separate chemistry and biology from nitric oxide. The inherent reactivity of HNO requires new and mechanistically unique donors for the detailed study of HNO chemistry and biology. Oxidation of cyclohexanone oxime with lead tetraacetate yields 1-nitrosocyclohexyl acetate, whereas oxidation of oximes in the presence of excess carboxylic acid gives various acyloxy nitroso compounds. These bright blue compounds exist as monomers as indicated by their infrared, proton, and carbon NMR spectra, and X-ray crystallographic analysis reveals the nitroso groups possess a "nitroxyl-like" bent configuration. Hydrolysis of these compounds produces nitrous oxide, the dimerization and dehydration product of HNO, and provides evidence for the intermediacy of HNO. Both thiols and oxidative metal complexes inhibit nitrous oxide formation. Hydrolysis of these compounds in the presence of ferric heme complexes forms ferrous nitrosyl complexes providing further evidence for the intermediacy of HNO. Kinetic analysis shows that the rate of hydrolysis depends on pH and the structure of the acyl group of the acyloxy nitroso compound. These compounds relax pre-constricted rat aortic rings similar to known HNO donors. Together, these results identify acyloxy nitroso compounds as a new class of HNO donors.     

Applications of ESCA to polymer chemistry: Studies of some nitroso rubbers

Molecular core binding energies of the polymers formed by copolymerization of CF₃NO with CF₂?CF₂, CF₂?CFCl, and CF₂?CFH, respectively, have been studied by means of ESCA. The results are interpreted in terms of CNDO/2 SCF MO calculations on some model systems. Some evidence for structural irregularity is found for the copolymers with CF₂?CFCl and with CF₂?CFH. The reaction mechanism for the polymerization is also discussed in terms of the experimental results and INDO SCF MO calculations.     

Radical addition‐coupling polymerization with various nitroso compounds

Four nitroso esters were prepared by oxidation of 4,4‐dimethyl dihydro‐1,3‐oxazine or 4,4‐dimethyl‐2‐oxazoline with two equiv of m‐chloroperoxybenzoic acid. All of them can be applied in radical addition‐coupling polymerization to produce periodic polymer together with introduction of ester group at side chain. Compared with 2‐methyl‐2‐nitrosopropane, 2‐nitroso‐2‐methyl‐4‐acetoxypentane and 2‐methyl‐2‐nitrosopropyl hexanoate present good stability at high temperature up to 70 °C and can result polymer with high molecular weight. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 810–815     

Peptide release upon photoconversion of 2-nitrobenzyl compounds into nitroso derivatives

The photoinduced conversion via the aci-nitro into the nitroso form was studied for 4,5-dimethoxy-2-nitrobenzyl alcohols attached to various leaving groups: amino acids histidine (NHis) and aspartate (NAsp) as well as their fluorenylmethoxycarbonyl derivatives (FHis) and (FAsp). In addition, two peptides containing either of the two amino acids were studied, carrying the photoreactive group attached to a histidine (PHis), or to an aspartate (PAsp). The aci-nitro forms with maximum at λ(aci) = 420 nm were observed for FHis and FAsp after the decay of a triplet-triplet absorption, analogous to those of other 2-nitrobenzyl type compounds. For both FHis and FAsp the quantum yield of photoconversion Φ(p) is 0.03 and for the peptides PHis and PAsp ca 0.01 and 0.005, respectively.     

Photolysis of nitroso compounds—III: 2-Nitro-2-nitrosopropane

The photodecomposition of 2-nitro-2-nitrosopropane (2-propylpseudonitrole) with light of λ > 540 nm was studied. The product distribution changes drastically with the nature of the solvent but can be explained readily by homolytic cleavage of the CNO bond. No evidence of photoreduction by an excited state of the nitrosocompound was obtained.In aprotic solvents the major products were acetone, 2,2-dinitropropane, 2-nitropropene, nitrogen dioxide, nitric oxide and nitrogen. In methanol methyl nitrite, acetoxime, acetone dimethylketal and acetone together with dinitrogen monoxide and water were the main products. This pronounced solvent influence is shown to be caused by the solvolysis (in methanol) or secondary thermal decomposition (in aprotic solvents) of labile intermediates.The 2-nitropropyl radical formed in the primary dissociative step does not take part in any hydrogen abstraction reactions under the experimental conditions employed.     

Synthesis of N′-methoxydiazene N-oxides from methoxyamine and nitroso compounds

The reaction of methoxyamine with nitroso compounds in the presence of oxidizing agents is rather general in nature and may serve as a convenient method for the synthesis of aliphatic, aromatic, and heterocyclic N-alkoxydiazene N-oxides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2155–2158, September, 1990.     

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%     

The pyrolysis of 2-nitrosoisobutane and the bond dissociation energies of nitroso compounds

Study of the reaction by very-low-pressure pyrolysis (VLPP) in the temperature range of 550–850°K yields for the high-pressure Arrhenius parameters where θ = 2.303RT in kcal/mole. These in turn yield for the high-pressure second-order recombination of tBu + NO, k_?1 = (3.5 ± 1.7) × 10⁹ 1./mole·sec at 600°K. For the competing reaction l./mole·sec and E₄ ≥ 4.2 kcal/mole. The bond dissociation energy DH^o (tBu-NO) was determined to be (39.5 ± 1.5) kcal/mole, both from the equilibrium constant and from the activation energy of reaction (1), obtained from RRKM calculations. A ‘free-volume’ model for the transition state for dissociation is consistent with the data. A limited study of the system at 8–200 torr showed an extremely rapid inhibition by products and a very complex set of products.