The photochemical behaviour of bis aryl-1,3 triazenes

The photolysis of bis aryl-1,3 triazenes carried out in non-aromatic solvents gives products whose structures are consistent with a cage recombination process of homolytically formed radicals and the subsequent abstraction of hydrogen from the solvent molecules by these arylamino radicals.In aromatic solvents, a free-radical chain process leads to the formation of products resulting from the homolytic substitution on the solvent.     

Diazo reactions with unsaturated compounds: VIII. Reaction of 1,3-butadiene and isoprene with aromatic and aliphatic-aromatic triazenes in the presence of sulfur(IV) oxide

1,3-Butadiene and 2-methyl-1,3-butadiene react with 1,3-diphenyltriazene, 1,3-di-p-tolyltriazene, and 1-aryl-3,3-dimethyl-1-triazenes in a sulfur(IV) oxide-saturated water-acetic acid-acetone solution containing NaCl or hydrochloric acid, and catalytic amounts of copper(I) chloride to form 1,4-arylsulfonyl-chlorination products.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 9, 2004, pp. 1495–1497.Original Russian Text Copyright © 2004 by Naidan, Smalius.For communication VII, see [1].This revised version was published online in April 2005 with a corrected cover date.     

KF-Al_2O_3催化下达米酮与查尔酮的麦克尔加成反应

5，5-二甲基-1，3-环己二酮（达米酮）、1，3-二芳基-2-丙烯-1-酮（查尔酮 ）在KF-Al_2O_3催化下，在DMF中进行麦克尔加成反应，生成产物为1，3-二芳基- 3-（5，5-二甲基-3-羟基-2-环己烯-1-酮-2-基）-1-丙酮，产率良好。     

Contrastive photoreduction pathways of benzophenones governed by regiospecific deprotonation of imidazoline radical cations and additive effects

[Reaction: see text]. In the photoreaction of benzophenones with 1,3-dimethyl-2-phenylbenzimidazoline (DMPBI), benzhydrols were major products. Addition of H2O accelerated the reaction with no change in the product distribution, while AcOH, PhOH, and metal salts such as LiClO4 and Mg(ClO4)2 were effective additives to produce benzpinacols. In contrast, benzpinacols were exclusively formed regardless of the solvent and the additive in the reactions with 2-(o-hydroxyphenyl)-1,3-dimethylbenzimidazoline (o-HPDMBI). These observations are consistent with the hypothesis that DMPBI*+ donates a proton at the C2 position to the benzophenone ketyl radicals while o-HPDMBI*+ donates a phenol proton.     

Etude en série triazénique. IV. Synthèse et réactivité d'aryl-3-(diméthyl-3,4-isoxazolyl-5)-1-triazènes et d'arylazo-4-diméthyl-3,4-isoxazolones-5

Synthesis and reactivity of 3-aryl-1-(3,4-dimethyl-5-isoxazolyl)-triazenes and 4-arylazo-3,4-dimethylisoxazol-5-ones According to the experimental conditions and the nature of the substituents on the aromatic ring, aryldiazonium salts react with 5-amino-3,4-dimethylisoxazole ( 3 ) leading to either 3-aryl-1 (3,4-dimethyl-5-isoxazolyl)-triazenes ( 1A ) or 4-arylazo-3,4-dimethylisoxazol-5-ones ( 4 ). Analyses of the products resulting from thermal decomposition of these triazenes in aromatic substrates and in DMSO and their behaviour in acidic medium show that it is essentially the arylazo form 1B which is reactive.     

Radiation Chemistry of Organic Molecules in Solid Rare Gas Matrices: 2. Selective Deprotonation of the Primary Radical Cations upon Irradiation of Oxygen-Containing Molecules in Xenon Matrices

The composition of radical products trapped after irradiation of various ethers (dimethyl ether, tetrahydrofuran, methylal, 1,3-dioxolane) or acetaldehyde in xenon matrices at 15–17 K in the presence of electron scavengers was studied by an ESR technique. It was shown that the primary radical cations give corresponding deprotonation products (carbon-centered radicals), rather than stabilize in xenon, under the given experimental conditions. The deprotonation process is characterized by extremely high selectivity; i.e., the only type of radicals resulting from deprotonation at maximum spin density position was observed in each of the cases. The possible mechanism of the reactions and the nature of their selectivity are discussed.     

The reactions of imidazol-2-ylidenes with the hydrogen atom: a theoretical study and experimental confirmation with muonium

The possible radicals resulting from hydrogen atom addition to the imidazole rings of 1,3-bis(isopropyl)-4,5-dimethylimidazol-2-ylidene (1) and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (2) have been studied by means of density functional calculations (B3LYP). The calculations included solvent effects estimated via the polarized continuum model (PCM) and an empirical treatment of vibrational averaging of hyperfine constants. Addition of a hydrogen (or muonium) atom to the carbeneic carbon of 1,3-bis(isopropyl)-4,5-dimethylimidazol-2-ylidene was found to give a radical 60.46 kJ mol(-)(1) more stable than the radical resulting from addition to the double bond. Estimation of the activation barriers for reaction at the two sites shows that addition at the carbeneic carbon is favored. The site of addition was confirmed experimentally using muonium (Mu), which can be considered a light isotope of hydrogen. Muon spin rotation and muon level-crossing spectroscopy were used to determine muon, (13)C, and (14)N hyperfine coupling constants (hfc's) for the radical products of addition to the two carbenes. Good agreement between the experimental and calculated hfc's confirms that Mu (and hence H) adds exclusively to the carbeneic carbon. The radicals that are produced have nonplanar radical centers with most of the unpaired electron spin density localized on the alpha-carbon.     

The scope and limitations of 1,3-stannyl shift-promoted intramolecular cyclizations of alpha-stannyl radicals with a formyl group

Alpha-tributylstannyl radicals can be generated from the corresponding bromides or xanthates. These radicals undergo efficient intramolecular 1,5-cyclizations with a formyl group. The resulting beta-stannyl alkoxy radicals proceed through a 1,3-stannyl shift from carbon to oxygen to afford beta-stannyloxy radicals. This novel rearrangement is most likely irreversible and serves as a driving force to promote the cyclizations. Although the cyclization rates can be accelerated when the formyl group carries alpha-dimethyl substituents, unfortunately beta-scission of the alkoxy radicals becomes competitive with the 1,3-stannyl shift. The beta-stannyloxy radicals can be employed in further cyclizations to obtain tandem cyclization products.     

Initiation mechanisms in copolymerization: Reaction of t-butoxyl radicals with co-monomers ethyl vinyl ether and methyl methacrylate

The radical trapping technique employing 1,1,3,3-tetramethyl-1,3-dihydro-1H-isoindol-2-yloxyl as a scavenger has been used to investigate the reaction of t-butoxyl radicals with mixtures of ethyl vinyl ether and methyl methacrylate. The range of identified products includes those from both addition and hydrogen abstraction with both monomers, head addition with ethyl vinyl ether, and some second monomer addition products. Relative rate constants have been obtained for various pairs of constituent reactions. t-Butoxyl radicals add to ethyl vinyl ether one to two times faster than to methyl methacrylate, depending on which monomer is in excess. The ratio is less than 1 in nonolefinic solvents and as high as 6 in t-butanol. This solvent effect is thought to be due to the radicals complexing to either methyl methacrylate or t-butanol (H-bonding), thereby increasing its electrophilic character. © 1997 John Wiley & Sons, Inc.     

Décomposition du percarbonate de O,O-t-butyle et O-isopropényle en solution dans des cyclanes

Thermolysis of O,O-t-butyl and O-isopropenyl percarbonate in cyclohexane involves free-radical acetonylation of solvent. Free radicals derived from solvent add to the percarbonate double bond and after a double β-scission reaction, cyclohexylacetone carbon dioxide and t-butoxy radicals are formed. Abstracting H atoms from the solvent, t-butoxy radicals regenerate free radicals from solvent, and the reaction becomes a chain process. Extending the study to other cycloalkanes it has been shown that the process is a general synthesis method for cycloalkylacetones. On the other hand, competitive reactions of pairs of solvents have shown that the reactivity of the substrates depends on H atom lability and on more complex phenomena like transfers between hydrocarbons and C-centered free-radicals.     

High pressure photochemistry of alkenes. 6. the caee of 1-methylcyclopentene at 184.9 and 147.0 nm

The degradaiion of the 184.9 nm photoexcited 1-methyl-1-cyclopentene molecule shows the involvement of various excited isomers. The most important fragmentation products are 1- and 2-methyl-1,3-cyclopentadiene. These products are probably the result of a one-step elimination process of a hydrogen molecule. This process has also been observed in the case of the 184.9 nm photochemistry of cyclopenten. On the other hand, the involvement of isomers, although possible, is not so obvious at 147.0 nm. Moreover, in this case, the 1- and 2-methyl-1,3-cyclopentadiene formation is the result of hydrogen atom elimination in a two-step process. Cyclopentadiene, ethylene, and various C₃ and C₄ compounds are formed as well as methyl radicals and hydrogen atoms. These products are probably formed in successive elimination reactions as this is also observed in acyclic alkenes.     

Polarographic oxidation of some 5,10-dihydrophenazine derivatives

The polarographic anode oxidation of 5-substituted dihydrophenazines in an aprotic medium and an aqueous acetone solution has one-electron or two-electron character. It was shown by means of the electronic and ESR spectra that the intermediates in the anode oxidation of dihydrophenazine and 5-methyldihydrophenazine are cation radicals and that the products of one-electron oxidation of 1,3-dinitro-5-aryl-substituted dihydrophenazines are phenazyl radicals. The final products of anode oxidation are phenazinium salts.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 548–551, April, 1976.     

Investigation of the decomposition of 1,3-diaryl-5-(3-chloro-2-quinoxalyl)-formazans by PMR and MASS spectrometry

In contrast to triarylformazans, 1,3-diaryl-5-(3-chloro-2-quinoxalyl)formazans are unstable in ordinary organic solvents. When they are heated in chloroform, they undergo acidic cleavage, which leads to the formation of 3-chloro-2-quinoxalylhydrazones of p-substituted benzaldehydes and arenediazonium cations. These compounds, as a result of a redox reaction with the participation of the solvent, are converted to 4-chloro-1-(4-Y-phenyl)-1,2,4-triazolo[4,3-a]quinoxalines, substituted benzenes, nitrogen, and hydrogen chloride. The formation of the latter transforms the entire decomposition process into an autocatalytic process. Effects of chemical polarization of the nuclei (CPN), which unambiguously indicate the intermediate formation of diazoaryl radicals during the process, are observed in the PMR spectra of the final products. Such CPN effects, which were also observed in dimethyl sulfoxide (DMSO) and glacial acetic acid, indicate a process involving the oxidative formation of annelated triazoles from -azahetarylhydrazones via a radical pathway within a solvent cage.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 413–420, March, 1985.     

Diazo reactions with unsaturated compounds: XII. Reaction of 1-(<Emphasis Type="Italic">p</Emphasis>-Carboxybenzenesulfonyl)-1,3-butadiene with aryldiazonium chlorides, 1-aryl-3,3-dimethyl-1-triazenes,and aryldiazonium tetrachlorocuprates(II)

1-(p-Carboxybenzenesulfonyl)-1,3-butadiene reacts in aqueous acetone with aryldiazonium chlorides and 1-aryl-3,3-dimethyl-1-triazenes in the presence of copper(II) chloride and with tetrachlorocuprates(II) to form 1-(p-carboxybenzenesulfonyl)-4-aryl-3-chloro-1-butenes.     

Reaction of diaryltriazenes with dimethyl acetylenedicarboxylate and PPh<Subscript>3</Subscript> as a method for synthesis of polyfunctional trisubstituted triazenes

A series of triazene derivatives with polyfunctional substituents, such as the ylide moiety and ester groups, were synthesized by the reaction of dimethyl acetylenedicarboxylate with 1,3-diaryl-1-triazenes in the presence of triphenylphosphine in ethyl acetate. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 512–514, March, 2007.     

Diazo reactions with unsaturated compounds: XI. Reactions of benzene-, p-methylbenzene-, and p-methoxybenzenesulfonyl-1,3-butadienes with arenediazonium chlorides and 1-aryl-3,3-dimethyl-1-triazenes

1-(p-Methylbenzene)-and 1-(p-methoxybenzenesulfonyl)-1,3-butadienes in aqueous acetone in the presence of copper(I) or copper(II) chlorides react with arenediazonium chlorides and 1-aryl-3,3-dimethyl-1-triazenes to form 1-(p-methylbenzene)-and 1-(p-methoxybenzenesulfonyl)-4-aryl-3-chloro-1-butenes, respectively. 1-(Benzenesulfonyl)-1,3-butadiene undergoes tarring under the same conditions.     

Mechanisms of the Photochemical Rearrangement of Diphenyl Ethers

The mechanism of the photochemical rearrangement of diphenyl ether (1a) was studied. Irradiation of 1a in ethanol gave 2-phenylphenol (2, 42%) and 4-phenylphenol (3, 11%) as rearrangement products, in addition to phenol (4, 30%) and benzene (5, 25%) as diffusion products. Cross-coupling experiments employing [(2)H(10)]1a demonstrated that the formation of 2- and 4-phenylphenol was an intramolecular process. Irradiation of 1a in benzene or in toluene gave biphenyls in good yields. The combined yields of rearrangement products (2and 3) increased with increase of solvent viscosity, with a concomitant decrease in the formation of 4. All the results can be rationalized in terms of excitation of 1a to the singlet state and dissociation to a radical pair intermediate involving phenoxy and phenyl radicals. Intramolecular recombination of these radicals gives rearrangement products, and escape followed by hydrogen abstraction from the solvent gives diffusion products. When position 4 of 1a was occupied by an electron-donating substituent (1b-e), aryloxy-phenyl bond cleavage to give the corresponding rearrangement products prevailed over phenoxy-aryl bond cleavage. The opposite was the case for substrates with an electron-withdrawing substituent at position 4 (1h,i).     

Addition of atomic hydrogen to acetylene. Chain reactions of the vinyl radical

The main reaction products resulting from the addition of atomic hydrogen to acetylene are shown to be ethylene, 1,3-butadiene, and benzene. The mechanism involves chain reactions of the vinyl and butadienyl radicals, which regenerate atomic hydrogen. Some of the rate parameters are estimated.     

Model simulation studies of complex free radical reactions: The graft copolymerization of styrene and acrylonitrile onto ethylene-propylene-isopropylidendicyclopentadiene terpolymer

A kinetic analysis without steady approximation of the graft copolymerization of styrene-acrylonitrile onto ethylene- propylene-isopropylidendicyclopentadiene terpolymer (EP-IPDCP) is described. Some of the kinetic constants were experimentally determined. The grafting process is interpreted mainly in terms of the attack on EP-IPDCP by benzoyloxy radicals; phenyl radicals play a minor negative role by enhancing the rate of homopolymerization. A major contribution to the grafting yield is made by the propagation steps in graft polymerization and by crossed termination between grafted and ungrafted chains; of minor importance are the cross terminations between ungrafted growing chains and rubber radicals. The ole played by the solvent (benzene) and by saturated and unsaturated units in the EP-IPDCP chains is analyzed. Diffusion effects caused by the poor solvent compatibility of grafted and ungrafted chains were taken into account by allowing the termination and propagation rate constants to change in a controlled way during the reaction. The trapping of EP-IPDCP units caused by the aggregation of polymer particles seems to be indispensable to explain the decreasing trend of the grafting efficiency curve. Other information of interest pertains to the distribution of initiating radicals among the various competing reactions in the process and to the data of concentrations versus reaction time for reactants, products, and free radical intermediates. The results of a sensitivity analysis and the rate constants used in the calculations are given.     

The capacity of an α-nitroalkyl radical for hydrogen abstraction

Photochemical decomposition of 2-iodo-2-nitroadamantane in several hydrogen donating solvents, gives rise to formation of α-nitroalkyl radicals. Such ambident radicals can abstract hydrogen from the solvent via oxygen, resulting in a nitronic acid which decomposes exlusively into adamantanone. Alternately the abstraction can take place via carbon to give 2-nitroadamantane. The product distribution is strongly influenced by electron-withdrawing substituents in the hydrogen donor. The oxidation products derived from the solvent have been detected. All the experiments point towards a minor stabilisation of a carbon radical by a nitro group. INDO-calculations on the nitromethyl radical are in good agreement with this lack of stabilization.