Showing papers on "Aryl radical published in 2011"

Organocatalysis and C-H activation meet radical- and electron-transfer reactions.

Abstract: A radical outlook: Recently published "organocatalytic C-H activation reactions" have now been interpreted as base-promoted homolytic substitutions. The addition of an aryl radical to an arene followed by deprotonation (see above) and electron transfer form part of the chain reaction. Although these new results are not conceptual breakthroughs, they could be experimental breakthroughs because they presage new transformations in radical (anion) chemistry. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mizoroki-heck-type reaction mediated by potassium tert-butoxide.

Abstract: The transition metal free reaction of various aryl halides with excess stilbenes (5 equiv.) proceeds through aryl radical intermediates and the iodides are found to be generally the most effective substrates.

A Mild Oxidative Aryl Radical Addition into Alkenes by Aerobic Oxidation of Arylhydrazines

Abstract: A mild and practical oxyarylation of alkenes by oxidative radical addition has been developed by using aerobic oxidation of hydrazine compounds. The use of a catalytic amount of potassium ferrocyanide trihydrate (K(4)[Fe(CN)(6)]⋅3H(2)O) and water accelerated this radical reaction to give peroxides or alcohols from simple alkenes in good yields. The environmentally friendly and economical radical reactions were achieved at room temperature in the presence of iron catalyst, oxygen gas, and water. A method involving aniline as a radical precursor is also described.

Spontaneous Grafting of Nitrophenyl Groups to Planar Glassy Carbon Substrates: Evidence for Two Mechanisms

Abstract: The covalent grafting of nitrophenyl functionalities to planar carbon substrates by reaction with 4-nitrobenezene diazonium salt at open circuit potential has been studied in aqueous acid and acetonitrile solutions. Atomic force microscopy and electrochemical measurements reveal that the reaction proceeds through two distinct mechanisms. Rapid film growth occurs via reduction of the 4-nitrobenezene diazonium cation by the substrate, giving an aryl radical that couples to the surface. Film growth by this mechanism ceases once the film has reached a thickness at which electron transfer through the passivating film is no longer possible. Slow film growth via a secondary, potential-independent mechanism continues even after the substrate-dependent reaction has ceased. We tentatively propose that slow film growth involves grafting of an aryl cation originating from thermal heterolytic decomposition of the diazonium cation.

Modern developments in aryl radical chemistry

Abstract: This review summarizes recent advances in the field of aryl radical chemistry In particular, modern developments of the well-known Meerwein, Pschorr, and Gomberg–Bachmann reactions are presented along with new applications in natural product syntheses Among the methods for the generation of aryl radicals, tin hydrides play a predominant role, but more and more attractive and promising alternatives are beginning to emerge

Facile Synthesis of 2,3-Dihydrobenzofuran-3-ylaceticAcids by Novel Electrochemical Sequential Aryl Radical Cyclization-Carboxylationof 2-Allyloxybromobenzenes Using Methyl 4-tert-Butylbenzoateas an Electron-Transfer Mediator

Abstract: Facile synthesis of 2,3-dihydrobenzofuran-3-ylacetic acids and related analogues was successfully carried out by a novel electrochemical aryl radical generation and its 5-exo cyclization followed by a carboxylation sequence of 2-allyloxybromobenzenes by using methyl 4-tert-butylbenzoate as an electron-transfer mediator.

Process for the preparation and isolation of 2-substituted tetrahydropyranols

Abstract: Process for the preparation of 2-substituted 4-hydroxy-4-methyltetrahydropyrans of the formula (I) where the radical R1 is a straight-chain or branched alkyl or alkenyl radical having 1 to 12 carbon atoms, an optionally alkyl-substituted cycloalkyl radical having in total 3 to 12 carbon atoms or an optionally alkyl- and/or alkoxy-substituted aryl radical having in total 6 to 12 carbon atoms, comprising the reaction of 3-methylbut-3-en-1-ol of the formula (II) with an aldehyde of the formula (III) R1—CHO (III), where the radical R1 has the same meaning as in formula (I) and where the reaction is carried out in the presence of water and in the presence of a strongly acidic cation exchanger, and then the isolation and/or the distillative separation is carried out in a dividing wall column or in an interconnection of (at least) two distillation columns in the form of a thermal coupling and one or more side take-off points at an absolute operating pressure of up to 500 mbar.

Grafting of thin organic films by electrooxidation of arylhydrazines

Abstract: Anodic oxidation of arylhydrazines in aqueous solution leads to formation of a chemisorbed monolayer on the electrode surface of both glassy carbon and gold. The grafting process occurs in a three-electron process, in which the arylhydrazine is oxidized to the actual grafting agent, that is, the corresponding aryl radical, via the formation of the aryldiazene as intermediate. Analysis of the modified surface by X-ray photoelectron spectroscopy and polarization modulation infrared reflection absorption spectroscopy shows conclusively that the bonding to the surface does not occur through the hydrazine group but rather through the aryl group after expulsion of nitrogen. In general, the method is found to be tolerant toward variations in the experimental conditions, but at high pH (>7), the grafting rate increases considerably and multilayers may be formed. The more efficient grafting at high pH can be attributed to an increase of the rate of the deprotonation steps in the oxidation mechanism, the result of ...

The Mechanism of the Modified Ullmann Reaction

Abstract: The copper-mediated aromatic nucleophilic substitution reactions developed by Fritz Ullmann and Irma Goldberg required stoichiometric amounts of copper and very high reaction temperatures. Recently, it was found that addition of relatively cheap ligands (diamines, aminoalcohols, diketones, diols) made these reactions truly catalytic, with catalyst amounts as low as 1 mol% or even lower. Since these catalysts are homogeneous, it has opened up the possibility to investigate the mechanism of these modified Ullmann reactions. Most authors agree that Cu(I) is the true catalyst even though Cu(0) and Cu(II) catalysts have also shown to be active. It should be noted however that Cu(I) is capable of reversible disproportionation into Cu(0) and Cu(II). In the first step, the nucleophile displaces the halide in the LnCu(I)X complex forming LnCu(I)ZR (Z = O, NR′, S). Quite a number of mechanisms have been proposed for the actual reaction of this complex with the aryl halide: 1. Oxidative addition of ArX forming a Cu(III) intermediate followed by reductive elimination; 2. Sigma bond metathesis; in this mechanism copper remains in the Cu(II) oxidation state; 3. Single electron transfer (SET) in which a radical anion of the aryl halide is formed (Cu(I)/Cu(II)); 4. Iodine atom transfer (IAT) to give the aryl radical (Cu(I)/Cu(II)); 5. π-complexation of the aryl halide with the Cu(I) complex, which is thought to enable the nucleophilic substitution reaction. Initially, the radical type mechanisms 3 and 4 where discounted based on the fact that radical clock-type experiments with ortho-allyl aryl halides failed to give the cyclised products. However, a recent DFT study by Houk, Buchwald and co-workers shows that the modified Ullmann reaction between aryl iodide and amines or primary alcohols proceeds either via an SET or an IAT mechanism. Van Koten has shown that stalled aminations can be rejuvenated by the addition of Cu(0), which serves to reduce the formed Cu(II) to Cu(I); this also corroborates a Cu(I)/Cu(II) mechanism. Thus the use of radical clock type experiments in these metal catalysed reactions is not reliable. DFT calculations from Hartwig seem to confirm a Cu(I)/Cu(III) type mechanism for the amidation (Goldberg) reaction, although not all possible mechanisms were calculated.

Organocatalysis and C—H Activation Meet Radical- and Electron-Transfer Reactions

Abstract: A radical outlook: Recently published "organocatalytic C-H activation reactions" have now been interpreted as base-promoted homolytic substitutions. The addition of an aryl radical to an arene followed by deprotonation (see above) and electron transfer form part of the chain reaction. Although these new results are not conceptual breakthroughs, they could be experimental breakthroughs because they presage new transformations in radical (anion) chemistry. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Mild Oxidative Aryl Radical Addition into Alkenes by Aerobic Oxidation of Arylhydrazines.

Abstract: An efficient oxyarylation of terminal and internal olefins by oxidative radical addition is presented.

Compounds of dibenzylidene sorbitol ester type, process of preparation, use, compositions comprising them and cosmetic treatment method

Abstract: The invention relates to novel compounds of dibenzylidene sorbitol ester type corresponding to the following formulae (I) and (II): in which: R, R′ and R″ represent a hydrogen atom or a —C(O)Y radical in which Y represents a C2-C25 hydrocarbon radical or an optionally substituted aryl radical; the R1, R2, R3, R4, R5, R′1, R′2, R′3, R′4 and R′5 radicals represent a hydrogen atom; a C1-C18 alkyl radical; a C1-C18 alkoxy radical; a phenoxy radical; an optionally substituted phenyl radical; or a benzyl radical; the divalent radical A represents, in the formula (II), a C1-C52 hydrocarbon radical; an optionally substituted arylene radical; or a silicone radical. The invention also relates to their process of preparation, to their use in structuring lipophilic media, in particular oils, to the cosmetic or pharmaceutical compositions comprising them and to a cosmetic treatment method employing them.

Radical Intramolecular Arylation of Pyridinium Salts: A Straightforward Entry to 7‐Hydroxypyrido[2,1‐a]isoquinolinylium Salts.

Abstract: The preparation of a series of compounds containing a hydroxyquinolizinium fragment fused to a benzene ring starts from the appropriate pyridinium salt, and proceeds through an aryl radical cyclization onto the pyridinium part.

Methods and apparatuses for water filtration using polyarylether membranes

Abstract: Membranes for use in methods and apparatuses for water filtration are composed of at least one polyarylethernitrile membrane having structural units of formula 1 and structural units of formula 2, 3, or a combination thereof wherein Z is independently a direct bond, O, S, CH2, SO, SO2, CO, RPO, CH2, alkenyl, alkynyl, a C1-C12 aliphatic radical, a C6-C12 cycloaliphatic radical, a C6-C12 aromatic radical or a combination thereof, and wherein R is equal to C6-C12 aryl radical; Q is a direct bond, O, S, CH2, alkenyl, alkynyl, a C1-C12 aliphatic radical, a C3-C12 cycloaliphatic radical, a C6-C12 aromatic radical or a combination thereof; R1, R2, R3 and R4 are independently H, halo, nitro, a C1-C12 aliphatic radical, a C3-C12 cycloaliphatic radical, a C6-C12 aromatic radical, or a combination thereof; a is 0, 1, 2 or 3; b, c, and d are independently 0, 1, 2, 3 or 4; and p, m and n are independently 0 or 1; and Q and Z are different.

Use of substituted methoxyhydroxyphenylalkyl derivatives as preservative and preserving method

Abstract: The present invention relates to the use as a preserving agent, in particular in a cosmetic or dermatological composition, of at least one compound of formula (I), in which R represents a hydrogen atom; or else a C1-C18 alkyl radical, or a C2-C18 alkene radical, it being possible for said radicals to be substituted by one or more OH groups; or else R represents -C(O)R' with R' representing an aryl radical or a C1-C12 alkyl radical or C2-C12 alkene radical, optionally substituted by one or more OH groups.

Process for preparation of elastomeric polymer using transition catalyst

Abstract: PURPOSE: A method for preparing an elastomeric polymer is provided to prepare an ethylene-popylene elastomeric copolymer or an ethylene-propylene-diene elastomeric copolymer of high molecular weight at a high temperature. CONSTITUTION: A method for preparing an elastomeric polymer comprises a step of polymerizing ethylene and propylene in the presence of a catalyst composition including a transition metal represented by chemical formula 1. In chemical formula 1, R1 and R2 are hydrogen, C1-20 alkyl radical, C2-20 alkenyl radical, C6-20 aryl radical, silyl radical, C7-20 alkylaryl radical, C7-20 arylalkyl radical, or Group 4 metalloid radical.

Stabilizer combination for pvc

Abstract: Stabilizer composition for halogen-containing polymers containing at least one antioxidant, at least one salt of a superacid, and at least one (un) substituted N-cyanoacetylurea of the general formula NC-CH2-CO-N (R1) -CO-N (R2), in which the radicals R1 and R2, independently of one another, are hydrogen, a branched or unbranched, linear or cyclic alkyl radical having 1 to 18 carbon atoms or an aryl radical having 5 to 18 carbon atoms, which may be substituted by one or more alkyl radicals having 1 to 6 carbon atoms can mean.

Mizoroki—Heck‐Type Reaction Mediated by Potassium tert‐Butoxide.

Abstract: The transition metal free reaction of various aryl halides with excess stilbenes (5 equiv.) proceeds through aryl radical intermediates and the iodides are found to be generally the most effective substrates.

Compounds of dibenzylidene sorbitol ester type, process of preparation, use, compositions comprising them and cosmetic treatment method

Abstract: The invention relates to novel compounds of dibenzylidene sorbitol ester type corresponding to the following formulae (I) and (II): in which: -R, R' and R" represent a hydrogen atom or a -C(O)Y radical in which Y represents a C2-C25 hydrocarbon radical or an optionally substituted aryl radical; the R1, R2, R3, R4, R5, R'1, R'2, R'3, R'4 and R'5 radicals represent a hydrogen atom; a C1-C18 alkyl radical; a C1-C18 alkoxy radical; a phenoxy radical; an optionally substituted phenyl radical; or a benzyl radical; the divalent radical A represents, in the formula (II), a C1-C52 hydrocarbon radical; an optionally substituted arylene radical; or a silicone radical. The invention also relates to their process of preparation, to their use in structuring lipophilic media, in particular oils, to the cosmetic or pharmaceutical compositions comprising them and to a cosmetic treatment method employing them.