Origins of regioselectivity in radical arylation of aniline: A computational study

The radical arylation of the para‐substituted anilines under three different conditions (A: arylhydrazines as the radical precursors and MnO₂ as the oxidant in acetonitrile; B: arylhydrazine hydrochlorides as the radical precursors and O₂ as the oxidant in aqueous sodium hydroxide solution; C: arenediazonium salts as the radical precursors and TiCl₃ as the reductant in aqueous hydrochloric acid solution) has been theoretically studied and the origins of the ortho/meta regioselectivity have been explored. The arylation process is suggested to contain three steps: radical generation, radical addition, and rearomatization. Calculations show that the arylation of the neutral anilines is kinetically controlled under conditions A and B, and the regioselectivity is determined by the radical addition. As a directing group, ? NH₂ plays an important role in these cases with the assistance of Mn(OH)₂ (the reduced product of MnO₂ under condition A) and Na⁺ (condition B). As for the arylation of the protonated anilines under condition C, the regioselectivity is affected by the substituents in the para‐position of anilines. Electron‐donating groups support meta‐addition and the selectivity is decided by the radical addition. Conversely, electron‐withdrawing groups favor ortho‐addition, and in this situation the arylation process is thermodynamically controlled and the regioselectivity is determined by the radical addition and rearomatization. © 2015 Wiley Periodicals, Inc.     

A convenient synthesis of phenols

Abstract

Anilines are rapidly, often within 60?minutes, converted into the corresponding phenols in up to 87% isolated yield. The presented experimentally simple protocol display broad compatibility with a variety of functional groups, and in particular, well suited for the preparation of methyl-substituted phenols. Such phenols are not easily available by other synthetic approaches. The formation of phenolic radical coupling products was not observed even for activated anilines using this open flask method.     

苯酚和苯胺类化合物对鲁米诺电致化学发光的增强和抑制作用

系统研究了不同pH下的NaHCO₃-Na₂CO₃和NaOH缓冲介质中, 36种苯酚和苯胺类化合物对鲁米诺电致化学发光(Electrochemiluminescence, ECL)体系的影响. 发现苯酚和苯胺类化合物的抑制和增强作用与化合物的结构、氧化电位和介质的pH有直接的关系: 具有较高氧化电位的苯酚和苯胺类化合物对鲁米诺的ECL没有影响; 而具有较低的氧化电位、苯环上有两个处于对位的-OH(或-NH₂)或苯环上有多个相邻的-OH的化合物, 在较低的pH下有增强作用, 在较高的pH下具有抑制作用; 其它的化合物则呈现抑制作用, 抑制作用的大小与化合物的结构有关. 通过研究化合物的氧化半峰电位、ECL光谱、荧光光谱等, 提出了增强和抑制作用的可能机理: 各种有机物的电氧化产物如醌、酮及具有醌、酮结构的聚合物等能够淬灭激发态3-氨基邻苯二甲酸根阴离子(3-AP^2－*)的发射, 导致了鲁米诺的ECL的降低; 同时, 反应过程中生成的半醌自由基中间体或 会促进鲁米诺的发光反应, 呈现增强作用.     

Inhibition of Ru Complex Electrochemiluminescence by Phenols and Anilines

The effect of 30 phenols and anilines on typical Ru complex electrochemiluminescence (ECL) was systematically investigated under different conditions. It was found that all the tested compounds showed an ECL inhibiting signal. The magnitude of ECL inhibition was related to the position of the substituting group in the benzene ring and decreased in the following order: meta‐>ortho‐>para‐. The oxidation potential of the tested compounds, the ECL spectra and UV‐visible absorption spectra of Ru(bpy) /tripropylamine (TPrA) in the presence of phenols and anilines, and the direct ECL between Ru(bpy) and phenols/aniline were studied. The mechanism of ECL inhibition has been proposed due to energy transfer from the excited state Ru(bpy) to a quinone or ketone or their polymer formed by electro‐oxidation of phenols and anilines. The potential of analytical application was explored by use of the inhibited ECL. The results demonstrate that numerous compounds are detectable with the detection limits in the range of 10^?8–10^?9 mol/L for Ru(bpy) /TPrA system and in the range of 10^?6–10^?7 mol/L for Ru(bpy) /C₂O system, respectively.     

Effect of Type and Concentration of Organic Modifier in Aqueous Eluents on Retention in Reversed Phase Systems

Abstract

Retention - eluent composition relationships were determined for 18 compounds (phenols, quinoline bases, anilines) in chromatographic systems of water + organic modifier - oleyl alcohol (fixed on cellulose). Six organic modifiers were investigated: methanol, acetone, acetonitrile, 1,4-dioxane, dimethyl sulphoxide, acetic acid. Different eluotropic series were obtained depending upon the donor-acceptor properties of the solutes; for instance, dimethyl sulphoxide exhibited high eluent strength relative to phenols and anilines and acetic acid - to quinolines and anilines.     

不同加成数C60精氨酸衍生物的合成及其清除活性氧自由基的性能

通过控制反应配比, 首次合成了三种具有不同加成数目的水溶性C₆₀精氨酸衍生物, C₆₀[HNC(NH)NH(CH₂)₃CH(NH₂)COOH]_nH_n (n＝2, 6, 8). 采用FT-IR, UV, RF, ¹H NMR, ¹³C NMR, LC-MS, EA, 粒径分析, 透射电镜等手段对其结构进行了表征. 同时采用化学发光法考察了三种具有不同加成数目的C₆₀精氨酸衍生物对活性氧自由基(超氧阴离子O₂^－.及羟自由基•OH)清除能力, 结果表明, C₆₀精氨酸衍生物对活性氧自由基具有优良的清除能力, 且清除能力与加成基团供电效应、空间位阻及C₆₀精氨酸衍生物在水中的聚集形态等因素密切相关.     

Synthesis, crystal structure, and conducting properties of a new molecular conductor (DBTTF)11(TeCl6)4

The structure and conducting properties of a new radical cation salt of dibenzotetrathiafulvalene (DBTTF),viz., (DBTTF)₁₁(TeCl₆)₄ (1), were studied. According to the X-ray diffraction data, the crystal of1 contains six crystallographically independent DBTTF radical cations alternating with stacks of the (TeCl₆)²⁻ anions. At room temperature, the conductivity of the crystals is 15 S cm⁻¹ and it changes exponentially as the temperature decreases. It was found that an increase in the size of the anion in compounds of type1 results in the appearance of interactions between the stacks and in an enhancement of the two-dimensional character of the conductivity. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 370–372, February, 2000.     

Irradiation treatment of azo dye containing wastewater: An overview

The radiation-induced decolouration and degradation of aqueous solutions of azo dyes and their model compounds (anilines, phenols, triazines) are reviewed together with practical applications and the experimental methods (pulse radiolysis, steady-state gamma radiolysis, as well as end-product analysis) used for studying the reactions. The proposed mechanisms and the rate coefficients for the reactions of OH, e_aq⁻ and H water radiolysis intermediates with the dye molecules and with model compounds are summarized.     

Proximity and the heteroatom effects on the carbon-13 chemical shifts of methyl-substituted phenols,anilines and thiophenols

Upfield substituent-induced ¹³C chemical shifts for aryl carbons of polymethyl substituted benzenes, phenols, anilines and thiophenols were investigated as a function of the proximity between substituents X and CH₃ (X = CH₃, NH₂, OH and SH). The results indicate that the induced shifts of the substituted aryl carbons are, in general, independent of the polar substituent but depend on the number of adjacent substituted aryl carbons. A ?2.0 ppm upfield shift was found for a substituted aryl carbon adjacent to one substituted aryl carbon and a ?3.8 ppm upfield shift for a substituted aryl carbon bound by two substituted aryl carbons. It is suggested that the near additivity of the upfield shifts is the result of changes in the bond order between the aromatic ring carbons in the region of the substituted aryl carbons due to distortion of the ring. The ¹³C chemical shifts of the methyl substituents for methyl substituted phenols, anilines and thiophenols were determined, and it was found that the values could be predicted from the additivity parameters reported for the analogous methylbenzenes plus an additional pair-interaction term associated with the through-space electronic influence of the heteroatom.     

Iron catalyzed demethylation of acetic acid*

Abstract

The iron(IV)-oxo catalyzed cleavage of acetic acid is reported. Iron(II) complexes are used as catalyst precursors and H₂O₂ as oxidant in reactions in aqueous solution with an excess of chloride and, in some experiments, with ascorbic acid added as an OH^. radical scavenger. It is shown that the acetic acid is cleaved into CO₂ and a methyl radical. In the presence of O₂ and OH^. radicals, the initially generated methyl radicals produce methanol and formate. Halogenated alkanes are also formed and, in the absence of O₂ and OH^. radicals, methane is obtained as the major product. A mechanism for the formation of various environmentally important volatile C₁ compounds is deduced from the present results and published studies, and its relevance as an additional source for these compounds in the atmosphere is discussed.     

A Novel QSAR Approach for Estimating Toxicity of Phenols

Abstract

Toxicity values (log IGC^?1 ₅₀) for 60 phenols tested in the 2-d static population growth inhibition assay with the ciliate Tetrahymena pyriformis were tabulated. Each chemical was selected so the series formed uniform coverage of the hydrophobicity/ionization surface. A high quality hydrophobicity-dependent (log K _ow) structure-toxicity relationship (log IGC^?1 ₅₀ = 0.741 (log K_ow) ?1.433; n = 17; r² = 0.970; s = 0.134; F = 486.55; Pr > F = 0.0001) was developed for phenols with pK_a values > 9.8. Similarly, separate hydrophobicity-dependent relationships were developed for phenols with pK_a values of 4.0, 5.1, 6.3, 7.5, and 8.7. Comparisons of intercepts and slopes, respectively, revealed phenols with pK_a values of 6.3 to be the most toxic and the least influenced by hydrophobicity. These relationships were reversed for the more acidic and basic phenols. Plots of toxicity versus pK_a for nitro-substituted phenols and phenols with log K_ow values of either 1.75 or 2.50 further demonstrated bilinearity between toxicity and ionization. In an effort to more accurately model the relationship between toxicity and ionization, the absolute value function |6.3-pK_a| was used to model ionization affects for derivatives with pK_a values between 0 and 9.8. For derivatives with pK_a value > 9.8, a value of 3.50 was used to quantitate ionization effects. The use of log K_ow in conjunction with this modified pK_a (ΔpK_a) resulted in the structure-toxicity relationship (log IGC^?1 ₅₀ = 0.567 (log K_ow)-0.226 (ΔpK_a-0.079; n = 54; r² = 0.926; s = 0.215; F = 321.06; Pr > F = 0.0001). Derivatives with a nitro group in the 4-position typically did not model well with the above equation.     

Four tri-spin lanthanide–nitronyl nitroxide (LnIII = GdIII,DyIII, ErIII,and HoIII) complexes: syntheses,structures, and magnetic properties

Four radical–Ln(III)–radical complexes, [Ln(hfac)₃(NITPhSCH₃)₂] (Ln?=?Gd (1), Dy (2), Er (3), Ho (4); hfac?=?hexafluoroacetylacetonate; NITPhSCH₃?=?4′-thiomethylphenyl-4,4,5,5tetramethyl-imidazoline-1-oxyl-3-oxide), have been synthesized, and structurally and magnetically characterized. The X-ray crystal structures show that the structures of the four complexes are similar, consisting of isolated molecules in which Ln(III) ions are coordinated by six oxygen atoms from three hfac and two oxygen atoms from nitronyl radicals. The temperature dependencies of magnetic susceptibilities for the four complexes show that in the Gd(III) complex, ferromagnetic interactions between Gd(III)–radical and antiferromagnetic interactions between the radicals coexist with J _Rad–Gd?=?1.09?cm^?1, J _Rad–Rad?=??1.85?cm^?1.     

Modular Synthesis of Triarylamines and Poly(triarylamine)s through a Radical Mechanism

A modular protocol for the triarylamine synthesis has been developed using diarylamines and electron-rich arenes, such as phenols, as the building blocks. The KI/KIO₄ system proves to be highly efficient for the cross-dehydrogenative coupling of phenothiazines/phenoxazines with phenols/anilines. A wide range of functional groups attached to both coupling partners were well tolerated. Through the manipulation of reaction temperatures, the sequential assembly of bis-triarylamines could be achieved to provide the unsymmetrically bis-aminated phenols efficiently. Furthermore, the multiple aminated polyphenols were rapidly constructed in good to high yields by a single operation.     

Highly efficient copper/palladium-catalyzed tandem Ullman reaction/arylation of azoles via C-H activation: synthesis of benzofuranyl and indolyl azoles from 2-(gem-dibromovinyl)phenols(anilines) with azoles

In this paper, a novel and highly efficient copper/palladium-catalyzed tandem intramolecular Ullman-type C-O(N) coupling reaction of 2-(gem-dibromovinyl)phenols(anilines) followed by an intermolecular arylation of azoles through C-H activation has been developed. In the presence of CuBr with Pd(PPh₃)₂Cl₂ used as co-catalyst, and LiO^tBu as a base, the one-pot reactions of 2-(gem-dibromovinyl)phenols and 2-(gem-dibromovinyl)anilines with a variety of azoles, including oxazoles, imidazoles, thiazoles, and oxadiazoles underwent smoothly in toluene at 100 °C to generate the corresponding biheteroaryl products in high yields. A tentative mechanism of copper/palladium-catalyzed tandem reaction was described.     

ESR study of free radicals formed upon UV irradiation of nitropentafluoroacetone in various solvents

The formation of CF₃C(O)CF₂N(O^.)O₂CF₂C(O)CF₃ free radicals upon the UV irradiation of nitropentafluoroacetone (1) in toluene and mesitylene is established by ESR. The most likely cause of their formation is the one-electron oxidation of the solvents by photoexcited1 followed by decay of the radical anion formed from1 with the expulsion of an NO₂ anion and attachment of the radical to a molecule of original1. The irradiation of 1 in triethylsilane results in the elimination of a fluoride ion and fixation of a CF₃COCFN(O^–)O' radical. UV irradiation of ketone1 in pentane results in the abstraction of a hydrogen atom from the solvent and the formation of a CF₃COCF₂N(OH)O ' radical.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 512–514, March, 1993.     

Quantitative Relationships of Structure-Activity and Volume Fraction For Selected Nonpolar and Polar Narcotic Chemicals

Abstract

The relative toxicity of selected industrial organic chemicals was secured from the literature for the static 48-h Tetrahymena pyriformis 50% population growth impairment and the flow-through 96-h Pimephales promelas 50% mortality endpoints. Chemicals were selected to represent the nonpolar narcosis (aliphatic alcohols and aliphatic ketones) and polar narcosis (anilines and phenols) mechanisms of toxic action. molar volume (MV) and 1-octanol/water partition coefficient (log K _ow) data were generated for each chemical. High-quality, log K _ow dependent quantitative structure-activity relationships were observed for each chemical class and mechanism of action for both endpoints. The volume fraction (V _t) for each chemical in the target phase was determined from the toxicant concentration in the water (toxicity data), the MV, and the target/water partition coefficient (K _tw) with K _tw considered equal to K _ow ^(1-a). Analyses of target sites, by way of “a” revealed that “a” was constant for a mechanism of action regardless of chemical class, but distinct for a given test system. Mean V _t was constant for each mechanism of action regardless of chemical class or test system. These results suggest, at least for reversible physical mechanisms, that volume fraction analyses are significant in determining the mechanism of toxic action of a chemical.     

IR spectroscopic study of allylperoxy radical and products of its phototransformations in the Ar matrix

Matrix IR spectra of an allylperoxy radical (1) obtained by co-condensation of allyl radicals and molecular oxygen into an argon matrix at 12 K have been studied. The bands observed in the matrix IR spectrum are assigned to normal vibrations on the basis of ab initio calculations of radical1 and its isotope-substituted analog CA 18_{O 2} (1a). The band at I128.6 cm^–1 is assigned to the stretching vibration of the 0-0 bond. The products of photodecomposition of radical1 under UV irradiation ( > 248 nm) have been studied. A vinylacyl radical (2) with a characteristic high vibrational v(C=0) frequency of 1823.I cm -1 has been observed among the products of photolysis of1. According to the data of quantum chemical calculations, some delocalization of a free electron between an oxygen atom and two C atoms is observed in radical 2.Preliminary results were presented at the XII International Conference on Physical Organic Chemistry (Padova, Italy) in 1994.¹⁵ Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. I, pp. 109–116, January, I996.     

Effect of Solvent on the Radical Copolymerizability of Styrene with 3(2-Methyl)-6-methylpyridazinone

Abstract

The radical copolymerization of styrene (St, M₁) with 3(2-methyl)-6-methylpyridazinone (I, M₂) has been carried out in several p-substltuted phenols at 60 and 70°C. Monomer reactivity ratios (r₁) and activation parameters of copolymerization were found to be affected by phenols. The values of the activation energy (δδE?) and entropy (δδS?) increased with the increase of the interaction of I with the solvents. Linear relationships were observed between the [sgrave]-values of p-substituents of phenols and the values of log 1/r₁ and also of δδE? and δδS?. The radical copolymerization of St (M₁) with 6-substituted 3(2-methyl)-pyridazinone was also carried out.     

Reaction of the carbonate radical with substituted anilines

Rate constants for the reaction of carbonate radical with aniline and some parasubstituted anilines have been determined by the flash photolysis technique. Using σ⁺ para values the rate constants at pH 8.5 correlate very well with the Hammett equation yielding ρ= − 1. The carbonate radical oxidises aniline giving the anilino radical. The products so formed have been identified through studies under conditions of continuous irradiation.