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101.
Juan Llor 《Journal of solution chemistry》2001,30(7):641-655
An extensive collection of data has been used to study the effects of solvent, structure, and temperature on the ionization equilibrium constants of some substituted phenols and pyridinium ions in water–1,4-dioxane mixtures (0–70% weight fraction in dioxane) and temperatures ranging from 10 to 50°C. The effects of structure and solvent are explained using Hammett's equation and the Marshall–Quist model at all temperatures. An equation allowing an analysis of the three effects together on the pK values has been developed. The pK data under all experimental conditions fit this equation well, with standard errors of less than 0.3 pH units. Hammett's reaction constant for the ionization of phenols and pyridinium ions has been obtained for all the experimental conditions. The pK and Hammett's reaction constants for the different ionizations in water–1,4-dioxane mixtures correlate well with Kamlet and Taft's solvatochromic parameters * and , which measure the dipolarity/polarizability and hydrogen-bonding capacity of the solvent, respectively. These correlations explain more thoroughly the different contributions and origin of the effects of the solvent on the pK. 相似文献
102.
Polysubstituted phenol derivatives were synthesized regioselectively starting from the Baylis-Hillman adducts via the formal [4+2] annulation protocol as the key step. 相似文献
103.
104.
Lead(IV) oxide-graphite composite electrodes: application to sensing of ammonia, nitrite and phenols
Carbon powder modified with lead(IV) oxide was synthesised by a wet impregnation procedure from concentrated lead(II) nitrate solution. The impregnated powder was subsequently thermally treated at 823 K. Electrochemical and spectroscopic characterisation of the modified powder showed that lead(IV) oxide has been formed during the procedure. A novel composite lead(IV) oxide modified carbon powder epoxy electrode was developed for electrocatalytic sensing of gaseous, inorganic and organic analytes. The behaviour and analytical advantages of the composite electrode are evaluated with respect to determination of ammonia, nitrite ions and several different phenols. It has been demonstrated that the composite electrode can be used to analyze these analytes in standard aqueous solutions with competitively low limits of detection. 相似文献
105.
106.
m- or p-Iodinated, or brominated ω-phenoxyalcohols and phenols as well as halogenated indoles were subjected to halogen-magnesium exchange reactions with isopropyl magnesium bromide (iPrMgBr) or isopropyl magnesium di-n-butyl lithium ate complexes (iPrMgnBu2Li) at −78 °C to room temperature. iPrMgnBu2Li proved superior to prevent ortho-metallation of these substituted arenes. 相似文献
107.
Padilla-Sánchez JA Plaza-Bolaños P Romero-González R Barco-Bonilla N Martínez-Vidal JL Garrido-Frenich A 《Talanta》2011,85(5):2397-2404
An analytical methodology has been developed for the simultaneous extraction of 13 phenolic compounds, including chlorophenols (CPs), nitrophenols (NTPs), cresols and alkylphenols (APs) in different types of wastewater (WW) effluents. A solid-phase extraction (SPE) method has been optimized prior to the determination by gas chromatography coupled to triple quadrupole tandem mass spectrometry (GC-QqQ-MS/MS). Due to the complexity of the matrix, a comparison study of matrix-matched-calibration (MMC) and standard addition calibration (SAC) was carried out for quantification purposes. The optimized procedure was validated using the SAC approach since it provided the most adequate quantification results (in terms of recovery and precision values). Recoveries were in the range 60-135% (0.5 μg L−1), 70-115% (1 μg L−1), and 78-120% (5 μg L−1), with precision values (expressed as relative standard deviation, RSD) ≤30% (except for 2-nitrophenol) involving intra-day and inter-day precision studies. Limits of detection (LODs) and quantification (LOQs) were also evaluated, and LOQs ranged from 0.03 μg L−1 to 2.5 μg L−1. The proposed method was applied to the analysis of 8 real WW effluent samples, finding some phenolic compounds (e.g. 2-chlorophenol, 2,4,6-trichlorophenol and 4-tert-octylphenol) at concentrations higher than the established LOQs. 相似文献
108.
Farhad Shirini Katayoun Marjani Hossein Taherpour Nahzomi Mohammad Ali Zolfigol 《中国化学快报》2007,18(8):909-911
Silica triflate,as a new silica-based reagent,can be used for the efficient synthesis of 4-substituted coumarins via a Pechmann reaction under solvent-free reaction conditions.All reactions were performed at 80℃in good to high yields. 相似文献
109.
Various phenols, methoxy aromatic compounds, 3- and 4-hydroxycoumarins and enols smoothly condense with 2-hydroxy-2,2′-biindan-1,1′,3,3′-tetrone 1 in an acid medium producing 2-aryl/alkyl-2,2′-biindan-1,1′,3,3′-tetrones in high yields. The adducts of resorcinol, 1,3,5-trihydroxybenzene and α- and β-naphthols of 1 preferably remain in the intramolecular hemi-ketal form, confirmed by X-ray diffraction studies. On the other hand para and meta substituted phenols condense with 1 in an acid medium to produce 6 or 7 substituted 2′,4-spiro(1′,3′-indanedion)-indeno[3,2-b]chromenes in good yields. 相似文献
110.
《Electroanalysis》2005,17(7):589-598
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. 相似文献