Separation of Phenols by Capillary Electrophoresis in a Polyethyleneimine-Coated Capillary

The use of polyethyleneimine-coated capillaries for the capillary electrophoretic separation of substituted phenols has been demonstrated. Efficient separation of phenols has been achieved in the coated capillaries.     

Chromatographic Behaviour of Phenols on Aliphatic Amines Impregnated Thin Layers

Abstract

The chromatographic behaviour of 40 phenols on silica gel G plates impregnated with ethylenediamine, diethylenetriamine, triethylenetetramine and hexamine has been studied and its correlation with the equilibrium constants of the adducts formed by the interaction of phenols with ethylenediamine as an impregnant has been attempted. A suitable separation scheme for these phenols on silica gel G plates impregnated with ethylenediamine and hexamine has been worked out.     

Relationship between the electrochemical and antioxidant activities of alkyl-substituted phenols

Oxidation potentials and rate constants have been determined for reactions between alkyl-substituted phenols with various structures and the styryl peroxy radical. The overall inhibiting activity of the phenols in the thermal autooxidation of lard has been studied. The interrelation between the structure, physicochemical properties, and antioxidant activity of the phenols is discussed.     

Effect of concomitant organic compounds on the value of phenolic index

The contribution of organic compounds to the value of phenolic index has been determined. It has been found that, in the determination of the given index, other oxygen-containing aromatic compounds can be determined along with phenols and a series of toxic chlorinated phenols.     

Iron(III) Diethanolamine as a Ne Adsorbent for Chromatographic Separations of Phenols

Abstract

A new adsorbent iron(III) diethanol amine has been utilized for the chromatographic separations of phenols. R_F values of 31 phenols in ethanol and ammonia solution of four different concentrations have been studied. On the basis of difference in R_F values various analytically important qualitative separations of phenols on impregnated papers and quantitative separations on columns of iron(III) diethanolamine have been achieved.     

Determination of the substituent effect on the O-H bond dissociation enthalpies of phenolic antioxidants by the EPR radical equilibration technique

The bond dissociation enthalpies (BDE) of several phenols containing electron-withdrawing substituents in the para position have been determined by means of the EPR radical equilibration technique. It has been found that CN, NO(2), CHO, COOR, and COOH induce an increase of the BDE value of the O-H bond, thus producing a worsening of the antioxidant activity of phenols, while Cl, Ph, and CH[double bond]CHPh show an opposite effect. The contributions of these substituents for the calculation of the BDE values in polysubstituted phenols by using the group additivity rule have also been derived. It is shown that this rule provides quite reliable predictions of bond strengths, so that the method can be conveniently used to estimate new data on substituted phenols.     

Investigation into the determination of phenols extracted from automobile exhaust gases

A method is described in which phenols extracted from the condensate of automobile exhaust gases are determined directly by GLC. The quantities of various phenols found are calculated by using tridecane as an internal standard. The emission of phenols from cars running on fuels containing different concentrations of aromatics, and on leaded and lead-free fuels, has also been considered. The results show that the concentration of total phenols is dependent on the type of sample, and is strongly dependent on the concentration of aromatic hydrocarbons and of tetraethyl-lead in the fuel.     

One-pot conversion of phenols to anilines via Smiles rearrangement

A convenient one-pot synthesis of phenols to anilines using 2-chloroacetamide/K₂CO₃/DMF system catalyzed by KI via Smiles rearrangement has been described. The synthesis of extensive amino aromatic products from phenols containing electron withdrawing group, has been performed in moderate to excellent yields to demonstrate the potentiality of this method in bio-medicinal and pharmaceutical applications.     

Mechanisms of antioxidant action: Synergism between a 2-hydroxybenzophenone uv stabiliser and autosynergistic antioxidants in polypropylene

Synergism between a uv stabiliser (2-hydroxy-4-octoxybenzophenone (I)) and phenolic antioxidants has been studied during the photo-oxidation of polypropylene. It has been found that hindered phenols containing benzylic sulphur (II) are more effective synergists at the same molar concentration than conventional hindered phenols and that optimum synergism occurs at high molar ratios (I/II). The autosynergistic phenols (II) are shown to protect the uv stabiliser against the effects of hydroperoxides under photo-oxidative conditions by catalytically destroying them and scavenging radicals formed from them. The ‘uv absorber’ (I) also appears to deactivate excited species formed in the photo-decomposition of oxidation products of (II).     

New ortho-quinone methide formation: application to three-component coupling of isocyanides, aldehydes and phenols

Herein, we wish to report a new three-component formation of heterocyclic scaffolds based on a one-pot process from simple phenols. The key step of this procedure involves an ortho-quinone methide formation from Mannich adducts under alkylative conditions. The transient o-quinone methide has been trapped in situ with indole and diketone using lithium perchlorate as catalyst. The interest of this procedure has been furthermore demonstrated by a new three-component aminobenzofuran formation from phenols, aldehydes and isocyanides.     

Chromatographic behaviour of phenols on thin layers of cation and anion exchangers. II. Dowex 50-X4 and Rexyn 102.

The chromatographic characteristics of 58 phenols on Rexyn 102 and Dowex 50-X4 thin layers in both the acidic and sodium salt forms have been studied, using elution with water, water-alcohol mixtures and aqueous salt solutions at different pH values. The influence of the percentage of alcohol, the pH and the ionic strength on the chromatographic behaviour of these phenols was investigated. The validity of the relationships among the RF values, the pH of the eluent and the pKa of the phenol has been verified on Dowex 50-X4 (Na+) thin layers. It has been shown that from the RFac, RFalk and pKa values of the different phenols, it is possible to predict their behaviour over the whole pH range and therefore to select the best conditions for their chromatographic separation.     

Solid-phase extraction of phenols

Sample preparation for phenol analysis using solid-phase extraction (SPE) is reviewed. The scope of the review has been restricted to the literature dealing with the analysis of phenols as the main objective. The use, advantages and disadvantages of silica sorbents, polymeric, functionalized, carbon-based and mixed available sorbents, when applied to the separation and preconcentration of phenols, as well as the available experimental devices, are discussed. Other aspects such as phenol derivatisation prior to SPE, solid-phase microextraction, matrix effects and the storage of phenols in SPE cartridges, have been also discussed.     

Determination of phenolic compounds in waste water by solid-phase micro extraction

The solid-phase micro extraction technique (SPME) using a polyacrylate coated fibre has been examined with the aim to determine phenolic components in strong contaminated waste water. Considering the high contents and the great variety of accompanying organic material, the feasibility of SPME-GC-MS analysis has been tested. In this connection the influence of matrix components on the SPME results are discussed. EPA-604 phenols and some other phenolic components have been sampled by a polar fibre under standard conditions and in original waste water. The effects of defined concentrations of humic acids and surfactants on the recovery of phenols have been studied. The influence of other organics, e.g. hexachlorocyclohexane isomers, on the recoveries of phenols are discussed. Finally, a comparison between results of a liquid-liquid extraction and SPME describes the performance of SPME regarding the phenol analysis of strong-loaded water.     

Zinc Silicate as a New Adsorbent for Paper Chromatographic Separation of Phenols

Abstract

A new adsorbent zinc silicate has been used for the paper chromatographic separations of different phenols. R_F values have been determined and compared with those obtained on plain papers. A new term R_i has been calculated for various phenols. The dependance of R_i and R_F on various factors have also been studied and discussed.     

Kinetic evaluation of phenolase activity of tyrosinase using simplified catalytic reaction system

A very simple tyrosinase reaction system has been developed using borate anion as a trapping agent of catechols and hydroxylamine as an external reductant to evaluate the phenolase activity without the interference of catecholase activity. Reactivities of variously para-substituted phenols in this system were compared directly to those of the phenols in the model reactions, demonstrating that the enzymatic oxygenation reaction of phenols proceeds via the same mechanism as the model reaction, that is, electrophilic aromatic substitution mechanism.     

Triethylphosphate/Phosphorus Pentoxide as an Efficient Reagent for the Phosphorylation of Phenols

Abstract

A simple, efficient, and novel method has been developed for the phosphorylation of phenols. Treatment of phenols with a mixture of triethylphosphate/phosphorus pentoxide gives the corresponding phosphate derivatives in good yields. This method is easy, rapid, and offers good yields for the phosphorylation of phenols. The reaction of triethylphosphate with phosphorus pentoxide was also studied by variable-temperature ³¹P-NMR spectroscopy.     

Extraction of phenols using polyurethane membrane

The extraction of various phenols from aqueous and organic solutions using polyurethane membrane has been investigated. The effects of solution concentration, extraction time, surface area, pH, salts, and temperature on extraction were studied. The phenols are extracted as neutral species and the extraction is governed by a combined effect of intra- and intermolecular hydrogen bonding and nonspecific hydrophobic interactions. The ether-type membrane showed higher extraction capability for the phenols than the ester-type polyurethane membrane.     

An alternative approach to para-C-H arylation of phenol: palladium-catalyzed tandem γ-arylation/aromatization of 2-cyclohexen-1-one derivatives

An efficient approach to prepare para-aryl phenols has been developed by using a Pd-catalyzed tandem γ-arylation/aromatization of 2-cyclohexen-1-one derivatives with aryl bromides. This approach provides various p-aryl phenols from the phenol surrogates, 2-cyclohexen-1-one derivatives, in a single reaction step on the basis of C-H arylation.     

Formal Direct Cross‐Coupling of Phenols with Amines

The transition‐metal‐catalyzed amination of aryl halides has been the most powerful method for the formation of aryl amines over the past decades. Phenols are regarded as ideal alternatives to aryl halides as coupling partners in cross‐couplings. An efficient palladium‐catalyzed formal cross‐coupling of phenols with various amines and anilines has now been developed. A variety of substituted phenols were compatible with the standard reaction conditions. Secondary and tertiary aryl amines could thus be synthesized in moderate to excellent yields.     

Catalytic activity of anion-exchange resins modified with metal-porphine in oxidative reactions of phenols

Anion-exchange resins modified with metal-porphine (M-Pr) have been investigated to develop a solid catalyst in the oxidative reaction of phenols by O2 in air. Co-Pr, which is easily prepared and separable from the reaction mixture, has been proved to accelerate the oxidative reaction of phenols such as 3,5-di-tertbutyl-4-hydroxyanisole. The resulting main oxidative products were identified to be quinones by using the GC-MS method.