Reactions of polyhydric phenols with nitrogen-containing acetals in the synthesis of polyphenols and heterocyclic compounds

The review systematizes and summarizes the data on the reactions of nitrogen-containing acetals with phenols. Both intra- and intermolecular reactions leading to acyclic, macrocyclic, and heterocyclic compounds are considered.     

Prediction of the separation of phenols by capillary zone electrophoresis

The effect of pH and ionic strength on the migration of neutral acids in capillary zone electrophoresis (CZE) has been studied for several phenols. The mobilities of the phenols and the efficiency of the capillary have been related to the studied factors. The mobility can be related to the pH of the running buffer through the mobility of the phenolate ion, and the conditional acidity pK value of the phenol at the working ionic strength. This allows prediction of the migration of the phenol, solely from its pK_a^′ value (literature pK_a corrected for the ionic strength of the solution) and mobility of the anion, which can be easily calculated from the mobility at a basic pH value and the pK_a^′ value. Combination of the predicted mobility with the efficiency allows estimation of the resolution of the consecutive peaks obtained for a mixture of phenols. This method has been tested for two groups of phenols of environmental interest.     

Prediction of retention time of phenols in liquid chromatography

The chromatographic behavior of phenols in reversed-phase mode liquid chromatography differs from that of non-ionic compounds such as alkyl alcohols, alkylbenzenes, halogenated benzenes, polyaromatic hydrocarbons, and aromatic acids. Therefore, the retention times of 61 phenols were measured in a system of an octadecyl bonded silica gel and acetonitrile/water mixtures. The logarithm of the capacity ratio (log k') was found to be a linear function of the hydrophobicity (log P) in acidic acetonitrile/water mixtures. This result was applied to a different octadecyl bonded silica gel. Eight phenols were selected as standard compounds, and their log k' values were measured in 0.05 M phosphoric acid in 10 to 90% acetonitrile/water mixtures. An empirical polynomial relation was obtained between the concentration of acetonitrile and the slope of the log k' vs log P curve. Finally the capacity ratio of all phenols were calculated in given eluents by the equations derived from the measurements of standard compounds and the calculated log P values. The difference between predicted capacity ratios and measured ones was within 10%.     

Mechanisms of antioxidant action: Auto-synergistic behaviour of sulphur-containing phenols

The powerful antioxidant activity of 3,5-di-tert-butyl-4-hydroxybenzyl sulphides has been shown to be due to the generation of a Lewis acid catalyst which may destroy > 3 × 10⁵ moles of hydroperoxide per mole of sulphur compound. The same catalytic species formed from a variety of benzylic sulphides and is believed to be an inorganic sulphur acid (probably S0₃). Dibenzyl monosulphide itself is not initially an antioxidant and one function of the hindered phenolic group in the auto-synergists is believed to be the removal of free radicals formed during the early stages of the reaction.     

Prediction of the behaviour of a single flow-injection manifold

This paper suggests a handy method of obtaining equations to predict the fundamental parameters of an FIA peak--travel time, baseline-to-baseline time, peak height and appearance time of the maximum for a simple configuration--by performing a small number of preliminary experiments in the region in which FIA system usually operates.     

Mechanisms of antioxidant action: Effect of processing on the behaviour of hindered phenols in polypropylene

It is shown that in the case of two hindered phenol antioxidants (I R = H and II) products are formed which are considerably more effective than the phenols themselves. Both dimeric products and polymer-bound antioxidants contribute to this effect but the former is considered to be more important under the conditions examined.     

Prediction of the behaviour of organic pollutants using cloud point extraction

A preconcentration study based on the cloud point phenomenon was carried out for a set of triazine herbicides, three of them chloro-substituted and three of them methylthio-substituted. Concentration factors and recoveries were calculated as function of the percentage of the non-ionic surfactant Triton X-114 employed. From these values, obtained from a cloud point extraction (CPE) procedure, the distribution coefficient between the Triton X-114 micelles and water, Kc, prior to CPE was calculated for each triazine and related to the corresponding octanol-water partition coefficient, Kow. In order to confirm the results obtained with the triazine herbicides, two sets of data from chemically different organic pollutants--organophosporous and chlorophenols--obtained from the literature were assessed, concluding that they display a similar behaviour to that of the triazine herbicides. This can be used to predict the CPE behaviour of other organic pollutants from their octanol-water partition coefficients. The Kc values were compared with the analyte concentration ratio in the surfactant-rich phase and aqueous phase (Ksa) with a view to obtaining a link between the analyte behaviour prior to and after cloud point extraction procedures.     

Prediction of the isothermal behaviour of solid-gas systems from non-isothermal data

A new procedure for the prediction of the isothermal behaviour of the solid-gas system from non-isothermal data is suggested. It bypasses the use of various approximations of the temperature integral that ground the integral methods of prediction. The procedure was checked for: (1) simulated data corresponding to a first order reaction; (2) experimental data obtained in the isothermal and non-isothermal decompositions of ammonium perchlorate. For the simulated data, a very good agreement between calculated isotherms and those evaluated by means of the suggested procedure was obtained. A satisfactory agreement (errors in time evaluation corresponding to a given degradation lower than 18%, for 0.10￡a￡0.37 and lower than 10% for 0.37￡a￡0.70) was obtained for the experimental data corresponding to the decomposition of ammonium perchlorate. In this last case, the mentioned differences between experimental and calculated data can be due both to the inherent errors in the evaluation of the decomposition isotherms and to the dependence of the activation energy on the conversion degree. This revised version was published online in July 2006 with corrections to the Cover Date.     

Prediction of the chromatographic behaviour for a series of diuretic compounds

Summary The proportion of organic modifier and the pH of the acetonitrile-water mixtures used as mobile phases were optimized in order to separate a group of diuretic compounds covering a wide range of physyco-chemical properties. The Linear Solvation Energy Relationship (LSER) formalism based either on the multiparameter π^*, β and α scales or the single solvent polarity parameterE _T ^N , have been used to predict their chromatographic behaviour as a function of the percentage of acetonitrile in the eluent. Moreover, correlation established between retention and pH of the aqueous-organic mobile phases have been used to predict the chromatographic behaviour of the diuretic compounds studied as a function of the eluent pH. Linear correlation between a function of the eluent pH. Linear correlation between the chromatographic retention and theE _T ^N polarity parameter of mobile phases containing different percentages of organic modifier has been obtained Based on the knowledge of the acid-base dissociation constant the relation between retention and mobile phase pH has also been linearized. These relationship allowed an important reduction of the experimental retention data needed for developing a given separation and a great improvement in chromatographic optimization schemes.     

Prediction of polyurethane behaviour via time-temperature superposition: Meanings and limitations

Two main issues are essential nowadays for practitioners in the field of polymeric materials: how a polymer will behave under dynamic loading conditions and for how long a polymer is reliable. In this sense, the time-temperature superposition principle was applied to the main viscoelastic properties (E′, E″ and tan δ) of a series of polyurethane coatings (PU-DEG-TMP) tested for mechatronic devices. Polyurethanes are derived from an ester glycol (poly(ethylene adipate) glycol), an aromatic diisocyanate (4,4′-dibenzyldiisocyanate) and di/trifunctional chain extenders - diethylene glycol (DEG) and trimethylol propane (TMP). Despite polyurethane intrinsic rheologic complexity, the moduli/loss factor curves superimpose well over several decades of reduced frequency at the glass transition temperature (T_g), 0 °C and 15 °C, the last temperature being considered the midpoint of the practical testing range. Three criteria were for checking the applicability of the time-temperature superposition: the Cole-Cole plot, the similarity between the a_T calculated from both moduli (E′, E″) and the visual appearance of the final master curve. The presence of both hydrogen bonding and chemical joint points, along with some dangling chains put in a broader context the discussion of the microstructural features resulted from the application of the William-Landell-Ferry (WLF) equation.     

Mechanism for the chemiluminescent photooxidation of phthalhydrazides

Conclusions The rate constants were determined for the oxidation of phthalhydrazides sensitized by methylene blue, and a mechanism was proposed. The key role of the Superoxide ion in the generation of chemiluminescence was confirmed. The reaction of the methylene blue radical by oxygen was shown to be the major channel for the generation of the superoxide ion.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2811–2814, December, 1985.The authors thank L. S. Ter-Vartanyan for providing samples of SOD and A. S. Tatikolova, V. I. Sklyarenko, L. A. Shvedova, and S. R. Marulidi for helpful advice and discussions of this work.     

Prediction of the swelling behaviour of amphiphilic hydrogels and the determination of average molecular weight between cross-links

Prediction of swelling behaviour of hydrogels containing cationic and anionic moieties, sensitive to pH and ionic strength changes of the swelling medium was investigated. The equations derived for the prediction of the theoretical swelling curves are based on the phantom network theory and the approaches of Peppas et al. For all predictions, a number of polymer based parameters, solution property parameters and polymer–solvent combination type parameters were evaluated typical of amphiphilic copolymers. The advantages of the derived equations for the determinations of average molecular weight between the cross-links, and also polymer–solvent interaction parameter have been exemplified.     

Prediction of phase separation behaviour from thermodynamic measurements in the one phase region

When a polymer blend is heated to within the unstable region of the temperature - composition diagram spinodal decomposition may be observed using small angle neutron scattering. In the one phase region scattering has been used to obtain the temperature and composition dependence of the second derivative with respect to composition of the Gibbs free energy of mixing. Correlation of these two types of measurement not only tests the current theories of spinodal decomposition, but provides insight into the molecular parameters controlling domain morphology in phase separation blends.     

Nonamethylene-bridged phenols and tropones

Novel phenols (4 and 6) having the OH group surrounded by nonamethylene chain were prepared from cyclododecanone. 2,7-Nonamethylene bridged tropone (11) was obtained by stepwise bromination-dehydrobromination of bicyclo[9.4.1]hexadecan-16-one (7). The aliphatic chain of these phanes has been proved to reside on the one side of the respective aromatic ring. Spectroscopic studies indicate that the phenol 6 belongs to “intermediately hindered” phenol. The reactivity of the hindered OH group and of the strained benzene ring was examined with respect to 6, which is susceptible to methylation and acetylation but not to isopropylation. 12-Methyl[9]metacyclophane (15) was obtained by mesylation of 6, followed by the reduction of the resulting sulfonate. The constraint caused in the conjugate base of 6 by the nonamethylene bridge possibly is responsible for the selectivity in the dichlorocarbene addition giving 16 exclusively. Reaction of 6 with monochlorocarbene afforded bridged tropylidene 24 which was easily thermolysed to 3,4-bridged toluene 25 under ring-contraction.     

Deoxyfluorination of phenols

An operationally simple ipso fluorination of phenols with a new deoxyfluorination reagent is presented.     

Applications of the luminol chemiluminescent reaction in analytical chemistry

This critical review discusses the results published between 2000 and 2005 on the development of analytical systems based on the luminol chemiluminescent and electrochemiluminescent reactions. An increasing number of non-specific detection systems based on the enhancing, inhibiting or catalysing effect of a large range of compounds have been published. Possible detected compounds and their concomitant presence in samples are discussed. Chemiluminescent and electrochemiluminescent reactions were also found to merge in biochip and microarray development as a possible substitute to the well-established but hardly quantitative fluorescent detections.     

Mechanistic insight into the chemiluminescent decomposition of firefly dioxetanone

The peroxide decomposition that generates the excited-state carbonyl compound is the key step in most organic chemiluminescence, and chemically initiated electron exchange luminescence (CIEEL) has been widely accepted for decades as the general mechanism for this decomposition. The firefly dioxetanone, which is a peroxide, is the intermediate in firefly bioluminescence, and its decomposition is the most important step leading to the emission of visible light by a firefly. However, the firefly dioxetanone decomposition mechanism has never been explored at a reliable theoretical level, because the decomposition process includes biradical, charge-transfer (CT) and several nearly degenerate states. Herein, we have investigated the thermolysis of firefly dioxetanone in its neutral (FDOH) and anionic (FDO(-)) forms using second-order multiconfigurational perturbation theories in combination with the ground-state intrinsic reaction coordinate calculated via the combined hybrid functional with Coulomb attenuated exchange-correlation, and considered the solvent effect on the ground-state reaction path using the combined hybrid functional with Coulomb attenuated exchange-correlation. The calculated results indicate that the chemiluminescent decomposition of FDOH or FDO(-) does not take place via the CIEEL mechanism. An entropic trap was found to lead to an excited-state carbonyl compound for FDOH, and a gradually reversible CT initiated luminescence (GRCTIL) was proposed as a new mechanism for the decomposition of FDO(-).