- Mechanisms of interference of p-diphenols with the Trinder reaction
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p-Diphenols, such as homogentisic acid, gentisic acid, etamsylate, and calcium dobesilate, interfere with diagnostic tests utilizing the Trinder reaction but the mechanisms of these effects are not fully understood. We observed substantial differences both in oxidation of p-diphenols by horseradish peroxidase and their influence on oxidation of 4-aminoantipyrine and various phenolic substrates. Homogentisic acid was rapidly oxidized by the enzyme and completely blocked chromophore formation. Enzymatic oxidation of the remaining p-diphenols was slow and they only moderately inhibited chromophore formation. However, in the presence of standard substrates all tested p-diphenols were rapidly converted to p-quinones. Hydrogen peroxide consumption was significantly accelerated by homogentisic acid but not much affected by the other p-diphenols. The magnitude and mechanisms of interference caused by p-diphenols therefore depend on their structure which determines their electrochemical properties – while for homogentisic acid with an electron-donating substituent and a lower reduction potential both enzymatic oxidation and reduction of the peroxidase-generated radicals occur, for p-diphenols with electron-withdrawing substituents and higher reduction potentials only the second mechanism is significant. Correlation of the effects on the Trinder reaction with reduction potentials of interfering compounds allows prediction of such properties for a wide range of other reducing compounds based on this parameter. It also explains why compounds with very different structures but strong reducing properties show such effects.
- G?sowska-Bajger, Beata,Tarasek, Damian,Wojtasek, Hubert
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supporting information
(2020/03/10)
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- Nitration of phenolic compounds and oxidation of hydroquinones using tetrabutylammonium chromate and dichromate under aprotic conditions
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In this work, we have reported a mild, efficient and selective method for the mononitration of phenolic compounds using sodium nitrite in the presence of tetrabutylammonium dichromate (TBAD) and oxidation of hydroquinones to quinones with TBAD in CH2Cl2. Using this method, high yields of nitrophenols and quinones were obtained under neutral aprotic conditions. Tetrabutylammonium chromate (TBAC) can also be used as oxidant at same conditions. Indian Academy of Sciences.
- Pourali, Ali Reza,Goli, Arezou
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scheme or table
p. 63 - 67
(2012/01/13)
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- Mechanistic study of electrochemical oxidation of 2,5-dihydroxybenzoic acid and 3,4-dihydroxybenzaldehyde in the presence of 3-hydroxy-1H-phenalene-1-one
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The mechanism of the electrochemical oxidation of 2,5-dihydroxybenzoic acid and 3,4-dihydroxybenzaldehyde in the presence of 3-hydroxy-1H-phenalene-1-one as a nucleophile has been studied in water/acetonitrile (80/20 v/v) solution using cyclic voltammetry and controlled-potential coulometry methods. The results indicate that the quinones derived from oxidation of 2,5-dihydroxybenzoic acid and 3,4-dihydroxybenzaldehyde participate in Michael addition reactions with 3-hydroxy-1H-phenalene-1-one and via ECE and ECEC mechanisms convert to the different products, with good yield under controlled potential conditions, at carbon electrode.
- Nematollahi, Davood,Amani, Amaneh
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experimental part
p. 513 - 517
(2009/04/11)
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- Oxidation of aspirin by a new oxidant diperiodatoargentate(III) in aqueous alkaline medium
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The kinetics of oxidation of aspirin by diperiodatoargentate(III) (DPA) in alkaline medium at a constant ionic strength of 1.0 mol dm-3 has been studied spectrophotometrically. The reaction between DPA and aspirin in alkaline medium exhibits 1: 2 stoichiometry (aspirin: DPA). The reaction is of first order in [DPA] and has less than unit order in both [ASP] and [alkali]. However, the order in [ASP] and [alkali] changes from first order to zero order as the concentration changes from lower to higher concentration. A decrease in the dielectric constant of the medium increases the rate of the reaction. The effect of added products and ionic strength of the reaction medium have been investigated and a mechanism is proposed.
- Kiran,Nandibewoor
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p. 431 - 436
(2007/10/03)
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- Oxidation of benzenediols by hexabromoiridate(IV): Kinetics at ambient and elevated pressures
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The kinetics of oxidation of several benzenediols by the hexabromoiridate(IV) ion have been studied spectrophotometrically by the stopped-flow method. In 0.010 mol dm-3 HClO4 and an ionic strength of 0.10 mol dm-3 (NaClO4) at 25.0°C the second-order rate constants (the reaction is first order in each reactant concentration), vary from 1.26 × 102 to 9.3 × 104 dm3 mol-1 s-1. The enthalpies of activation range from about 44 kJ mol-1 for the slowest reacting substrate to about 20 kJ mol-1 for the faster reactions. The ΔS? values do not vary over a wide range; the reaction rates are governed more by the enthalpy barrier. Application of pressure (up to 125 MPa) causes significant rate accelerations, giving rise to ΔV? values in the -17 to -26 cm3 mol-1 range, consistent with the large, negative ΔS? values. This indicates that the rate limiting step is largely characterised by an increase in species ordering and electrostriction, and in the present case slightly less than for the corresponding reactions with the less bulky hexachloroiridate(IV) ion.
- Ciosto, Cornelia,Bajaj, Hari C.,Van Eldik, Rudi,Hubbard, Colin D.
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p. 1503 - 1507
(2007/10/03)
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- Unsaturated polymerizable cyanoquinodimethane monomers
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Polymeric compositions having inherent electroconductive properties and unsaturated electron-donor and electron-receptor polymerizable monomers for producing such compositions in the form of blends of homopolymers of such monomers or as copolymers of such monomers.
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- Kinetics of the Oxidation of Ascorbic Acid and Substituted 1,2- and 1,4-Dihydroxybenzenes by the Hexacyanoruthenate(III) Ion in Acidic Perchlorate Media
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The kinetics of oxidation of ascorbic acid and a series of substituted 1,2- and 1,4-dihydroxybenzene compounds (H2Q) by 3- have been investigated in acidic perchlorate media.The inverse dependences of the rate constants on acid concentrations for 2,3-dicyano-1,4-dihydroxybenzene, 4,5-dihydroxybenzene-1,3-disulphonate, and ascorbic acid have been attributed to concurrent rate-determining pathways involving the one-electron oxidations of H2Q or HQ(-) by 3- to the corresponding semiquinone or ascorbate radical intermediate.The cross-reaction rate constants have been correlated with the semiquinone or ascorbate reduction potentials in terms of the Marcus relationship to yield a 3--4- electron self-exchange rate constant of (1.0 +/- 0.8) . 105 dm3mol-1s-1.This is compared with those for other low-spin d5-d6 transition-metal complex couples and discussed in terms of the inner-sphere and solvent reorganization energies.
- Hoddenbagh, J. Mark A.,Macartney, Donal H.
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p. 615 - 620
(2007/10/02)
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- Quinone derivatives, their production and use
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New quinone derivatives of the formula: STR1 wherein R1 is methyl or methoxy, or two of R1 combine to represent --CH=CH--CH=CH--, R is amino which may be substituted or --OR4 wherein R4 is hydrogen, C1-4 alkyl or --CH2 --CH=C(CH3 --CH2 --m H (wherein m is an integer of 1 to 10), and n is an integer of 1 to 10 when R is amino which may be substituted, or n is an integer of 2 to 10 when R is --OR4, and their hydroquinone forms, have useful physiological activities such as blood-pressure decreasing and antiallergic activities.
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- Kinetics of Periodate Oxidation of Salicylic Acid
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Kinetics of oxidation of salicylic acid by sodium metaperiodate follows second order kinetics, first order in each reactant.The effect of dielectric constant and effect of radical capture reagent have been investigated and the results indicate that the reaction is ionic, being an ion-molecular reaction.The rate is only slightly decreased by using heavy water as the medium.The rate-pH profile suggests that different species of periodate may be involved in the oxidation process. 1,4-Benzoquinone-2-carboxylic acid has been identified as the main reaction product.The various thermodynamic parameters have been evaluated and a suitable reaction mechanism has been proposed.
- Srivastava, S. P.,Bhattacharjee, G.,Kumar, Anil,Pal, Satya
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p. 578 - 579
(2007/10/02)
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