Estimation of homogeneous rate constants of reaction of electrochemically generated ortho‐benzoquinones with 1,3‐indandione

Electrochemical oxidation of some catechol derivatives has been studied in the presence of 1,3‐indandione as nucleophile in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate the participation of electrochemically produced o‐benzoquinones in the Michael reaction with 1,3‐indandione to form the corresponding new catechol derivatives. On the basis of the EC mechanism, the observed homogeneous rate constants (k_obs) of reaction of produced o‐benzoquinones with 3‐indandione were estimated by comparing the experimental cyclic voltammograms with the digitally simulated results. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 605–613, 2007     

Voltammetric study of the oxidation of quercetin and catechin in the presence of cyanide ion

The reaction of electrochemically generated o-benzoquinones from oxidation of quercetin and catechin as Michael acceptors with cyanide ion as nucleophile has been studied using cyclic voltammetry. The reaction mechanism is believed to be EC; including oxidation of catechol moiety of these antioxidants followed by Michael addition of cyanide ion. The observed homogeneous rate constants (k _obs) for reactions were estimated by comparing the experimental voltammetric responses with the digitally simulated results based on the proposed mechanism. The effects of pH and nucleophile concentration on voltammetric behavior and the rate constants of chemical reactions were also described.     

Estimation of heterogeneous rate constants of reaction of electrochemically generated o‐benzoquinones with various nucleophiles containing thiol group

The reaction of o‐benzoquinone derived by the oxidation of catechols ( 1a–c ) with some nucleophiles containing thiol group ( 2a–f ) has been studied in various conditions, such as pH, nucleophile concentration, and scan rate, using cyclic voltammetry. In various conditions, based on an EC electrochemical mechanism (“E” represents an electron transfer at the electrode surface and “C” represents a homogeneous chemical reaction), the observed homogeneous rate constants (k_obs) were estimated by comparison of the experimental cyclic voltammetric responses with the digital simulated results for each of the nucleophile. The results show that the magnitude of k_obs is dependent on the nature of the substituted group on the catechol ring and nucleophilicity of nucleophile. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 426–431, 2009     

Electrochemical behavior of catechol in the presence of 2-methyl-1,3-cyclopentanedione: application to electrosynthesis

Abstract  

Electro-oxidation of catechol in the presence of 2-methyl-1,3-cyclopentanedione as a nucleophile was investigated in water–acetonitrile (90:10 v/v) solution. The results indicate that the o-benzoquinone electrogenerated participates in a Michael addition reaction with this nucleophile. The electrosynthesis of 2-(3,4-dihydroxyphenyl)-2-methylcyclopentane-1,3-dione was carried out. The product was characterized by NMR, MS, FT-IR, and elemental analysis. An EC mechanism was deduced from voltammetric and spectroscopic data. Also, the Michael addition reaction rate constant (k _m) was estimated using digital simulation of voltammograms.     

Electrochemical behavior of catechol in the presence of 2-methyl-1,3-cyclopentanedione: application to electrosynthesis

Abstract  Electro-oxidation of catechol in the presence of 2-methyl-1,3-cyclopentanedione as a nucleophile was investigated in water–acetonitrile (90:10 v/v) solution. The results indicate that the o-benzoquinone electrogenerated participates in a Michael addition reaction with this nucleophile. The electrosynthesis of 2-(3,4-dihydroxyphenyl)-2-methylcyclopentane-1,3-dione was carried out. The product was characterized by NMR, MS, FT-IR, and elemental analysis. An EC mechanism was deduced from voltammetric and spectroscopic data. Also, the Michael addition reaction rate constant (k _m) was estimated using digital simulation of voltammograms. Graphical abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Cerium(IV) oxide as a neutral catalyst for aldehyde-induced decarboxylative coupling of l-proline with triethyl phosphite and nitromethane

The application of cerium(IV) oxide (CeO₂) as a neutral and heterogeneous catalyst for aldehyde-induced decarboxylative coupling of l-proline with triethyl phosphite and nitromethane is described. In addition, a [3+2] cycloaddition reaction of the in situ generated 1,3-dipolar intermediate with benzaldehyde in the absence of a nucleophile is also reported.     

Investigation of the electro-oxidation and oxidation of catechol in the presence of sulfanilic acid

The electrochemical oxidation of catechol (1) in the presence of sulfanilic acid (2) was investigated. Some electrochemical (EC) techniques such as cyclic voltammetry and controlled-potential coulometry were used. The oxidation reaction of catechol (1) with periodate in the presence of sulfanilic acid (2) was also investigated spectrophotometrically. The results indicate that the o-quinone derived from catechol participate in Michael addition reaction with sulfanilic acid (2). In addition, according to the ECE mechanism, the observed homogeneous rate constant (k_obs) for the reaction of o-quinone derived from catechol (1) with sulfanilic acid (2) has been estimated by digital simulation of cyclic voltammograms.     

Study of the oxidation of some catechols in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole by digital simulation of cyclic voltammograms

Electrochemical oxidation of catechol and its derivatives ( 1a–d ) has been studied in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole ( 3 ) at various pHs. Some electrochemical techniques such as cyclic voltammetry using the diagnostic criteria derived by Nicholson and Shain for various electrode mechanisms and controlled‐potential coulometry were used. Results indicate the participation of catechols ( 1a–d ) with 3 in an intramolecular cyclization reaction to form the corresponding 1,2,4‐triazino[5,4‐b]‐1,3,4‐thiadiazine derivatives. In various scan rates, based on an electron transfer–chemical reaction–electron transfer–chemical reaction mechanism, the observed homogeneous rate constants (k_obs) for Michael addition reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results. The oxidation reaction mechanism of catechols ( 1a–d ) in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole ( 3 ) was also studied. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 340–345, 2007     

Kinetics study of electrochemically induced michael reaction of benzoquinones with triphenylphosphine

The electrochemical oxidation of 3,4-dihydroxybenzaldehyde (1), 3,4-dihydroxybenzoic acid (2) and 2,5-dihydroxybenzoic acid (3) were studied in the presence of triphenylphosphine (4) as a nucleophile using cyclic voltammetry and controlled-potential coulometry. The results indicate that the quinones derived from oxidation of 3,4-dihydroxybenzaldehyde, 3,4-dihydroxybenzoic acid and 2,5-dihydroxybenzoic acid participate in Michael addition reaction with triphenylphosphine (4). In this work, based on an EC mechanism, the observed homogeneous rate constants (k _obs) of the reaction of produced benzoquinones with triphenylphosphine (4) were estimated by comparing the experimental cyclic voltammograms with the digitally simulated results.     

Theoretical Aspects of a Surface Electrode Reaction Coupled with Preceding and Regenerative Chemical Steps: Square‐wave Voltammetry of a Surface CEC’ Mechanism

Large number of lipophilic substances, whose electrochemical transformation takes place from adsorbed state, belong to the class of so‐called “surface‐redox reactions”. Of these, especially important are the enzymatic redox reactions. With the technique named “protein‐film voltammetry” we can get insight into the chemical features of many lipophilic redox enzymes. Electrochemical processes of many redox adsorbates, occurring at a surface of working electrode, are very often coupled with chemical reactions. In this work, we focus on the application of square‐wave voltammetry (SWV) to study the theoretical features of a surface electrode reaction coupled with two chemical steps. The starting electroactive form Ox_(ads) in this mechanism gets initially generated via preceding chemical reaction. After undergoing redox transformation at the working electrode, Ox_(ads) species got additionally regenerated via chemical reaction of electrochemically generated product Red_(ads) with a given substrate Y. The theory of this so‐called surface CEC’ mechanism is presented for the first time under conditions of square‐wave voltammetry. While we present plenty of calculated voltammograms of this complex electrode mechanism, we focus on the effect of rate of regenerative (catalytic) step to simulated voltammograms. We consider both, electrochemical reactions featuring moderate and fast electron transfer. The obtained voltammetric patterns are very specific, having sometime hybrid‐like features of voltammograms as typical for CE, EC and EC’ mechanisms. We give diagnostic criteria to recognize this complex mechanism in SWV, but we also present hints to access the kinetic and thermodynamic parameters relevant to both chemical steps, and the electrochemical reaction, too. Indeed, the results presented in this work can help experimentalists to design proper experiments to study chemical features of important lipophilic systems.     

Electrochemical oxidation of catechol and 4-tert-butylcatechol in the presence of 1-Methyl-1H-imidazole-2-thiol: Synthesis and kinetic study

Electrochemical oxidation of catechol 1a and 4-tert-butylcatechol 1b has been studied in the presence of 1-methyl-1Himidazole- 2-thiol 3 as nucleophile in aqueous solution, using cyclic voltammetry and controlled-potential coulometry. The results indicate the participation of catechol 1a and 4-tert-butylcatechol 1b in Michael reaction with 3 to form the corresponding catechol thioethers 6a and 4b. Based on the observed EC mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with digital simulated results.     

Investigation of the electro-oxidation and oxidation of catechol in the presence of sulfanilic acid

The electrochemical oxidation of catechol (1) in the presence of sulfanilic acid (2) was investigated. Some electrochemical (EC) techniques such as cyclic voltammetry and controlledpotential coulometry were used. The oxidation reaction of catechol (1) with periodate in the presence of sulfanilic acid (2) was also investigated spectrophotometrically. The results indicate that the o-quinone derived from catechol participate in Michael addition reaction with sulfanilic acid (2). In addition, according to the ECE mechanism, the observed homogeneous rate constant (k _obs) for the reaction ofo-quinone derived from catechol (1) with sulfanilic acid (2) has been estimated by digital simulation of cyclic voltammograms.     

New natural product -an efficient antimicrobial applications of new newly synthesized pyrimidine derivatives by the electrochemical oxidation of hydroxyl phenol in the presence of 2-mercapto-6-(trifluoromethyl) pyrimidine-4-ol as nucleophile

Some new pyrimidine derivatives have been synthesised by electrochemical oxidation of catechol (1a) in the existence of 2-mercapto-6-(trifluoromethyl) pyrimidine-4-ol (3) as a nucleophile in aqueous solution using Cyclic Voltammetric and Controlled Potential Coulometry. The catechol has been oxidised to o-quinone through electrochemical method and participative in Michael addition reaction, leading to the development of some new pyrimidine derivatives. The products were achieved in good yield with high pureness. The mechanism of the reaction has been conformed from the Cyclic Voltammetric data and Controlled Potential Coulometry. After purification, the compounds were characterised using modern techniques. The synthesised materials were screened for antimicrobial actions using Gram positive and Gram negative strain of bacteria. These new synthesised pyrimidine derivatives showed very good antimicrobial activity.     

Bronsted酸催化合成α-氨基膦酸酯

以芳香胺和肉桂醛为原料,合成的芳香族亚胺为亲电试剂,亚磷酸二乙酯或亚磷酸三乙酯为亲核试剂,在10%（摩尔分数）磷酸催化剂（Bronsted acid）的作用下,通过催化剂与亲电试剂、亲核试剂之间共同形成的双氢键或单氢键的作用,成功地合成了α-氨基膦酸酯类化合物,收率可达到79%～85%。     

Cyclic Voltammetric Study of the Oxidation of Catechols in the Presence of Cyanide Ion

Electrochemical oxidation of catechols has been studied in the presence of cyanide ion as nucleophile in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate that the participation of catechols in the Michael reaction with cyanide ion to form the corresponding o‐dihydroxybenzonitrile. Based on an EC mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results.     

Electrochemical Oxidation of Catechols (=Benzene‐1,2‐diols) in the Presence of Benzoylacetonitrile: Synthesis of New Derivatives of 5,6‐Dihydroxybenzofuran

The electrochemical oxidation of catechol (=benzene‐1,2‐diol; 1a ) and some of its derivatives in H₂O/MeCN 1 : 1 containing benzoylacetonitrile (=β‐oxobenzenepropanenitrile; 3 ) as a nucleophile was studied by cyclic voltammetry and controlled‐potential coulometry. The voltammetric data showed that electrochemically generated o‐benzoquinones (=cyclohexa‐3,5‐diene‐1,2‐diones) from catechol ( 1a ) and 3‐methylcatechol ( 1b ) participate in a Michael‐addition reaction with 3 to form the corresponding 5,6‐dihydroxybenzofuran‐3‐carbonitrile 8 (Scheme 1). In this work, we report an efficient one‐pot method with high atom economy for the synthesis of new substituted 5,6‐dihydroxybenzofuran‐3‐carbonitriles in an undivided cell under ambient conditions.     

Mechanistic study of homogeneous reactions coupled with electrochemical oxidation of catechols

The electrochemical oxidation of catechols was described and has shown that these compounds can be oxidized to related o-benzoquinones. The electrochemically generated o-benzoquinones are quite reactive and can be attacked by a variety of nucleophiles under various mechanistic disciplines such as CE, EC, EC′, ECE, ECEC, ECEC ₂, ECECE, ECECEC, ECECECE and trimerization, in which E represents an electron transfer at the electrode surface, and C represents a homogeneous chemical reaction. The mechanistic pathways and final products are depending on some parameters such as electron withdrawing or donating properties of nucleophile, electrolysis medium (solvent, acidity or pH) and nature of catechol.     

Kinetic study of electrochemically induced Michael reaction of1,4-dihydroxyanthraquinone with acetylacetone and benzoylacetone

The electrochemical oxidation of 1,4-dihydroxyanthraquinone has been studied in the presence of acetylacetone and benzoylacetone as nucleophiles in a mixture of ethanol/water by means of cyclic voltammetry as a diagnostic technique.The results indicate the participation of electrochemically produced anthraquinone in the Michael addition reaction with acetylacetone and benzoylacetone to form the corresponding new anthraquinone derivatives.On the basis of the EC mechanism,the observed homogeneous rate constants（kobs）of the reaction of anthraquinone with acetylacetone and benzoylacetone were estimated by comparing the experimental cyclic voltammograms with the digitally simulated results.     

Reaction of 2,4-Difunctional Esters of 5-tert-Butylfuran-3-carboxylic Acid with Nucleophilic Reagents

Ethyl 5-tert-butyl-4-(chloromethyl)-2-methylfuran-3-carboxylate was brominated with N-bromo-succinimide to obtain the corresponding 2-bromomethyl derivative. The latter is selectively phosphorylatedwith trimethyl, triethyl phosphites by the bromomethyl group. The resulting [4-(chloromethyl)furyl]methyl-phosphonates in the presence of secondary amines and sodium butanethiolate behave as alkylating agents,while sodium phenolate causes their decomposition. 4-Acetoxymethyl- and 4-phenoxymethyl derivatives of the starting product are also selectively brominated with N-bromosuccinimide by the 2-methyl group. The first of the 2-(bromomethyl)furans formed is smoothly phosphorylated with trimethyl phosphite, while the second one under the action of triethyl phosphite gives a mixture of phosphorylation and debromination products. In all the cases, an additional electron-acceptor group in position 4 of alkyl 2-(bromomethyl)-5-tert-butylfuran-3-carboxylate considerably accelerates the Arbuzov reaction.     

The chemistry of carbazole. VI. On the formation of N-ethylcarbazoles in the cadogan reaction

Reaction of 2′,6-dimethyl-2-nitrobiphenyl with triethyl phosphite gave 4,5-dimethyl-9-ethylcarbazole besides 4,5-dimethylcarbazole. In this reaction, 4,5-dimethylcarbazole was ethylated by triethyl N-(2′,6-dimethybiphenyl-2-yl)phosphorimidate and diethyl N-(2′,6-dimethylbiphenyl-2-yl)phosphoramidate, which arose from a nitrene-intermediate and triethyl phosphite. Analogous ethylations of carbazole with other phosphorimidate and phosphoramidates were investigated.