scholarly journals Réduction électrochimique de 4H-1,3-thiazines: obtention de 6H-1,3-thiazines et (ou) de pyrroles substitués

1992 ◽  
Vol 70 (1) ◽  
pp. 14-20 ◽  
Author(s):  
Abdesselam Abouelfida ◽  
Jean Paul Pradère ◽  
Michel Jubault ◽  
André Tallec
Keyword(s):  
Acidic Medium ◽  
Acetate Buffer ◽  
Buffer Medium ◽  
Mercury Cathode ◽  
Controlled Potential

Controlled potential electroreduction (protic medium, mercury cathode) of substituted 2-ethoxy and 2-phenyl-4H-1,3-thiazines leads to 6H-1,3-thiazines and (or) pyrroles. The nature of the isolated products appears strongly dependent on pH of the medium and type of substitution: pyrrole formation takes place in acidic medium (0.5 mol L−1 H2SO4) and is favoured by phenyl and alkoxycarbonyl groups at positions 2 and 4, respectively; formation of 6H-1,3-thiazines and their reduction products (substituted thiobenzamides, carbamates and 2-thiazoline) occurs in weakly acidic (acetate buffer) or basic (ammoniacal buffer) medium. Keywords: electrochemical reductions, substituted 4H- and 6H-1,3-thiazines, pyrroles, 2-thiazoline, cyclic regression.

Electrolytic reduction of o-nitrobenzyl thiocyanate in buffered solutions on mercury

1985 ◽  
Vol 50 (1) ◽  
pp. 33-41 ◽  
Author(s):  
Jaromír Hlavatý
Keyword(s):  
Acidic Medium ◽  
Reaction Path ◽  
Electrolytic Reduction ◽  
Buffer System ◽  
Height Ratio ◽  
Preparative Electrolysis ◽  
Clear Explanation ◽  
Ec Mechanism ◽  
Controlled Potential

The o-nitrobenzyl thiocyanate (I) behaves differently on the DME and on a large mercury pool electrode. Polarography did not give a sufficiently clear explanation of the reaction mechanism, only the preparative experiments yielded useful results. Whereas polarographic curves in solutions of Britton-Robinson buffer system with 50% by vol. ethanol exhibit two cathodic waves within the pH region 1-12, corresponding according to their height ratio to an uptake of 4 e and 2 e respectively, the controlled potential preparation electrolysis (CPE) and coulometry results indicate a more complicated reaction path. In the CPE carried out at the concentration of I 1 . 10 -2 mol/l the electroreductive splitting of CH2-SCN occurs as the first step. Nitrobenzyl radicals so formed react in the follow-up dimerization resulting in dibenzyl or toluene structures. Simultaneously or at a later stage the completion of the electrolytic reduction of the nitro group proceeds to the hydroxylamino group. In solution of 9 > pH > 1 the CPE of nitro compound I takes place by an ECEC mechanism yielding dibenzodiazocine III, its N-oxide IV and 2,2'-dimethylazoxybenzene (V). In course of preparative electrolysis in strongly acidic medium 2-amino-benzo(l,3)-thiazine-l-oxide (II) is formed by an EC mechanism.

scholarly journals Reduction of Toluidine Blue by Sulfur(IV) in Acetate Buffer Medium: Kinetics and Mechanism

2015 ◽  
Vol 27 (4) ◽  
pp. 1439-1443
Author(s):  
Pratik K. Sen ◽  
Rabindra N. Bera ◽  
Biswajit Pal
Keyword(s):  
Toluidine Blue ◽  
Kinetics And Mechanism ◽  
Acetate Buffer ◽  
Buffer Medium

Polarography of aromatic azo compounds. II. Kinetic study of the disproportionation of 4-Aminohydrazobenzene-4'-sulphonic acid

1965 ◽  
Vol 18 (5) ◽  
pp. 619 ◽  
Author(s):  
TM Florence
Keyword(s):  
Mercury Electrode ◽  
Sulphonic Acid ◽  
Azo Compounds ◽  
Rate Determining Step ◽  
A Value ◽  
Controlled Potential Electrolysis ◽  
Mercury Cathode ◽  
Dropping Mercury Electrode ◽  
Controlled Potential ◽  
Aromatic Azo Compounds

Solutions of 4-aminoazobenzene-4'-sulphonic acid were reduced by controlled potential electrolysis at a mercury cathode, and the disproportionation rate of the hydrazo derivative determined by spectrophotometry and polarography. The kinetics of the reaction were found to be first-order with respect to both hydrazo and hydrogen ion concentrations, although the overall reaction involved two molecules of the hydrazo compound. In the rate law, -d[hydrazo]/dt = k[H+][hydrazo], k was calculated to be (5.0�0.3) x 106 l. mole-1 sec-1 from spectrophotometric measurements, and (4.5�0.5) x 106 l. mole-1 sec-1 by polarography (25�). A reaction mechanism based on a rate determining step involving a quinonediimine intermediate has been proposed. Another value of the disproportionation rate constant was obtained from the effect of drop time on the limiting currents of 4-aminoazobenzene-4'-sulphonic acid at the dropping mercury electrode. A value of k of (22�5) x 106 l. mole-1 sec-1 was determined by this method. Reasons for the discrepancy between this result, and those found by direct measurement, are discussed.

Electronic Conduction in Polymers. II. The Electrochemical Reduction of Polypyrrole at Controlled Potential

1963 ◽  
Vol 16 (6) ◽  
pp. 1076 ◽  
Author(s):  
BA Bolto ◽  
DE Weiss
Keyword(s):  
Electrochemical Reduction ◽  
Alkali Treatment ◽  
Iodine Content ◽  
Molecular Iodine ◽  
Reduction Potentials ◽  
Mercury Cathode ◽  
Current Passage ◽  
Controlled Potential ◽  
Polymer Electrodes ◽  
A Charge

Molecular iodine was removed from polypyrrole by electrochemical reduction of slurries at a mercury cathode. This method was found to be more effective than the treatment of rigid or packed polymer electrodes. Voltammetric plots indicated that two reductions occurred, at potentials insensitive to pH. The current passage was dependent on the iodine content, while partial reduction or solvent extraction deleted the first current peak. Complete reduction or alkali treatment removed both peaks, whereas iodide in solution increased the reduction potentials. From this evidence it is postulated that the first peak is due to iodine in solution, the second to iodine present as a charge-transfer complex of polypyrrole. By estimating the amount of iodine and iodide present in the electrolyte the reduction potential for dissolved iodine was calculated and found to agree with that observed for the first peak in the slurry reduction. Confirmation of this potential was obtained in the reduction of a blank containing the found amounts of iodine and iodide. Quantitative data were obtained for the reduction of slurries in neutral electrolytes. There was reasonable agreement between coulometric estimations and the iodine removed, after correction for iodide already present, provided that the anode reaction did not supply reducible material to the catholyte. Reduction of iodine by polypyrrole itself did not appear significant in neutral suspensions. Iodine was readily removed electrochemically from the early polymers which contained only about 2.2 m-equiv/g. A later polymer contained almost a third more iodine and required prolonged reduction times which were cut considerably by the use of a silver anode to mop up iodide ion as it was formed. The reduction products were compared for changes in acidity, resistivity, and oxygen content. I.

scholarly journals Peningkatan Kualitas Biji Kakao Non Fermentasi Melalui Perlakuan Pendahuluan Sebelum Inkubasi

2016 ◽  
Vol 3 (1) ◽  
pp. 11
Author(s):  
M. Iqbal Prawira Atmaja ◽  
Haryadi Haryadi ◽  
Supriyanto Supriyanto
Keyword(s):  
Acetate Buffer ◽  
Polyphenol Content ◽  
Cocoa Beans ◽  
Total Polyphenols ◽  
Total Polyphenol ◽  
Buffer Medium ◽  
Biochemical Laboratory ◽  
Physical Treatments ◽  
Two Stages

<em><span>The cocoa beans produced by farmers in Indonesia are mostly non</span><span>fermented </span><span lang="EN-US">with </span><span>unfavo</span><span lang="EN-US">u</span><span>rable taste and </span><span lang="EN-US">flavour</span><span>. </span><span lang="EN-US">I</span><span>ncubati</span><span lang="EN-US">ng the</span><span> cocoa beans in acetate buffer medium </span><span lang="EN-US">has been shown to</span><span> improv</span><span lang="EN-US">e</span><span> the quality of </span><span lang="EN-US">non </span><span>fermented dried cocoa beans. </span><span lang="EN-US">Pre-incubation treatments of non fermented cocoa beans by physical treatments such as soaking and crushing them prior to the incubation in acetate buffer is expected to improve the beans quality (i.e. fermentation index and polyphenol). The aim of the research was</span><span> to determine the </span><span lang="EN-US">effect </span><span>of </span><span lang="EN-US">pre-incubation </span><span>treatment </span><span lang="EN-US">of non fe</span><span>rmented dried cocoa beans in acetate buffer medium on fermentation index and total polyphenols</span><span lang="EN-US"> content</span><span>.</span><span lang="EN-US">The research </span><span>was carried out in </span><span lang="EN-US">Process Engineering Laboratory, Food Chemical and Biochemical Laboratory, and Postharvest Technology Laboratory at </span><span lang="EN-US">Gadjah Mada</span><span lang="EN-US">University from April to December 2013</span><span>. </span><span lang="EN-GB">The research used three treatments, first: the crushed </span><span>bean</span><span lang="EN-US">s</span><span lang="EN-GB"> size 4 mm, whole beans soaked in water </span><span lang="EN-US">(45°C; 16 hours)</span><span lang="EN-GB">, and beans without soaking (control). The incubation was performed in two stages, the first stage was in the acetate buffer medium at pH 2.7; 600 mM for 24 hours, then subconsequently at pH 5.5; 600 mM for 12 hours. The results showed that </span><span>crushed bean </span><span lang="EN-GB">treatment</span><span> of </span><span lang="EN-US">non </span><span>fermented cocoa beans</span><span lang="EN-GB"> prior to incubation increased the </span><span lang="EN-GB">fermentation index values, from </span></em><em><span lang="EN-GB">1.15 </span><span lang="EN-US">to</span><span lang="EN-US">1.54</span></em><span lang="EN-US"> <em>and</em> </span><em><span lang="EN-GB">decreased total polyphenol content from </span></em><em><span>55.69 </span><span lang="EN-US">to</span><span> 24.16</span></em><span lang="EN-GB">mg <em>GAE</em>/g</span><span>.</span>

Sign in / Sign up

Export Citation Format

Share Document