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Indirect electrochemical cyclisation of bromoalkoxylated derivatives using envi...
Duñach, E.; Medeiros, Maria José; Olivero, S.The electrochemical intramolecular cyclization of bromoalkoxylated derivatives 1 using Ni(II) complex as mediator of electron transfer was carried out in ethanol by constant-current electrolysis in one-compartment cell in the absence of sacrificial anodes as an environmentally friendly systems. It is demonstrated that the electroreduction reaction of bromoalkoxylated derivatives was catalyzed by the electrogene...
Electrochemical applications of electrolytes based on ionic liquids
Neto, M. J.; Leones, R.; Sentanin, F.; Esperança, J.; Medeiros, Maria José; Pawlicka, A.; Silva, Maria ManuelaThe potential utility of room temperature ionic liquids as electrolytes in current electrochemical applications has been explored. Hence, the electrochemical behavior of [Ni(tmc)]Br2 complex at a glassy carbon electrode in the absence or in the presence of unsaturated halides in the ionic liquids, 1-ethyl-3- methylimidazolium ethylsulfate, [C2mim][C2SO4] and N,N,Ntrimethyl- N-(2-hydroxyethyl) ammonium bis(trifl...
Reductive intramolecular cyclization of D-glucose-based unsaturated substrates ...
Dias, T. A.; Durães, C.; Esteves, Ana Paula; Medeiros, Maria José; Pletcher, D.Radical cyclisation continues to be a central methodology for the preparation of natural products containing heterocyclic rings. Hence, some electrochemical results obtained by cyclic voltammetry and controlled-potential electrolysis in the study of electroreductive intramolecular cyclisation of ethyl (2S, 3R)-2- bromo-3-propargyloxy-3-(2’,3’,4’,6’-tetra-O-acetyl-β-D-glucopyranosiloxy) propanoate (1) promoted b...
Electrosynthesis of nitrogen heterocycles using environmentally friendly method...
Chaminade, X.; Duñach, E.; Esteves, Ana Paula; Medeiros, Maria José; Neves, C. S. S.; Olivero, S.Cyclic voltammetry and constant-current electrolysis in a one-compartment cell with a sacrificial anode has been used to study the indirect electroreduction of N-allyl- -haloamides by electrogenerated Ni(I) complexes conducted inN,N-dimethylformamide (DMF) and acetonitrile (ACN) and the resultswere compared with those obtained in protic solvents such as EtOH and EtOH–H2O mixtures. It was observed that the indir...
Electroepoxidation of natural and synthetic alkenes mediated by sodium bromide
Massuquinini, Inês; Mendonça, António J.; Esteves, Ana Paula; Mendonça, Dina I.; Medeiros, Maria JoséElectroepoxidation of synthetic alkenes (styrene, trans-stilbene and trans-b-methylstyrene) and of some natural terpenes (limonene, terpinolene, geraniol, a-terpinene, g-terpinene and a-terpineol) mediated by sodium bromide was performed in MeCN:H2O (4:1) at platinum electrodes. The indirect electrochemical oxidation of the olefins led to the corresponding epoxides in yields ranging from 23% to 79%. ; L’électr...
Study of the electrochemical reduction of amoebicide teclozan and its amperomet...
Santos,André L.; Takeuchi,Regina M.; Stradiotto,Nelson R.; Esteves,Ana Paula; Medeiros,Maria JoséThe electrochemical reduction of amoebicide Teclozan (TEC) was studied on a glassy carbon electrode in acetonitrile. Controlled-potential electrolyses were performed for coulometric and preparative purposes. The electrogenerated products were isolated by liquid-liquid extraction and characterized by ¹H NMR. It was observed that TEC presents two voltammetric peaks, each one associated with the cleavage of two C-...
Indirect electrochemical cyclization of bromoalkoxylated derivatives mediated b...
Duñach, E.; Medeiros, Maria JoséAn improved procedure has been developed using a catalytic amount of a nickel(II) complex in the efficient and selective electrochemical cyclization of propargyloxy and allyloxy bromo derivatives into substituted tetrahydrofurans using ethanol and ethanol–water mixtures as environmental-friendly systems. The reduction of the substrates proceeded via one-electron cleavage of the carbon–bromine bond to form a rad...
The catalysis of carbon dioxide hydration by acetate ion
Medeiros, Maria José; Pletcher, Derek; Sidorin, DmitryRotating disc voltammetry has been used to demonstrate that acetate ion is a catalyst for the hydration of carbon dioxide. In 0.05 M sodium chloride solution, the addition of 50 mM sodium acetate leads to an increase in the rate constant for the hydration of carbon dioxide from 0.9 to 8.9 s 1 at 333 K. The rate of hydration decreases with increasing ionic strength and decrease in temperature.
Organic cyclisations of propargyl and allyl bromoesters in microemulsions catal...
Esteves, Ana Paula; Neves, C. S. S.; Medeiros, Maria José; Pletcher, D.While the reductive intramolecular cyclisation of propargyl and allyl bromoesters catalysed by [Ni(tmc)]+ gives good yields of the desired products using N,N-dimethylformamide as the solvent, the use of this aprotic solvent presents practical, safety and environmental issues. This paper therefore reports the search for non-toxic alternatives, in particular the study of microemulsions prepared from water, hydroc...
Radical-type reactions in protic and aprotic media : comparisons in nickel-cata...
Dunach, E.; Esteves, Ana Paula; Medeiros, Maria José; Neves, C. S. S.; Olivero, S.The electrochemical reductive cyclisation of unsaturated organic halides in the presence of Ni(II) complexes as catalysts was examined in aprotic solvents such as DMF and in protic solvents such as ethanol, butanol or ethanolewater mixtures. The presence of the alcohol media enhanced the rate of recycling of the catalytic species. ; La cyclisation réductive électrochimique d’halogénures insaturés en présence d...
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