Substituent Effects in the Reduction Behaviour of Thio- and Oxopyrimidines in Non-Aqueous Solvents

2003 ◽  
Vol 56 (12) ◽  
pp. 1233 ◽  
Author(s):  
Marco Borsari ◽  
Maria Cannio ◽  
Daniela Dallari ◽  
Claudio Fontanesi ◽  
Giovanna Gavioli ◽  
...  
Keyword(s):  
Electrochemical Reduction ◽  
Theoretical Calculations ◽  
Electrochemical Behaviour ◽  
Substituent Effects ◽  
Reduction Process ◽  
Major Product ◽  
Electrochemical Process ◽  
Reduction Potentials ◽  
Ring Nitrogen ◽  
Mercury Electrodes

The electrochemical reduction of a series of thio- and oxopyrimidine derivatives has been investigated in organic solvents on mercury electrodes. In all cases the electrochemical process gave a dimeric species as the major product. The overall reduction mechanism is the same for oxo and thio derivatives, and is found to be dependent only on the nature of the ring nitrogen substituent. A ‘father–son reaction’ is observed when hydrogen is bound to the ring nitrogen atom: the radical anion obtained from the first electron transfer draws out the nitrogen proton of a non-reduced molecule and this then dimerizes. In the presence of a protonating agent as well as for the N-substituted derivatives, the ‘father–son reaction’ is not observed. Theoretical calculations have been performed to gain insight into the proposed mechanisms: the LUMO energy and the vertical electron affinity show a linear correlation with the reduction potentials. Analysis of the theoretical parameters has allowed step-by-step determination of the electrochemical reduction process. The manner in which solvent properties influence electrochemical behaviour has been examined, and the role of the acceptor number (AN) has been discussed.

Characterization of Tris(Diselenocarbamato)Cobalt(III) and Pentakis(Diselenocarbamato)Dicobalt(III) Complexes by Electrochemical, Cobalt-59 N.M.R. and Mass-Spectrometric Techniques. Comparisons With Dithiocarbamate Analogs

1986 ◽  
Vol 39 (9) ◽  
pp. 1385 ◽  
Author(s):  
AM Bond ◽  
R Colton ◽  
DR Mann ◽  
JE Moir
Keyword(s):  
Electrochemical Oxidation ◽  
Chemical Shifts ◽  
Chemical Reactivity ◽  
Mercury Electrode ◽  
Substituent Effects ◽  
Reduction Process ◽  
Reduced Form ◽  
Platinum Electrodes ◽  
Redox Potentials ◽  
Mercury Electrodes

A series of Co(RR′dsc)3 and [Co2(RR′dsc)5]+ complexes (R, R′ = two alkyl groups or one heterocyclic group; dsc = NCSe2) have been synthesized and their redox behaviour, chemical reactivity and spectroscopic properties compared with the corresponding dithiocarbamate (RR′dtc) complexes. Electrochemical oxidation of Co(RR′dsc)3 in dichloromethane at platinum electrodes occurs at potentials about 0.34 V less positive than for Co(RR′dsc)3. The formally cobalt(IV) complexes [Co(RR′dsc)3]+ can be identified as a product which is then converted into [Co2(RR′dsc)5]+ via dimerization and an internal redox reaction. Despite the enhanced thermodynamic stability implied by the redox potentials, [Co(RR′dsc)3]+ has similar kinetic stability to the analogous dithiocarbamate complexes. Co(RR′dsc)3 is reduced at fairly negative potentials on both platinum and mercury electrodes with extremely rapid loss of [RR′dsc]-. [Co(RR′dsc)3]- is therefore thermodynamically and kinetically more unstable than [Co(RR′dtc)3]- . The [Co2(RR′dsc)5]+ complexes are also more readily oxidized and harder to reduce than the sulfur analogues. Oxidation of [Co2(RR′dsc)5]+ produces [Co2(RR′dsc)5]2+ at low temperatures and fast scan rates, but no stable reduced form of the dimer is accessible on the voltammetric time scale examined. The reduction process for the dimer is consistent with the reaction [Co2(RR′dsc)5]+ +e- → Co(RR′dsc)3+ Co(RR dsc)2. Electrochemical oxidation data obtained at mercury electrodes for the diselenocarbamate complexes are complicated by adsorption but are similar to that found at platinum electrodes. This contrasts with the dithiocarbamates where a mercury electrode specific pathway is observed. Cobalt-59 n.m.r. spectroscopy in dichloromethane shows the non- equivalence of the two cobalt atoms in [Co2(RR′dsc)5]+. The chemical shifts for Co(RR′dsc)3 complexes exhibit similar substituent effects to the dithiocarbamates in cobalt-59 n.m.r. measurements as was the case in oxidative electrochemistry. Cobalt-59 n.m.r. spectroscopy and mass spectrometry demonstrate that exchange, substitution and redox reactions can lead to the formation of mixed ligand diselenocarbamate complexes and mixed dithiocarbamate/diselenocarbamate complexes for both the cobalt(III) monomers and dimers.

scholarly journals Substituent Effects on EI-MS Fragmentation Patterns of 5-Allyloxy-1-aryl-tetrazoles and 4-Allyl-1-aryl-tetrazole-5-ones; Correlation with UV-Induced Fragmentation Channels

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3282
Author(s):  
Alina Secrieru ◽  
Rabah Oumeddour ◽  
Maria L. S. Cristiano
Keyword(s):  
Theoretical Calculations ◽  
Substituent Effects ◽  
Radical Cations ◽  
Electronic Effects ◽  
Diverse Range ◽  
The Matrix ◽  
Electron Impact Mass ◽  
Fragmentation Patterns ◽  
Tetrazole Derivatives ◽  
Impact Mass

1,4- and 1,5-disubstituted tetrazoles possess enriched structures and versatile chemistry, representing a challenge for chemists. In the present work, we unravel the fragmentation patterns of a chemically diverse range of 5-allyloxy-1-aryl-tetrazoles and 4-allyl-1-aryl-tetrazolole-5-ones when subjected to electron impact mass spectrometry (EI-MS) and investigate the correlation with the UV-induced fragmentation channels of the matrix-isolated tetrazole derivatives. Our results indicate that the fragmentation pathways of the selected tetrazoles in EI-MS are highly influenced by the electronic effects induced by substitution. Multiple pathways can be envisaged to explain the mechanisms of fragmentation, frequently awarding common final species, namely arylisocyanate, arylazide, arylnitrene, isocyanic acid and hydrogen azide radical cations, as well as allyl/aryl cations. The identified fragments are consistent with those found in previous investigations concerning the photochemical stability of the same class of molecules. This parallelism showcases a similarity in the behaviour of tetrazoles under EI-MS and UV-irradiation in the inert environment of cryogenic matrices of noble gases, providing efficient tools for reactivity predictions, whether for analytical ends or more in-depth studies. Theoretical calculations provide complementary information to articulate predictions of resulting products.

Electrochemical reduction of isatic acid at mercury electrodes in aqueous media

1997 ◽  
Vol 354 (1-3) ◽  
pp. 365-373 ◽  
Author(s):  
Yuwu Chi ◽  
Hongqin Chen ◽  
Guonan Chen
Keyword(s):  
Electrochemical Reduction ◽  
Aqueous Media ◽  
Mercury Electrodes

Performance of poly-o-phenylenediamine and its carbon dot composite electrode in the removal of Cu2+ from its aqueous solution

2021 ◽  
pp. 2151037
Author(s):  
Yu Meng ◽  
Qing Zhong ◽  
Arzugul Muslim
Keyword(s):  
Aqueous Solution ◽  
Electrochemical Reduction ◽  
Composite Electrode ◽  
Reduction Process ◽  
Order Kinetic ◽  
Carbon Dot ◽  
First Order ◽  
Oxidation Reduction ◽  
Order Kinetic Model ◽  
Optimal Ph

Because −NH2 and −NH− in poly-[Formula: see text]-phenylenediamine (P[Formula: see text]PD) can interact strongly with the empty orbitals of Cu to show unique electrochemical activity, P[Formula: see text]PD is suitable for the removal of Cu[Formula: see text] by electrochemical oxidation–reduction process. In this study, with P[Formula: see text]PD and its carbon dot composite (CDs/P[Formula: see text]PD) as working electrodes, the electrochemical reduction and removal of Cu[Formula: see text] in the aqueous solution were carried out with the potentiostatic method. According to effects of voltage, pH of the solution, initial concentration of Cu[Formula: see text], and electrochemical reduction time on the Cu[Formula: see text] removal, the Cu[Formula: see text] removal ratios of P[Formula: see text]PD and CDs/P[Formula: see text]PD were up to 64.69% and 73.34%, respectively, at −0.2 V and the optimal pH. Additionally, results showed that these processes were in line with the quasi-first order kinetic model. Both P[Formula: see text]PD and CDs/P[Formula: see text]PD showed good reproducibility in six cycles. After five times of repeated usage, the regeneration efficiencies of P[Formula: see text]PD and CDs/P[Formula: see text]PD dropped to 77.04% and 79.36%, respectively.

scholarly journals Electrochemical Behaviour of N′-(p-toluenesulphonyl)-3-methyl-4-(4′-substituted arylhydrazono) pyrazolin-5-ones

2012 ◽  
Vol 9 (4) ◽  
pp. 1864-1874
Author(s):  
V. Nagaraju ◽  
R. Sreenivasulu ◽  
P. Venkata Ramana
Keyword(s):  
Electrochemical Behaviour ◽  
Reduction Process ◽  
Effect Of Solvent ◽  
Buffer Solutions ◽  
Diffusion Controlled ◽  
Controlled Potential Electrolysis ◽  
Dc Polarography ◽  
Controlled Potential ◽  
Ph Range ◽  
And Diffusion

The electrochemical behaviour of N′-(p-toluenesulphonyl)-3-methyl-4-(4′-substituted arylhydrazono) pyrazolin-5-ones has been investigated at dme and gc electrodes in buffer solutions of pH 2.0, 4.0, 6.0, 8.0 and 10.0 using dc polarography and cyclic voltammetry and coulometry. The compounds exhibit one well defined wave in the entire pH range of study. The process is irreversible and diffusion controlled. Controlled potential electrolysis indicates the involvement of four electrons in the reduction process. The effect of solvent, cations and anions, temperature and substitutents on the mechanism of reduction has been studied. Based on the results obtained the mechanism of reduction has been suggested.

Structure and electrochemical behaviour of 2-nitrosoquinoxaline

1981 ◽  
Vol 59 (12) ◽  
pp. 1711-1716 ◽  
Author(s):  
Joseph Armand ◽  
Yvette Armand ◽  
Line Boulares ◽  
Michèle Philoche-Levisalles ◽  
Jean Pinson
Keyword(s):  
Equilibrium Constant ◽  
Electrochemical Reduction ◽  
Acidic Medium ◽  
Electrochemical Behaviour ◽  
Monomeric Form ◽  
X Ray ◽  
X Ray Crystallography

It is shown by X-ray crystallography that 2-nitrosoquinoxaline crystallizes as a dimer, the structure of which is established. In solution the monomeric form predominates and the dimerisation equilibrium constant is measured. The electrochemical reduction of 2-nitrosoquinoxaline in acidic medium leads to the oxime of quinoxaline (1H)-2-one (3) through the intermediate hydroxylamine. 3 is electrochemically reoxidized directly to 2-nitrosoquinoxaline.

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