A study of the anodic polarography of catechol in 0.100 F sodium perchlorate is presented. A new wave is observed in alkaline solutions which is different from the simple oxidation wave of catechol to ortho-quinone observed by previous workers. The importance of buffer materials is discussed and a possible explanation of the new wave is suggested. A study of the polarography behavior of Fe(II) and Fe(III) in the presence of catechol is reported. In the case of reduction of Fe(III) in the presence of catechol, two steps occur at about -1.5 and -1.8 volts (vs. SCE) at pH higher than 11.6 corresponding to one electron reduction of Fe(III) to Fe(II) and successive two electron reduction of Fe(II) to Fe(s). At lower pH these two steps are too close together to be resolved. An oxidation wave and a reduction wave are recorded for the electrolysis of Fe(II) in the presence of catechol: the oxidation wave is observed between pH 7 and 12.3. The curve showing dependence of the limiting current on pH is similar to the distribution curve of Fe(cat). It is therefore suggested that only Fe(cat) is oxidized and observed here. The reduction wave of Fe(II) in the presence of catechol is irreversible and shifted from -1.5 to -1.8 volts upon complex formation. A calculation of formation constants, 81 and 82, was achieved according to an equation which relates the shifts of halfwave potential to the formation constants.

This investigation applied the techniques of polarography and controlled potential electrolytic reduction to the study of a series of unsymmetrical benzils. Eleven unsymmetrical benzils were synthesized and studied in 50% ethanol-water (by volume) solvent systems buffered at pH 1, 5, and 13. The results showed that, with unsymmetrical benzils substituted with electron-withdrawing or electrondonating groups, the carbonyl closest to the ring with the least electron-donating power was the preferred reaction site. However, the dicarbonyl system was nevertheless reduced as a unit, and Hammett sigma values of disubstituted symmetrical benzils were approximately additive. This was ascertained by comparing the ease of reduction of eight unsymmetrical benzils to the ease of reduction of the corresponding disubstituted symmetrical benzils. It was proposed that the electrons were added to the oxygen of one carbonyl, and that the second carbonyl was involved in the reduction chiefly through complete polarization of the dicarbonyl system at the electrode. In general, the reduction of unsymmetrical benzils appeared to follow the same path previously reported for symmetrical benzils.

No description available.

No description available.

Proefschrift--Amsterdam. / Summary in English. "Stellingen": [2] p. inserted. Bibliography: p. [115]-116.

Made available in DSpace on 2014-10-09T12:27:37Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:29Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:27:37Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:29Z (GMT). No. of bitstreams: 0 / Cloreto estanoso (SnCl2.2H2O) é o composto mais utilizado na redução do íon pertecnetato (TcO4-), obtido pela eluição do gerador, para a marcação de reagentes liofilizados para radiodiagnóstico. Estes reagentes liofilizados contêm um ligante, cloreto estanoso, e diferentes excipientes. Muitos métodos analíticos para a determinação de estanho não conseguem distinguir entre os íons estanoso (Sn(II)) e estânico (Sn(IV)) em soluções. Os dois métodos, descritos na literatura, para determinação seletiva de Sn(II) são análise titrimétrica e polarografia. O método mais confiável descrito para a quantificação do íon estanoso é a polarografia (voltametria) e pode ser utilizado para a determinação em concentrações de mg e g de Sn(II) e Sn(IV) (0,06-1,0 mg), com boa seletividade. Foi realizada análise titrimétrica, para quantificação de Sn(II), na matéria-prima e em 3 lotes consecutivos de 9 reagentes liofilizados produzidos pelo IPEN-CNEN/SP, utilizando-se sulfato cérico 0,1 mol L-1, diluído 10 vezes e iodo 0,05 mol L-1, diluído 10 vezes, como soluções titulantes. Polarografia por pulso diferencial foi utilizada com configuração convencional composta por três eletrodos: eletrodo de trabalho de gota de mercúrio, eletrodo referência de Ag/AgCl (saturado com KCl) e eletrodo auxiliar de platina. O intervalo de potencial analisado foi de -250 a -800 mV e o pico atribuído à redução de Sn(II) foi encontrado em -370 mV em eletrólito suporte de H2SO4 3 mol L-1 e, para Sn(IV), -470 mV, em eletrólito suporte de HCl 3 mol L-1. Para retirada do oxigênio da solução na cela polarográfica utilizou-se nitrogênio 5.0 por 5 minutos, antes e após cada introdução de amostra. Para determinação de Sn(IV) foi feita a oxidação do Sn(II), por adição de peróxido de hidrogênio, em 37 ± 5 ºC, por 5 minutos, seguida de purga com nitrogênio, e análise. A análise polarográfica desenvolvida mostrou-se adequada para a determinação de Sn(II), na presença de Sn(IV), e de estanho total nos kits radiofarmacêuticos estudados. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The purpose of this investigation is to study the polarographic characteristics of p-nitroacetophenone.

A series of eight compounds with bis-diamine cores were prepared and their electrochemical behavior was explored polarographically. The behavior of the compounds was studied at the dropping mercury electrode and the rotating platinum electrode. Trans-dinitro-bis-(ethylenediamine) cobalt (III) nitrate shows reversible behavior in well-buffered solutions at the dropping mercury electrode, The mechanism for the reduction is proposed as; rapid, reversible election transfer; decomposition of the reduced species; and, in solutions sufficiently alkaline, the formation of tris-(ethylenediamine) cobalt (II), thereby accounting for the observed second wave. The reduction of cis dithiocyanato-bis-(ethylenediamine) cobalt (III) thiocyanate and oxalato-bis-(ethylenediamine) cobalt (III) chloride both give irreversible waves, thereby complicating any proposal of a mechanism. The observed second reduction wave, though, appears to be caused by the formation of tris-(ethylenediamine) cobalt (II), as in the case of the dinitro compound. A proposal of the mechanism for the other five compounds was not possible as they either reduced at too positive a potential, aquated too rapidly, or both. / Master of Science

Faculty of Science School of Chemistry 0204045a tspmkwi@hotmail.com / New possibilities in collection of polarographic and potentiometric experimental data in studies of metal–ligand systems by automated instrumental methods, and subsequent treatment of the polarographic data, whereby the degree of reversibility of the electrode processes varies, have been investigated in this work. An automated instrumental set–up was developed for applications in studies of metal–ligand solution equilibria by potentiometry and sampled Direct Current Polarography (DCP). The new set–up was designed based on virtual instrumentation principles whereby several commercially– available hardware units as well as custom–built electronic components, were interfaced to a personal computer that was equipped with appropriate hardware and control programs. The instrumental set–up was tested and validated by studying the protonation equilibria of the ligand glycine by Glass Electrode Potentiometry (GEP) as well as the complexation of the ligand glycine with Cd2+ by GEP and DCP. The new set–up provides increased versatility, accuracy and convenience in obtaining large numbers of experimental points in solution equilibria studies by DCP and GEP as opposed to the use of tedious and time–consuming manual methods. Nonlinear curve–fitting procedures, based on closed–form models that were derived here from suitable theoretical equations identified from literature, have been investigated in this work for applications in analysis of DC curves recorded on metal–ligand systems with variation in electrochemical reversibility. The applicability and limitations of the curve–fitting procedures developed have been tested in analysis of the DCP data collected on several metal–ligand systems involving Cd2+, Pb2+, Zn2+ and the ligands glycine and sarcosine, whereby the DCP studies of these systems exhibited reversible, quasi–reversible or irreversible electrochemical processes. Information on applicability and limitations of the proposed methods investigated in this work was derived by comparison of the results obtained from DCP, using the proposed methods, with either reported literature data and/or results obtained in this work by the independent analytical technique of GEP, which was deployed wherever it was found to be applicable to study the metal–ligand systems considered.