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Doctoral Thesis
DOI
10.11606/T.46.2016.tde-02022016-161249
Document
Author
Full name
Helena Redigolo Pezza
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1997
Supervisor
Committee
Coichev, Nina (President)
Fatibello Filho, Orlando
Krug, Francisco Jose
Massaro, Sergio
Zagatto, Elias Ayres Guidetti
Title in Portuguese
Estudo da autoxidação de [Ni(cyclam)]2+ induzida por óxidos de S(IV)
Keywords in Portuguese
Autoxidação
Catálise
Físico-química
Método ótico
Ni cyclam 2
Óxidos de S IV
Abstract in Portuguese
A autoxidação de [Ni(cyclam)]2+ (cyclam = 1,4,8,11-tetraazociclotetradecano) induzida por S(IV) foi estudada acompanhando-se espectrofotometricamente, em função do tempo, a formação de [Ni(cyclam)]3+ em soluções saturadas com oxigênio contendo: [Ni(cyclam)]2+ 6,0 x10-3 mol L-1, [Ni(cyclam)]3+ (inicial) 8,0x10-6 mol L-1, cyclam 6,0x10-3 mol L-1, S(IV) (1,0 - 5,0)x10-4 mol L-1 e HClO4 1,0 mol L-1 a T = 25,0 °C e força iônica 1,0 mol L-1. A reação de autoxidação exibe um comportamento autocatalítico no qual o período de indução depende da concentração inicial de Ni(III). O estudo cinético da redução de Ni(III) por S(IV), sob condições anaeróbicas, e a autoxidação de Ni(II) mostraram que a etapa determinante da velocidade da reação é a redução de Ni(III) por S(IV) para produzir o radical SO3•-, que reage com o oxigênio dissolvido produzindo SO5•- o qual rapidamente reoxida o Ni(II). Os resultados mostram claramente um ciclo redox que depende do balanço entre a concentração de S(IV) e oxigênio. Quando a reação se processa na presença de Co(III) (10-6 a 10-4 mol L-1) e de Mn(II) (10-3 a 10-2 mol L-1) constatou-se a ocorrência de efeito sinérgico positivo na formação de [Ni(cyclam)]3+.
Title in English
Study autoxidation [Ni(cyclam)]2+ induced by oxide S(IV)
Keywords in English
Catalysis
Ni cyclam 2
Optical method
Oxidation
Oxides S IV
Physical chemistry
Abstract in English
The autoxidation of [Ni(cyclam)]2+, cyclam = 1,4,8,11-tetraazacyclotetradecane, accelerated by sulfur dioxide was studied by spectrophotometrically monitoring the formation of [Ni(cyclam)3+ under the conditions: [Ni(cyclam)]2+ = 6.0 x 10-3 mol L-1; initial [Ni(cyclam)]3+ = 8.0 x 10-6 mol L-1; [cyclam] = 6.0 x 10-3 mol L-1 ; [S(IV)] = (1.0 - 5.0) x10-4 mol L-1 and 1.0 mol L-1 perchloric acid in oxygen saturated solutions at 25.0 °C and ionic strength 1.0 mol L-1. The autoxidation reaction exhibits an autocatalytic behavior in which the induction period depends on the initial Ni(III) concentration. The kinetic study of the reduction of Ni(III) by S(IV), under anaerobic conditions, and autoxidation of Ni(II) showed as the rate-determining step the reduction of Ni(III) by S(IV) to produce SO3•- radical, which reacts with dissolved oxygen to produce SO5•- and rapidly oxidizes Ni(II). The results clearly show a redox cycling process which depends on the balance of S(IV) and oxygen concentration. The sinergystic effect of the Co(III) and Mn(II) was studied. Both exhibit a positive synergistic effect in the sulfite-induced aLrtoxidation of Ni(II).
 
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Publishing Date
2016-02-02
 
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