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Doctoral Thesis
DOI
10.11606/T.75.2017.tde-30032017-092449
Document
Author
Full name
Thiago Hideyuki Kobe Ohe
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2016
Supervisor
Committee
Cardoso, Daniel Rodrigues (President)
Boscolo, Mauricio
Faria, Joao Bosco
Polito, Wagner Luiz
Silva, João Batista de Almeida e
Title in Portuguese
Estudo das principais rotas de formação de carbamato de etila em aguardente de cana
Keywords in Portuguese
Aguardente de cana
carbamato de etila
íons cianato
Abstract in Portuguese

As propriedades de fluorescência da 2,4-(1H,3H)-quinazolinediona, produto da reação entre o íon cianato e o ácido 2-aminobenzóico possibilitaram o desenvolvimento de um método simples, sensíveis, seletivo e reprodutível para a análise de íons cianato em meio aquo etanólico. O método foi aplicado a análises de íons cianato em diferentes frações do destilado de cana e os dados sugerem uma forte correlação entre a presença de ureia no vinho, e as concentrações de íons cianato e de carbamato de etila (CE) no destilado. A citrulina apresenta-se também como uma fonte de íons cianato, tendo como um de seus produtos o CE na presença do etanol. Acompanhando-se no destilado recém-obtido as variações nas concentrações de íons cianato e de carbamato de etila em função do tempo, observa-se que à medida que diminui a concentração de íons cianato há um aumento na concentração de carbamato de etila. Foram estudados os aspectos cinéticos e termodinâmicos da formação de CE por meio da reação entre íons cianato e o etanol. Os valores das constantes de velocidade para o consumo do íon cianato e para a de formação de CE são de (8‚0 ± 0‚4) × 10-5 e de (8‚90 ± 0‚4) × 10-5 s-1, respectivamente, a 25 °C em solução etanólica 48% (v⁄v) com pH 4‚5. Nas condições experimentais, as constantes de velocidade são independentes das concentrações de etanol e dos íons cianato, porém são dependentes da acidez pH e apresentam os valores dos parâmetros de ativação de ΔH = 19‚4 ± 1 kcal⁄mol, ΔS = -12‚1 ± 1 cal⁄K e ΔG = 23‚0 ± 1 kcal⁄mol. Cálculos computacionais empregando-se teoria do funcional de densidade (DFT) sugerem que os valores calculados de ΔH1 ΔS1 e ΔG1 estão de acordo com os obtidos experimentalmente e condizem com o mecanismo proposto. Observa-se que íons de Cu(II) catalisam a oxidação de íons cianeto à cianato promovendo a formação de CE. Além disso, íons de Cu(II) pode se coordenar com alguns precursores de CE.

Title in English
Main formation routes of ethyl carbamate in sugarcane spirit
Keywords in English
cyanate
ethyl carbamate
sugarcane spirit
Abstract in English

Based on the fluorescence properties of 2,4-(1H,3H)-quinazolinedione, a product of the reaction between cyanate and 2-aminobenzoic acid, a simple, sensitive, selective, and reproducible method for the cyanate analysis in aqueous ethanolic media is proposed. The method was applied to cyanate analysis in different fractions of sugarcane distillate and the data strongly suggest a correlation between the presence of urea in wine, and cyanate and ethyl carbamate (EC) concentrations in the spirit. Citrulline also presents itself as a cyanate source, having EC as one of its products in the presence of ethanol. Monitoring changes in cyanate and EC concentrations as function of the time in freshly distilled sugar cane spirit, it was observed that as the cyanate concentration decreases, the EC concentration increases. Thermodynamic and kinetic aspects of EC formation through the reaction between cyanate and ethanol were investigated. The rate constant values for cyanate ion decay and EC formation are (8.0 ± 0.4) × 10-5 s-1 and (8.90 ± 0.4) × 10-5 s-1, respectively, at 25 °C in 48% ethanolic solution at pH 4.5. Under the investigated experimental conditions, the rate constants are independent of the ethanol and cyanate concentrations but increase as the temperature increases ΔH = 19.4 ± 1 kcal⁄mol, ΔS = -12.1 ± 1 cal⁄K and ΔG = 23.0 ± 1 kcal⁄mol) and decrease as pH solution increases. According to molecular modeling (DFT) that was performed to analyze the reaction mechanism, Isocyanic acid is the active EC precursor. The calculated ΔH1 ΔS1 and ΔG1 values are in very good agreement with the experimental ones. The copper effect on EC formation reaction was also studied. Copper acts on the cyanide oxidation reaction and could coordinate with some EC precursors.

 
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Publishing Date
2017-03-30
 
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