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Master's Dissertation
DOI
Document
Author
Full name
Ricardo Alexandre Demant
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2000
Supervisor
Committee
Viertler, Hans (President)
Ferraz, Helena Maria Carvalho
Oliveira, Jose Eduardo de
Title in Portuguese
Oxidação eletroquímica de 2-ariloxi-1-(3,4,5-trimetoxifenil)-etanonas e álcoois correspondentes
Keywords in Portuguese
Compostos aromáticos
Físico-química orgânica
Abstract in Portuguese
A investigação de degradação de compostos-modelo de lignina por meios eletroquímicos integra a linha de pesquisa desenvolvida neste grupo há um certo tempo. Neste trabalho utilizou-se 4 compostos-modelo de lignina cujos anéis aromáticos representam unidade siringila, ou seja, três átomos de oxigênio ligados ao anel. São eles: 2-(4-metoxifenóxi)-1-(3,4,5-trimetoxifenil)-etanona (CM-I), 2-(2-metoxifenóxi)-1-(3,4,5-trimetoxifenil)-etanona (CM-II) e os dois álcoois correspondentes (CM-III) e (CM-IV), respectivamente. Para sintetizar estes 4 compostos, foi necessário realizar uma rota sintética que se iniciou com a metilação do ácido 3,4,5-tri-hidroxibenzóico até chegar ao composto chave 2-bromo-1-(3,4,5-trimetoxifenil)-etanona (4). A etapa de bromação da 3,4,5-trimetoxiacetofenona (3) foi a mais problemática pois em vários métodos distintos de bromação a cetona dibromada era obtida como produto secundário. A reação de bromocetona com o fenol 2- ou 4-metoxilado conduziu às cetonas (CM-I) e (CM-II) desejadas. Ambas foram reduzidas aos álcoois (CM-III) e (CM-IV) com borohidreto de sódio Os experimentos eletroquímicos de voltametria cíclica dos 4 compostos-modelo usando anodo de Pt em acetonitrila contendo perclorato de sódio revelaram que suas oxidações eram irreversíveis. Eletrólises preparativas foram feitas principalmente em metanol contendo metóxido de sódio. Quanto à eletrólises preparativas das duas cetonas CM-I e CM-II, observou-se que na oxidação de CM-I houve formação de mistura complexa de produtos enquanto que na de CM-II, parte do material de partida foi recuperado. Já nas oxidações dos álcoois, os resultados obtidos dependeram principalmente da posição da metoxila no grupo fenóxi ligado à cadeia lateral. Quando esta metoxila se encontrava na posição orto, as misturas de reação continha como componente principal o material de partida. Com a metoxila na posição para, dois compostos principais foram isolados, e os seus dados espectroscópicos são coerentes com os esperados para derivados do 1,4-dioxaspiro-[4,5]deca-6,9-dieno.
Title in English
Electrochemical oxidation of 2-aryloxy-1-(3,4,5-trimethoxyphenyl)-ethanones and corresponding alcohols
Keywords in English
Aromatic compounds
Organic chemistry
Abstract in English
The investigation of the electrochemical degradation of lignin model compounds has been part of the research developed in this group for a certain time. In the present work 4 lignin model compounds, in which one of the aromatic rings is representative of syringyl units, were used. They are, 2-(4-methoxyphenoxy)-l(3,4,5-trimethoxyphenyl)-ethanone ( CM-I), 2-(2-methoxyphenoxy )-1-(3,4,5-trimethoxyphenyl)-ethanone (CM-II) and their corresponding alcohols (CM-III) and (CM-IV), respectively. To synthesize these 4 compounds, a synthetic route was developed, beginning with the methylation of the 3,4,5-trhydroxy-benzoic acid. The key compound of this synthetic route was 2-bromo-1-(3,4,5-trimethoxyphenyl)-ethanone (4). The bromination of the 3,4,5-trimethoxyacetophenone was the most problematic step, because the dibromated ketone was obtained as a by product in distinct methods. The reaction of the 2-bromo-1-(3,4,5-trimethoxyphenyl)-ethanone with 2- and 4- methoxylated phenols afforded CM-I and CM-II. Both were reduced to CM-III and CM-IV with sodium borohydride. The cyclic voltammetric experiments of the 4 model compounds using platinum anode in MeCN/ 0,1 M NaClO4 revealed that their oxidations were irreversible. Preparative electrolyses were made mostly in MeOH/MeONa. The electrolyses of the two ketones showed that when CM-I was oxidized a complex mixture of products was obtained, while in the oxidation of CM-II part of the starting material was recovered. In the oxidations of the two alcohols, the results obtained depended mostly on the position of the methoxy group in the phenoy group connected to the carbon-carbon side chain. When the methoxy group was at the ortho position, the reaction mixture contained the starting material as the main product. When this methoxy group was at the para position, two major compounds were isolated, and their spectroscopic data are consistent with those expected for 1,4-dioxaspiro-[4,5]-deca-6,9-diene derivates.
 
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Publishing Date
2019-05-31
 
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