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Abstract(s)
Os pinheiros são coníferos, dos quais se pode adquirir a madeira e extrair o “tall oil” bruto, a resina e a goma da madeira. Através da destilação da resina podemos adquirir a colofónia e terebintina. A colofónia consiste numa mistura complexa de terpenos neutros e diterpenos ácidos, onde se incluem os abietanos, que são diterpenoides tricíclicos aos quais o ácido abiético (AA) e dehidroabiético (DHA) pertencem.
A eletroquímica combina a transferência de eletrões no elétrodo com uma reação química, sendo que podem ser controladas utilizando corrente ou potencial constante. Acabam por ser reações “mais verdes”, seguras, eficientes e económicas. A eletrólise pode ser direta, onde se oxida/reduz diretamente a molécula, ou indireta, onde um se utiliza mediadores, reagentes capazes de oxidar/reduzir seletivamente a molécula.
A eletroquímica em fluxo é uma técnica que permite o scale up industrial da eletroquímica, tendo vantagens sobre esta como o oferecer uma maior proximidade entre elétrodos e uma maior área de superfície do elétrodo, o que diminui o tempo de reação e permite a dispensa do uso de eletrólitos de suporte.
Neste contexto, o principal objetivo desta investigação assentou em acrescentar valor biossintético à colofónia e aos seus abietanos, utilizando reações orgânicas clássicas, eletroquímica e química em fluxo para sintetizar novos derivados e estudar os potenciais de oxidação destes compostos.
Relativamente ao trabalho experimental, começou se por preparar os derivados metil éster do AA e do DHA, pois seriam compostos mais estáveis. Estudamos os potenciais de oxidação destes compostos. Desenvolvemos e otimizamos protocolos para a oxidação eletroquímica, onde conseguimos alcançar a oxidação benzílica direta tanto do DHA como do MDHA com bons rendimentos, a oxidação indireta do MDHA (utilizando Cl4NHPI como mediador) e também conseguimos alcançar a oxidação de AA e MAA com rendimentos moderados. Por fim estudou-se o uso de eletroquímica em fluxo para realizar estas oxidações, usando-se o DHA como material de partida.
Pine trees are coniferous, from which we can extract wood, raw tall oil, wood gum, and gum. Through the distillation of gum, we can acquire turpentine and colophony. Colophony is a complex mixture of neutral terpenes and acidic diterpenes, including abietanes, which are tricyclic diterpenoids to which abietic acid (AA) and dehydroabietic acid (DHA) both belong. Electrochemical reactions combine the electron transfer at an electrode with a chemical reaction and can be controlled using constant current or constant potential. Overall, they are very environmentally friendly, safer, efficient, and economical. The electrolysis process can be direct, where we are able to directly oxidize/reduce the molecule, or indirect, where we use a mediator – a selective oxidizing/reducing reagent. Flow electrochemistry is a technique that allows the industrial scale up of electrochemistry, having advantages over it such as offering greater proximity between electrodes and a higher surface area of the electrode, which decreases the reaction time and allows the dispensation of the use of supporting electrolytes. In this regard, the main objective of this research was to add biosynthetic value to colophony and its abietanes, using classic organic reactions and electrochemistry to synthesize new derivates and then study the oxidation potentials of these compounds. Regarding the experimental work, we started by preparing the methyl ester derivatives of AA and DHA, as they would be more stable compounds. We studied the oxidation potentials of these compounds. We developed and optimized protocols for electrochemical oxidation, where we achieved the direct benzylic oxidation of both DHA and MDHA with good yields, the indirect oxidation of MDHA (using Cl4NHPI as a mediator) and we also achieved the oxidation of AA and MAA with moderate yields. Finally, we studied the use of flow electrochemistry to achieve these oxidations using DHA as starting material.
Pine trees are coniferous, from which we can extract wood, raw tall oil, wood gum, and gum. Through the distillation of gum, we can acquire turpentine and colophony. Colophony is a complex mixture of neutral terpenes and acidic diterpenes, including abietanes, which are tricyclic diterpenoids to which abietic acid (AA) and dehydroabietic acid (DHA) both belong. Electrochemical reactions combine the electron transfer at an electrode with a chemical reaction and can be controlled using constant current or constant potential. Overall, they are very environmentally friendly, safer, efficient, and economical. The electrolysis process can be direct, where we are able to directly oxidize/reduce the molecule, or indirect, where we use a mediator – a selective oxidizing/reducing reagent. Flow electrochemistry is a technique that allows the industrial scale up of electrochemistry, having advantages over it such as offering greater proximity between electrodes and a higher surface area of the electrode, which decreases the reaction time and allows the dispensation of the use of supporting electrolytes. In this regard, the main objective of this research was to add biosynthetic value to colophony and its abietanes, using classic organic reactions and electrochemistry to synthesize new derivates and then study the oxidation potentials of these compounds. Regarding the experimental work, we started by preparing the methyl ester derivatives of AA and DHA, as they would be more stable compounds. We studied the oxidation potentials of these compounds. We developed and optimized protocols for electrochemical oxidation, where we achieved the direct benzylic oxidation of both DHA and MDHA with good yields, the indirect oxidation of MDHA (using Cl4NHPI as a mediator) and we also achieved the oxidation of AA and MAA with moderate yields. Finally, we studied the use of flow electrochemistry to achieve these oxidations using DHA as starting material.
Description
Trabalho Final de Mestrado Integrado, Ciências Farmacêuticas, 2021, Universidade de Lisboa, Faculdade de Farmácia.
Keywords
Colophony Abietanes Electrochemistry Mediators Continuous flow Mestrado integrado - 2021