Estudos sobre a utilização do pentacloreto de nióbio na síntese de derivados cumarínicos com estrutura doador-π-aceptor com potencial aplicação como corantes sensibilizadores em dispositivos fotoeletroquímicos de Gratzel
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Data
2019-04-08
Autores
Oshiro, Paula Beatriz
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Universidade Estadual Paulista (Unesp)
Resumo
Derivados de cumarina representam uma grande e importante classe de produtos naturais com diversas atividades biológicas. Entretanto, com a eletrônica orgânica e a utilização de novos materiais como absorvedores de luz, derivados de cumarina têm despertado grande interesse da comunidade científica. As cumarinas possuem grande absorção na região visível e alto rendimento quântico de fluorescência, o que sugere ser um material promissor para aplicação como corantes em células solares. Entre os métodos de síntese de cumarina descritos na literatura, podemos citar a reação de Knoevenagel, Pechmann e Perkin. A reação multicomponente (RMC) é outro método de síntese dos derivados de cumarina e foi desenvolvido pelo nosso grupo de pesquisa. As RMCs ocorrem entre três ou mais reagentes em uma única etapa reacional, no mesmo frasco. Os compostos de interesse foram obtidos através dos reagentes de partida: 4-aminocumarina, derivados de aldeído e benzoilacetato de etila, catalisados por ácidos de Lewis. A reação ocorreu na presença de NbCl5, em N2, sob refluxo, em DCM, DCE, MeCN, MeOH ou THF durante 5, 24 ou 48 h. Essas foram as condições reacionais estudadas para se estabelecer protocolos de síntese para a formação dos produtos de interesse. Os resultados mais promissores foram obtidos em 24 h, com DCE e NbCl5, com rendimentos que variam entre 38 e 58%. As caracterizações ópticas mostraram um comprimento de onda de absorção em torno de 355 nm, emissão de fluorescência em torno de 420 nm e rendimento quântico de fluorescência chegando a 0,129%. Também foram utilizados os reagentes: furan-2-carboxaldeído, 2-tiofenocarboxaldeído, 4-metoxifenol, 3,5-dimetoxifenol, 3,4,5-trimetoxifenol, β-naftol, malonato de dimetila, ácido 3-etoxi-3-oxopropanóico e acetoacetato de metila, para a síntese de outros derivados de cumarina. Essas reações ocorreram na presença de NbCl5, em N2, a temperatura ambiente ou 50 ºC, em DCM, DCE, MeCN ou MeOH, durante 48 h, 24 h, 12 h, 3 h ou 10 min. O pentacloreto de nióbio, que apresenta grande aplicabilidade em reações orgânicas, demonstrou ser capaz de catalisar apenas algumas dessas reações mencionadas, demonstrando um baixo rendimento e difícil purificação de inúmeros produtos formados.
Coumarin derivatives represent a large and important class of natural products with diverse biological activities. However, with organic electronics and the use of new materials as light absorbers, coumarin derivatives have aroused great interest from the scientific community. Coumarins have high absorption in the visible region and high fluorescence quantum yield, which suggests to be a promising material for application as dyes sensitized solar cells. Among the methods of coumarin synthesis described in the literature, we can mention the reaction of Knoevenagel, Pechmann and Perkin. The multicomponent reaction (MCR) is another method of synthesis of coumarin derivatives and was developed by our research group. MCRs occur between three or more reactants in a single reaction step, in the same flask. Compounds of interest were obtained from the starting reagents: 4-aminocoumarin, aldehyde derivatives and ethyl benzoylacetate, catalysed by Lewis acids. The reaction occurred in the presence of NbCl5, in N2, under reflux in DCM, DCE, MeCN, MeOH or THF for 5, 24 or 48 h. These were the reactional conditions studied to establish synthesis protocols for the formation of the products of interest. The most promising results were obtained in 24 h with DCE and NbCl5 with yields ranging from 38 to 58%. The optical characterizations showed an absorption wavelength around 355 nm, fluorescence emission around 420 nm and fluorescence quantum yield reaching 0.129%. Also, the reactants: furan-2-carboxaldehyde, 2-thiophenecarboxaldehyde, 4-methoxyphenol, 3,5-dimethoxyphenol, 3,4,5-trimethoxyphenol, β-naphthol, dimethyl malonate, 3-ethoxy-3-oxopropanoic acid and methyl acetoacetate for the synthesis of other coumarin derivatives. These reactions occurred in the presence of NbCl5, in N2 at room temperature or 50 °C in DCM, DCE, MeCN or MeOH for 48 h, 24 h, 12 h, 3 h or 10 min. Niobium pentachloride, which has great applicability in organic reactions, has been shown to be able to catalyze only some of these reactions, demonstrating a low yield and difficult purification of the numerous products formed.
Coumarin derivatives represent a large and important class of natural products with diverse biological activities. However, with organic electronics and the use of new materials as light absorbers, coumarin derivatives have aroused great interest from the scientific community. Coumarins have high absorption in the visible region and high fluorescence quantum yield, which suggests to be a promising material for application as dyes sensitized solar cells. Among the methods of coumarin synthesis described in the literature, we can mention the reaction of Knoevenagel, Pechmann and Perkin. The multicomponent reaction (MCR) is another method of synthesis of coumarin derivatives and was developed by our research group. MCRs occur between three or more reactants in a single reaction step, in the same flask. Compounds of interest were obtained from the starting reagents: 4-aminocoumarin, aldehyde derivatives and ethyl benzoylacetate, catalysed by Lewis acids. The reaction occurred in the presence of NbCl5, in N2, under reflux in DCM, DCE, MeCN, MeOH or THF for 5, 24 or 48 h. These were the reactional conditions studied to establish synthesis protocols for the formation of the products of interest. The most promising results were obtained in 24 h with DCE and NbCl5 with yields ranging from 38 to 58%. The optical characterizations showed an absorption wavelength around 355 nm, fluorescence emission around 420 nm and fluorescence quantum yield reaching 0.129%. Also, the reactants: furan-2-carboxaldehyde, 2-thiophenecarboxaldehyde, 4-methoxyphenol, 3,5-dimethoxyphenol, 3,4,5-trimethoxyphenol, β-naphthol, dimethyl malonate, 3-ethoxy-3-oxopropanoic acid and methyl acetoacetate for the synthesis of other coumarin derivatives. These reactions occurred in the presence of NbCl5, in N2 at room temperature or 50 °C in DCM, DCE, MeCN or MeOH for 48 h, 24 h, 12 h, 3 h or 10 min. Niobium pentachloride, which has great applicability in organic reactions, has been shown to be able to catalyze only some of these reactions, demonstrating a low yield and difficult purification of the numerous products formed.
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Palavras-chave
Pentacloreto de Nióbio, Reações multicomponentes, Cumarinas, Célula solar, Niobium Pentachloride, Multicomponent reaction, Coumarin, Solar cell