Estudos sobre a aplicação de óxido de nióbio em reações de oxidação de compostos orgânicos
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Data
2018-02-26
Autores
Carvalho, José Henrique Lázaro
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Universidade Estadual Paulista (Unesp)
Resumo
Os hidrocarbonetos se constituem na função mais simples da química orgânica. Mesmo sendo formados apenas por carbono e hidrogênio, esta classe é uma das mais diversas, onde se destacam os hidrocarbonetos alquil aromáticos (HAA) e os hidrocarbonetos aromáticos policíclicos (HAP). Por possuírem baixa reatividade e serem lipossolúveis, os HAA e HAP tendem a se acumular na natureza e nos tecidos vivos podendo levar a mutações genéticas e ao câncer. Funcionalizações oxigenadas nestes hidrocarbonetos ampliam suas aplicações industriais e auxiliam na sua remediação ambiental. A oxidação radicalar utilizando radicais hidroxila via TBHP (t-butil-hidroperóxido) é uma rota promissora devido à ausência de resíduos metálicos nocivos no processo. Paralelamente, o uso de metais do bloco-d, como o nióbio, como catalisadores heterogêneos, que são conhecidos por apresentarem boa estabilidade térmica, porosidade, maior superfície de contato e podendo ser recuperado e reutilizado, vem sendo descrito como bons catalisadores para a reação, permitindo rendimentos maiores e condições reacionais mais brandas. O nióbio tem despertado o interesse de muitos grupos de pesquisa devido às suas propriedades e aplicabilidades na metalurgia, supercondutores e supercapacitores, e na síntese orgânica. Este trabalho focou no estudo da aplicação do óxido de nióbio como catalisador heterogêneo em reações de oxidação de HAA e HAP usando o TBHP como oxidante. Diferentes variáveis reacionais como o solvente, a concentração e morfologia do catalisador, temperatura, dentre outras, foram investigadas a fim de otimizar a reação para a melhor conversão no derivado oxigenado. A melhor condição obtida foi utilizando Nb2O5 amorfo em 10% em mol de reagente, em acetonitrila e em refluxo com mais de 40 % de conversão em derivado oxigenado para qualquer substrato de hidrocarboneto estudado.
Hydrocarbons are the simplest function of organic chemistry. Although formed only by carbon and hydrogen, this class is one of the most diverse, in which the alkyl aromatic hydrocarbons (AAHs) and the polycyclic aromatic hydrocarbons (PAHs) stand out. These substances are mostly fossil raw materials widely used in industry in diverse applications. Because they have low reactivity and are liposoluble, AAHs and PAHs tend to accumulate in nature and in living tissues, leading to genetic mutations and cancer. Oxygenated functionalities in these hydrocarbons broaden their industrial applications and assist in their environmental remediation. Radical oxidation using hydroxyl radicals via TBHP (t-butylhydroperoxide) is a promising route due to the absence of noxious metal residues in the process. At the same time, the use of d-block metals, such as niobium, as heterogeneous catalysts, which are known to have good thermal stability, porosity, larger contact surface and be able to be recovered and reused, have been described as good catalysts for the reaction, allowing for higher yields and softer reaction conditions. Niobium has attracted the interest of many research groups because of its properties and applications in metallurgy, superconductors and supercapacitors, and in organic synthesis. This work focused on the study of the application of niobium oxide as a heterogeneous catalyst in oxidation reactions of AAHs and HAP using TBHP as oxidant. Many reactional variables like the solvent, the catalyst concentration and morphology, as well as temperature have been investigated in order to optimize the reaction for the better conversion to oxygen derivatives. The best obtained condition was using 10 % in mol amorphous Nb2O5 in acetonitrile under reflux with a conversion yield of more than 40 % for any studied hydrocarbon substrate.
Hydrocarbons are the simplest function of organic chemistry. Although formed only by carbon and hydrogen, this class is one of the most diverse, in which the alkyl aromatic hydrocarbons (AAHs) and the polycyclic aromatic hydrocarbons (PAHs) stand out. These substances are mostly fossil raw materials widely used in industry in diverse applications. Because they have low reactivity and are liposoluble, AAHs and PAHs tend to accumulate in nature and in living tissues, leading to genetic mutations and cancer. Oxygenated functionalities in these hydrocarbons broaden their industrial applications and assist in their environmental remediation. Radical oxidation using hydroxyl radicals via TBHP (t-butylhydroperoxide) is a promising route due to the absence of noxious metal residues in the process. At the same time, the use of d-block metals, such as niobium, as heterogeneous catalysts, which are known to have good thermal stability, porosity, larger contact surface and be able to be recovered and reused, have been described as good catalysts for the reaction, allowing for higher yields and softer reaction conditions. Niobium has attracted the interest of many research groups because of its properties and applications in metallurgy, superconductors and supercapacitors, and in organic synthesis. This work focused on the study of the application of niobium oxide as a heterogeneous catalyst in oxidation reactions of AAHs and HAP using TBHP as oxidant. Many reactional variables like the solvent, the catalyst concentration and morphology, as well as temperature have been investigated in order to optimize the reaction for the better conversion to oxygen derivatives. The best obtained condition was using 10 % in mol amorphous Nb2O5 in acetonitrile under reflux with a conversion yield of more than 40 % for any studied hydrocarbon substrate.
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Palavras-chave
HAA e HAP, Oxidação radicalar, TBHP, Nióbio, Catálise heterogênea, AAHs and PAHs, Radical oxidation, Niobium oxide, Heterogeneous catalyst