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Desenvolvimento de Novas Técnicas de Síntese para Derivados de Celulose
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A celulose é um polímero natural biodegradável e reutilizável. Este é o polímero mais
abundante na natureza, sendo as suas aplicações amplamente estudadas. A sua derivatização
à escala industrial é realizada maioritariamente em meio heterogéneo, o que apresenta limita-
ções no controlo da reação. Este problema pode ser contornado recorrendo a condições ho-
mogéneas de síntese, que requerem a dissolução total do polímero, que, dada à sua estrutura
supramolecular, é dificilmente alcançada nos solventes convencionais.
Este trabalho teve como objetivo a otimização das condições de síntese de dicarboxime-
tilcelulose (DCMC) e dos seus análogos, em meio heterogéneo e homogéneo.
Iniciou-se pela síntese do eletrófilo para a derivatização de DCMC, o bromomalonato de
sódio (NaBMA), na qual uma via reacional permitiu o isolamento do produto desejado, e as
restantes oito vias resultaram numa mistura de produtos ou no material de partida. Procedeu-
se à síntese de quatro líquidos iónicos (LI), sendo estes o acetato de 8-etil-1,8-diazabici-
clo[5.4.0]undec-7-eno ([DBUH][OAc]), o acetato de 1,5-diazabiciclo[4.3.0]non-5-eno
([DBNH][OAc]), o dietilfosfato de 1,5-diazabiciclo[4.3.0]non-5-eno ([DBUEt][DEP]) e o dietilfos-
fato de 1,5-diazabiciclo[4.3.0]non-5-eno ([DBNEt][DEP]). A estes LIs adicionou-se diferentes
frações molares de co-solventes orgânicos dimetilsulfóxido (DMSO) ou dimetilformamida
(DMF), criando assim diferentes sistemas de solventes para a síntese homogénea de DCMC.
Nestas reações, fez-se variar parâmetros como o tipo de agitação, a percentagem de celulose
dissolvida de celulose e o número de equivalentes de NaBMA. Os polímeros foram caracteri-
zados por espectroscopia de infravermelho (FTIR), emissão atómica (ICP-AES), ressonância
magnética nuclear (NMR) de protão, carbono, fósforo e de domínio de tempo, e a sua estrutura
cristalina foi avaliada por difração de raio-X (XRD). Verificou-se um grau de substituição (DS)
inferior para as amostras sintetizadas homogeneamente, com um valor entre 0,00 e 0,1, não
havendo diferenças significativas entre as diferentes condições reacionais. Por outro lado, as sínteses heterogéneas alcançaram um DS de 0,423. Os seus análogos apresentaram valores de
DS entre 0,066 e 2,14.
Os LIs foram reciclados e caracterizados, concluindo-se que estes retêm iões de sódio
do eletrófilo, e que, somente o [DBNH][OAc] junto com DMF não se degradou após a primeira
síntese. A reutilização deste LI não teve uma influência significativa no DS do derivado.
Cellulose is a biodegradable and reusable natural polymer. It is the most abundant polymer, and its applications are widely studied. Its derivatization in the industries is mostly carried out in heterogeneous media, which presents limitations on the reaction control. This problem can be overcome by using homogeneous synthesis conditions, which require the total dissolution of the polymer, that, given its supramolecular structure, is difficult to achieve in conventional solvents. This work aimed to study the synthesis of dicarboxymethylcellulose (DCMC) and its ana- logues, in heterogeneous and homogeneous conditions. Firstly, the electrophile for the derivatization of DCMC, sodium bromomalonate (NaBMA), was synthetised, in which one reaction route allowed the isolation of the desired product, and the remaining eight routes resulted in a mixture of products or of starting material. Secondly, four ionic liquids (ILs) were synthesized: 8-ethyl-1,8-diazabicyclo[5.4.0]undec-7-ene acetate ([DBUH][OAc]), 1,5-diazabicyclo[4.3.0]non-5-ene acetate ([DBNH][OAc]), 1,5-diazabi- cyclo[4.3.0]non-5-ene diethylphosphate ([DBUEt][DEP] ) and 1,5-diazabicyclo[4.3.0]non-5-ene diethylphosphate ([DBNEt][DEP]). Different molar fractions of the organic co-solvents dimethyl sulfoxide (DMSO) or dimethylformamide (DMF) were added to these ILs, thus creating different solvent systems for the homogeneous synthesis of DCMC. Several parameters in the synthesis were altered and compared, such as the mixing type, the percentage of dissolved cellulose and the number of NaBMA equivalents. The polymers were characterized by infrared spectroscopy (FTIR), atomic emission (ICP-AES), proton, carbon, phosphorus and time domain nuclear mag- netic resonance (NMR), and its crystal structure was evaluated by X-ray diffraction (XRD). A lower degree of substitution (DS) was observed for the homogeneously synthesized samples, with values between 0.00 and 0.01, with no significant differences between the different reaction conditions. On the other hand, the heterogeneous properties reached a DS of 0.423. Their analogues showed a DS between 0.066 and 2.14. The ILs were recycled and characterized, concluding that they retain sodium ions from the electrophile, and that only [DBNH][OAc] mixed with DMF didn't suffer degradation after the first synthesis. The reuse of this IL did not have a significant influence on the DS of the derivate.
Cellulose is a biodegradable and reusable natural polymer. It is the most abundant polymer, and its applications are widely studied. Its derivatization in the industries is mostly carried out in heterogeneous media, which presents limitations on the reaction control. This problem can be overcome by using homogeneous synthesis conditions, which require the total dissolution of the polymer, that, given its supramolecular structure, is difficult to achieve in conventional solvents. This work aimed to study the synthesis of dicarboxymethylcellulose (DCMC) and its ana- logues, in heterogeneous and homogeneous conditions. Firstly, the electrophile for the derivatization of DCMC, sodium bromomalonate (NaBMA), was synthetised, in which one reaction route allowed the isolation of the desired product, and the remaining eight routes resulted in a mixture of products or of starting material. Secondly, four ionic liquids (ILs) were synthesized: 8-ethyl-1,8-diazabicyclo[5.4.0]undec-7-ene acetate ([DBUH][OAc]), 1,5-diazabicyclo[4.3.0]non-5-ene acetate ([DBNH][OAc]), 1,5-diazabi- cyclo[4.3.0]non-5-ene diethylphosphate ([DBUEt][DEP] ) and 1,5-diazabicyclo[4.3.0]non-5-ene diethylphosphate ([DBNEt][DEP]). Different molar fractions of the organic co-solvents dimethyl sulfoxide (DMSO) or dimethylformamide (DMF) were added to these ILs, thus creating different solvent systems for the homogeneous synthesis of DCMC. Several parameters in the synthesis were altered and compared, such as the mixing type, the percentage of dissolved cellulose and the number of NaBMA equivalents. The polymers were characterized by infrared spectroscopy (FTIR), atomic emission (ICP-AES), proton, carbon, phosphorus and time domain nuclear mag- netic resonance (NMR), and its crystal structure was evaluated by X-ray diffraction (XRD). A lower degree of substitution (DS) was observed for the homogeneously synthesized samples, with values between 0.00 and 0.01, with no significant differences between the different reaction conditions. On the other hand, the heterogeneous properties reached a DS of 0.423. Their analogues showed a DS between 0.066 and 2.14. The ILs were recycled and characterized, concluding that they retain sodium ions from the electrophile, and that only [DBNH][OAc] mixed with DMF didn't suffer degradation after the first synthesis. The reuse of this IL did not have a significant influence on the DS of the derivate.
Descrição
Palavras-chave
Dicarboximetilcelulose (DCMC) Derivatização de celulose Líquidos iónicos