Enantiomer separation through biocatalysis using NADES

• Autor(a) principal: Sousa, Cristiana Sofia Ferreira de
• Data de Publicação: 2015
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/24086
• topic: Candida rugosa lipase; Enantioselectivity; Racemic menthol; Deep eutectic solvents; Green solvents; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

Currently, the separation process of racemic secondary alcohols has a great environmental impact because it involves the use of large amounts of organic solvents and energy. Based on the principles of green chemistry, the main purpose of this work is the development of a sustainable process, without the use of organic solvents and using reusable catalysts (enzymes) in order to make the most efficient separation process in terms of energy and reduce the associated environmental impact. In this work we developed a process for the separating of the enantiomers of (±)-menthol, via a transesterification reaction with vinyl decanoate. At optimum conditions, this reaction will yield the pure enantiomer (-)-menthyl decanoate, while (+)-menthol will remain unreacted. The use of reusable biological catalysts is possible due to the enantioselectivity of the enzyme, allowing the resolution of secondary alcohols to obtain pure enantiomers of high added value. Candida Rugosa lipase is a selective enzyme capable of selectively converting the (-)-menthol into a different chemical compound and with different characteristics the (+)-menthol. At the end of the reaction, the menthol enantiomers will be present in the reaction medium in the form of (+)-menthol and (-)-menthyl decanoate. As such it is necessary to use a method based on the properties of alternative solvents to physically separate the compounds. The main objective of this study is to evaluate deep eutectic solvents as solvents for the transesterification reaction, but also to experiment if whether they themselves are able to act as substrates. Another approach is to test whether they can also act as separating agents of (+)-menthol and menthyl decanoate. In the first phase it is intended to develop a DES using combinations of choline chloride, urea, and glycerol. The second objective is to synthesize DES based on menthol, containing one or both of the reaction substrates in the composition. The transesterification reaction is conducted in these solvents in order to assess whether the reaction is feasible in the presence of a biocatalyst. After the reaction, the enantiomers can be separated, since they are different entities. This separation is based on the interaction of the compounds with the DES, which allows the physical separation of the two compounds ((+)-menthol and (-)-menthyl decanoate). Through this work, we got the required proof of concept for all experiments performed in DES. Using hexane as reaction medium, a (±)-menthol conversion of 26.3 % was achieved, nevertheless controlling the water content in the reaction medium and in the atmosphere a maximum conversion of 50.9 % was achieved after 24 hours at 40°C. In DES ChCl:glycerol (1:2) and ChCl:urea (1:2) conversions are similar to those obtained in hexane at the same conditions, with values of 10.9 % and 10.2 % respectively. In DES menthol:camphor (4:1) was obtained 23% conversion at 40°C after 50 hours. In DES menthol:lauric acid (2:1) and menthol:phenylpropionic acid (1:1) conversions are higher with a maximum of 79.6 % and 62.1 % respectively. For the separation of compounds, DES choline dodecanediote:glycerol (1:1) was most effective with a separation factor of 16±6.5.