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Tejsav enantioszelektiv eszterezese Cyphos 104 ionos folyadekban

2-hydroxypropionic acid can be found in the nature, for example in milk products, cabbage, and it is an intermedier in some meabolism. It is the smallest chiral carboxylic acid, which is produced by fermentation of various renewable resources. Among the lactic acid derivatives, lactates are really valuable products since they can be applied in food industry as a flavour component, and in the pharmaceutical and cometic industry. In addition, ethyl lactate is a natural flavouring compound and can be used as a green solvent, as well. This compound contains a carboxyl and a hydroxyl group, which make it a very reactive molecule. The esterification of lactic acid has a unique industrial importance, since this is the only purification process, which separates other organic acids from lactic acid. Esterification of lactic acid is an equilibrium reaction, therefore the maximal yield can be influenced using an excess of one of the substrates (usually the alcohol) or removing the product ester or the side-product water. Water content plays an important role during the reaction. In one hand the enzyme needs a monomolecular water layer, in the other hand the lactic acid undergoes selfesterification when there is not enough water present in the reaction mixture. Ionic liquids constitute one of the hottest areas in chemistry these days. These chamicals are molten salts at room temperature with a melting point below 100 °C, which can be achieved by incorporating a bulky asymmetric cation into the structure together with a weakly-coordinating anion. Their unique, highly solvating features provide an attracting medium for various types of chemical processes. Practically, they have no vapour pressure, which is a great advantage against conventional solvents. When a certain application requires a new solvent, ILs can be made task specific for it by a judicious variation in the lenght and branching of the alkyl chain and the anionic precursor. This is the reason why they are designated as tailor-made molecules. It is not negligible that the structure effects the environmentally features like biodegradability or toxicity. In the past few years the researchers and collaborators of the Research Institute of Chemical and Process Engineering, Veszprem carried out several reactions in ionic liquids. The enantioselective esterification of lactic acid in ILs is a brand new research area. The proper ILs were chosen to be the solvent for the reations of lactic acid. Several phosphonium type ionic liquids were tested. Cyphos 163 was the best solvent to achieve the best ester yield, but it catalyzes the reaction itself, so does the Cyphos 202. Cyphos 104 was the chosen solvent where our experiments were carried out. It does not catalyze the reaction itself and priduce a quite beneficial ester yield. With this solvent the enantioselectivity of the enzyme can be investigated. The enzyme enantioselectivity can be manipulated by the substrates and the reaction conditions. In some cases small amount of co-solvent was added to the reaction mixture, which resulted in higher activity, stability and the enantiomeric excess was much higher. The esterification of lactic acid with ethanol was carried out using Novozyme 435 (Candida antarctica lipase B), Amano PS-IM and Candida cilindraca enzymes).The reaction mixture contained 3, 6 mmol monomer lactic acid and 44 mmol ethanol, respecitvely, and 600 mg Cyphos 104 ionic liquid. In order to reach the higher enantiomeric excess the temperature (40 and 60 °C) and the ethanol excess (3, 6 and 12 times) were modified. The reactions were carried out in a thermostated, stirred (500 rpm) bioreactor, and the reaction time was 24 h. The two latter enzymes did not show enantioselectivity, but the enantiomeric excess was considerable with the CALB.

ionic liquid; lipase; Cyphos 104; esterification

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