Fig. 7. Lipase-catalyzed polytransesterification of divinyl adipate and 1,4-butanediol.
5. Add hexane (HPLC degree) in a 10-fold excess. Shake strongly the IL-hexane biphasic mixture for 3 min and decant to extract hydrophobic compounds. Repeat this washing step twice. GC analysis of the hexane fraction can be used to check the cleaning degree, repeating the washing steps if necessary.
6. Recover the IL fraction and remove traces of solvents by vacuum evaporation at 50°C.
7. Keep the IL under dry conditions over P2O5 in a dessicator at room temperature.
8. For ILs miscible with water, the IL-H2O fraction can be filtered directly in the same system. Remove water by vacuum evaporation to concentrate the IL.
1. Many references describe protocols to synthesize ionic liquids. A comprehensive review focused on the synthesis and purification of ILs is included in ref. 2.
2. Some start-up and chemical manufacturers of ILs are listed below:
a. Solvent Innovation GmbH (http://www.solvent-innovation.com).
b. Cytec (http://www.cytec.com/)
c. Acros Chemical (http://www.fisherchemicals.co.uk/) markets ILs samples produced by QUILL (Ionic Liquids Laboratory, Queen's University of Belfast).
d. Sigma Chemical Co. (http://www.sigmaaldrich.com/).
e. Merck (http://pb.merck.de/servlet/PB/menu/1122050/index.htmI). This includes an excellent database, which allows a search for ILs according to their physical properties.
3. ILs are colorless and look like water. Traces of starting materials, oxidation products, thermal degradation products, halides, and so on are common impurities that could be present in commercial ILs. Purification of commercial ILs by treatment with carbon active and/or by washing with pure solvents is recommended to avoid undesired effects (see Subheading 3.6.). Keep ILs under dry conditions over P2O5 in a dessicator at room temperature.
4. Substrates are insoluble in dry bmim+ PF6-, and it is necessary to saturate the IL with water beforehand. If an excessive amount of water is used, an undesirable wet IL-water biphasic system is formed. The aqueous phase must be decanted.
5. Before opening a screw-capped test tube, place it in an ice bath for 10 s to prevent the evaporation of substrates and products.
6. Increased concentrations of mmim+ MeSO4- produced a progressive decay in enzyme activity. A 25% (v/v) is sufficient to produce a decrease in Aw, which has been associated with a reduction in the undesirable hydrolysis of substrate and synthetic product (see Fig. 6).
7. Care should be taken during thermal deactivation to avoid evaporation of the sample. The authors did not described the procedure used.
8. The authors did not indicate the amount of enzyme used; 50 mg of Novozym 435 may be appropriate.
9. The authors did not describe the procedure to extract the polymeric product separately from the IL and immobilized enzyme, respectively. Polyester product could be recovered by centrifugation of the reaction mixture at 2800 g for 30 min. The resulting precipitated fraction can be re-dissolved with tetrahydrofuran (e.g., 5 mL), and centrifuged again (e.g., 2800 g for 5 min) to separate immobilized enzyme particles. By this way, a clear solution of reaction products suitable for HPLC analysis can be obtained.
10. The authors proposed a system containing three gel permeation columns in series to achieve sufficient separation in the molecular weight range 500-30,000.
Work partially supported by CICYT (Ref.: PPQ2002-03549) and SENECA
Foundation (Ref.: PB/75/FS/02) grants.
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