Ionic liquids new technologies
Gurbisz, Monika (2012) Ionic liquids new technologies. PhD thesis, Dublin City University.
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Novel methylimidazolium and pyridinium ionic liquids (ILs), derivatives of 3,4-dimethoxy-3,4-methylenedioxy- and 3,4-dihydroxy- mandelic acid, have been synthesised to serve as low-toxic and biodegradable solvents for catalytic asymmetric reactions. These ILs were prepared with three types of counteranion (halide, OctOSO3−, NTf2−) via a simple 3-5 step scalable synthetic route. The stability of the prepared ILs on aqueous conditions was studied. Although of the prepared ILs were chiral, they were obtained as racemic mixtures. Various methods were attempted to obtain ILs in the optically pure form and with the use of a chiral auxiliary approach, a diastereomerically enriched IL was obtained. Further synthetic work involved the optimisation and large scale (40-120 g) preparation of known achiral and chiral ILs. Both optically pure and achiral ILs were obtained in a 3-4 step synthesis, without the need for chromatographic purification. Preliminary ecotoxicological assessment of novel ILs was carried out; including, antimicrobial and antifungal screening as well as biodegradation studies. The majority of the ILs tested proved to be of low toxicity towards microorganisms and two ILs proved to be non-toxic towards bacteria at concentration as high as 100 mM. In the biodegradation test of halide ILs, one IL was found to pass the test (66 %) and for the remaining ILs values between 13–52 % were reached in the 28 day test. Selected ILs were tested as solvents in asymmetric reactions with chiral catalysts. With the use of organic co-solvents, very good eantioselectivities, short reaction times and catalyst recycling were achieved. In the presence of the novel ILs, derivatives of 3,4-disubstituted mandelic acids, asymmetric hydrogenation of the enamide double bond, together with aromatic ring reduction, was achieved at very mild conditions.
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