The biocatalytic synthesis of anisyl acetate fragrance was carried out by direct esterification of acetic acid with
anisyl alcohol in sponge-like ionic liquids (SLILs), e.g. N,N,N,N-hexadecyltrimethylammonium bis(trifluoromethylsulfonyl)
imide ([C16tma][NTf2], N,N,N,N-octadecyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([C18tma] [NTf2]),
etc. as reaction/separation media under conventional and microwave (MW) heating. These SLILs are temperatureswitchable
ionic liquid/solid phases that behave as sponges. As liquid phases, they are excellent monophasic reaction media
for the lipase-catalyzed synthesis of anisyl acetate, the product yield being improved up to 100% for 2 hour reaction
under the appropriate reaction conditions (i.e. SLIL concentration, alcohol: acid molar ratio, enzyme amount, dehydrating
molecular sieves, temperature and MW heating). As a function of the phase behaviour of different SLIL/anisyl acetate
mixtures, a new clean separation protocol based on the centrifugation of the solid IL/flavour ester through nylon membranes
was proposed, which provided a nearly full separation of the solid SLIL and the easy recovery of the reaction mixture.
The enzymatic synthesis of anisyl acetate in [C16tma] [NTf2] under MW assistance, followed by the separation step
of the solid SLIL, provided a nearly solvent-free fragrance product with up to 0.89 g/mL concentration. The catalytic activity
of the enzyme / SLIL system remained unchanged for ten consecutive operational cycles. This work reports a
straightforward and sustainable approach for producing anisyl acetate as a natural flavour and demonstrates to be suitable
for scaling-up, providing a high potential for practical application.
Keywords: Anisyl acetate, anisyl alcohol, biocatalysis, biocatalytic process, clean process, enzymatic synthesis, esterification,
flavours, fragrances, green chemistry, ionic liquids, lipase, neoteric solvents, pure products, solvent-free, sponge-like ionic liquids,
sustainable chemistry, switchable ionic liquids.
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