A Green Approach for Producing Solvent-free Anisyl Acetate by Enzymecatalyzed Direct Esterification in Sponge-like Ionic Liquids Under Conventional and Microwave Heating
Juana M. Bernal,
M. Isabel Burguete,
Santiago V. Luis.
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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