No abstract

With increasing demand for perfumes, flavors, beverages, and pharmaceuticals, the various associated industries are resorting to different approaches to enhance yields of desired compounds. The use of fixed-bed biocatalytic reactors in some of the processes for making fine chemicals will be of great value because the reaction times could be reduced substantially as well as high conversion and yields obtained. In the current study, a continuous-flow packed-bed reactor of immobilized Candida antarctica lipase B (Novozym 435) was employed for synthesis of various geraniol esters. Optimization of process parameters such as biocatalyst screening, effect of solvent, mole ratio, temperature and acyl donors was studied in a continuous-flow packed-bed reactor. Maximum conversion of ~ 87% of geranyl propionate was achieved in 15 min residence time at 70 °C using geraniol and propionic acid with a 1:1 mol ratio. Novozym 435 was found to be the most active and stable biocatalyst among all tested. Ternary complex mechanism with propionic acid inhibition was found to fit the data.

Enzymatic synthesis of molecules such as flavors, perfumes and fragrances has a great commercial advantage of being marketed as “natural” and also it offers exquisite selectivity of enzymes that can be superior over chemical catalysis. The current work focuses on the enzymatic synthesis of geranyl acetate as model compound, including optimization of reaction conditions such as nature of catalyst, reaction media, speed of agitation, mole ratio and temperature. A variety of esters were also synthesized. Geraniol was esterified with various acids, aromatic esters and vinyl esters in 1:4 molar ratio. Among all vinyl ester was the best giving in good yield (77–100 %) as compared to aromatic esters (5–82 %) and acids (7–31 %). Novozym 435 was found to be most active catalyst with ~96 % conversion and 100 % selectivity in 60 min at 55 °C in n-heptane as solvent for geranyl acetate. The maximum reaction rate was estimated (Vmax = 0.2712 mol L−1 min-1) by using the double reciprocal plot. It is a ternary complex (ordered bi-bi) mechanism with inhibition by geraniol.

No abstract

Here, we have demonstrated the flow chemistry approach for kinetic resolution of (R,S)-α-tetralol using the packed-bed reactor of immobilized Candida antarctica lipase B (Novozym 435). We have investigated the performance of different enzymes including Lipozyme RM IM, Lipozyme TL IM, and Novozym 435 and compared their activity and enantioselectivity in nonaqueous media. The kinetics of transesterification of (R,S)-α-tetralol using vinyl acetate as the acylating agent was studied in a packed bed of immobilized enzyme. A continuous-flow packed bioreactor shows better behavior in terms of enantioselectivity and conversion vis-a-vis a stirred-tank reactor. A conversion of ∼50% of the (R,S) mixture with ∼100% selectivity (E) for (R)-α tetralol (eep ≥ 99.99%) was obtained at 65 °C with a 3 min residence time using Novozym 435 as the catalyst in the continuous-flow packed-bed reactor, whereas a 43.6% conversion of racemic mixture (eep ≥99.99%) was obtained in a stirred-tank batch reactor in 8 h under identical conditions. There was no back-mixing in the fixed-bed bioreactor having laminar−plug flow. The enzyme remains stable up to the seventh reuse, which shows viability of a continuous operation over a longer period. Inhibition by vinyl acetate with the ping pong bi-bi mechanism was proposed using Lineweaver−Burk plots.