Acyl donor/alcohol molar ratio

In this research the kinetic resolution of 1-phenylethanol catalyzed by commercially available immobilized lipase from CALB was assayed in non-aqueous conditions in SC-CO2 and IL/SC-CO2 systems with the aim of studying the enan-tioselectivity of Novozym 435. The influence of different reaction parameters, such as pressure, the acyl donor/alcohol molar ratio and different ILs, on the enantio-merically pure compound (R)-l-phenylethyl acetate formation via kinetic resolution of 1-phenylethanol was investigated. 

Acyl donoriAlcohol molar ratio Figure 8.3 Influence of acyl donor/alcohol molar ratio on the kinetic resolution of 1-phenylethanol, catalyzed by Immobilized CALB in SC-CO2 after 5 hours of reaction bars-dependence of the conversion on the pressure spots-dependence of the enantiomeric excess on the pressure. 

Effect of the Acyl Donor/Alcohol Molar Ratio... 

For a reversible reaction an increase in the acyl donor concentration results in higher product yields. In this case the chemical equilibrium is shifted towards synthesis. On the other hand, high concentrations of substrates may cause inhibition and the reaction is slowed down. For (R)-l-phenylethyl acetate formation the effect of the substrate vinyl acetate/l-phenylethanol molar ratio on the final conversion was studied. The results are presented on Figure 8.3. A higher yield of the enantiopure compound was achieved when raising the acyl donor molar concentration with respect to the alcohol concentration. A conversion of 49.9% was obtained at an acyl donor/alcohol molar ratio of 9/1. After 5 h of reaction at tested conditions a complete conversion of (R)-l-phenylethanol into the enantiopure (R)-l-phenylethyl acetate was attained. The enantiomeric excess for reactants (eeR) was 99.9%. 

Figure 8.7 Acyl donor/alcohol molar ratio effect on the reaction of the enzymatic kinetic 1 -phenylethanol resolution by CALB in [bmimKPFel/SC-COz.

It has been clearly demonstrated in the literature that in the case of direct esterification, the chain length of acid and alcohol affects the ester yield (16-19). In the present work, we investigated the reactivity of acyl donors of various chain lengths, ranging from butyric (C4) to palmitic acid (C16) in the esterification of butanol. The reaction medium consisted of amounts of the required acid and butanol at a fixed molar ratio (1.5) and 25 mg/mL of POS-PVA lipase. The molar conversion of butanol was calculated after 24 h of reaction, and the values attained for each acyl donor tested are displayed in Fig. 3. 

In order to investigate the effect of the substrates molar ratio on the reaction performance, the concentrations of the enzyme and antioxidant were kept constant, whereas that of the acyl donor was increased. In the case of rutin, independently of the molar ratio, used the acylation proceeded with low yields, while only monoesters were formed in all reaction systems used. The same behavior was observed in the case of silybin using tert-amyl alcohol and tert-butyl alcohol as reaction media (data not shown). In contrast, when acetone was used as medium the conversion yield for the acylation of silybin increased as the molar ratio was increased (Table 9.2). 

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