Esterification modeling approaches

Three modeling approaches can be applied to the esterification reaction kinetics the molecular species model, the functional group model, and the overall reaction model. These are schematically illustrated in Scheme 4.5. 

Esterification and polycondensation kinetics of PPSu synthesis can be well described on the basis of rather simple simulation models, taking into account the reaction kinetics and the functional group modeling approach. The latter is a very beneficial technique which includes aspects of the reaction mechanism although with the minimum computational effort. 

The common intermediate in two published biomimetic routes to Lythraceae alkaloids was substituted 4-phenylquinolizid-2-one. In one approach based on a biogenetic hypothesis of Ferris et al. (62), Wrobel and Gol biewski condensed pelletierine (126) with isovanillin (128) and obtained a transfused quinolizidine derivative (130, jS H-5) (64) in 75% yield. A model condensation of pelletierine (126) with benzaldehyde which resulted in a mixture of quinolizidones was reported earlier by Matsunaga et al. (65). In another approach Rosazza et al. (52) condensed A -pjperideine (132) with /J-ketoester 133 to get 134. The next stage in both approaches was reduction of the ketone and esterification or transesterification with derivatives of p-hydroxycinna-mic acid (135 or 136). Investigations into the oxidative coupling of 137 were unsuccessful. 

For the esterification with n-butanol, Liu, Zhang, and Chen (2001) used a cross-linked PVA-ceramic composite membrane (in the temperature range of 60—90 °C). This paper is a rare case of use of the Zr(S04)2 -4H20 catalyst. On the basis of a simple Fickian model, the influence of several esterification process variables, such as process temperature, initial mole ratio of acetic acid to n-butanol, the ratio of the effective membrane area to the volume of reacting mixture, and catalyst content, were discussed. A more rigorous model was defined by Liu and Chen (using a kinetic approach) comparing model outcomes with experimental outcomes (Inoue et al., 2007). 

The synthesis of another macrocyclic model compound was communicated by Notegen, Tori and Tamm in 1981 and is summarized in Scheme 28 (109). Selective protection (72%) of the C-4 hydroxy moiety as the acetal (237) allowed esterification with acid (238) to take place at C-15. The hydroxy acid (239), devoid of protecting groups, was then lactonized, this time onto the C-4 hydroxy group of verrucarol, to yield the model macrocycle (240). These early examples established that macrolactonization, either at C-4 (Scheme 28) or at the primary hydroxy group of the side chain (Scheme 27) would be equally valid approaches to the naturally occurring verrucarins, a fact which has since been substantiated by synthesis of the natural products 121, 133). 

For the purpose of developing a trickle-bed reactor model for esterification reactions the approach used by Rajshekharam et. al. (1998) was used. They have... 

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