Model esterification reaction

As a model esterification reaction, the formation of ethyl lactate has been studied and its complete kinetic and thermodynamic analysis has been performed. The formation rate of ethyl lactate has been examined as a function of temperature and catalyst loading. In early experiments, it was determined that lactic acid itself catalyzes esterification, so that there is significant conversion even without ion exchange resin present. The Arrhenius plot for both resin-catalyzed and uncatalyzed reactions indicates that the uncatalyzed... 

With these kinetic data and a knowledge of the reactor configuration, the development of a computer simulation model of the esterification reaction is iavaluable for optimising esterification reaction operation (25—28). However, all esterification reactions do not necessarily permit straightforward mathematical treatment. In a study of the esterification of 2,3-butanediol and acetic acid usiag sulfuric acid catalyst, it was found that the reaction occurs through two pairs of consecutive reversible reactions of approximately equal speeds. These reactions do not conform to any simple first-, second-, or third-order equation, even ia the early stages (29). 

In this article we critically review most of the literature concerning non-catalyzed, proton-catalyzed and metal-catalyzed polyesterifications. Kinetic data relate both to model esterifications and polyeste-rificatiom. Using our own results we analyze the experimental studies, kinetic results and mechanisms which have been reported until now. In the case of Ti(OBu)f catalyzed reactions we show that most results were obtained under experimental conditions which modify the nature of the catalyst. In fact, the true nature of active sites in the case of metal catalysts remains largely unknown. 

One of the main assumptions which have been made in the study of polyesterifications is the concept of equal reactivity of functional groups. It was first postulated by Flory1 who, studying various polyesterifications and model esterifications, found the same orders of reaction and almost the same rate constants for the two systems. He concluded that the reaction rate is not reduced by an increase in the molecular weight of the reactants or an increase in the viscosity of the medium. The concept of equal reactivity of functional groups has been fully and carefully analyzed by Solomon3,135 so that we only discuss here its main characteristics. Flory clearly established the conditions under which the concept of equal reactivity can be applied these are the following ... 

Fiery1 252-254) studied only the last stage of the reactions, i.e. when the concentration of reactive end groups has been greatly decreased and when the dielectric properties of the medium (ester or polyester) no longer change with conversion. Under these conditions, he showed that the overall reaction order relative to various model esterifications and polyesterifications is 3. As a general rule, it is accepted that the order with respect to acid is two which means that the add behaves both as reactant and as catalyst. However, the only way to determine experimentally reaction orders with respect to add and alcohol would be to carry out kinetic studies on non-stoichiometric systems. 

In Figure 2.4, data for the equilibrium constants of esterification/hydrolysis and transesterification/glycolysis from different publications [21-24] are compared. In addition, the equilibrium constant data for the reaction TPA + 2EG BHET + 2W, as calculated by a Gibbs reactor model included in the commercial process simulator Chemcad, are also shown. The equilibrium constants for the respective reactions show the same tendency, although the correspondence is not as good as required for a reliable rigorous modelling of the esterification process. The thermodynamic data, as well as the dependency of the equilibrium constants on temperature, indicate that the esterification reactions of the model compounds are moderately endothermic. The transesterification process is a moderately exothermic reaction. 

Fortunato, B., Munari, A. and Manaresi, P., Inhibiting effect of phosphorus compounds on model transesterification and direct esterification reactions catalysed by titanium tetrabutylate, Polymer, 35, 4006 (1994). 

A process performance study has been conducted by David et al. [47] taking the coupling of pervaporation with the esterification reactions of 1-propanol and 2-pro-panol with propionic acid as a model system. Toluene sulfonic acid was appHed as the homogeneous acid catalyst A PVA-based composite membrane from GFT was used. Fig. 13.5 shows the comparison between the esterification reaction with and without pervaporation. Without pervaporation, the conversion factor reaches a hm-it, which corresponds to the equihbrium of the esterification reaction. Coupling of the esterification to pervaporation allows the reaction to reach almost complete conversion. 

The equilibrium-stage model seems to be suitable for esterification reaction in CD processes (see Refs. 35 and 74). However, it cannot be recommended for all reaction types, especially those with higher reaction rates. 

Here, we report the application of this procedure for immobilizing Mucor miehei lipase. A catalytic test was aimed at producing esters by direct esterification reactions with a large range of carboxylic acids (from C4 to C16), and a diversity of alcohols (from C4 to C8). Several reaction model systems are analyzed in order to illustrate the kind of products that can be made by using an experimental preparation of lipase immobilized on POS-PVA particles. 

Mujtaba and Macchietto (1997) and Greaves (2003) simulated the esterification of ethanol and acetic acid using a Type V-CMH model. The reaction products are ethyl acetate (main product) and water. The reversible reaction scheme together with the boiling point temperatures are shown below ... 

Lehtonen et al. (1998) considered polyesterification of maleic acid with propylene glycol in an experimental batch reactive distillation system. There were two side reactions in addition to the main esterification reaction. The equipment consists of a 4000 ml batch reactor with a one theoretical plate distillation column and a condenser. The reactions took place in the liquid phase of the reactor. By removing the water by distillation, the reaction equilibrium was shifted to the production of more esters. The reaction temperatures were 150-190° C and the catalyst concentrations were varied between 0.01 and 0.1 mol%. The kinetic and mass transfer parameters were estimated via the experiments. These were then used to develop a full-scale dynamic process model for the system. 

Krupiczka R and Koszorz Z. Activity-based model of the hybrid process of an esterification reaction coupled with pervaporation. Sep PunfTechnol 1999 16(l) 55-59. 

Flory [3, 48] found that the esterification reactions between model compounds on the one hand and polyfunctional reactants on the other are substantially identical. Thus the reaction of two monofunctional compounds (lauric acid, lauryl alcohol), of a bifunctional compound with a monofunctional one (adipic acid, lauryl alcohol) and two bifunctional compounds (adipic acid, decamethylene glycol) followed essentially third-order kinetics. In the absence of added strong-acid catalyst a second molecule of the carboxylic acid functions as catalyst. Thus when the concentrations (C) of the reacting groups are identical, the rate is given by ... 

On the basis of the data reviewed in this chapter, it seems likely that there are functionally distinct pools of cholesterol in the intestinal epithelial cell that serve different metabolic functions. These pools are illustrated diagrammatically in the model of an epithelial cell shown in Fig. 14. Pool A is defined as having been derived largely from the uptake of luminal unesterified cholesterol (arrow 1) and serves as a major substrate for the CoA-dependent esterification reaction (arrow 2). The cholesterol esters that result from this reaction are incorporated into the hydro-phobic core of the chylomicron particle. Following cholesterol feeding there is a marked increase in apparent ACAT activity in the intestinal epithelium that seems to be related to an increase in the amount of intracellular cholesterol available to the enzyme under the in vitro conditions of the assay rather than to an increase in the... 

The first pervaporation membrane reactor model which takes into account solution non-idealities was developed and validated experimentally by Zhu et al [5.90]. Prior studies [5.89, 5.91] also made note of such non-idealities, but offered no unified means for accounting for these phenomena in the description of PVMR. Since the model of Zhu et al. [5.90] appeared, other groups have also utilized similar models [5.92]. A more comprehensive analog of this model was, for example, recently presented and validated experimentally by Park [5.93], and by Lim et al. [5.94]. Zhu et al. [5.90] analyzed a tubular PVMR, in which the homogeneously catalyzed esterification reaction of acetic acid with ethanol to produce ethyl acetate and water took place. The reaction can be expressed generally as ... 

Two overall reactions will be considered in the kinetic model esterification of acetic acid with methanol and esterification of hydrogen iodide to methyl iodide. The overall reactions can be written as follows ... 

Nukui, M., PET resin development from tire Mitsubishi Chemical Company latest UV baiTier polyester resin and heat resistant resin, presentation (Session 1X12-6) given at die Polyester 2000 5th World Congress - The Polyester Chain, Zurich, Switzerland, 28 November-1 December, 2000. Fortunato, B., Munari, A. and Manaresi, P., Inhibiting effect of phosphoras compounds on model ttansesterification and direct esterification reactions catalysed by titanium tettabutylate. Polymer, 35, 4006 (1994). 

Scheme 9.1 Hypothetical model of esterification reaction between the hydroxyl groups of sisal fibers and anhydride rings of MAPP [74].

Chromatographic batch reactors are employed to prepare instable reagents on the laboratory scale (Coca et al., 1993) and for the production of fine chemicals. These applications include the racemic resolution of amino acid esters (Kalbe, Hbcker, and Berndt, 1989), acid-catalyzed sucrose inversion (Lauer, 1980) and production of dextran (Zafar and Barker, 1988). Sardin, Schweich, and Viller-maux (1993) employed batch chromatographic reactors for different esterification reactions such as the esterification of acetic acid with ethanol and the transesterification of methylacetate. Falk and Seidel-Morgenstern (2002) have investigated the hydrolysis of methyl formate. Strohlein et al. (2006) measured the esterification of acrylic acid with methanol and validated the transport dispersive model for process simulation. 

The successful scale-up of advancement and modification of rubber-modified epoxy resins is discussed. Mechanisms are proposed for both advancement and esterification reactions as catalyzed by triphenylphosphine which are consistent with experimental results. A plausible mechanism for the destruction of the catalyst is also presented. The morphology of these materials is determined to be core-shell structures, dependent upon composition and reaction and processing conditions. Model studies have been performed to determine the effects of thermal history on the kinetics of reaction. These efforts have resulted in the successful scale-up and use of rubber-modified epoxy resins as functional coatings in the electronics industry. 

Goto et al. 1998). None of them probably reflects properly the enzyme activity over the real substrate, so it will be a matter of judgment and experience to select the most pertinent assay with respect to the actual use of the enzyme. Hydrolases are currently assayed with respect to their hydrolytic activities however, the increasing use of hydrolases to perform reactions of synthesis in non-aqueous media make this type of assay not quite adequate to evaluate the synthetic potential of such enzymes. For instance, the protease subtilisin has been used as a catalyst for a trans-esterification reaction that produces thiophenol as one of the products (Han et al. 2004) in this case, a method based on a reaction leading to a fluorescent adduct of thiophenol is a good system to assess the transesterification potential of such proteases and is to be preferred to a conventional protease assay based on the hydrolysis of a protein (Gupta et al. 1999 Priolo et al. 2000) or a model peptide (Klein et al. 1989). 

Naphadzokova, L. Kh. Kozlov, G. V. Zaikov, G. E. Description of the model trans-esterification reaction within the framework of a strange diffusion concept. J. Appl. Polymer Sci., 2008,109(5), 2791-2794. 

The development of these molecular descriptors have been based on the physical model of transition states in acid-catalyzed esterification reaction of carboxylic acids and alcohols and acid hydrolysis of esters - standard reactions used by Taft for the development of Eg s empirical steric parameter in the frame of LFER (linear free energy relationship). The physical meaning of the (8, G) shape descriptors is depicted in Fig. 15.3. 

Mathematical Modeling of the Esterification Reaction for the Synthesis of Aliphatic Polyesters... 

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