An Esterification Reaction

From each spectrum it is possible to determine, directly and quantitatively, the extent of conversion within that local volume. In Fig. 41, the regions within which the individual volume-selective spectra were acquired are identified and color coded by the extent of conversion as determined from the spectrum recorded from that particular local volume. All images in Fig. 41 show that there is significant heterogeneity in conversion within a single transverse section through the bed, perpendicular to the direction of superficial flow fractional variations in conversion of up to approximately 20% were found to be typical under steady-state operating conditions. 

Visualization of mean conversion, A, within selected volumes located within the slice section identified in Fig. 40. The local volumes have in-plane dimensions of 1.5 mm x 1.5 mm and a depth (image slice thickness) of 500 pm. Data are shown for three feed flow rates (a) 0.025. (b) 0.05, and (c) 0.1 niLinin . As flow rate increases, the residence time characterizing the bed decreases, and it therefore follows that conversion will decrease. Reprinted from reference (84) with permission of Springer Science and Business Media. 

Although such studies are in their early stages, this example clearly demonstrates that we have the measurement tools to investigate the complex interaction of hydrodynamics and chemical kinetics in the complex porous medium represented by a fixed bed. Looking to the future, we may expect experiments of this nature to demonstrate how a catalyst with intrinsic high selectivity can produce a far wider product distribution when operated in a fixed-bed environment as a result of the spatial heterogeneity in hydrodynamics and hence, for example, mass transfer characteristics between the inter-pellet space within the bed and the internal pore space of the catalyst. 

In Fig. 42, the full-width at half maximum of the (narrower) exchange propagator provides an estimate of the effective diffusion coefficient of water molecules moving between the pore space of the catalyst and the inter-particle space of the bed. In this example, the value is 2 x lO- m s which gives a lower limit to the value for the mass transfer coefficient of 4x 10 ms This value was obtained by defining a mass transfer coefficient as Djd where d is a typical distance traveled to the surface of the catalyst that we estimate as half a typical bead dimension (approximately 500 pm). This value of the mass transfer coefficient is consistent with the reaction occurring under conditions of kinetic as opposed to mass transfer control. 

The same reaction can be followed in 3-D using CSI (Section II.C.l). In Fig. 43, the color code indicates the extent of conversion. As expected from the 2-D study, conversion is heterogeneous within transverse sections through the bed at any position along the direction of superficial flow. 

---

Catalysts. The choice of the proper catalyst for an esterification reaction is dependent on several factors (43—46). The most common catalysts used are strong mineral acids such as sulfuric and hydrochloric acids. Lewis acids such as boron trifluoride, tin and zinc salts, aluminum haHdes, and organo—titanates have been used. Cation-exchange resins and zeoHtes are often employed also. 

Polyesters are the most important class of synthetic fibers. In general, polyesters are produced by an esterification reaction of a diol and a diacid. Carothers (1930) was the first to try to synthesize a polyester fiber by reacting an aliphatic diacid with a diol. The polymers were not suitable because of their low melting points. However, he was successful in preparing the first synthetic fiber (nylon 66). In 1946, Whinfield and Dickson prepared the first polyester polymer by using terephthalic acid (an aromatic diacid) and ethylene glycol. 

Highly concentrated ether carboxylic acids with a low degree of ethoxylation even at room temperature can give an esterification reaction with the non-converted nonionic, especially with the fatty alcohol, to several percentage points. The result may be that a too low value is found for the ether carboxylate content. This mistake in analysis can be avoided by saponification of the formed ester [238]. Two hundred to 300 mg matter and ca 100 mg NaOH were weighed in a 50-ml Erlenmeyer glass, heated with 20 ml ethanol under reflux, and after cooling supplied with water to 100 ml. Afterward a two-phase titration was carried out. 

Despite its widespread application [31,32], the kinetic resolution has two major drawbacks (i) the maximum theoretical yield is 50% owing to the consumption of only one enantiomer, (ii) the separation of the product and the remaining starting material may be laborious. The separation is usually carried out by chromatography, which is inefficient on a large scale, and several alternative methods have been developed (Figure 6.2). For example, when a cyclic anhydride is the acyl donor in an esterification reaction, the water-soluble monoester monoacid is separable by extraction with an aqueous alkaline solution [33,34]. Also, fiuorous phase separation techniques have been combined with enzymatic kinetic resolutions [35]. To overcome the 50% yield limitation, one of the enantiomers may, in some cases, be racemized and resubmitted to the resolution procedure. 

The peculiarity of this material is that it consists of a mixture of acids and not triglycerides therefore, its transformation in biodiesel requires only an esterification reaction instead of a irans -esterification one and therefore does not produce glycerol, making the total economy lighter and independent of the critical... 

Alternatively, esterification of carboxylic acid can be carried out in aqueous media by reacting carboxylic acid salts with alkyl halides through nucleophilic substitutions (Eq. 9.10).20 The reaction rate of alkyl halides with alkali metal salts of carboxylic acids to give esters increases with the increasing concentration of catalyst, halide, and solvent polarity and is reduced by water. Various thymyl ethers and esters can be synthesized by the reactions of thymol with alkyl halides and acid chlorides, respectively, in aqueous medium under microwave irradiation (Eq. 9.11).21 Such an esterification reaction of poly(methacrylic acid) can be performed readily with alkyl halides using DBU in aqueous solutions, although the rate of the reaction decreases with increasing water content.22... 

The actual building blocks for the nucleic acids are the nucleotides, which are formed in an esterification reaction between nucleosides and phosphate three OH functions of ribose, and two of deoxyribose, can undergo esterification ... 

Specific catalytic activity of the composites obtained was at least several times higher than the same value for the random copolymer Nafion (even in an esterification reaction considered to be a diffusion-uncontrolled reaction). For the oligomerization reaction of decene-1 with strong diffusion control, the specific catalytic activity of the composites was 35 times higher than that for the random copolymer. Esterification of acrylic acid and alkylation of mesitilene by a substituted phenol were also performed using the composite catalyst. 

During the first decade when solid-phase synthesis was executed using Fmoc/tBu chemistry, the first Fmoc-amino acid was anchored to the support by reaction of the symmetrical anhydride with the hydroxymethylphenyl group of the linker or support. Because this is an esterification reaction that does not occur readily, 4-dimethylaminopyridine was employed as catalyst. The basic catalyst caused up to 6% enantiomerization of the activated residue (see Section 4.19). Diminution of the amount of catalyst to one-tenth of an equivalent (Figure 5.21, A) reduced the isomerization substantially but did not suppress it completely. As a consequence, the products synthesized during that decade were usually contaminated with a small amount of the epimer. In addition, the basic catalyst was responsible for a second side reaction namely, the premature removal of Fmoc protector, which led to loading of some dimer of the first residue. Nothing could be done about the situation,... 

The reaction of a carboxylic acid with an alcohol to form an ester is called an esterification reaction. An esterification reaction is one type of condensation reaction. In a similar type of condensation reaction, an amide can be formed from a carboxylic acid and an amine, but this process is slightly longer and will not be discussed here. 

What is the connection between a condensation reaction and an esterification reaction ... 

Guizard et al. (1986), Cot, Guizard and Larbot (1988) and Larbot et al. (1989) used a sol-gel method to prepare zirconia membrane top layers on an alumina support. The water necessary for the hydrolysis of the Zr-alkoxide was obtained from an esterification reaction. The complete hydrolysis was done at room temperature and resulted in a hydrated oxide. The precipitate was peptized with nitric or hydrochloric acid at pH <1.1 and the final sol... 

C.A. McGill, A. Nordon, D. Littlejohn, Comparison of in-line NIR, Raman and UV-visible spectrometries, and at-line NMR spectrometry for the monitoring of an esterification reaction. Analyst, 127, 287-292 (2002). 

There are several examples of dehydrations of chemicals derived by renewable resources by use of heteregeneous catalytic approaches in the literature. These can be categorized into three types of reactions (a) reactions in which one (or more) molecule(s) of water is eliminated from a single substrate molecule, (b) reactions in which one (or more) molecule(s) of water is generated as the result of an esterification reaction between an alcohol and a carboxylic acid or carboxylic acid derivative and (c) reactions in which one (or more) molecule(s) of water is generated due to an etherification reaction between two alcohol functionalities. 

Deters (14) vibromilled a blend of cellulose and cellulose triacetate. The acetic acid content of cellulose acetate decreased with grinding time (40 h) while that of the cellulose increased, suggesting the formation of a block or graft copolymer or of an esterification reaction by acetic acid developed by mechanical reaction. Baramboim (/5) dissolved separately in CO polystyrene, poly(methyl methacrylate), and poly(vinyl acetate). After mixing equal volumes of solutions of equivalent polymer concentration, the solvent was evaporated at 50° C under vacuum and the resultant product ball-milled. The examination of the ball-milled products showed the formation of free radicals which copolymerized. 

Tiedemann and Riveros (1974) first discussed the gas-phase reactions which are equivalent to an esterification reaction. An icr study of alcohols and acetic acid revealed that the formation of protonated acetic acid by ion-molecule reactions of fragment ions with acetic acid is followed by the rapid reaction (72). 

Fio. 11. Concentration profiles as measured with the equipment depicted in Fig. 10 (open symbols) and by GC analysis (closed symbols) for an esterification reaction between octanol and hexanoic acid. Conditions 200 ml, of reactant, 0.4mol/L of octanol, 0.4mol/L of hexanoic acid, l.Og Nafion resin/ silica, 447 K. The profiles were constructed from signals at 1720 and 1745 cm , and the spectra were corrected for solvent, octanol, and catalyst (74). 

Suppose that in an esterification reaction in which an organic acid RCOOH reacts with an alcohol R OH in an organic solvent to produce an ester RCOOR, ... 

McGill, C.A. Nordon, A. Littlejohn, D. Comparison of In-Line NIR, Raman and UV-Visible Spectrometries, and At-Line NMR Spectrometry for the Monitoring of an Esterification Reaction Analyst 2002, 127, 287-292. 

A-3. The species whose structure is shown is an intermediate in an esterification reaction. Write the complete, balanced equation for this process. 

The performance of an algorithm using the approach just described is illustrated in Table III for an example involving an esterification reaction. The performance is compared with that of the conventional algorithm of Sanderson and Chien ( ) ... 

The feasibility of film flow monolithic reactors has been demonstrated for an esterification reaction 188,189,215). In esterification, water is formed as a by-product. The presence of water has two negative consequences it inhibits the catalytic reaction (216) and limits the maximum... 

Numerical application. This application concerns the conversion of one reactant by an esterification reaction occurring in a discontinuous and stirred reactor. It is a function of the temperature (factor A), the alcohol-acid molar ratio (factor B), the reaction time (factor C) and the catalyst concentration (factor D). A CFE 2 plan is used to investigate the different effects of the factors. The levels of the factors have been established in order to obtain a good reactant conversion. These levels are temperatures Aj = 110 °C, A2 = 130 °C alcohol-acid molar ratio Bj =... 

Table 5.67 Presentation of the blocks in the example of an esterification reaction.

At this point, we have to verify the eorreetness of the selection of the unification relations. When S sSint we can conclude that our selection for the unification relations is good in this case, we can also note that the calculations have been made without errors. Otherwise, if computation errors have not been detected, we have to observe that the selected interactions for the unification of blocks are strong and then they carmot be used as unification interactions. In this case, we have to carry out a new experimental research with a new plan. However, part of the experiments realized in the previous plan can be recuperated. Table 5.68 contains the synthesis of the analysis of the variances for the current example of an esterification reaction. We observe that, for the evolution of the factors, the molar ratio of reactants (B) prevails, whereas all other interactions, except interaction AC (temperature-reaction time), do not have an important influence on the process response (on the reaction conversion). This statement is sustained by all zero hypotheses accepted and reported in Table 5.68. It should be mentioned that the alcohol quality does not have a systematic influence on the esterification reaction efficiency. Indeed, the reaction can be carried out with the cheapest alcohol. As a conclusion, the analysis of the variances has shown that conversion enhancement can be obtained by increasing the temperature, reaction time and, catalyst concentration, independently or simultaneously. 

Table 5.68 Synthesis of the variance anaiysis for CFE 2, exampie of an esterification reaction.

---