Esterification, rate

Chlorendic Acid. Chlorendic acid [115-28-6] and its anhydride [115-27-5] are widely used flame retardants. Chlorendic acid is synthesized by a Diels-Alder reaction of maleic anhydride and hexachlorocyclopentadiene (see CyclopentadlENE and dicyclopentadiente) in toluene followed by hydrolysis of the anhydride using aqueous base (60). The anhydride can be isolated directly from the reaction mixture or can be prepared in a very pure form by dehydration of the acid. The principal use of chlorendic anhydride and chlorendic acid has been in the manufacture of unsaturated polyester resins. Because the esterification rate of chlorendic anhydride is similar to that of phthalic anhydride, it can be used in place of phthalic anhydride in commercial polyester... 

Chemical Properties. Neopentyl glycol can undergo typical glycol reactions such as esterification (qv), etherification, condensation, and oxidation. When basic kinetic studies of the esterification rate were carried out for neopentyl glycol, the absolute esterification rate of neopentyl glycol with / -butyric acid was approximately 20 times that of ethylene glycol with / -butyric acid (7). 

A very interesting steric effect is shown by the data in Table 7-12 on the rate of acid-catalyzed esterification of aliphatic carboxylic acids. The dissociation constants of these acids are all of the order 1(T, the small variations presumably being caused by minor differences in polar effects. The variations in esterification rates for these acids are quite large, however, so that polar effects are not responsible. Steric effects are, therefore, implicated indeed, this argument and these data were used to obtain the Es steric constants. Newman has drawn attention to the conformational role of the acyl group in limiting access to the carboxyl carbon. He represents maximum steric hindrance to attack as arising from a coiled conformation, shown for M-butyric acid in 5. 

When no protonic catalyst is added it is the carboxylic acid which acts as a catalyst in 1896, Goldschmidt already showed that in this case the reaction order with respect to acid is greater than unity and Hinshelwood2511 suggested the following relation for the esterification rate ... 

The kinetics of reactions of bifunctional compounds are especially significant in relation to polymer reactions. The esterification rate constants shown in the third column (B) of Table V for the homologous series of dibasic acids do not differ greatly from those for the monobasic acids. These differences vanish as the length of chain separating the carboxyl groups increases. 

Materials DNQ was synthesized by esterification of o-cresol formaldehyde novolac resin (Mw=900) and of l,2-diazonaphthoquinone-5-sulfonyl chloride. The esterification rate was ca. 0.4. The novolac-based resist used in EB lithography to compare with SPP was... 

Figure 2.5 Esterification rate constants in the homogeneous phase for different combinations of reacting molecules at 190 °C, as published by Krumpolc and Malek [26]...

Figure 2.6 Esterification rate constants as a function of pKa for different carboxylic acids, according to Otton and Ratton [18]...

LCAT acts preferentially on lipids transported by HDL (so-called a-LCAT activity), but also on lipids transported by apoB-containing lipoproteins (so-called jS-LCAT activity) [58, 85]. In practice, LCAT activity is measured either as the activity required to esterify radioactive cholesterol that has been exogenously incorporated into native HDL or into artificial HDL-like particles (a-LCAT activity) or which has been equilibrated with endogenous lipoproteins of the plasma sample (cholesterol esterification rate, CER) [21, 58, 85]. Several variations of these assays have been reported, some of which are available as commercial test kits (e.g., Roar Biomedical, New York, USA). In addition, LCAT concentration can be determined by either laboratory-made tests or by a commercial ELISA kits [57]. However, the decrease in LCAT concentration is difficult to judge since it also decreases secondary to HDL deficiency due to causes other than LCAT deficiency. Plasma from patients with LCAT deficiency fails to esterify radioactive cholesterol provided by any substrate. By contrast, plasmas of patients with fish-eye disease show a near-normal cholesterol ester-fication rate but have a selective inability to esterify radioactive cholesterol provided to plasma with native HDL or reconstituted HDL (a-LCAT activity) [58, 85]. 

CER The fractional esterification rate (FER) is calculated as [cpm [3H] cholesteryl esters/(cpm [3H]cholesteryl esters + cpm unesterified [3H] cholesterol)]. 

Patients with classical LCAT deficiency fail to esterify cholesterol in any substrate and hence have both an undetectable or very low cholesterol esterification rate and a-LCAT activity. Patients with fish-eye disease usually have a normal cholesterol esterification rate and a selective a-LCAT deficiency. 

Dobiasova M, Frohlich J (1996) Measurement of fractional esterification rate of cholesterol in plasma depleted of apoprotein containing lipoprotein methods and normal values. Physiol... 

In Helfferich s relation it is implicitly assumed that the diffusion of the reactants through the pore liquid is fast enough so that equilibrium between the pore liquid and the supernatant solutions exists. Several papers, however, report a particle size effect on the esterification rate [428—... 

The effect of group (a) (non-polar solvents) was examined in the esterification of benzoic acid with 1-butanol over a Dowex-W X2 catalyst [454]. The solvent affected both the Helfferich distribution coefficients and the esterification rates. Dielectric constants, corresponding to the composition of the pore liquid, were estimated and the kinetic data related to the polar properties of the medium within the catalyst. In Fig. 18 are plotted specific rate coefficients versus the reciprocal value of dielectric constant of the pore liquid. The slope of the correlation is positive as for... 

It was observed that the presence of sulphuric acid promotes the hydrolysis of esters (e.g. [104,107,109]). The rate of hydrolysis is for the most part significantly lower than the esterification rate. Moreover, as already discussed above, in addition to the main reaction producing alcohol and nitrating acid, the hydrolysis process is generally accompanied by side reactions. Acids other than sulphuric, or perchloric [104], e.g. acetic [106] or phosphoric, if present in the esterifying mixture, hydrolyse esters to a markedly smaller extent than sulphuric acid. The acid make up of an esterification mixture in industry is established experimentally. Economic factors also plays a part here. 

A12. Albers, J. J., Chen, C.-H., and Adolphson, J. L., Lecithimcholesterol acyltransferase (LCAT) mass its relationship to LCAT activity and cholesterol esterification rate. /. Lipid Res. 22, 1206-1213 (1981). 

P8. Patsch, W., Lisch, H. J., Sailer, S., and Braunsteiner, H., Initial cholesterol esterification rate in hyperlipoproteinemia Effects of triglyceride-rich lipoproteins. Eur. J. Clin. Invest. 8, 209-213 (1978). 

As Table 1.1 shows, fluorine is the second smallest element, with size approximately 20% larger than the smallest element, hydrogen. Table 1.2 summarizes four steric parameters for various elements and groups (i) Taft steric parameters Es [44], (ii) revised Taft steric parameters E [45], (iii) Charton steric parameters o [46], and (iv) A values [47], The steric parameters, Es, E, and u are determined on the basis of relative acid-catalyzed esterification rates, while the A values are derived from the Gibbs free energy difference calculated from the ratios of axial and equatorial conformers of monosubstituted cyclohexanes by NMR. 

The results show that the K1481 catalyst is more active by a factor of 2 than Amberlyst 119, which indicates that particle size influences the esterification rate. As the K1481 catalyst is a powder, it has a significant outer surface area and acid centres located on this surface are easily accessible. 

Esterification rates indicated that the hydroxyl groups are primary and secondary. The postulation of a primary hydroxyl limits its position to the side-chain 1-methyl group. 

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