Hydrolysis and Esterification

An ester is a compound formed between an acid RO2H and an alcohol or oxyanion R OEl by the elimination of water according to the reaction  

The ester RO2R can be thought of as the compound formed from the Lewis base, RO2, and the Lewis acid, R , and its stability will be determined by the similarity of their cation and anion bonding strengths. 

Values in parentheses are corrected for the influence of carbon-bonded H. 

It is well known that esterification and hydrolysis are equilibrium processes  

Undoubtedly the same intermediates are involved in the forward and reverse reactions. Since it is much easier experimentally to study hydrolysis than esterification, much of what is known about the process is based upon hydrolysis experiments. Accordingly, this discussion deals mostly with the hydrolysis of esters. 

In general, hydrolysis may be carried out in acidic or basic media. 

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The Ingold248 classification of esterification and hydrolysis reactions is reported in Table 4. Basic compounds are seldom used as catalysts for esterifications, at least in diluted media. Thus, in Table 4 all arrows are oriented right to left. However, some authors (Naudet193, Kutepov27 ) carried out base-catalyzed esterifications in concentrated media and proposed mechanisms. 

Taft RW Jr. Linear free-energy relationships from rates of esterification and hydrolysis of aliphatic and ortho-substituted benzoate esters. / Am Chem Soc 1952 74 2729-32. 

A survey of the literature shows that the most reliable kinetic data on esterification and hydrolysis have been gained by experiments with model systems. For... 

Problem 16.39 Use the mechanism of esterification to explain the lower rates of both esterification and hydrolysis of esters when the alcohol, the acid, or both have branched substituent groups. -e... 

These considerations can be formulated by schemes (e)—(g) below (R1 = H or alkyl). Scheme (e), in which the acid (ester) is protonated and alcohol reacts in non-adsorbed state, corresponds to the mechanisms Aac1 or Aac2 proposed for homogeneous esterification and hydrolysis with ion exchanger catalysts, the mechanism (e) was assumed to be operating in the liquid phase esterification of salicyclic acid with methanol [449] and in the transesterification of ethyl acetate with the same alcohol in dioxan as... 

The rate of esterification and hydrolysis of these complexes is rapid, and equilibrium occurs within one second. 

IV. Selective Esterification and Hydrolysis 1. Tosyl and Mesyl89 Esters... 

Various methods have been developed to shift the equilibrium between esterification and hydrolysis toward the ester formation.6 For example, as an acetyl donor, vinyl acetate and isopropenyl acetate have been used because the resulting unnecessary alcohol, vinyl or isopropenyl alcohol, spontaneously changes to the corresponding aldehyde or ketone as shown in Figure 6(c).6a... 

Figure IS. Examples for optical resolutions through esterifications and hydrolysis of fluoro compounds...

W. Yu, K. Hidajat, A. K. Ray, Determination of adsorption and kinetic parameters for methyl acetate esterification and hydrolysis reaction catalyzed by Amberlyst 15. Appl. Catal. A, 2004, 260 (2), 191-205. 

Neenan and Miller [118] reported the preparation of poly (arylester) dendrons using a convergent iterative sequence consisting of esterification and hydrolysis reactions as illustrated in Scheme 14. The key intermediate in the synthesis of these dendrons is 5-(te/V-butyldimethylsiloxy)isophthaloyl dichloride, 48, which is first converted to the diester with phenol, followed by hydrolysis to the diester phenol. This dendron is designated [3-OH] indicating it contains three phenyl... 

Reviews Concerning Enzyme-Mediated Esterification and Hydrolysis of Esters 348... 

Figure 13.3 shows the profiles of the DBSA-catalysed reaction of lauric acid with 3-phenyl-1-propanol (1 1) at 40°C in water (closed circle). The reaction reached its maximum yield of 84% in 170 hours. We also conducted hydrolysis of the corresponding ester (open square). Both esterification and hydrolysis finally led to the same composition of the reaction mixture, indicating that the reaction reached its equilibrium position. 

Saponification.—As we shall see later, this is the kind of reaction which takes place when soap is made from fats and on that account it is termed an action of saponifikation. In this way the acids are obtained as salts from the naturally occurring fats, oils and waxes in which they are present in the form of esters. The hydrolysis of esters or ethereal salts is then the general reaction by which, with the taking up of the elements of water, an ester is reconverted into the two compounds from which it was formed, viz., into an acid and an alcohol. Esterification and hydrolysis or saponification are, therefore, complementary names applying to the reversible reaction effecting the synthesis and decomposition of esters. The reversible character of the reactions of esterification and... 

Problem 20.18 Account for the fact (Sec. 18.16) that the presence of bulky substituents in -either the alcohol group or the acid group slows down both esterification and hydrolysis. 

Taft, R.W. (1952). Polar and Steric Substituent Constants for Ahphatic and o-Benzoate Groups from Rates of Esterification and Hydrolysis of Esters. J.Am.Chem.Soc., 74,3120-3128. 

A free -OH group of the tyro.syl residue is necessary for the activity of pepsin. Both the -OH of serine and the imidazole portion of histidine appear to be necessary parts of the active center of certain hydrolytic cn/ymes, such as trypsin ami chymotrypsin. and furnish the electrostatic forces involved in a proposed mechanism (Fig. 2S-3). in which E denotes enzyme and the other symbols are self-evident. (Alternative mechanisms have been propo.sed esterification and hydrolysis were studied extensively hy M. L. Bender sce Journal of the American Chemical Soeieiv 79 1258. IM7 80 5.3.38. 1958 82 1900. 1960 86 .3704. 53.30. 1964]. D. M. Blow reviewed studies concerning the structure and mechanism of chymotrypsin (.sec Accounts of Chemical Re-,twr<7i 9 145. 1976].)... 

Both enzymatic esterification and hydrolysis are useful tools for resolution of racemic fluorinated building blocks. Among them, lipase-catalyzed reaction is reliable and most... 

In discussing esterification and hydrolysis, however, most authors prefer to show the proton on the ethereal oxygen atom and to consider this form... 

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