Acid hydrolysis of esters

Acidic hydrolysis of esters gives directly carbojqrlic acids while basic hydrolysis gives carboxylates, which on acidification give corresponding carboxylic acids. 

Vai der Waals Radii And Related Sterlc Parameters Van der Waals radii have long been considered a valid meas ure of atomic size Taft proposed the first valid set of sterlc parameters for correlation analysis defined from acid hydrolysis of esters caiarton derived equations for the calculation of Van der Waals radii, ry of symmetric top MZs groups( ) These values of the Van der Waals radii were used, together with that for H, to show that Es Is a linear function of i>y ... 

In addition to the above-mentioned reactions, metal complexes catalyze decarboxylation of keto acids, hydrolysis of esters of amino acids, hydrolysis of peptides, hydrolysis of Schiff bases, formation of porphyrins, oxidation of thiols, and so on. However, polymer-metal complexes have not yet been applied to these reactions. 

Concerning electrophilic side reactions, intramolecular Friedel-Crafts condensations have been reported for example, fluorenone is formed from 2-benzoylbenzenediazonium tetrafluorobo-rate.241 The strong Lewis acid boron trifluoride can also be responsible for side reactions, such as the extensive formation of tars from nitro-substituted arenediazonium tetrafluorobor-ates or the acidic hydrolysis of ester substituents, especially in the case of 2-(ethoxycar-bonyl)benzenediazonium tetrafluoroborate.105,242... 

The most numerous cases of homogeneous catalysis are by certain ions or metal coordination compounds in aqueous solution and in biochemistry, where enzymes function catalytically. Many ionic effects are known. The hydronium ion H3O and the hydroxyl ion OH catalyze hydrolyses such as those of esters ferrous ion catalyzes the decomposition of hydrogen peroxide decomposition of nitramide is catalyzed by acetate ion. Other instances are inversion of sucrose by HCl, halogenation of acetone by H and OH , hydration of isobutene by acids, hydrolysis of esters by acids, and others. 

The validity of these assumptions was tested by applying the derived steric substituent constants to reactions in which the transition states resembles that of the acid hydrolysis of esters. It was found that very few reactions obey equation 54. These are exemplified by the acid catalyzed methanolysis of 2-naphthyl esters in methanol (86) and the reaction of 2-alkylpyridines with methyl iodide (87) and with trimethylboron (88) in nitrobenzene. 

The search for an influence of steric effects on biological activity results from their well-established effects in chemical systems. As far back as 1894 (85), "steric hindrance" was invoked to account for the difficult esterification of 2,6-disub-stituted benzoic acids. However, inspection of equation 53 suggests that the substitutent constant, Eg, should include contributions from electronic effects as well. Indeed, acidic hydrolysis of esters of benzoic acids (4) have p values in the range -0.2 to +0.5. These p values are small and lie on both sides of zero, leading to the conclusion that electronic contributions to E are negligible (90). Proof for the existence of electronic effects in Es comes from Hancock s work (15) in which the electronic effects were attributed to a hyperconjugative effect of a-hydrogen atoms. 

In considering the acid hydrolysis of esters, we should remember that esters are weak bases. Most of them show a molar freezing point depression of two when they are dissolved in 100 per cent sulfuric acid. Presumably the two species arise from the reaction (see p. 36) ... 

Many reactions are catalysed by acids. Hydrolysis of esters and the reverse reaction, esterification, are important examples both in the laboratory and in living systems (reaction 5.38). In the forward direction, the initial rate is proportional to [H30 + ][71] in the reverse direction the kinetic dependence is on [H30+][74][Et0H]. By the principle of microscopic reversibility (Chapter 1), the reaction must have the same mechanism in both directions. The third-order kinetic dependence of... 

The vast literature on applications of PTC in substitution reactions is mainly restricted to nucleophilic substitution reactions with an anionic reagent. However, recently the use of PTC in electrophilic reactions, like diazotization andazocou-pling C-and N-nitrosation, C-alkylation, acid hydrolysis of esters, chloromethylation, nitrite-initiated nitrations, and so on have been reported(Velichko et al., 1992 Kachurin et al., 1995). Alkylbenzene sulfonates and lipophilic sodium tetrakis[3,5-bis(trifluoromethyl)phenylboranate are typical electrophilic PT catalysts. Lipophilic dipolar molecules of the betaine type and zwitterionic compounds also function well as PT agents for both nucleophilic as well as electrophilic reactions. 

The reactions of fatty acids are identical to those of short-chain carboxylic acids. The major reactions that they undergo include esterification, acid hydrolysis of esters, saponification, and addition at the double bond. 

Fatty acids are saturated and unsaturated carboxylic acids containing between twelve and twenty-four carbon atoms. Fatty acids with even numbers of carbon atoms occur most frequently in nature. The reactions of fatty acids are identical to those of carboxylic acids. They include esterification, production by acid hydrolysis of esters, saponification, and addition at the double bond. Prostaglandins, thromboxanes, and leukotrienes are derivatives of twenty-carbon fatty acids that have a variety of physiological effects. 

The acid hydrolysis of esters and esterification are mutually reversible processes, and, therefore, they take place by the same mechanism in the direction ... 

Polymer acids or polyanions can catalyze the acid hydrolysis of esters, amides, and ethers. This is because the local proton concentration in the polymer dommn is hi r than that in the bulk phase. The rate acceleration caused by this effect is moderate. However, when substrate molecules are attracted to the polymer molecule by electrostatic and hydrophobic forces, the catalytic efficiency increases (up to ca. 100 fold compared with mineral acids). Similar results were obtained for the alkali hydrolysis in the presence of polycations. 

An interesting example is observed in the reactions of ester hydrolysis. In the alkaline hydrolysis of benzoic esters, changes in the substituent cause changes in rate wholly accounted for by changes in the activation energy. In the acid hydrolysis of esters and also in the acid-catalysed esterification reaction there is a marked compensation of the energy and the entropy terms. The alkaline and acid hydrolysis reactions may be formulated as follows ... 

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. 

In eqn (1.3) three substituent parameters n, cj, and E, are used to describe the hydrophobic, electronic, and steric properties of substituents. The substituent constant E, due to Taft (1956), is based on the measurement of rate constants for the acid hydrolysis of esters of the following type... 

A new variation of the ozone cleavage is performed in the presence of tetracyanoethylene With dimethyl sulfoxide, prim, alcohols can be differentially oxidized to aldehydes The dimethyl sulfoxide-potassium terf-butoxide system has been recommended for Wittig syntheses In the same system, equatorial mesylates can be efficiently hydrolyzed without inversion. Under these conditions, tosylates give predominantly olefins Favorable conditions for acidic hydrolysis of esters, with methanesulfonic acid as catalyst, have been established... 

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