Sulphonate esters hydrolysis

When 1,2-diols are subjected to the same reaction conditions required for the formation of sulphonic esters, oxiranes are produced [27]. Presumably, the mono ester is initially formed and, under the basic conditions, intramolecular elimination occurs to produce the oxirane. Partial hydrolysis and ring-closure of a,p-di(tosyloxy) compounds under basic phase-transfer catalytic conditions provides a convenient route to carbohydrate oxiranes [e.g. 28, 29]. Oxiranes have been produced by an analogous method via carbonate esters from partially protected carbohydrates [30],... 

Even sulphonate esters 109 are powerful directing groups, competing well with tertiary amides. No substitution accompanies ortholithiation of ethyl or isopropyl benzene-sulphonate by BuLi. Hydrolysis and chlorination of the products 110 gives functionalized sulphonyl chlorides 111 (Scheme 48) °°. 

The diffusion of the large sucrose molecule may be so slow that a large proportion of the sulphonic acid groups inside the polymer become inaccessible and cannot participate in the reaction [506,508], as was also assumed for esterification (p. 361) and ester hydrolysis (p. 377). 

This would have both a solvent effect and a mass law effect on the rate of ester formation. The error is systematic, since it is most serious for the slower ester formation reactions, and consequently the p value calculated by Jaffe144 from the data of Hartman and Borders142 is not accurate. Later workers allowed for this side-reaction 46 or used aromatic sulphonic acids rather than HC1 as the catalyst145147. However, whatever the exact p values, it is quite clear that the polar effects of substituents on acid-catalyzed ester hydrolysis and formation are small. 

Sulphonate esters313,314 and sulphonamides299,315 are also readily hydrolysed to produce the sulphonic acid. There is evidence to suggest that hydrolysis of some sulphonate esters proceeds via a sulphene intermediate314. These reactions are unlikely to have synthetic utility. 

The determination of the Arrhenius parameters for the alkaline hydrolysis of a series of sulphonate esters (Table 2) shows that the reactivity difference in sulphonates arises from a combination of entropy and enthalpy effects, although the latter is likely to be the dominant factor156. The different mechanism of hydrolysis (ElcB) of phenyl toluene-a-sulphonate 43 shows up clearly in the anomalous value of AS. ... 

In practical work a great deal of trouble is avoided by making the measurements at equal intervals x1 - 0, x2 — xlf..., xn-xn v R. Wegscheider (Zeit. phys. Chem., 41, 52, 1902) employed Simpson s rule for integrating the velocity equations for the speed of hydrolysis of sulphonic esters and G. Bredig and F. Epstein (Zeit. anorg. Chem., 42, 341, 1904) in their study of the velocity of adiabatic reactions. 

Examples of good a correlations are for the alkaline hydrolysis of amino-sulphonate esters (MeNHSOj-OAr) [37], acyloxysilanes (EtjSiOAr) [38] and acyl benzene sulphonates (PhSOj-OAr) [39]. These results indicate that the ArO- bond is being cleaved in the transition state of the rate-limiting step. A typical example is illustrated (Fig. 10) for the alkaline hydrolysis of substituted phenyldimethylphos-phinates [40] where the a dependence is consistent with ArO-P cleavage in the transition state of the rate-limiting step (Eqn. 52). 

Raphael, the iodoaromatic (227) is first coupled with the acetylenic alcohol (228) in the presence of Pd° leading to the central intermediate (229). Meyer-Schuster rearrangement of (229) in the presence of methane sulphonic acid then gave rise to (231) presumably via the initially formed ketone (230). Reduction of (231) followed by dehydration next led to (232), which was elaborated to virantmycin, via epoxidation, reduction, deprotection, treatment with thionyl chloride, and finally ester hydrolysis. 

When the sulphonated ester is alkali-hydrolysed, not only does the ester group hydrolyse, as expected, but the sulphonate group is slowly removed as well. Saponification is therefore not a useful way of determining the main active. Acid hydrolysis destroys the ester group but has no effect on the sulphonate group. 

The ester cannot be determined by saponification because this slowly removes the sulphonate group as well as hydrolysing the ester group. It can be determined by acid hydrolysis followed by measurement of the a-sulphonated carboxylate salt produced, either by potentiometric titration of the weak acid or by two-phase titration with benzethonium chloride. Both procedures measure the a-sulphonated ester plus the unsulphonated ester. If the latter is present at a significant level, it can be determined (section 5.11.2) and corrected for. 

Any sulphate with a-sulphonated fatty ester. BEC titration in alkaline solution after acid hydrolysis gives twice the a-sulphonated ester (approximately—see above) plus any sulphonated hydrocarbon, less the sulphate. Determine the sulphate separately by measuring any one of its decomposition products. 

Although there are other convenient procedures for the conversion of sulphides into sulphoxides and sulphones, the phase-transfer catalysed reaction using Oxone has the advantage that the oxidation can be conducted in the presence of other readily oxidized groups, such as amines, alkenes, and hydroxyl groups, and acid-labile groups, such as esters and carbamates [6, 7], Hydrolysis of very acid-labile groups, such as ketals, can result in production of the keto sulphone. 

Solid esters are easily crystallisable materials. It is important to note that esters of alcohols must be recrystallised either from non-hydroxylic solvents (e.g. toluene) or from the alcohol from which the ester is derived. Thus methyl esters should be crystallised from methanol or methanol/toluene, but not from ethanol, n-butanol or other alcohols, in order to avoid alcohol exchange and contamination of the ester with a second ester. Useful solvents for crystallisation are the corresponding alcohols or aqueous alcohols, toluene, toluene/petroleum ether, and chloroform (ethanol-free)/toluene. Carboxylic acid esters derived from phenols are more difficult to hydrolyse and exchange, hence any alcoholic solvent can be used freely. Sulphonic acid esters of phenols are even more resistant to hydrolysis they can safely be crystallised not only from the above solvents but also from acetic acid, aqueous acetic acid or boiling n-butanol. 

By use of benzene sulphonic acid or phosphoric acid. When the ester yields on hydrolysis products which become coloured in presence of alkali and air, Method 1 is inapplicable. If the acid produced on hydrolysis is volatile in steam, benzene sulphonic or phosphoric acid may be used as hydrolytic agent, and the acid (from the ester) after separation by steam distillation is titrated with standard alkali. (See Estimation of Acetyl Group, p. 479.)... 

Deprotection is effected in the case of methyl or ethyl esters by hydrolysis, usually under basic conditions (Section 9.6.17, p. 1266). t-Butyl esters are de-protected by mild acidic conditions, for example, formic acid at room temperature,159 toluene-p-sulphonic acid in benzene solution, or hydrogen bromide in acetic acid at 10°C.160... 

N-Benzylamides are recommended when the corresponding acid is liquid and/or water-soluble so that it cannot itself serve as a derivative. The benzyl-amides derived from the simple fatty acids or their esters are not altogether satisfactory since they are often low melting those derived from most hydroxy acids and from polybasic acids or their esters are formed in good yield and are easily purified. The esters of aromatic acids yield satisfactory derivatives but the method must compete with the equally simple process of hydrolysis and precipitation of the free acid, an obvious derivative when the acid is a solid. The procedure fails with esters of keto acids, sulphonic acids and inorganic acids and some halogenated aliphatic esters. 

Carbon-13 n.m.r. spectroscopy has been used to study benzylisoquinoline and tetrahydroisoquinoline alkaloids and their JV-methyl quaternary salts.30 N-Benzylpapaverinium bromide has been shown to undergo aerial oxidation in alkaline solution to 2-benzyl-6,7-dimethoxyisoquinolone and to give bases of general structure (10) with methylamine, benzylamine, and pyrrolidine.31 Chlorosulphonation of papaverinol affords the sulphonic acid ester (11), mild hydrolysis of which yields the acid (12), which with diazomethane is esterified and dehydrated to (13).32 N-Methyl-l,2-dihydropapaverine has been shown by kinetic studies and orbital-symmetry requirements to rearrange to the salt (14) by the route previously postulated.33... 

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