Sulfonic acids desulfonation

Excess acidity correlations have been used to show that some aromatic sulfonic acid desulfonations have an A-SE2 mechanism.188,189 This mechanism (alternative terminologies are Ad-E2 and A(E) +A(N))190 has also been found to apply to the hydration of acetylene itself,191 to ynamines192 and to many other alkynes,193-195 as well as to many different alkenes196-199 and vinyl ethers.200-203 The excess acidity method has been used to evaluate aA values for several alkene hydrations.204 205... 

The sulfonation of naphthalene by concentrated sulfuric acid at 80 °C gives naphthalene-1-sulfonic acid. At 160 °C, naphthalene-2-sulfonic acid predominates (Scheme 12.6). The 1-isomer is the more readily formed and is stable at the reaction temperature of 80 °C. However, at 160 °C, not only is naphthalene-1-sulfonic acid desulfonated, but also there is sufficient energy to convert naphthalene into the 2-sulfonic acid, which is stable even at the higher temperature. The 2-substituted isomer is more... 

The synthesis of 2,4-dihydroxyacetophenone [89-84-9] (21) by acylation reactions of resorcinol has been extensively studied. The reaction is performed using acetic anhydride (104), acetyl chloride (105), or acetic acid (106). The esterification of resorcinol by acetic anhydride followed by the isomerization of the diacetate intermediate has also been described in the presence of zinc chloride (107). Alkylation of resorcinol can be carried out using ethers (108), olefins (109), or alcohols (110). The catalysts which are generally used include sulfuric acid, phosphoric and polyphosphoric acids, acidic resins, or aluminum and iron derivatives. 2-Chlororesorcinol [6201-65-1] (22) is obtained by a sulfonation—chloration—desulfonation technique (111). 1,2,4-Trihydroxybenzene [533-73-3] (23) is obtained by hydroxylation of resorcinol using hydrogen peroxide (112) or peracids (113). 

Naphthalenediol. This diol is made by the hydrolytic desulfonation of 2,3-naphthalenediol-6-sulfonic acid at ca 180°C. It is used as a coupler forming a2o dyes which are appHed in reprographic processes. 

Pigment Red 177 [4051-63-2] 65300 anthraquinone bimolecular debromination of l-amino-4-bromoanthraquiQone-2-sulfonic acid, foUowed by desulfonation... 

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

Sulfonic acids may be hydrolytically cleaved, using high temperatures and pressures, to drive the reaction to completion. As would be expected, each sulfonic acid has its own unique hydrolytic desulfonation temperature. Lower alkane sulfonic acids possess excellent hydrolytic stability, as compared to aromatic sulfonic acids which ate readily hydrolyzed. Flydrolytic desulfonation finds use in the separation of isomers of xylene sulfonic acids and other substituted mono-, di-, and polysulfonic acids. 

As in the nitration of naphthalene, sulfonation gives the 1-substituted naphthalene. However, because the reverse reaction (desulfonation) is appreciably fast at higher temperatures, the thermodynamically controlled product, naphthalene-2-sulfonic acid, can also be obtained. Thus it is possible to obtain either of the two possible isomers of naphthalene sulfonic acid. Under kineticaHy controlled conditions naphthalene-l-sulfonic acid [85-47-2] (82) is obtained thermodynamic control gives naphthalene-2-sulfonic acid [120-18-3] (83). 

Except for these studies of their protonation behavior, almost the only other aspect of the chemistry of sulfonic acids that has been investigated to any extent from a mechanistic point of view is the desulfonation of aromatic sulfonic acids or sulfonates. Since this subject has been well reviewed by Cerfontain (1968), and since the reaction is really more of interest as a type of electrophilic aromatic substitution than as sulfur chemistry, we shall not deal with it here. One should note that the mechanism of formation of aromatic sulfonic acids by sulfonation of aromatic hydrocarbons has also been intensively investigated, particularly by Cerfontain and his associates, and several... 

In addition, desulfonation generally has to be taken into account with benzamides and phthalimides that are sulfonated at the amine subunit. The sulfonamide linkage proved to be stable with sulfonated and nonsul-fonated sulfonamides. Compounds with electron-withdrawing substituents at the sulfonic acid-bearing ring were more stable with respect to the hydrolysis of sulfonic acid groups. 

Phenol was prepared before World War I through the distillation of coal tar. The first synthetic process involved the sulfonation of benzene followed by desulfonation with a base. In this process, benzene sulfonic acid is prepared from the reaction of benzene and sulfuric acid ... 

Decarboxylation of aromatic acids 1-41 Desulfonation of aromatic sulfonic acids... 

Pigment Red 177 [4051-63-2] has the chemical structure of 4,4 -diaminol,l -dianthraquinonyl and is prepared by intermolecular copper-catalyzed debromination of l-amino-4-bromoanthraquinone-2-sulfonic acid followed by desulfonation. It is the only known pigment with unsubstituted amino groups which are involved in both intra- and intermolecular hydrogen bonding (19). The bluish red pigment is used in plastics, industrial and automotive paints, and specialized inks (see Dyes, ANTHRAQUINONE). 

Desulfonation is slower than with naphthalene sulfonic acids.46 It is accomplished by heating the calcium salt with superheated steam in the presence of 85% phosphoric acid,660 or by heating the potassium salt with superheated steam in the presence of sulfuric acid.84... 

An observation reminiscent of this denitration is the corresponding ready decarboxylation or desulfonation of the acids (107) by action of hot mineral acid.46 This reaction evidently requires the o-i-amino group since the 2-nitro-4-carboxylic acid (107a), the corresponding sulfonic acid (107a), as well as p-nitrophenylanilines (104) are un-... 

Desulfonation Sulfonation is reversible, and a sulfonic acid group may be removed from an aromatic ring by heating in dilute sulfuric acid. In practice, steam is often used as a source of both water and heat for desulfonation. 

When an aromatic sulfonic acid is heated to 100-175° with aqueous acid, it is converted into sulfuric acid and an aromatic hydrocarbon. This desulfonation is the exact reverse of the sulfonation process by which the sulfonic acid was originally made. 

Sulfonation, like nitration and halogenation, occurs more rapidly at the a-position, since this involves the more stable intermediate carbonium ion. But, for the same reason, attack by hydrogen ion, with subsequent desulfonation, also occurs more readily at the a-position. Sulfonation at the j3-po ition occurs more slowly but, once formed, the jS-sulfonic acid tends to resist desulfonation. At low temperatures desulfonation is slow and we isolate the product that is formed faster, the alpha naphthalenesulfonic acid. At higher temperatures, desulfonation becomes important, equilibrium is more readily established, and we isolate the product that is more stable, the beta naphthalenesulfonic acid. 

The reaction occurs via the o-complex, the arenium carbocation, which is relatively unstable and reacts with the hydrogensulfate anion (HS04-) to regenerate the stable aromatic system (six -electrons). In sulfonation, all four steps are reversible consequently, sulfonation, unlike nitration, is a reversible process, so that by heating a sulfonic acid with dilute sulfuric acid the parent compound can be regenerated (desulfonation). 

Although there is no proof for the mechanism, many of the data known about the reaction can be interpreted in terms of three general steps (1) sulfonation (XXII to XXIV) (2) formation of a m- or p-disulfonic acid with the elimination of an alkyl carbonium ion if one of these positions is occupied (XXIII to XXVII and XXIII to XXIV) and (3) displacement of the more hindered sulfonic acid group by the eliminated carbonium ion (XXIV to XXVI and XXVII to XXVIII) or an oxonium ion (XXVII to XXIX). In agreement with (3) it has been found that the most hindered sulfonic acids are the most readily desulfonated.67... 

The reaction of benzene with fuming sulfuric acid or oleum (a mixture of sulfuric acid and sulfur trioxide) leads to the formation of benzene-sulfonic acid. The sulfonation is reversible, and this makes it a useful tool in organic synthesis for blocking certain positions on a benzene ring (see Section 7.8). Sulfonation is favoured using strong sulfuric acid, but desulfonation is favoured in hot, dilute aqueous acid. 

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