Acidity of sulfonic acids

On the basis of 193 nm photoionization experiments [45], the lifetime of the propene radical cation formed in the heterolysis step is <20 ns. As expected on the basis of the lower acidity of sulfonic acid compared with sulfuric, sulfonates are weaker leaving groups than sulfates, e.g. ... 

The high acidity of sulfonic acids creates a problem in the quantitative determination of their acid strengths in water, the standard medium. Even with some of the weaker sulfonic acids like methanesulfonic acid, a 0.1 M solution of the acid is more than 99.8% ionized, and the precise determination of the components of the equilibrium can be difficult. Media other than water, of course, may be used for the determination of acid strength, and some of these will be discussed in this chapter. The loss of comparability with the vast body of acidity data for aqueous solutions, and the intervention of other problems such as ion pairing, are, however, serious disadvantages to the use of solvent media other than water, and considerable effort has been devoted to finding acceptable pK values for the aqueous system. 

TABLE 2. Acidities of sulfonic acids in aqueous sulfuric acid solutions... 

The second source of sulfonic acid uses the following reaction scheme alkylation of benzene by a propylene oligomer then sulfonation of the alkylbenzene. 

Alkyl sulfonates are derivatives of sulfonic acids m which the proton of the hydroxyl group is replaced by an alkyl group They are prepared by treating an alcohol with the appropriate sulfonyl chloride usually m the presence of pyridine... 

IS reversible but can be driven to completion by several techniques Removing the water formed m the reaction for example allows benzene sulfonic acid to be obtained m vir tually quantitative yield When a solution of sulfur trioxide m sulfuric acid is used as the sulfonatmg agent the rate of sulfonation is much faster and the equilibrium is dis placed entirely to the side of products according to the equation... 

Among the variety of electrophilic species present m concentrated sulfuric acid sulfur tnoxide (Figure 12 4) is probably the actual electrophile m aromatic sulfonation We can represent the mechanism of sulfonation of benzene by sulfur tnoxide by the sequence of steps shown m Figure 12 5... 

Most xanthene dyes are classified as basic dyes by their method of appHcation acid dyes can be produced by introduction of sulfonic acid groups. The fluoresceins, which contain carboxy and hydroxy substituents, are also acid dyes for coloration of silk. Some of the fluoresceins in which the carboxy group has been esterified, are soluble in alcohol or other organic solvents and can be classified as solvent dyes. Mordant dyes can be produced by introducing o-dihydroxy or sahcyhc acid groups (2), which when metallised can have very good lightfastness. 

When aqueous solutions of sodium bisulfite are heated with butynediol, one or two moles add to the triple bond, forming sodium salts of sulfonic acids (61). 

Keta.Is, Trimethylpentanediol reportedly forms a cycHc ketal by heating it with benzophenone ia the presence of sulfonic acid catalysts at reflux temperatures ia toluene (64). These are said to be useful as aprotic solvents for ink-jet printing and as inflammation inhibitors for cosmetic preparations... 

Sulfonic acid hydrazides, RSO2NHNH2, are prepared by the reaction of hydraziae and sulfonyl haUdes, generally the chloride RSO2CI. Some of these have commercial appHcations as blowiag agents. As is typical of hydrazides generally, these compounds react with nitrous acid to form azides (26), which decompose thermally to the very reactive, electron-deficient nitrenes (27). The chemistry of sulfonic acid hydrazides and their azides has been reviewed (87). 

PyrogaUol has been cited for use in photosensitive compositions. It is used in the form of sulfonate esters of quinonediazides which hydrolyze when exposed to actinic light to Hberate the acid which, in turn, catalyzes further reaction of novolak resins (60). 

An asymmetric synthesis of estrone begins with an asymmetric Michael addition of lithium enolate (178) to the scalemic sulfoxide (179). Direct treatment of the cmde Michael adduct with y /i7-chloroperbenzoic acid to oxidize the sulfoxide to a sulfone, followed by reductive removal of the bromine affords (180, X = a and PH R = H) in over 90% yield. Similarly to the conversion of (175) to (176), base-catalyzed epimerization of (180) produces an 85% isolated yield of (181, X = /5H R = H). C8 and C14 of (181) have the same relative and absolute stereochemistry as that of the naturally occurring steroids. Methylation of (181) provides (182). A (CH2)2CuLi-induced reductive cleavage of sulfone (182) followed by stereoselective alkylation of the resultant enolate with an allyl bromide yields (183). Ozonolysis of (183) produces (184) (wherein the aldehydric oxygen is by isopropyUdene) in 68% yield. Compound (184) is the optically active form of Ziegler s intermediate (176), and is converted to (+)-estrone in 6.3% overall yield and >95% enantiomeric excess (200). 

Amides react ia certain cases to form ammonium salts of sulfonated amides (22). For example, treatment with ben2amide yields ammonium A/-ben2oylsulfamate [83930-12-5] C H CONHSO NH, and treatment with ammonium sulfamate yields dianmioiiiumimidodisulfonate [13597-84-17, HN(S020NH 2 Ammonium sulfamate or sulfamic acid and ammonium carbonate dehydrate Hquid or soHd amides to nitriles (27). 

Dyes, Dye Intermediates, and Naphthalene. Several thousand different synthetic dyes are known, having a total worldwide consumption of 298 million kg/yr (see Dyes AND dye intermediates). Many dyes contain some form of sulfonate as —SO H, —SO Na, or —SO2NH2. Acid dyes, solvent dyes, basic dyes, disperse dyes, fiber-reactive dyes, and vat dyes can have one or more sulfonic acid groups incorporated into their molecular stmcture. The raw materials used for the manufacture of dyes are mainly aromatic hydrocarbons (67—74) and include ben2ene, toluene, naphthalene, anthracene, pyrene, phenol (qv), pyridine, and carba2ole. Anthraquinone sulfonic acid is an important dye intermediate and is prepared by sulfonation of anthraquinone using sulfur trioxide and sulfuric acid. 

General Reaction Chemistry of Sulfonic Acids. Sulfonic acids may be used to produce sulfonic acid esters, which are derived from epoxides, olefins, alkynes, aHenes, and ketenes, as shown in Figure 1 (10). Sulfonic acids may be converted to sulfonamides via reaction with an amine in the presence of phosphoms oxychloride [10025-87-3] POCl (H)- Because sulfonic acids are generally not converted directiy to sulfonamides, the reaction most likely involves a sulfonyl chloride intermediate. Phosphoms pentachlotide [10026-13-8] and phosphoms pentabromide [7789-69-7] can be used to convert sulfonic acids to the corresponding sulfonyl haUdes (12,13). The conversion may also be accompHshed by continuous electrolysis of thiols or disulfides in the presence of aqueous HCl [7647-01-0] (14) or by direct sulfonation with chlorosulfuric acid. Sulfonyl fluorides are typically prepared by direct sulfonation with fluorosulfutic acid [7789-21-17, or by reaction of the sulfonic acid or sulfonate with fluorosulfutic acid. Halogenation of sulfonic acids, which avoids production of a sulfonyl haUde, can be achieved under oxidative halogenation conditions (15). 

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). 

In 1991, over 1 x 10 t sulfonic acids were produced in the United States (24). The materials, for the most part, were used as intermediates for the manufacture of sulfonates in the detergent market, dye manufacture, dispersing agents, catalysts, polymers, etc. Production of dodecjlbenzenesulfonic acids derivatives dominated the sulfonic acid market (Table 2). These had a 38% overall share. The differences between the production tons and the tons sold is accounted for by in-plant use by various manufacturers verses merchant market production. 

Table 2. U.S. Production, Sales, and Value of Sulfonic Acids ...

As of the end of 1991, there were over 60 manufacturers of sulfonic acids and sulfonates in the United States (25). In 1995, Stepan Company was... 

The quahty of sulfonic acids produced as iatermediates on an iadustrial scale is important to detergent manufacturers. Parameters such as color, water, free oil (unsulfonated material), and acid value (actual sulfonic acid) are all factors that determine the quaUty of a sulfonic acid. The quaUty of the feedstock prior to sulfonation, such as iodine value, water content, and sulfonatabiUty, affects the quaUty of the sulfonic acid produced. Sulfonation conditions, such as temperature, molar ratio, rate, etc, also affect the quaUty of sulfonic acid. 

Modem analytical techniques have been developed for complete characteri2ation and evaluation of a wide variety of sulfonic acids and sulfonates. The analytical methods for free sulfonic acids and sulfonate salts have been compiled (28). Titration is the most straightforward method of evaluating sulfonic acids produced on either a laboratory or an iadustrial scale (29,30). Spectroscopic methods for sulfonic acid analysis iaclude ultraviolet spectroscopy, iafrared spectroscopy, and and nmr spectroscopy (31). Chromatographic separation techniques, such as gc and gc/ms, are not used for free... 

Surfactants and Detergents Uses. Perhaps the largest use of sulfonic acids is the manufacture of surfactants (qv) and surfactant formulations. This is primarily owing to the dominance of linear alkylbenzenesulfonic acid production for detergent manufacture. In almost all cases, the parent sulfonic acid is an intermediate which is converted to a sulfonate prior to use. The largest volume uses for sulfonic acid intermediates are the... 

Sulfonic Acid-Based Dyestuffs. Sulfonic acid-derived dyes are utilized industrially in the areas of textiles (qv), paper, cosmetics (qv), foods, detergents, soaps, leather, and inks, both as reactive and disperse dyes. Of the principal classes of dyes, sulfonic acid derivatives find utiUty in the areas of acid, azoic, direct, disperse, and fiber-reactive dyes. In 1994, 120,930 t of synthetic dyes were manufactured in the United States, of which 5,600 t were acidic (74). The three largest manufacturers of sulfonic acid-based dyes for use in the United States are BASF, Bayer, and Ciba-Geigy. 

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