Alkenesulfonic acids

The actual sulfonation reaction consists largely of a concerted 2+2 cyclo addition of S03 and a-olefin yielding a highly reactive, unstable p or 1,2-sultone that can (1) react further to give alkenesulfonic acid and (2) rearrange itself to form y- or 1,3-sultone (a fast reaction), and 8- or 1,4-sultone (a slow reaction). Possible side reactions have been identified by Bakker and Cerfontain [28]. At molar ratios of S03/olefin below 1.0 the major sulfonation product is 1,3-sultone but larger proportions of alkenesulfonic acids will be formed for ratios... 

The next stage is neutralization of the alkenesulfonic acids with NaOH yielding water-soluble sodium alkenesulfonates, and hydrolysis of the sultones leading to sodium 3-hydroxyalkanesulfonates and sodium 4-hydroxyalkanesulfon-ates. The proportion of the latter two compounds in the mixture will depend on the conditions employed in the aging step. A hydrolysis temperature of 150-160°C and a hydrolysis time of 40-45 min ensures virtually complete hydrolysis of sultones 1,3-sultones will be present in ppb quantities and 1,4-sultones in ppm quantities. 

According to [4], the optimum conditions of the sulfonation stage are a reactor temperature of 15°C, an S03/I0 ratio of 1.08, and 2.8 vol % S03 in the gas stream. Such mild conditions lead to sulfonation mixtures consisting of 85% P-sultones (1) 10% alkenesulfonic acids (2) 5% y-sultones (3) and less than 5% unreacted olefins. The authors observe that the reaction has been completed to more than 95% at the outlet of the reactor. This means that the incomplete conversions found by earlier authors [15] must have been due to phenomena occurring after the sulfonation. Of equal importance is the observation that the reactivity of 10 toward gaseous S03 seems similar to that of AO. 

From a process point of view, the direct neutralization is clearly preferred moreover, the product quality (color) and free oil content deteriorates with aging (Table lb). The fact that the free oil and the inorganic sulfate level increase simultaneously upon aging is due to the fact that the formation of p-sultones from olefins is a reversible reaction [28], in competition with thermal rearrangement to alkenesulfonic acid and y- and 8-sultone. The effects of the reverse reaction of p-sultones are less with AOS because the rearrangement rates of AO-derived sultones are higher [29,35]. 

Alternatively, the 3- and 4-hydroxy sulfonates may be converted to the corresponding sultones by treatment with a strong mineral acid. An ether extract concentrates the organic components, sultones, and alkenesulfonic acid, which can be weighed and titrated potentiometrically with sodium hydroxide. 2-Hydroxyalkanesulfonate will not dehydrate to the sultone under these conditions and is not measured. 

The preparation and identification of four types of S03-sulfonated products of linear and branched 1-alkenes (C5-C14) are described by Boyer [121]. 13C-and, to a lesser extent, -NMR spectra were used to ascertain the structures of 2-alkenesulfonic acids, p-sultones (as 2-methoxyalkanesulfonic acids), y- and 5-sultones. The mass spectra of some methyl 2-methoxyalkanesulfonates and 4-alkyl-5-sultones were also studied. Sufficiently volatile mixtures were separated by GLC after methylation of the sulfonic groups. 

H-NMR spectroscopy can be used to determine alkenesulfonates in mixtures [115]. Under normal conditions, 1-alkenesulfonate shows a signal separated from the other positional isomers [122]. Moreover, the utilization of a lanthanide shift reagent makes possible even the separation of the signals of isomeric alkenesulfonic acids and hydroxyalkanesulfonic acids as their methyl esters [124]. 13C-NMR spectroscopy, which is not as quantitative, simply gives the cis/trans ratio of the main positional isomer. 

Hashimoto et al. [122-126] have used 13C-NMR as a tool for the determination of sulfonic acid and sulfonate species in AOS and its intermediates. The Na salts of C16 1-alkenesulfonic acid, Cu 2-alkenesulfonic acid, C18 9-alkene-sulfonic acid, 1-propylenesulfonic acid, and C16 3-hydroxyalkanesulfonic acid showed that alkenyl protons in 1-alkenesulfonic acids had NMR chemical shifts at 6.1-6.7 ppm, while other acids had chemical shifts at 5.4-5.9 ppm. The results were useful for rapid determination of 1-alkenesulfonic acid content. 

A = peak area of the methin proton signal of alkenesulfonic acid... 

Two types of sulfonate esters can be formed in the production of AOS. Neutral esters are formed by the addition of alkenesulfonic acid to alkene (Fig. 29). Acid esters are formed by the dimerization of two alkene mono- or disulfonic acids (Fig. 30). These would normally be expected to hydrolyze in the saponification stage of the process. 

FIG. 30 Production of dimer and higher oligomers from alkenesulfonic acids. 

Isomerization of the sultone intermediate to form the desired alkenesulfonic acid Disulfonic acid formation... 

During sulfonation a-olefins give a mixture of alkenesulfonic acid and sultones. The neutralization of this mixture is effected at 165-170°C to hydrolyze sul-... 

Several j3-sultones are claimed to be formed by treatment of alkenes with sulfuric acid or by heating alkenesulfonic acids. Treatment of 2,2-dimethyl-1,1-diphenyl-1-propanol with concentrated sulfuric acid at room temperature is said to give 3-(l,l-diphenylethyl)-3-methyl-l,2-oxathietane 2,2-dioxide (96% yield). Treatment of sodium 3-bromo-2-hydroxybutanesulfonate with phosphorus trichloride is reported to give a low yield of 4-(l-bromoethyl)-l,2-oxathietane 2,2-dioxide.1,2-Oxathietane 2,2-dioxide is suggested as an intermediate in the reaction of /3-hydroxyethanesulfonyl chloride with trimethylamine to give the zwitterion 502. The first four-membered monocycUc sulfurane oxides 502a have been reported. 

Boron trifluoride-triethylamine effects a ring-opening elimination of 4,4-difluoro-3-trifluoromethyl-l,2-oxathietane 2,2-dioxide to give fluorosulfonyl-trifluoromethylketene. Eliminations occur from intermediate 3-sultones, obtained by addition of sulfur trioxide to alkenes, to give alkenesulfonic acids. ... 

In such reactions the arylsulfonyl group always adds at the -position to the carboxyl group addition to the /raray-alkenesulfonic acid is appreciably slower than to the cw-isomers. 

The mixture has to be allowed to age for rearrangement of the unstable 1,2-sultone to alkenesulfonic acids and 1,3- and 1,4-sultones. That is carried out to minimize the content of the 1,2-sulfone, or otherwise this would be transformed by hydrolysis to the insoluble 2-hydroxyalkanesulfonate. The highly reactive 1,2-sulfone, the rearranged sultones or the formed alkenesulfonic acid may further react with SO3 to give disulfonic acids and sultone sulfonic acids. 

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