Chlorosulfuric Acid Sulfonation of Alpha Olefins Hurni R. Alul Research and Development Department, Inorganic Chemicals Division, Monsanto Co., S t . Louis, M o . 63166
Contrary to earlier reports in the literature, the dehydrohalogenation of 2-chloroalkane-1 -sulfonic acids affords a mixture of both 1 and 2-alkenesulfonic acids instead of the 1 isomer alone. A simple explanation for the formation of each isomer i s given. The formation of the 1 isomer probably occurs by an ordinary E:, mechanism, but that of the 2 isomer involves participation of the neighboring group, SO3-.
-
A l p h a olefin sulfonates are gaining widespread attention as detergent' base materials. The recent availability of CYolefins and the fuiictioiial performance and biodegradability of the products have been emphasized by several recent publicatioiis (McCutcheon, 1967; Davidsohn and Milwidsky, 1968; Marquis, 1968). Formation of the olefin sulfonates may be accomplished by the direct' action of gaseous SO, on aolefins and subTquent neutralization with NaOH. The product, however, is a complex mixture of a large number of coinpounds which include hydroxyalkanesulfoiiate and alkencsulfonates with the double bond dist'ributed over t'he entire chain. 011 the other hand, sulfonation with chlorosulfuric acid affords far fewer products, and t'he mixture is readily isolated a d analyzed. Because of the apparent generality of t,his method, it is possible to synthesize individual compounds such as 2-hydrosyalkaiiesulfoiiic acids and 2-alkenesulfonic acids, until now available only with difficulty (Pueschel aiid Kaiser, 1964,1965). The primary product of the reaction of chlorosulfuric acid with a-olefins in the prebence of diethyl ether is t'he chloriiiated sulfonic acid (1) (Gilbert, 1965). lI--CH=CH?
ether + ClSOBH + R-CH-CH2-SO3H
C1 1
Hydrolysis in the presence of KaaC03a t 10°C results in 2hydrosyalkane-1-sodium sulfonate (2) in 80y0 yield. Keact,ion of t,he chlorinated sulfonic acid (1) with XaOH a t room temperature has been reported to afford in addition to the hydroxysulfonate, 1-alkenesulfoiiate, obtained by the elimination of HC1 (Gilbert, 1965).
I c1
RCH--CH2-SO3ICTa I
OH I
2
358 Ind. Eng. Chem. Prod. Res. Develop., Vol. IO, No. 3, 1971
Careful isolation and aiialysis of the alkenesulfoiiate produced in the reaction with S a O H showed that the product is actually a mixture of 1- and 2-alkenesulfonates, R-CH= CH-S03?rTa and R-CH=CH--CH2SO3Ka: in about equal amounts rather than the 1 isomer alone. The reactioii was carried out with 1-hesene, and the sodium hexeiiesulfonates were isolated and analyzed by nmr. Two sets of olefinic protons in the spect'rum, oiie a t 5.7 ppm and the other a t 6.5 ppm, suggested the presence of more than oiie hexeiiesulfonate and probably a mixture of the 1 and 2 isomers with the protons of t'he first oiie appearing downfield a t 6.5 ppm. To check this result we chose a long-chain a-olefin, such as 1-hexadecene, and reacted it with C1S03H and then NaOH in the same manner. The alkenesulfonate portion of t.he product was analyzed by ninr and by oxidation to the carboxylic acids by a procedure similar to that used for the determiriat,ioii of the position of the double bond across the chain of a mixture of alkenesulfonates (von Rudloff, 1956; Marquis et al., 1966). The carboxylic acids were then esterified with CH30H 13F3,and the methyl esters were analyzed by glc. The chromatogram showed only two bands unequivocally iderhfied by the use of authenbic samples of the methyl esters of Cl?,C14,and C16carboxylic acids. The formation of the 1 isomer probably occurs by ail ordinary E? mechanism in which the initial step involves an attack by the base on the proton of the activated 1 carbon atom (McLennan, 1967; Ingold, 1969). Also, a strong base, such as S a O H , is required for the formation of the 1 isomer which is absent when t,he reaction is carried out in a weak base. Sodium hydroxide failed to isomerize the 2 isomer to the conjugated 1 isomer under the same experimental condit,ioiis. Therefore, the formation of the latter occurs directly aiid independently from the 2 isomer. On t,he basis of the present data it' is not possible to distinguish between an E? and an ElcB mechanism, both of which require n strong base. The Elc13 mechanism, less common than t'he E: mechanism, appears to operate in eliminations which form an olefin double bond conjugat'ed with ail electronegative unsaturated group, thus creating a situation similar to the present one (Ingold, 1969). However, since the initial step in this reaction is neutralization of t.he sulfonic acid, the formation of a carbanion is hindered by the presence
of the negatively charged sulfonate group on the adjacent carbon atom, making a true ElcB mechanism unlikely. The formation of the 2 isomer may be explained by a cyclic mechanism involving participation of the neighboring sulfonate group in the following manner: CI
c'L
/
R-CH,)
H -CH
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