Sulfonations alkenes, sulfur trioxide

Sulfur trioxide reactivity can also be moderated through the use of SO adducts. The reactivity of such complexes is inversely proportional to their stabihty, and consequentiy they can be selected for a wide variety of conditions. Whereas moderating SO reactivity by adducting agents is generally beneficial, the agents add cost and may contribute to odor and possible toxicity problems in derived products. CeUulosic material has been sulfated with SO.—trimethyl amine adduct in aqueous media at 0 to 5°C (16). Sulfur trioxide—triethyl phosphate has been used to sulfonate alkenes to the corresponding alkene sulfonate (17). Sulfur trioxide—pyridine adduct sulfates oleyl alcohol with no attack of the double bond (18). 

Phenyliodonium sulfate 289, which is obtained from the reaction of iodo-sobenzene and sulfur trioxide at -50°C, behaves as a 1,4-dipole in the reactions with several alkenes (86ZOR450) to give intermediate [4 + 2] cycloadduct 290. Decomposition of this unstable adduct affords cyclic sulfates 291 (Scheme 73). Likewise, another 1,4-dipole 292 undergoes cycloaddition reaction to give cyclic sulfone 293 (88ZOR888). The 1,4-dipole 292 thermally decomposes to give 294 (86DOK1374) (Scheme 74). 

Sulfur trioxide is a more powerful sulfonating agent than concentrated sulfuric acid, and consequently it will sulfonate benzene at low temperatures (0-10°C). Sulfur trioxide also reacts with terminal alkenes (38) to yield the sulfonic acids (39) (Scheme 20). 

Aliphatic y-sultones and 8-sultones may be synthesised by the sulfonation of alkenes by reaction with the sulfur trioxide-dioxan complex or gaseous sulfur trioxide (Scheme 66). 

Reaction of an alkene with an excess of SO3 gives a cyclic sulfonate-sulfate anhydride, also referred to as carbyl sulfate or pyrosulfate (eq 5). This carbyl sulfate is formed by a slow insertion of SO3 into the intermediate -sultone. The complex of sulfur trioxIde with dimethyl sulfide reacts with alkenes and alkynes to afford sulfobetaines in good yields (eq 6). These sulfobetaines are produced by nucleophilic attack of the dimethyl sulfide on the initially formed -sultones. 

Another class of sulfonates is the a-olefin sulfonates which are prepared by reacting linear a-olefin with sulfur trioxide, typically yielding a mixture of alkene sulfonates (60-70%), 3- and 4-hydroxyalkane sulfonates ( 30%) and some disulfonates and other species. The two main a-olefin fractions used as starting material are C12-C16 and Cig-Cig. 

The major sulfonation process uses sulfur trioxide as the reactant and yields alkene sulfonic acids as preliminary products, together with various sultones (mainly 1,3 and 1,4 sultones corresponding to the more probable positions of the intermediate carbonium ion in the successive molecular rearrangements). Further alkaline hydrolysis of sultones yields hydroxyalkane sulfonates and alkene sulfonates (illustrated belo for 1,3 alkane sultone). An acidic hydrolysis of sultones produces alkene sulfonates as major products. 

Sulfonation of suitable alkenes 34, by treatment with chlorosulfonic acid or sulfur trioxide, yields a-alkenesulfonates 35 (Equation 3), see also Chapter 5, p 148. 

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