Sulfur Trioxide-1,4-Dioxane1

(x unspecified)

[54287-50-2] (x = 1)

[20769-58-8; 35346-47-5]  · C4H8O5S  · Sulfur Trioxide-1,4-Dioxane  · (MW 168.19) (x = 2)

[52922-31-3]  · C4H8O8S2  · Sulfur Trioxide-1,4-Dioxane  · (MW 248.26) (x = 3)

[52922-32-4]  · C4H8O11S3  · Sulfur Trioxide-1,4-Dioxane  · (MW 328.33)

(useful for effecting Beckmann rearrangements;8 sulfonation of alkenes11 and arenes16)

Physical Data: mp 75 °C,2 but almost never isolated.

Solubility: generated as a solution in dioxane, with or without other solvents.

Preparative Methods: the Organic Synthesis procedure2 involves reaction of Sulfur Trioxide (as Sulfan B) with dioxane in 1,2-dichloroethane. The complex precipitates and is used immediately. An alternate procedure involves treatment of dioxane with ClSO3TMS,3 itself prepared by reaction of Chlorotrimethylsilane and Chlorosulfonic Acid.4

Handling, Storage, and Precautions: reacts vigorously with water, alcohols, etc. It has been reported to decompose violently upon standing at rt2 or upon heating to 75 °C.5 The chemistry is essentially that of SO3 with some attenuation in reactivity. Safety precautions in the handling of SO3, which can be an unexpectedly strong oxidant, should be followed.1c


Sulfur trioxide forms addition complexes of varying stability and reactivity with Lewis bases. The stronger the base, the more stable and less reactive is the complex. The reactions of these complexes are essentially those of SO3 and so it is possible to tune the reactivity of SO3 to suit the reaction or substrate of interest. Frequently used bases, in order of decreasing reactivity of their SO3 complexes, are N,N-Dimethylformamide, 1,4-dioxane, Pyridine, and Trimethylamine.1c The dioxane adducts are hydrolyzed instantly in cold water, whereas the pyridine adduct is stable in aqueous solution. Dioxane-SO3 adducts with the stoichiometry of 1:1, 1:2, 1:3, and 1:4 have all been identified. The second and third equivalents of SO3 in the 1:2 and 1:3 complexes are much more reactive than the first. The following paragraphs refer specifically to the 1:1 complex.

Sulfation Reactions.

Reactions of alcohols proceed with extraordinary ease.1c When aromatic nuclei are present, simple control of stoichiometry is sufficient to prevent aromatic substitution. In many cases, reaction of the dioxane-SO3 complex with amines (sulfamation) is too vigorous to be convenient and a tamer (pyridine-SO3) complex is preferable. The OH group undergoing sulfation may be part of another group, e.g. an oxime.6,7 The oxime-O-sulfonate may occasionally be isolated, but more commonly is directly transformed into the amide (Beckmann rearrangement) by heating (eq 1).8

Sulfonation of Alkenes.

Alkenes undergo sulfonation. The initial product is the cyclic b-sultone which is formed by a concerted mechanism9 and stereospecifically.10 These are rapidly hydrolyzed in the presence of water or alcohols. Products range from 2-hydroxysulfonic acids to vinyl or allyl sulfonic acids (eq 2).1c,11-13

Sulfonation of Carbonyl Compounds.

Carboxylic acids form acyl sulfates which rearrange into a-sulfo acids. Similarly, aldehydes and ketones sulfonate in the a-position.14 Aryl-substituted alkanoic acids sulfonate a to the acid without aromatic substitution. This is contrary to their reaction with Sulfuric Acid, which affords ring-sulfonated products.

Sulfonation of Aromatic Compounds.

Cerfontain and co-workers have published many papers dealing with the mechanism of this reaction.1b,15 Benzene and its derivatives do not react unless highly activated. Polycyclic aromatics react via sultones which may be isolated or may open to give sulfonic acids. For example, anthracene affords the 9-sulfonic acid;16 9-alkylanthracenes afford principally side-chain sulfonated materials,17 whereas alkyl substitution on ring A leads to sultones whose structures depend on the substitution pattern (eq 3).18 The isomeric composition of the sulfonic acid products may differ substantially from that obtained using sulfuric acid. Dioxane-SO3 is the reagent of choice for the sulfonation of moderately acid-sensitive aromatics (e.g. thiophene),19 but it is still too reactive to use with Furan and pyrrole. The patent literature is replete with references to sulfonation of various polymers using SO3 in various for ms, but this is beyond the scope of this report.

Related Reagents.

Sulfur Trioxide; Sulfur Trioxide-Pyridine.

1. (a) Gilbert, E. E. Sulfonation and Related Reactions; Wiley: New York, 1965. (b) Cerfontaine, H. Mechanistic Aspects in Aromatic Sulfonation and Desulfonation; Wiley: New York, 1968, (c) Sandler, S. R.; Karo, W. Organic Functional Group Preparations; Academic: New York, 1972; Vol. 3.
2. Sisler, H. H.; Audrieth, L. F. Inorg. Synth. 1946, 2, 173.
3. Hofmann, K.; Simchen, G. S 1979, 699.
4. Schmidt, M.; Schmidbauer, M. AG 1958, 70, 657.
5. Suter, C. M.; Evans, P. B.; Kiefer, J. M. JACS 1938, 60, 538.
6. Fukui, K.; Uchida, M.; Masaki, M. BCJ 1973, 46, 3168.
7. Kelly, K. K.; Matthews, J. S. JOC 1971, 36, 2159.
8. Turbak, A. F. Ind. Eng. Chem., Prod. Res. Dev. 1968, 7, 189.
9. Bakker, B. H.; Schonk, R. M.; Cerfontain, H. RTC 1990, 109, 485.
10. Nagayama, M.; Okumura, O.; Noda, S.; Mandai, H.; Mori, A. BCJ 1974, 47, 2158.
11. Nakanishi, S.; Yoshimura, F. Kogyo Kagaku Zasshi 1971, 74, 2297 (CA 1972 76, 45 782s).
12. Bordwell, F. G.; Osborne, C. E. JACS 1959, 81, 1995.
13. Bordwell, F. G.; Peterson, M. L. JACS 1959, 81, 2000.
14. Truce, W. E.; Alfieri JACS 1950, 72, 2740.
15. Van Lindert, H. C. A.; Koeberg-Telder, A.; Cerfontain RTC 1992, 111, 379.
16. Koeberg-Telder, M. A.; Cerfontain, H. RTC 1972, 91, 22.
17. (a) Van de Griendt, F.; Cerfontain, H. JCS(P2) 1980, 23. (b) Van de Griendt, F.; Cerfontain, H. JCS(P2) 1980, 19. (c) Van de Griendt, F.; Cerfontain, H. JCS(P2) 1980, 13.
18. Van de Griendt, F.; Visser, C. P.; Cerfontain, H. JCS(P2) 1980, 911.
19. Shustareva, T. K. Khim. Geterotsikl. Soedin 1987, 9, 1183 (CA 1988, 108, 221 531z).

John M. McIntosh

University of Windsor, Ontario, Canada

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