Sodium Thiosulfate1

Na2S2O3
(Na2S2O3)

[7772-98-7]  · Na2O3S2  · Sodium Thiosulfate  · (MW 158.12) (Na2S2O3.5H2O)

[10102-17-7]  · H10Na2O8S2  · Sodium Thiosulfate  · (MW 248.22)

(general reducing agent; reagent for nucleophilic introduction of sulfur2)

Physical Data: mp (pentahydrate) 40-45 °C; d 1.73 g cm-3.

Solubility: insol alcohol; v sol water.

Form Supplied in: both the pentahydrate and anhydrous form are widely available as white solids.

Handling, Storage, and Precautions: reported to be an irritant. The anhydrous form is hygroscopic.

Functional Group Reductions.

Na2S2O3 is a sufficiently powerful reducing agent to effect a number of useful synthetic transformations. Vicinal dibromides are efficiently dehalogenated to the corresponding alkenes in warm DMSO.3 Anilines are obtained by reduction of aryl nitroso compounds4 or aryl azides,5 and nitrosamides can be reduced to amides.6 Peroxides are reduced to the corresponding alcohols7 when exposed to aqueous Na2S2O3, and reductive workup of an ozonolysis with NaI/Na2S2O3 has been employed in the isolation of a ketone.8 Saturation of activated alkenes by Na2S2O3 has been reported, including the reduction of a quinone9 and of 1,2-dibenzoylethylene.10

Introduction of Sulfur.

Nucleophilic attack by thiosulfate on alkyl halides results in the formation of S-alkyl thiosulfates, commonly known as Bunte salts. Extensive reviews on the preparation and classical reactions of Bunte salts have appeared.2 In addition to alkyl halides, thiosulfate has been reported to add to epoxides,2b oxetanes,11 activated alkenes,2b and even acylaziridines.12 Probably the most well-known classical application of Bunte salts is their conversion to thiols, which can be accomplished via acidic hydrolysis13 or reduction.11 Extension of this methodology to the synthesis of aryl thiols is possible by the addition of Na2S2O3 to quinones (eq 1).14 When the hydrolysis is performed under oxidative conditions, sulfonic acids or sulfonyl chlorides are obtained.2,15

Much of the useful chemistry of Bunte salts results from the leaving group potential of the sulfite moiety. Nucleophilic displacement by thiolates results in the synthesis of unsymmetrical disulfides (eq 2).16 In a mechanistically similar manner, symmetrical trisulfides are available by the reaction of Bunte salts with sodium sulfide.17

The sulfite group of Bunte salts may also function as a leaving group via an E2 elimination, comprising a convenient and mild method for generating thiocarbonyl compounds. This reaction was first noted when the carbamoyl derivatives RNHCOCH2SSO3Na were reacted with primary and secondary amines RŽ2NH, affording thiooxamides RNHCOCSNRŽ2.18 Dimerization of the reactive thiocarbonyl intermediates to 1,3-dithietanes has also been observed.19 The thiocarbonyl group is a good dienophile and will trap 1,3-dienes at low temperatures.20 The resulting cycloadducts can be rearranged stereoselectively under basic conditions to cyclopentenyl sulfides (eq 3).21


1. (a) Swaine, J. W., Jr. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Grayson, M.; Eckroth, D., Eds.; Wiley: New York, 1983; Vol. 22, pp 974-989. (b) Kahrasch, N.; Arora, A. S. PS 1976, 2, 1.
2. (a) Milligan, B.; Swan, J. M. Rev. Pure Appl. Chem. 1962, 12, 72. (b) Distler, H. AG(E) 1967, 6, 544. (c) Hogg, D. R. In Comprehensive Organic Chemistry; Barton, D. H. R.; Ollis, W. D., Eds.; Pergamon: Oxford, 1979; Vol. 3, p 307.
3. Ibne-Rasa, K. M.; Tahir, A. R.; Rahman, A. CI(L) 1973, 232.
4. McLamore, W. M. JACS 1951, 73, 2221.
5. Adams, R.; Blomstrom, D. C. JACS 1953, 75, 3405.
6. White, E. H. JACS 1955, 77, 6008.
7. Isayama, S. BCJ 1990, 63, 1305.
8. Kametani, T.; Honda, T.; Ishizone, H.; Kanada, K.; Naito, K.; Suzuki, Y. CC 1989, 646.
9. Brockmann, H.; Laatsch, H. CB 1973, 106, 2058.
10. Overberger, C. G.; Valentine, M.; Anselme, J. P. JACS 1969, 91, 687.
11. Whistler, R. L.; Luttenegger, T. J.; Rowell, R. M. JOC 1968, 33, 396.
12. Jpn. Patent 57 206 653, 1983 (CA 1983, 98, 215 998r).
13. Wardell, J. L. In The Chemistry of the Thiol Group; Patai, S., Ed.; Wiley: London, 1974; Part 1, Chapter 4, p 192.
14. Alcalay, W. HCA 1947, 30, 578.
15. Ziegler, C.; Sprague, J. M. JOC 1951, 16, 621.
16. (a) Mattes, K. C.; Chapman, O. L. JOC 1977, 42, 1814. (b) Alonso, M. E.; Aragona, H. OSC 1988, 6, 235.
17. Milligan, B.; Saville, B.; Swan, J. M. JCS 1963, 3608.
18. Milligan, B.; Swan, J. M. JCS 1959, 2969.
19. (a) Zehavi, U. JOC 1977, 42, 2821. (b) Hartnedy, R. C.; Dittmer, D. C. JOC 1984, 49, 4752.
20. Kirby, G. W.; Lochead, A. W.; Sheldrake, G. N. CC 1984, 922.
21. Larsen, S. D. JACS 1988, 110, 5932.

Scott D. Larsen

The Upjohn Co., Kalamazoo, MI, USA



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