Carbon Oxysulfide1

O=C=S

[463-58-1]  · COS  · Carbon Oxysulfide  · (MW 60.07)

(agent for the thiocarboxylation of Grignard reagents,2 enolates,3 and other carbanions, and for the preparation of thiocarbonates,1,4 ureas,1 and various heterocycles1)

Alternate Names: carbon oxide sulfide; carbonyl sulfide.

Physical Data: bp -50.2 °C; mp -138.2 °C; critical temp 105 °C; density (liquid) 1.25 g cm-3 at -87 °C; density (gas) 1.073 g L-1 at 0 °C.

Solubility: 54 mL/100 mL in H2O at 20 °C; sol EtOH, CS2.

Form Supplied in: compressed gas. Drying: pass gas through conc H2SO4.

Handling, Storage, and Precautions: carbon oxysulfide is a colorless, odorless, toxic gas. Use in a fume hood.

Reactions of Carbon Oxysulfide with Grignard Reagents, Enolates, and Other Carbanions.

Carbon oxysulfide reacts in a similar manner to carbon dioxide with a range of anionic substrates to form carbothioic acids [RC(=O)SH], with the option of in situ alkylation to carbothioic esters [RC(=O)SRŽ]. While overreaction of COS with Grignard reagents (eq 1) to afford trialkyl carbinols2 appears to be more of a problem than with CO2, the trapping of enolates with COS followed by methylation proceeds in high yield (eq 2)3 and allows improved access (after HgII catalyzed transesterification) to b-keto esters,5 compared with the more direct CO2 based approach.6

Acylation of thioenolate derivatives varies according to the substrate, occurring either on carbon (with t-butyl methyl thioketone) or sulfur (with diisopropyl thioketone).7 Carbon oxysulfide has also been used to acylate phosphorus ylides8 and acyllithium intermediates [RC(=O)Li].9

Reactions of Carbon Oxysulfide with Alkoxides, Phenolates, and Amines.

Carbon oxysulfide reacts extremely slowly with dry ethanol to form ethanethiol, but in the presence of KOH, potassium ethanethiocarbonate [KSC(=O)OEt] is formed.1 Phenolate salts react similarly to give O-acylated products,4 in contrast to the Kolbe-Schmitt reaction with CO2.10 Amines are converted by COS into thiocarbamates [RNHC(=O)S- RNH3+] which, on heating, decompose to ureas and H2S.1

Heterocycle Formation.

Aminonitriles have been condensed with COS to afford thiazoles (eq 3),11 and a thioxopyrimidine (eq 4). The latter process allowed access to a pyrrolopyrimidinone after a more direct approach based on Ethyl Chloroformate failed.12

Related Reagents.

Carbon Dioxide; Carbon Disulfide; Methyl Magnesium Carbonate; Methyl Chloroformate.


1. Ferm, R. J. CRV 1957, 57, 621.
2. (a) Weigert, F. CB 1903, 36, 1007. (b) Kharasch, M. S.; Reinmuth, O. Grignard Reactions of Nonmetallic Substances; Prentice Hall: New York, 1954, p 1288.
3. Demuynck, C.; Thuillier, A. BSF 1969, 2434.
4. Chanyshev, N. T.; Kalashnikov, S. M.; Kuramshin, E. M.; Naimushin, A. I.; Imashev, U. B. ZOB 1990, 60, 2568.
5. Vedejs, E.; Nader, B. JOC 1982, 47, 3193.
6. (a) Stork, G.; Rosen, P.; Goldman, N.; Coombs, R. V.; Tsuji, J. JACS 1965, 87, 275. (b) Caine, D. OR 1976, 23, 1.
7. Couturier, R.; Paquer, D.; Vibet, A. BSF 1975, 1670.
8. Bestmann, H. J.; Saalbaum, H. BSB 1979, 88, 951.
9. Seyferth, D.; Hui, R. C. TL 1984, 25, 2623.
10. Lindsey, A. S.; Jesky, H. CRV 1957, 57, 583.
11. Cook, A. H.; Heilbron, I.; Hunter, G. D. JCS 1949, 1443.
12. Hernandez, M. A.; Chung, F-L.; Earl, R. A.; Townsend, L. B. JOC 1981, 46, 3941.

Lewis N. Mander

The Australian National University, Canberra, Australia



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