Reductvie Desulfurization

26 May, 2017 / by SK / in Reactions

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General Characteristics

Thioethers and thioacetals can be reductively desulfurized by treating them with Raney nickel. The reduction of the latter is a common way to deoxygenate carbonyl groups.

Similar desulfurization can be done under the Barton-McCombie free-radical conditions (AIBN, Bu₃SnH).

General References
Pettit, G. R.; van Tamelen, E. E. Org. React.1962, 12, 356.
Free radical desulfurization: Gutierrez, C. G.; Stingham, R. A.; Nitasaka, T.; Glasscock, K. G. J. Org. Chem. 1980, 45, 3393. DOI: 10.1021/jo01305a004

Reaction Mechanism

The reductant is the hydrogen adsorbed on the metal surface during the preparation of Raney nickel.

Examples

A typical example of the convertion of ketone to methylene group by desulfurization of thioacetal.

Experimental Procedure
Experimental Tips

One should be careful that the reactivity of Raney nickel often differs depending on how it is prepared, and that Raney nickel is pyrophoric when it is dried.

The use of nickel boride Ni₂B (= NiCl₂ + NaBH₄) is a way to effect the same transformation avoiding these problems. Olefins are not reduced either under these conditions.^[1]

References

[1] (a) Brown, C. A. J. Org. Chem. 1970, 35, 1900. DOI: 10.1021/jo00831a039 (b) Brown, C. A.; Ahuja, V. K. J. Org. Chem. 1973, 38, 2226. DOI: 10.1021/jo00952a024
[2] (a) Boar, R. B.; Hawkins, D. W.; McGhie, J. F.; Barton, D. H. R. J. Chem. Soc. Perkin Trans. 1973, 654. (b) Zaman, S. S.; Sarmah, P.; Barua, N. C. Chem. Ind. 1989, 806 .