Tris(ethylthio)borane1

(EtS)3B

[998-26-5]  · C6H15BS3  · Tris(ethylthio)borane  · (MW 194.23)

(used as an ethanethiol donor)

Physical Data: bp 78-81.5 °C/1.3 mmHg; d 1.0191 g cm-3.

Preparative Methods: by reaction of bis(ethylthio)lead with boron trichloride1,2 or sulfurated borohydride with ethanethiol.3

Handling, Storage, and Precautions: store and use in the absence of moisture.

General Discussion.

Like other thioboranes, tris(ethylthio)borane is a reactive intermediate for the synthesis of organic sulfur compounds, relying on the extreme lability of the B-S bond. The major application of tris(ethylthio)borane is as an alternative to Ethanethiol; it is readily available and more easily handled than ethanethiol.

Tris(ethylthio)borane converts both aromatic and aliphatic carboxylic acids to the corresponding ethyl thioesters (eq 1).2,4

It has been shown that ketones and aldehydes are transformed to thioacetals by reaction with tris(ethylthio)borane. In contrast to the usual procedure for the formation of thioacetals, this reaction proceeds smoothly in neutral medium at ambient temperature (eq 2). The driving force is believed to be the formation of the strong B-O bond.5

Epoxides are cleaved in the presence of tris(ethylthio)borane, with attack generally occurring at the less substituted carbon (eq 3). This procedure has been shown to be superior for these transformations.6

Other reactions of tris(ethylthio)borane include those with benzenesulfonic acid esters to afford asymmetric disulfides (eq 4),7 and with isocyanates to give N-ethylthiocarbonylureas (eq 5).8


1. Goubeau, J.; Wittmeier, H. W. Z. Anorg. Chem. 1952, 270, 16.
2. Pelter, A.; Levitt, T. E.; Smith, K. JCS(P1) 1977, 1672.
3. Lalancette, J. M.; Lachance, A. CJC 1969, 47, 859.
4. Pelter, A.; Levitt, T.; Smith, K. CC 1966, 435.
5. (a) Bessette, F.; Brault, J.; Lalancette, J. M. CJC 1965, 43, 307. (b) Samson, M.; De Clercq, P.; De Wilde, H.; Vandewalle, M. TL 1977, 3195.
6. Klein, H. A. CB 1979, 3037.
7. Cragg, R. H.; Husband, J. P. N.; Weston, A. F. CC 1970, 1701.
8. Mukaiyama, T.; Inomata, K.; Yamamoto, S. TL 1971, 1097.

Lianhong Xu

Abbott Laboratories, Abbott Park, IL, USA



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