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Issue 3, 2007
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Mechanism of the sulfurisation of phosphines and phosphites using 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride)

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Abstract

Contrary to a previous report, the sulfurisation of phosphorus(III) derivatives by 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride) does not yield carbon disulfide and cyanamide as the additional reaction products. The reaction of xanthane hydride with triphenyl phosphine or trimethyl phosphite yields triphenyl phosphine sulfide or trimethyl thiophosphate, respectively, and thiocarbamoyl isothiocyanate which has been trapped with nucleophiles. The reaction pathway involves initial nucleophilic attack of the phosphorus at sulfur next to the thiocarbonyl group of xanthane hydride followed by decomposition of the phosphonium intermediate formed to products. The Hammett ρ-values for the sulfurisation of substituted triphenyl phosphines and triphenyl phosphites in acetonitrile are ∼ −1.0. The entropies of activation are very negative (−114 ± 15 J mol−1 K−1) with little dependence on solvent which is consistent with a bimolecular association step leading to the transition state. The negative values of ΔS and ρ values indicate that the rate limiting step of the sulfurisation reaction is formation of the phosphonium ion intermediate which has an early transition state with little covalent bond formation. The site of nucleophilic attack has been also confirmed using computational calculations.

Graphical abstract: Mechanism of the sulfurisation of phosphines and phosphites using 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride)

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Article information


Submitted
07 Nov 2006
Accepted
30 Nov 2006
First published
18 Dec 2006

Org. Biomol. Chem., 2007,5, 478-484
Article type
Paper

Mechanism of the sulfurisation of phosphines and phosphites using 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride)

J. Hanusek, M. A. Russell, A. P. Laws, P. Jansa, J. H. Atherton, K. Fettes and M. I. Page, Org. Biomol. Chem., 2007, 5, 478 DOI: 10.1039/B616298C

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