There have been many reports on the kinetics and mechanisms of the solvolysis [1] and aminolysis [2] of chloroformates. Nevertheless, the solvolysis [3] and aminolysis [4] of chlorothioformates and chlorothionoformates has received little attention. Furthermore, except a study on the solvolysis of phenyl chlorodithioformate (PClDTF), to our knowledge there have been no investigations concerning the kinetics of the aminolysis of aryl chlorodithioformates.

In this work we undertake a kinetic investigation on the reactions of secondary alicyclic (SA) amines with PClDTF. A specific objective is to assess the influence of two sulphur atoms on the mechanism and on the reactivity of the substrate. The reactions were studied spectrophotometrically, in water and in ethanol (44 % wt) aqueous solution at 25.0±0.1ºC and ionic strength 0.2 M (maintained with KCl). Pseudo-first-order rate constants (k_obs) were found in all cases and the second-order rate constants (k_N) were obtained as slopes of linear plots of k_obs vs. free amine concentration, and were pH independent.

The Brønsted-type plots are linear in both solvents, with slopes consistent with a stepwise mechanism with the formation of a zwitterionic tetrahedral intermediate (T^±) as the rate determining step, in accordance with the found for the reactions of the same series of amines with aryl chloroformates [2] and aryl chlorothionoformates [4a].

The rate constant values obtained for the T^± formation are 3-4 times smaller than those of the same aminolysis of PCITF. This result is explained by the softer nature of the carbonyl group in PClDTF and the fact that SA amines are considered relatively hard bases.

We thank FONDECYT of Chile (project 1060593) for financial support. M. G. thanks CONICYT for a Doctoral scholarship.

[1] a) S. Possidonio, F. Siviero, O. A. El Seoud, J. Phys. Org. Chem. 1999, 12, 325-332. b) J. B. Kyong, B. C. Park, C. B. Kim, D. N. Kevill, J. Org. Chem. 2000, 65, 8051. c) J. B. Kyong, H. Won, D. N. Kevill, Int. J. Mol. Sci. 2005, 6, 87.

[2] a) E. A. Castro, M. G. Ruiz, S. Salinas, J. G. Santos, J. Org. Chem. 1999, 64, 4817. b) E. A. Castro, M. G. Ruiz, J. G. Santos, Int. J. Chem. Kinet. 2001, 33, 281.

[3] a) A. Queen, T. A. Nour, M. N. Paddon-Row, K. Preston, Can. J. Chem. 1970, 48, 522. b) D. M McKinnon, A. Queen, Can. J. Chem. 1972, 50, 1401. c) D. N. Kevill, M. J. D'Souza, J. Org. Chem. 1998, 63, 2120. d) D. N. Kevill, M. D'Souza, J. Can. J. Chem. 1999, 77, 1118.

[4] a) E. A. Castro, M. Cubillos, J. G. Santos, J. Org Chem. 1997, 62, 4395. b) E. A. Castro, M. Aliaga, M. Gazitúa, J. G. Santos, Tetrahedron 2006, 52, 4863.

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