The reactions of S-methyl 4-nitrophenyl thiocarbonate (SMNPTC) and S-methyl 2,4-dinitrophenyl thiocarbonate (SMDNPTC) with a homogeneous series of benzenethiolate anions are subjected to a kinetic investigation in water, 25.0° C, ionic strength 0.2 M (KCl). Under benzenethiolate excess over the substrate all these reactions obey pseudo-first-order kinetics and are first order in the nucleophile.

The Brönsted-type plots for the nucleophilic rate constants are linear, with slopes β = 0.55 and β = 0.70 for the reaction of SMNPTC, and SMDNPTC respectively with benzenethiols suggesting a concerted mechanism [1].

SMDNPTC is more reactive than SMNPTC toward benzenethiolate ions due to a carbonyl carbon more positively charged and a better leaving group.

A comparison of these results with those for the concerted phenolysis of the same substrates indicates that benzenethiolates are better nucleophiles toward thiocarbonates than isobasic phenoxides [2].

M.A. thanks CONICYT of Chile (AT-24050119) for doctoral fellowships.

[1] E. A. Castro, P. Pavez, J. G. Santos, J. Org. Chem. 2001, 66, 3129.

[2] E. A. Castro, P. Pavez, J. G. Santos, J. Org. Chem. 2003, 68, 3640-3645.

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