Kinetics and Mechanism of the Metal Ion-promoted Hydrolysis of 2-Phenyl-1,3-dithiane in Aqueous Dioxane Solution

DOI: 10.1039/P29870000513

Source and publish data:

Journal of the Chemical Society. Perkin transactions II p. 513 - 516 (1987)

Update date:2022-08-17

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Authors:

Satchell, Derek P. N.

Satchell, Rosemary S.

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Article abstract of DOI:10.1039/P29870000513

In 1percent (v/v) aqueous dioxane the hydrolysis of 2-phenyl-1,3-dithiane (1) is promoted by thallium (III), mercury(II), mercury(I), and silver(I) ions; the qualitative sequence of their efficiencies is Tl³⁺>/=Hg²⁺>Hg₂²⁺>Ag⁺.Kinetic studies suggest the reaction mechanism with the thallium and mercury ions involves the rapid formation of a 1:1-adduct between the metal ion and the dithiane (formation constant, K 54.5, 3.0E4,and 630 dm³ mol^-1 for Tl³⁺, Hg²⁺, and Hg₂²⁺, respectively at 25 deg C) followed by a slow ring-opening step (k₂ 77, 0.20 and 0.07 s^-1, respectively) which may not involve water.Added chloride ions inhibit the mercury(II) ion promotion: HgCl⁺ and HgCl2 have, respectively, ca. 90percent and ca. 14percent of the reactivity of Hg²⁺.An increase in the dioxane content of the solvent to 20percent (v/v) has relatively little effect on the reaction.The general kinetic pattern, and level of reactivity, is similar to that observed previously for the Tl³⁺- and Hg²⁺-promoted hydrolysis of 2-phenyl-1,3-dithiolane (4).Both (1) and (4) are less basic towards Tl³⁺ than towards Hg²⁺, and the thallium adducts of (1) and (4) both react more rapidly than the corresponding Hg²⁺ adducts.However, (1) is less basic than (4) towards Tl³⁺, whereas the reverse is true for Hg²⁺, and the Tl³⁺ adduct of (1) is more reactive than that of (4), whereas the reverse is true of the reactivities of the corresponding Hg²⁺ adducts.These differences of detail suggest that the (unknown) conformations of the adducts control to some extent the values of K and k².