82280-76-0Relevant academic research and scientific papers
Reaction of Methoxide Ion with Dibenzo-1,2-dithiin 1,1-Dioxide: Surprising Behavior in the Reaction of an Aryl Thiolsulfonate with an Alkoxide
Boduszek, Bogdan,Kice, John L.
, p. 995 - 1000 (1983)
Although the six membered cyclic thiosulfonate dibenzo-1,2-dithiin 1,1-dioxide (1) reacts with such nucleophiles as RS-, CN-, or SO32- at a rate only slightly slower than they react with an acyclic aryl thiosulfonate (PhSSO2Ph), it reacts with methoxide ion over 1E4 times slower than does PhSSO2Ph, and in methanol the equilibrium constant for the reaction of 1 with CH3O- to form the ring-opened sulfenate ester 2a (eq 3) is so small that at equilibrium only a few percent of 1 is converted to 2a, even at quite high methoxide concentrations.The equilibrium constant for the conversion of 1 to 2a is, as might be expected, much larger in dimethyl sulfoxide (Me2SO)-methanol, and the rate constants for both the forward and reverse steps of the equilibrium can be determined in 70-90 percent Me2SO by stopped-flow spectrophotometry.The rate for the conversion of 1 to 2a is found to increase markedly with an increase in the Me2SO content of the medium, but the rate of the reverse reaction (2a->1+MeO-) is not significantly dependent on solvent composition.It is shown that all these results can seemingly be satisfactorily explained only if the reaction of 1 with methoxide to form 2a is assumed to take place by a stepwise mechanism (eq 8) in which a hypervalent sulfur species (6a) is present on the reaction coordinate as an intermediate which lies in a potential well of sufficient depth that there is a substantial ΔG* for collapse of 6a to 2a.Because of the six-membered ring in 6a, ΔG* for 6a going to 2a is 5-6 kcal/mol larger than ΔG* for the collapse of the equivalent intermediate (6o) to PhSOCH3 plus PhSO2- in the reaction of PhSSO2Ph with methoxide.In the reactions of RS-, CN- or SO32- with 1, the free energy of 6b, the intermediate analogous to 6a, is substantially higher, so much so that ΔG* for collapse of 6b to ring-opened products is in no case more than 1-2 kcal/mol.For this reason there is little difference for these nucleophiles in the rates for 1 vs.PhSSO2Ph.The preceding explanations are all in accord with expectations based on the findings of Martin and co-workers10,11 regarding the relative stability of isolable hypervalent sulfur species containing apical ligands of differing electronegativity and the influence of a ring on the stability of such species.
Reaction of Thiolate, Sulfite, and Cyanide Ions with Cyclic Aryl Thiolsulfinates: Dibenzo-1,2-dithiin and Naphtho-1,2-dithiole 1-Oxides
Boduszek, Bogdan,Kice, John L.
, p. 3199 - 3207 (2007/10/02)
The behavior of cyclic thiolsulfinates 5 and 6 (dibenzo-1,2-dithiin 1-oxide and naphtho-1,2-dithiole 1-oxide> upon treatment with either sulfite, cyanide, or t-BuS(1-) ions has been examined and compared with the behavior of the corresponding thiolsulfonates 1 and 2 (dibenzo-1,2-dithiin and naphtho-1,2-dithiole 1,1-dioxides).Very marked differences are observed.Whereas thiolsulfonates 1 and 2 are converted essentially quantitatively to ring-open substitution products (3 and 4) upon treatment with excess sulfite, cyanide, or t-BuS(1-), with thiolsulfinates 5 and 6 the equilibrium constants for opening of the sulfur-containing ring are so much smaller that only in the case of 5 and t-BuS(1-) is the equilibrium constant large enough that a significant fraction of the thiolsulfinate is converted to ring-opened product (7 or 8) at equilibrium.Kinetic studies of the rates of nucleophile-catalyzed racemization of optically active 5 and 6 show that the major factor responsible for the dramatic difference in the magnitude of the equilibrium constants is not a decrease in the rate constant for opening of the ring by the nucleophile but rather a huge increase in the rate constant for the reverse of the ring-opening reaction, which in the case of the thiolsulfinates involves displacement of the nucleophile from SNu by a sulfenate group, whereas for the thiolsulfonates it is a sulfinate group that performs the same displacement.In the 5-t-BuS(1-) system the rate constant for the displacement by the sulfenate is 30000 times faster than the rate constant for the corresponding displacement in the 1-t-BuS(1-) system involving the sulfinate; this provides thefirst quantitative measure of just how much more reactive a sulfenate ion is as a nucleophile than the corresponding sulfinate.Other aspects of the kinetics of the reactions of 5 and 6 with these nucleophiles provide additional information on the behavior of 7 and 8 and their conjugate acids and thereby furnish new insight into the chemistry and reactivity and of arenesulfenates and arenesulfenic acids.
