Reaction of Thiolate, Sulfite, and Cyanide Ions with Cyclic Aryl Thiolsulfinates: Dibenzo[c,e 1-1,t-dithiin and Naphtho[ 1,8-cd]-lY2-dithiole 1-Oxides (original) (raw)

The behavior of cyclic thiolsulfiiates 5 and 6 (dibenzo[c,e]-l,2-dithiin 1-oxide and naphtho[l,&cd]-l,2-dithiole 1-oxide) upon treatment with either sulfite, cyanide, or t-Bus-ions has been examined and compared with the behavior of the corresponding thiolsulfonates 1 and 2 (dibemo[c,e]-1,2-dithiin and naphtho[l,&cd]-l,2-dithiole 1,l-dioxides). Very marked differences are observed. Whereas thiolsulfonates 1 and 2 are converted essentially quantitatively to ring-open substitution produds (3 and 4) upon treatment with exceas sulfite, cyanide, or t-Bus-, with thiolsulfiites 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-is the equilibrium constant large enough that a significant fraction of the thiolsulfinate is converted to the ring-opened product (7 or 8) at equilibrium. Kinetic studies of the rates of nucleophilmtalyzed racemization of optically active 5 and 6 show that the major factor reaponsible 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 (Nu-) from SNu by a sulfenate (SO-) group, whereas for the thiolsulfonates it is a sulfinate (SOz-) group that performs the same displacement. In the 5-t-BUS-system the rate constant for the displacement by the sulfenate is 30 OOO times faster than the rate constant for the corresponding displacement in the 1-t-Bus-system involving the sulfmate; this provides the first 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. Upon treatment with excess thiolate, sulfite, or cyanide ion the thiolsulfonate ring in cyclic thiolsulfonates 1 and 2 is rapidly cleaved, and the thiolsulfonates are quantitatively converted to 3 and 4 (Nu = RS, SO3-, or CN) as shown in eq 1 and 2 (step kNu).1*2 The reactions are analogous to the reactions3 of open-chain aryl thiol-sulfonates with the same reagents, i.e., Nu-+ ArSS02Ar-ArSNu + ArS02-. If the f d reaction solution is acidified with a carboxylic acid buffer sufficiently acidic to protonate RS-, SO?-, or CN-to RSH, HS03-, or HCN, then 3 and 4 revert readily and quantitatively (step k-Nu) to cyclic thiolsulfonates 1 and 2, respectively.lP2 By a suitable sequence of kinetic measurements one may obtain both kNu and k-Nu for such systems, and from these the equilibrium constant, Kq = kNu/k-Nu, for each reaction. Acyclic aryl thiolsulfinates, ArS(O)SAr, can also be cleaved by thiolate, sulfite, or cyanide ion, although at a (1) Chau, M. M.; Kice J. L. \ SNU 3a, Nu = RS b, Nu = SO,-c, Nu = CN 1 NuH NUS SO2 I I 2 4a, Nu = RS b, Nu = SO,-c , Nu = CN rate about 20-40 times slower than that for corresponding thiolsulfonate, ArS02SAr.4 The cleavage takes place by (4) Kice, J. L.; Liu, A. CC .