ABSOLUTE RATE CONSTANTS FOR THE REACTIONS OF SULFUR (P-3(J)) ATOMS INSOLUTION

The 248-nm laser flash photolysis of methyl isothiocyanate (MeNCS) was used to generate S(P-3(J)) ground state atoms in acetonitrile solutio n. The reaction of S(P-3(J)) atoms with the MeNCS precursor produces m olecular diatomic sulfur S-2((3) Sigma(g)(-)) in its ground state, whi ch possesses an absorption at ca. 270 nm. The first-order growth of th is absorption was used to monitor the decay kinetics of the sulfur (P- 3(J)) atoms and to measure the rate constants for their reactions with additives. The rate constants obtained for a number of olefins, e.g., 9.7 x 10(7) M(-1) s(-1) for ethyl vinyl ether, hydrogen donors, e.g., 3.1 x 10(9) M(-1) s(-1) for tributyltin hydride, sulfur atom donors, e.g., 5.0 x 10(7) M(-1) s(-1) for carbon disulfide, and nucleophiles, e.g., 1.3 x 10(9) M(-1) s(-1) for chloride ions, demonstrate that S(P- 3(J)) atoms behave as reactive, yet very selective, intermediates in s olution; the highest reactivity was observed toward nitrogen and phosp horus nucleophiles, e.g., 1.2 and 2.1 x 10(10) M(-1) s(-1) for hydrazi ne and triethyl phosphite. The comparison with known nucleophilicity c onstants, e.g., for methyl iodide as electrophile, suggests further th at S(P-3(J)) atoms act as potent but relatively soft electrophiles. Th e reaction modes between S(P-3(J)) atoms and the additives are assumed to involve abstractions of single atoms or addition to double bonds o r lone electron pairs. The reaction rate constants for atomic sulfur S (P-3(J)) in solution are compared with previous gas phase data for S(P -3(J)) atoms and with the data far oxygen (P-3(J)) atoms in solution.