Hydrogen and deuterium atom abstraction from trideuteromethyl mercaptan by methyl radicals. Reactivity of methylthio radicals

Abstract

The reaction of methyl radicals with trideuteromethyl mercaptan has been studied in the temperature range 130-200°C in order to determine the rate at which hydrogen and deuterium atom abstraction occurs. Abstraction of the hydrogen atom is facile, the S-H bond being broken about 120 times faster than is the C-D bond. An unusual feature of the reaction is the abstraction of the mercapto group from the substrate by methyl radicals.Arrhenius parameters (based on a value of 1013.34 mole-1 cm3 sec-1 for the rate of recombination of methyl radicals) have been measured for the reactions :

PHOTOLYSIS OF GROUP VI HYDRIDES: I. SOLID H2S, H2S2, AND D2S

“…Although 1i.f.s. was not ol~served, this spectrum is assigned to IIS2, which is 1rno11,n t o form, together n-ith HS, in flashed HZS2 vapor (3). Absence of h.f.s.…”

“…Although the HS and DS spectra did not decay during several weeks storage a t 77 OK, sulfur polymers were present after very short periods of irradiation, which suggests that HS and DS are generated in a t least two types of lattice size, from one of which rapid chemical or physical migration is possible, prior to disproportionation (reaction [3]). The products of this reaction bear -42 Iical/n~ole of excess energy (10) which may induce local melting of the matrices facilitating polymerization of Sz.…”

“…spectra of the samples in inert lattices (HzS, Xe, or C3F8) are classified as chen~ical, and seem to be associated with increased ease of radical migration through the matrix a t temperatures above 77 OK. Thus HS and DS decay forming sulfur chains, presumably via reaction [3], and subsequent polymerization of Sz. Sulfur chains in these matrices decayed a t lower temperatures than those reported for decay of .…”

“…The products of this reaction bear -42 Iical/n~ole of excess energy (10) which may induce local melting of the matrices facilitating polymerization of Sz. Can Experiments with H2S showed that the disproportionation of HS radicals (reaction [3]) is rapid; therefore, if [4] is important, sulfur chains should be detected in photolyzed together with HSZ. In the gas phase photolysis, HS was observed strongly, as well as HSZ, indicating that reaction [5] is, a t best, moderately fast a t room temperature.…”

Free radicals by mass spectrometry. XXXVIII. Primary steps in the mercury-photosensitized decompositions of dimethyl sulfide and dimethyldisulfide

“…The displacement reaction has been reported (6) and the two-step sequence is possible in principle. However, reaction [6] would be -10' times slower (log A = 10.73 mole-' cm3 s-', E = 7.6 kcal/mole) than the radical combination reactions occurring in the titration. Moreover, the sequence of reactions [7] and [8] would lead to a continuous increase for curve A, Fig.…”