Knowledge Bank

The photolysis of tetra- and pentamethylene disulfides and 1,4-butanedithiol has been investigated for the pure liquids and for the liquids doped with alkali. The courses of the photochemical reactions were followed by observing the UV absorption in the region of $1850-2300\backslash AA$ of the vapors in equilibrium with the photolized liquid. Photolysis of the disulfides produced the corresponding dithiols whereas addition of alkaki resulted in formation of the respective cyclic monosulfides at a much faster rate. The 1,4-butanedithiol also produced a cyclic monosulfide with the rate of formation being greatly enhanced by the addition of NaOH. Reaction mechanisms are proposed as well as a somewhat general photochemical rule for solutions or any condensed medium to the effect that in those cases where photodecomposition occurs, it will proceed primarily from the lowest excited state unless the irradiation energy exceeds the ionization limit; furthermore, dependent on the magnitude of intersystem crossing rate constants, this lowest excited state may be either singlet, triplet, or both.