The Influence of Non-Electrolytes upon the Kinetics of the Reaction between Bromoacetate and Thiosulfate Ions^1,2

The Electrolyte Effect upon the Kinetics of the Bromoacetate–Thiosulfate Reaction in n-Propyl Alcohol–Water Solutions.

“…La Mer and Davis (6) determined the energy of activation of this reaction, using solvents of low dielectric constant (D = 20-35) in the presence and in the absence of lanthanum ion. The agreement in the values of AE (DT = constant) for the catalyzed and uncatalyzed reactions led these investigators to the conclusion that the enormous increase in the rate when lanthanum ion is present is primarily an electrostatic effect, which is exhibited as an entropy of activation (13,16). Hence, the addition of lanthanum ion creates a situation in which the reactant anions must cluster about the trivalent positive ion, giving rise to the formation of either ion-associated pairs of the type (LaSaOg)"1-or (LaBrAc)++, or a neutral triplet (LaSiOgBrAc)0 (14).…”

“…The technique of La Mer and Kamner (16) was employed to determine the reaction rate. One hour was allowed for temperature equilibrium before mixing the contents of the reaction vessels.…”

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The kinetics of the bromoacetate-thiosulfate reaction has been studied by BrCEUOO-+ S203--> S203CH2C00-+ Brã number of investigators (6,10,11,13,15,16,18, 19). The rate data exhibit in all cases positive salt effects, as predicted for a reaction between ions of the same sign.

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Ionic Recation Design. Solvent and Salt Effects

“…In addition to the dilute solution salt effect, the results of Debye-Hückel theory also were used to predict solvent effects (Scatchard, 1932 a). By differentiation of Equation 3, the infinite dilution rate constant varies with the dielectric constant of the solvent as ( log k'0/dt) = e2zAzB/ e2kBTa' (7) Thus K should be linear in 1/e, and this result was verified experimentally (Davis and LaMer, 1942;Eagle and Warner, 1936;LaMer and Kamner, 1935b). However, the bulk of the experimental work was done in pure water or in aqueous solvent mixtures.…”