Determination of the Standard Potentials and Equilibrium Constants for Eleven Organotin Compounds

Abstract

Eleven organotin compounds (OTC) were potentiometrically titrated in methanol to determine their standard potentials,E0, and ionization constants,Keq. The classical method for potentiometry yielded nonreproducible results; therefore an alternate titration method was developed using the OTC as the titrant. The standard potentials,E0, and ionization constants,Keq, were determined by extrapolating the potentiometric titration data to 1.0Mconcentration. The extrapolation yielded twoE0values for the two different species in the solution. The titrations yielded a different end point potentials for anion ligands attached to the same OTC moiety, yet all the equilibrium ionization constants for a given organotin moiety, e.g., Bu3Sn or Bu2Sn, were approximately the same (approximately TBT = 10−3and DBT = 10−4). This suggests a difference in the energy level of the cation species for the accepting of an electron but a dissociation constant which is independent of anion moiety. The twoE0potentials for each of the OTC in methanol are as follows: tri-n-butyltin fluoride, 0.02 and 0.07; tri-n-butyltin chloride, 0.13 and 0.17; tri-n-butyltin bromide, 0.17 and 0.23; tri-n-butyltin iodide, 0.21 and 0.22; tri-n-butyltin laurate, +0.01 and 0.03; tri-n-butyltin naphthalate, −0.01 and 0.00; tri-n-butyltin benzoate, 0.08 and 0.10; di-n-butyltin fluoride, 0.07 and 0.10; di-n-butyltin chloride, 0.22 and 0.49; di-n-butyltin bromide, 0.24, and 0.29; and diphenyltin chloride, 0.21 and 0.33.