Author:

Keywords:

0306 Physical Chemistry (incl. Structural), Chemical Physics, 3406 Physical chemistry, 4004 Chemical engineering

Abstract:

When increasing amounts of MgBr2 are added to a solution containing 10-4 to 2×10-3M dipolystyryl magnesium (PSt)2Mg in tetrahydrofuran, the specific conductance first markedly decreases till it reaches a flat minimum of 65 % of the initial value, at a molar ratio r between the two electrolytes of about 2. This unusual behaviour is explained by the partial dismutation of the ionophores: MgBr2 + (PSt)2Mg ⇄ 2 PStMgBr, and the fact that the dissociation constant Kdbp of the mixed ionophore is markedly smaller than that Kdpp of dipolystyryl magnesium. The origin of this difference lies in the conjugated steric hindrances that both PSt- groups exert on each other in (PSt)2Mg. A general equation is deduced for the conductance as a function of r. The calculated curve fits well with the experimental results when it is assumed that the ratio Kdpp Kdbp is approximately equal to the dismutation constant. The anions are predominantly PSt3Mg-, PSt2BrMg- and PStBr2Mg- but there exist only weak differences in the constants Kt governing their formation from the single anions and the three ionophores. © 1995.