Formation and Stability of Thallium(I) Halide in 1, 3-Dimethyl-2-imidazolidinone

Abstract

The titration curves for thallium( I ) ion with halide ions(X^-) in 1, 3-dimethyl-2imidazolidinone (DMI) were found to have well-defined equivalent points at C_X^-/C_Tl⁺ =1(mole ratio). Precipitates of thallium( I ) halide (T1X) appeared in the range of 15 to 30°C soon after the halide ions were added in DMI. Redissolution of TlX was not observed in the presence of an excess of X^-. Based on the Gibbs energies (ΔG⁰) calculated from the solubility products of TlX in DMI, the stability of TlX was found to decrease in the order of TlCl>TlBr>TlI for X^-, as in propylene carbonate (PC) and N, N-dimethylformamide (DMF). This order was reversed in water. The order of the stability of TlX in PC, DMI and DMF was PC>DMI>DMF.
The differencesin the stability of TlX for X^- in transfer from water to DMI depended on the Gibbse nergies (ΔG⁰_tr) of X^- in transfer from water to DMI. On the other hand, the differences in the stability of TlX for three nonaqueous solvents depended on the Gibbs energies (ΔG⁰_tr) of Tl⁺ in transfer from water to these solvents.
From the ΔG⁰_tr values of T⁺ the donor number of DMI was assumed to be betweent hose of PC and DMF.
The donor number of DMI was estimated to be 20-23 by measurements of the half-wave potentials for polarographicr eduction of several uni- and bivalent metal ions referred to tetraphenylarsoniumion. By comparing the donor number of DMI with those of DMF and PC, the order of PC>DMI>DMF for the stability of TlX in three solvents was reasonably interpreted.