Conductometric identification of triple-ion and quadrupole formation by the coordination forces from lithium trifluoroacetate and lithium pentafluoropropionate in protophobic aprotic solvents

Abstract

and quadrupole formation (M2X+ + X-e M,X,, W,, or M+ + MX; + M,X,, KL, ; KL, = KL, 5) in addition to t h e ion pair formation (M+ + X-e MX, KL, in t h e concentration range (0.4-6.0) x lo-, mol dm-3. Surprisingly, a great enhancement in quadrupole formation for LiCF3C02 and LiC2F5C0, was observed in propylene carbonate with t h e highest relative permittivity ( E , = 64.4 at 25°C) of all t h e solvents. For trifluoroacetate, t h e limiting molar conductivity (Ao = 72.65) given by t h e Shedlovsky analysis C(O.4-4.0) x mol dm-3] was much larger than that CAO,ca,c = 26.373 calculated by Kohlrausch's additivity law with strong electrolytes. Lithium pentafluoropropionate gave a similar excess in t h e A. value. Computer simulations showed an increase in t h e Shedlovsky A. value with increase in t h e quadrupole formation constant. At t h e same time, t h e apparent association constant (M+ + X-+ MX, K,) calculated by Shedlovsky analysis was 10 times larger t h a n t h e ion-pair formation constant (Ka, in propylene carbonate (owing to strong quadrupole formation) and was much smaller than t h e Kg, value in the other solvents (mainly owing to strong triple-ion formation). A distinct triple-ion formation from tributylammonium trifluoroacetate or tributylammonium pentafluoropropionate was observed in benzonitrile. Causes of t h e failure in t h e Shedlovsky analysis have been discussed from t h e standpoint of higher-ion aggregates.Conductometry has proved a powerful method to examine the species present in solutions. Higher-ion aggregates, such as triple ions and quadrupoles from uni-univalent salts could form in solvents with lower relative permittivities. Fuoss and Kraus'*2 proposed triple-ion formation by electrostatic forces in very low permittivity media. Many conductometric investigations have been performed to examine solute-solvent and solute-solute interactions in non-aqueous solution^.^-^ The * -CMICX12 ' Standard deviation of the relative error.

Conductometric Study on Higher Ion Aggregation of Lithium and Sodium Nitrophenolates in Aprotic Solvents

“…We have demonstrated − by means of spectrophotometry, polarography, and conductometry that the “minor” complexation ability of lithium and sodium ions can be definitely observed if very low solvation media are employed. The presence of “reverse-coordinated” species, (M + ) 2 X - , and “coordinated” species, M + (X - ) 2 , in nonaqueous solution has been discovered; where X - = RCO 2 - , − Cl - , SCN - , picrate ion, RSO 3 - , and (PhO) 2 PO 2 - , and M + = Li + and Na + for RCO 2 - , and Li + for other anions. Even in a protic solvent, EtOH, higher ion aggregates were observed for lithium and sodium tropolonates (C 7 H 5 O 2 - M + ) …”

Conductivity and Interparticle Interactions in the Solutions of 1-1 Electrolytes in Propylene Carbonate in the Wide Range of Temperatures

“…The value (g K γ D ) 0 corresponds to the pure solvent and can be calculated using Eqs. (19,20) from the physical properties of a solvent. Values Θ > 1 correspond to structure-making effect of an ion and decrease of molecules activity in its vicinity, and vice versa for Θ < 1.…”

Appearance of Maxima on Conductometric Titration Curves of Sulfonic Acids and the Evidence of Strong Homoconjugation Reactions in Benzonitrile

“…For obtaining association constants in the presence of higher aggregates, the conductivities of acids or salts were analyzed using our method. 4,14,18 Results and Discussion Figure 1 shows the conductometric titration curves of p-toluenesulfonic acid (p-TsOH, 25 ml) of various concentrations with triethylamine (Et 3 N) of the hundredfold concentrations in benzonitrile (PhCN) at 25˚C. When the concentration of p-TsOH was low (≤2×10 -3 mol dm -3 ), the conductance increased almost linearly with increasing amount of Et 3 N up to the equivalence point (250 µl).…”

“…12 The complexities in the Λ-C 1/2 curves suggested the presence of a variety of species, such as "triple ions" and other higher ion aggregates. On the other hand, trifluoromethanesulfonic acid in benzonitrile gave a monotonical Λ-C 27 We have determined, by means of conductometry, the dimer formation constants of not only acids in DMF 4 , but also salts, CF 3 COOLi in propylene carbonate 18 and sodium diphenyl phosphate (Na + (PhO) 2 PO 2 -) in acetone. 26 …”