| Abstract: | Dissociation equilibria of lithiumthiocyanate (LiSCN) in N,N-dimethylformamide (DMF) solutions of poly (propylene oxide) (PPO) were investigated by using infrared spectroscopy. The stretching bands due to the thiocyanate ions SCN?1 and the LiSCN ion pair were found at 2058 and 2072 cm?1, respectively. At high LiSCN concentration C of ca. 20 wt %, another weak band due to the dimer (LiSCN)2 was observed. From the ratio of the areas of the absorption bands, the dissociation constant K1 for the equilibrium LiSCN ? Li+ + SCN?1 and that K2 for (LiSCN)2 ? 2LiSCN have been determined. With increasing DMF content, K1 increases from 1 × 10?4 for bulk PPO to 4.8 × 10?1 for pure DMF at 299 K. Log K1 is not linear against inverse of the dielectric constant ? of the medium and decreases with increasing temperature. The enthalpy (ΔH) and entropy (ΔS) changes for the dissociation of LiSCN are both negative. ©1995 John Wiley & Sons, Inc. |
