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The stepwise formation constants of complex compounds formed from N-(m-substituted-phenyl) glycines (m-RC6H4NHCH2COOH(m-RPhG), R = H, CH3, CH3O, Cl, NO2) with Cu(II) and Ni(II) were determined by pH method at 15, 25 35`C in 30% (V/V) ethanol solution in the presence of 0.1m NaClO4. Their thermodynamical parameters were calculated. It was found that the N-(m-substituted-phenyl) glycine complexes also showed linear free energy relationships between the stability of complex compounds and the base strength of the ligands just as the para-substituted isomers reported previously. Linear relationships not only existed between their thermodynamical parameters and the base strength of the ligands but also existed between the formation enthalpy of complex compounds and the neutralization enthalpy of the ligands and between the formation entropy of complex compounds and neutralization entropy of the ligands as well. 相似文献
234.
自溶液中的吸附 VII: 硅胶自环己烷中吸附醇,酮和酯 总被引:3,自引:0,他引:3
The adsorption isotherms of some monofunctional alcohols, ketones and esters from cyclohexane onto silica gel have been determined at 30`C and 10`C. The silica gel used bad a BET area of 417 m2/g and an average pore radius of 45A. The concentrations of free and associated hydroxyls on the silica gel were 1.4 and 4.1/100A^2 respectively. The adsorption order is cyclohexanol>n-octyl alcohol>cyclohexanone>methyl isobutyl ketone>n-propyl acetate=n-amyl acetate. The adsorption decreases with increasing temperature as normal. Except at very low concentrations, the isotherms can be represented by the Langmuir equation. The limiting adsorption, nms, on the silica gel does not accord with the stoichiometric ratio (1:1) between the free surface hydroxyl groups of the adsorbent and the adsorbate. In addition to surface conditions and the functional group of the adsorbate, it seems that the limiting adsorption is also controlled by the other factors, including temperature, solvent, and, sometimes the chain length of the adsorbate. The standard free energy (ΔG0) and standard enthalpy (ΔH0) of the adsorbates in adsorptien processes have been determined from the Langmuir parameters. The results indicate that the absolute value of ΔH0 is higher than that of ΔG0 (in other words, standard entropy ΔS0 is negative), as in the case of the adsorption of gases. Since there is practically no difference in ΔG0 or ΔH0 of adsorption between alcohols or esters, it is suggested that in dilute solution only the polar groups take part in adsorption, and the hydrocarben chains remain in solution during the adsorption process. For ketones, the absolute values of ΔG0 and ΔH0 are somewhat lower for methyl isobutyl ketone than that for cyclohexanone. A possible explanation is that in the adsorbed state the isobutyl chain of the methyl isobutyl ketone may somewhat close to the surface and thus decreases the adsorption and changes the ΔG0 and ΔH0. 相似文献