Inorganic systems solvent exchange

Table 4. High-pressure kinetic studies of solvent exchange in inorganic systems...

Solvents. Solvent transfer parameters have been used from time to time in diagnosis of mechanisms of organic reactions. Now their first use in an inorganic system has been discussed. Comparisons between kinetic results and solvent transfer activity coefficients for solvolysis of [Cr(NCS)e] in DMSO, DMF, and dimethylacetamide have been considered in terms of a dissociative mechanism. The DMSO results can be accommodated by a dissociative model for the transition state, but those in DMF and dimethylacetamide fit less well. It is interesting to compare these conclusions with, for instance, the dissociative mechanism proposed by the same authors for anation of the [Cr(DMSO)e] + and [Cr(DMF)6] + cations, and the associative mechanism suggested on the basis of the determined activation volume for exchange of DMSO with [Cr(DMSO)e +. ... 

As in other fields of inorganic chemistry, some research on coordination compounds has been carried out in non-aqueous media. There are several reasons for this first, some compounds are not soluble in water, but will dissolve in other solvents (of course, solubilities can often be modified by judicious selection of the counter ion). In those cases in which the coordination compound reacts with water, the use of a non-aqueous solvent may be advantageous. A familiar example is the determination of the number of ions in a compound by measuring the conductivity in nitromethane or other highly polar solvent. In studying the self-exchange rate of the [Co(NH3)6]2+/3+system,... 

For less activated aromatic systems (those without a nitro substituent), the halogen-exchange reaction has been investigated with potassium fluoride in a variety of polar aprotic solvents in the presence or absence of a catalyst (see Table 13). Many different types of catalysts have been investigated these include crown ethers.169 quaternary ammonium salts,163 164 phos-phonium salts,158167 aminophosphonium salts.162 compounds containing a phosphorus and an amino function,161 and inorganic fluorides of boron, aluminum, tin, phosphorus, titanium and zirconium.162 Different forms of potassium fluoride have been used these include spray-dried potassium fluoride,167 freeze-dried potassium fluoride,168 potassium fluoride recrystallized from methanol,165 and potassium fluoride dispersed oil calcium fluoride.166... 

To make use of an isotopic fractionation for an enrichment of isotopes, a different isotopic distribution has to be carried out in two phases which can be easily separated. On the one hand, polyethers are soluble in various solvents On the other hand, these compounds can also be fixed as anchor groups at organic or inorganic matrices Therefore, as a heterogeneous exchange reaction for metal ions, liquid/liquid as well as liquid/solid systems can be used in connexion with polyethers. 

The best extractants in the above list of salts form complexes with the polyvalent metals that neutralize charges on the humic substances and link them to the inorganic soil colloids. These polyvalent ions are replaced by sodium ions from the salts. The efficiency of each solvent system will depend on the extent to which the resident cations are exchanged and removed from humic structures. Diffusion of the salts to the interior of solid humic substances is slow. Some channeling can take place, but extensive penetration would probably require the opening up from the outside of the macro-molecular structures. It would be necessary for these structures to remain open to allow exchange from the interior to take place. 

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