Hydrogen ion on cation-exchange processes

When studying the surface acid-base properties of montmorillonite, it is essential to understand that hydrogen ions and cations of the support electrolyte can also participate in cation-exchange processes. The processes on the internal and external surfaces have to be taken into consideration simultaneously, and they both have to be included into the equilibrium thermodynamical models. 

The alkaline error can be satisfactorily explained by assuming an exchange equilibrium between the hydrogen ions on the glass surface and the cations in solution. This process is simply the reverse of that shown in Equation 21-6 ... 

Since the last edition of this book an electrochemical process for manufacturing chromic acid has been realized industrially. This is carried out in an electrolysis cell with two chambers separated by a cation-exchanger membrane. The anode side is filled with aqueous sodium dichromate solution, the cathode side with sodium hydroxide. Upon applying direct current oxygen is produced at the anode and hydrogen is produced at the cathode. H+-ions are formed on the anode side and OH -ions are formed on the cathode side. 

At the end of the process the hydrogenation product was hydrolyzed with HBr (Fig. 13) and benzoic acid was recycled. The rhodium was recycled by adsorption on a cation exchanger KP2 from Wolfen (sulfonated polystyrene crosslinked by 2% divinylbenzene) [35], 80% of the rhodium could be removed, the residual rhodium accumulated in the final mother liquor which contained only a very small amount of L-dopa. This mother liquor and the loaded ion exchanger were ashed and the resulting rhodium reacted with chlorine under heating to redness to give rhodium(III)-chloride. This was used directly for the synthesis of the dimer rho-dium(I)-cyclooctadiene-chloride from which rhodium(I)-cyclooctadiene-acetylaceto-nate could easily be obtained. 

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