| This investigation was concerned with the effects of transition metal ion association with silicas which are used as packing materials in high-performance liquid chromatography (HPLC). It was shown that metal ions including iron, chromium, cobalt, and copper could be successfully bonded to silica packings through process modification without loss in chromatographic separation efficiency. The use of some of these metal ion-modified silica packings in columns which were used as reactors further demonstrated the feasibility of utilizing liquid chromatographic reactors for carrying out a variety of chemical reactions.;Metal ion-modified HPLC silicas showed distinctive properties with regard to catalytic activities and solute retentions. While iron(III) and chromium(III) ion-modified silica columns were active for on-column hydroquinone oxidation, the cobalt(II) ion-modified silica was active for the oxidation of phenols. For a series of phenolic compounds, solute capacity factors were greater on the iron(III) ion-modified silica column than those on the unmodified silica column. On the other hand, capacity factors for phenolic compounds were smaller on the copper(II) ion-modified silica column relative to the unmodified silica column. For other solutes, the effect on capacity factors with silica metal ion association was more diverse.;The cobalt(II) ion-modified silica catalyst offers a new, alternative means for phenol oxidations traditionally performed with cobalt Schiff base complex catalysts. The oxidations of phenol, o- and m-chlorophenols, o- and m-cresols, 2,6-dimethylphenol, and 2,6-di-tert-butylphenol were demonstrated in a cobalt(II) ion-modified silica column. Due to the separation and dynamic characteristics of chromatographic reactors, the oxidation of phenols was highly selective to form p-benzoquinones. The reaction is first order with respect to phenol reactants. Using inert standard methods, some pseudo-first order rate constants for the on-column oxidation of phenols were also obtained.;Hydroquinone oxidation and adsorption processes were studied in a chromium(III) ion-modified silica column. Adsorption equilibrium constants for hydroquinone and benzoquinone were measured on silica and chromium(III) ion-modified silica columns. On-column hydroquinone oxidation reaction rate parameters were evaluated and decoupled from the hydroquinone reactant desorption rate constants on the basis of a reaction rate model. It was demonstrated that results from the inert standard method were compatible with those from moment methods where it is feasible for both methods to be applied to chromatographic reactor kinetic studies. |
