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The effect of the pH of precipitation on the physical and chemical properties of hydrous aluminum oxide prepared by the reaction of aluminum chloride and strong ammonia solution NF; aluminum sulfate USP, and strong ammonia solution NF; and aluminum chloride, sodium bicarbonate USP, and sodium carbonate USP, was studied. During aging, changes may occur in the hydrous aluminum oxide structure which result in a loss in acid reactivity. This loss followed apparent first-order kinetics. The rate of loss was directly dependent on the pH of precipitation and continued until a constant end-point was reached. The percentage of theoretical reactivity remaining at the end-point was inversely related to the pH of precipitation. X-ray diffraction showed no differences in form, either initially or during aging. Gel stability appears to depend on the presence of anions in the gel structure. The concentration of these anions is related to the pH of precipitation. Data are presented which demonstrate that a stable, completely acid-reactive gel would be obtained if 1 mole of a monovalent anion such as chloride or bicarbonate or 0.5 mole of a bivalent anion such as sulfate is incorporated in the gel structure per mole of aluminum.

Mixtures of two amorphous alumina gels of different acid reactivity change physically and chemically upon aging until a constant state is reached. The gels, when individually aged, retain their initial properties. The end-point appearance, viscosity, X-ray diffraction pattern, DTA thermogram, acid-insoluble fraction, and acid reactivity of the mixture are identical to those of the gel having the lower acid reactivity. The change in properties appears to be due to the conversion of the gel having the higher reactivity into the less reactive form. The rate of conversion is first-order, temperature-dependent, and directly dependent on the initial concentration of the less reactive gel.

The formation of 1:1 molar complexes between sucrose and the following penicillins was studied: potassium penicillin G USP; potassium phenoxymethyl penicillin USP; sodium dicloxacillin, monohydrate; and ampicillin, anhydrous. Kinetic parameters, based on a model system, are presented for each interaction. The degree of complexation was greatest with sodium dicloxacillin and least with ampicillin. The rate of degradation of complexed penicillin was 5-6 times the rate for the uncomplexed penicillin. The relatively high equilibrium constant obtained for sodium dicloxacillin was consistent with the strong effect of sucrose on the observed rate constant. Ampicillin, whose observed rate constant was only slightly affected, had a very low equilibrium constant. Complexation involves the intact penicillin and accelerates the degradation of penicillin but does not appear to change the degradation pathway.