Coulometric generation of protons by oxidation of hydrogen dissolved in palladium, in non-aqueous media.
Coulometric generation of H(+) ions by the oxidation of hydrogen dissolved in palladium, in media such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, acetic anhydride and acetic acid-acetic anhydride mixture, for use in titration of bases, has been investigated. The hydrogen is oxidized at potentials which are much more negative than those of the bases and other components present in the solution. Titrations of numerous bases have established that the oxidation is quantitative and proceeds with 100% current efficiency.
Coulometric titration of bases in acetic acid and acetonitrile media.
The working conditions and the results for coulometric titration of milligram amounts of some bases in 0.1M sodium perchlorate in a mixture of acetic acid and acetic anhydride (1:6), are given. Determinations were made both by coulometric back-titration or direct titration at the platinum anode. Back-titration was done in the catholyte, by coulometric titration of the excess of added perchloric acid. The titration end-point was detected photometrically with Crystal Violet as indicator. The direct titration of bases was done at the platinum anode, in the same electrolyte, to which hydroquinone was added as anode depolarizer and as the source of hydrogen ions, Malachite Green being used as indicator. Similarly, bases can be determined in acetonitrile if sodium perchlorate, hydroquinone and Malachite Green are added to the solvent. Errors are below 1 %, and the precision is satisfactory.
Sensitive apparatus for obtaining freezing curves Purity of 4-aminopyridine.
Freezing curves of highly-purified 4-aminopyridine have been obtained with an instrument of new design employing a gold crucible, a platinum resistance thermometer, electrical heating elements on crucible and heat shield, and accessory electrical control devices such that the temperature difference between crucible and shield could be maintained constant within 0.005 degrees while the temperature of the 4-aminopyridine and crucible dropped through the freezing range. No stirring was used. Methods were devised for handling the data as the derivative of temperature with respect to time and of correcting the freezing curve for the heat capacity of the crucible and charge. Although interpretation of the freezing curves obtained on the 4-aminopyridine was confused by attack on the gold by the molten 4-aminopyridine, the initial impurity in the 4-aminopyridine was probably less than the detection limit, 0.001 mole %.