k~ Photometric titrations of 16 weak acids, mainly phenols, were performed in commercial isopropyl alcohol using tetra-n-butylammonium hydroxide in isopropyl alcohol as titrant. In favorable cases, up to four components in a mixture were resolved if a suitable change in wave length setting was made during the titration. Nonlinear phoiometric titration curves for phenols provide new evidence for complex formation between phenols and phenolate ions.

A polarogram for benzyl chloride in a supporting electrolyte of lithium chloride has a dip in the limiting current due to electrostatic repulsion from the interface of the monovalent anion produced by transfer of the first electron. The dip is decreased by the presence of electronegative substituents on the ring and is eliminated by a moderate concentration of surface-active tetra~ methylammonium ions in the solution.Benzyl bromide and iodide each undergo two widely separated one-electron reduction steps at concentrations less than 10-'M. At higher concentrations, adsorption phenomena are encountered in the region of potential between the two waves due to the presence of bibenzyl, a by-product of the first reduction step.The exploratory work of von Stackelberg and Stracke (1) showed that reductions of organic halogen compounds became easier on going from chloride to bromide to iodide. The over-all reaction usually involved replacement of the halogen atom with a hydrogen atom. The half-wave potentials were independent of pH, showing that addition of hydrogen did not occur in the rate-determining step, but after the transfer of electrons.The steps in the polarographic reduction of an organic halogen compound, RX, can be represented by the following reactions (1, 2) :RX + e--> RX- [1]

Polarograms were obtained in media in which reductions of each compound occurred on both sides of the electrocapillary maximum. Capillary‐active anions retarded the less cathodic reduction steps and capillary‐active tetramethylammonium ion facilitated the second reduction steps of carbon tetrachloride and the dibromoacetate ion. Capillary‐inactive calcium ion had little effect on the halogenated compounds, but it greatly facilitated the second reduction of p‐dinitrobenzene thereby suggesting ion‐pair formation with the known divalent intermediateGelatin, for the first time, was found to shift a reduction to less cathodic values. This occurred only in acidic media when the reduction took place on the negative branch of the electrocapillary curve. The shift was attributed to the presence of protonated gelatin in the double layer.

No abstract

No abstract