The Polarographic Reduction of the Platinum Metals

Abstract

April, 1945 POLAROGRAPHIC REDUCTION OF THE PLATINWM METALS 547 in size of the central atom or to radical differences in the reaction mechanism. The first possibility can be better evaluated only when more data are available on additional members of the tetra-alkyl groups. As for the second alternative, a more thorough examination of the decomposition of tetraethyl lead would undoubtedly yield valuable information concerning its mechanism and energy of activation.summary The thermal decomposition of tetramethyltin has been investigated between 440 and 493" over a range between 5 and 185 mm. initial pressure.By the criteria of half-life periods, times for a given fractional pressure increase and initial rates, the reaction was found to be predominantly of the first order above 80 mm. initial pressure. At lower initial pressures the order increases, approaching that of second.The specific velocity constant of the prima process was found to be KO = 8.32 X 1021 e-82,400/R?Rate constants calculated by an indirect method agreed well with those obtained directly. The reaction was found to be homogeneous once the reaction vessel was thoroughly coated with a deposit of tin and carbon.Nitric oxide produced no inhibition but instead caused a slight catalytic acceleration of the primary process.Chemical analyses made over the entire range of decomposition revealed the predominant gaseous product to be methane, together with some hydrogen and ethylene. Tin and carbon were also found as a deposit on the walls.Based upon the kinetic data and the chemical analyses, a probable reaction mechanism was proposed.An explanation is offered for the changes in activation energy observed in going from the methyl to ethyl to propyl tetra-alkyls thus far investigated.In a previous communication' the polarographic reduction of rhodium compounds was discussed in detail. In the present paper similar work is extended to the other platinum metals. With the exception of a recent paper on the polarographic reduction of osmium tetroxide12 the only published work in this field seems to be that dealing with catalytic hydrogen waves produced in acid solutions containing small amounts of the platinum metal chlorides.304Theory It was shown in the previous paper' that although rhodium trichloride itself was rapidly decomposed by mercury, complex salts of *rhodium could be obtained which were stable toward rnercury, and which were reducible a t the dropping electrode. In the present work it is shown that the other platinum metals also form stable complexes, which in some cases give polarographic steps.In order to calculate n, the number of electrons involved in each reduction step, the IlkoviP equation was applied and the log plot calculated in the previously described way. As explained before, in the calculation of the diffusion coefficient of a complex metal ion conductivity data for similar (1) Willis, THIS JOURNAL, 66, 1067 (1944). (2) Crowell, Heyrovsky, and Engelkemeir, iLid., 68, 2888 (1941). (3) Herasymenko and Slendyk, Coll. Cscch. Chem. Comm....

Electronic Configuration in Electrodeposition from Aqueous Solutions

“…Even high sublimation energies are not enough to make deposition possible from the very stable cyano complexes, with the possible exception of those of palladium (67,68) for which the cathode efficiency is less than 1%. However, reduction of cyano complexes to lower oxidation states is reported for all platinum metals.…”

“…Calculations indicating high efficiencies are probably in error because of the presence of lower oxidation states (69). At the dropping mercury electrode, platinum catalyzes hydrogen evolution (70) and is not deposited under usual circumstances (68,71).…”

“…The tetrachloropalladate(II) ion, although somewhat more stable than the corresponding platinum complex, is rapidly reduced in the cold by hydrogen (75). It is reported that palladium is deposited at the dropping mercury electrode (68).…”

Mechanism of Electrodeposition from Aqueous Solutions of Square Planar Complexes

“…Since the experimental evidences for the trans effect per se are limited largely to Pt(II) chemistry (4), it was of interest to investigate a series of Pt(II) complexes in order to provide further evidence and possible verification of the trans effect in electrodeposition. These studies were further of interest since efforts to study the deposition of platinum from aqueous solutions by polarographic methods have been unrewarding (5,6).…”

Polarographic Determination of Technetium and Ruthenium Radionuclides in Fission Products

“…Ruthenium dioxide and ruthenium sesquioxide might also be plated out on mercury if in certain supporting electrolytes their potentials are between those of mercury and the cation of the supporting electrolyte. Willis (11), using a dropping mercury electrode, found no reduction waves for ruthenium (IV) or (III) in any of the supporting electrolytes he tried, including some that were basic. Silverman and Levy (10), using platinum electrodes and a supporting electrolyte of sodium per-chlorate, obtained half-wave potentials of + 1.00 for the ruthenium(VII)-(VIII) couple and + 0.59 for the (VI)-(VII) couple.…”