Studies of Some Inorganic Reaction Mechanisms

Citation

Schweizer, Albert Edward, Jr. (1974) Studies of Some Inorganic Reaction Mechanisms. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/75es-0c18. https://resolver.caltech.edu/CaltechTHESIS:02082021-221037462

Abstract

Part I

The compound dihydridotetrakis (diethylphenylphosphonite)-iron(II) is known to undergo rapid rearrangement in solution. Considerable discussion has been presented to formulate a mechanism for this rearrangement. This discussion is based on a rearrangement between cis and trans dihydride isomers of octahedral stereochemistry. We present here some experimental evidence which shows the identification of one isomer (as the trans dihydride) is incorrect and also that the changes that occur are more complicated than the earlier workers proposed. Infrared, Raman, and very low temperature ¹H n. m. r. spectra of both the iron and ruthenium compounds are used to construct a different picture of this system. We identify three distinct reactions or rearrangements that are occurring and offer some proposals for the structures of the isomers. A non-classical six-coordinate structure based on a tetrahedral skeleton of phosphorus atoms about the central metal is considered the most reasonable identification of the non-cis isomer.

Part II

Nitric oxide undergoes many reactions to form transition metal nitrosyls of varying geometry. Under very special conditions, it then continues to react to form a species with nitrogen to nitrogen bonds. We have studied one of these reactions in detail: First, to establish the stoichiometry of the reaction exactly and second, to gain some insight into the mechanism of the dimerization step.

There is an initial rapid reaction of an ammoniacal Co(II) solution and NO with the stoichiometry one NO per cobalt(II). The NO pressure dependence of the ratio NO to cobalt is given experimentally. A qualitative proposal is made to explain this dependence, but we are still searching for a quantitative description.

There is a much slower reaction that consumes additional nitric oxide, producing N₂O and nitrite ions. If the initial cobalt(II) concentration is high, an additional product is obtained, the μ-hyponitrito bis(pentaammine cobalt(III)) ion, usually precipitated as the nitrate. The yield of the dimeric cation as a function of concentration, anion, and temperature are given. A proposal of a linkage isomerization of an unstable dimer of pentaamminenitrosyl cobalt(III) is offered to explain the experimental observations.

Part III

The decomposition of nitric oxide to elements in the gas phase is a thermodynamically favored reaction that is very slow at low temperatures (below 1000°K). Some catalysts are known for this reaction carried out in a heterogeneous reactor. Work has been performed jointly with the chemical engineering faculty to try to understand the reaction over one of the known catalysts. The rate limiting factor is shown to be the strong inhibition by the product oxygen rather than any intrinsically slow reaction of NO. An interpretation of both our results and the results of another group is offered in terms of a unimolecular decomposition on a surface.

Thesis Files