Degree Name

Master of Science (MS)

Semester of Degree Completion

1972

Thesis Director

Richard L. Keiter

Abstract

A kinetic and equilibrium study of the reaction of triphenylphosphine (PPh3) with pentacarbonylaminetungsten (O) [(CO)5WNH2C6H5] has been reported previously. Equilibrium constants for the reaction (CO)5WNH2C6H5 + PPh3 = (CO)5W[P(C6H5)3] + C6H5NH2 in toluene were reported to be 17.1, 49.2 and 65.7 respectively. In addition, the entropy change (ΔS) for the reaction was found to be 86±5 cal mol-1 deg-1.

In this study the above reaction was reinvestigated in order to determine the cause of the abnormally large entropy change. The reaction was investigated spectrophotometrically by monitoring the absorption of the aniline complex at 406 nm. Other reactants and products of the reaction do not absorb significantly at this wavelength. The reaction was examined over a range of ligand concentrations and reaction temperatures.

When the conditions of the previous work were duplicated it was found that the absorption due to the aniline complex disappeared completely. Concentrations of starting reactants were adjusted in order to shift the equilibrium position to the left. In no experiment was there obtained any evidence for equilibrium. Therefore, if an equilibrium does exist, the equilibrium constant must be much larger than that previously reported. Furthermore, it was previously reported that equilibrium for the reaction is established in two days. In this study it was found that the aniline complex continues to react beyond two days in all experiments.

An attempt to determine the equilibrium constant for the reaction by approaching the equilibrium from the opposite direction was not successful. The intensity of the carbonyl absorption of (CO)5WPPh3 did not diminish with time upon treatment of this compound with a large excess of aniline nor was there any appearance of aniline complex. It is concluded that the position of equilibrium cannot be determined by the methods utilized in the previous study.

The previous workers reported that the aniline complex is stable in the presence of a large excess of aniline. In this study it has been found that this is not true for temperatures above 30° and that at temperatures above 40° rapid decomposition occurs.

It is the conclusion of this study that the thermodynamic data previously reported are unreliable.

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