Decomposition of Phosphines

The decomposition of phosphine is a first-order reaction that proceeds according to the following stoichiometric equation. 

The decomposition of phosphine [4PH3(g) Pffg) + 6H2(g)] is first-order with respect to... 

The vapor phase decomposition of phosphine is irreversible first order and is in accord with the stoichiometry,... 

The kinetics of the thermally induced homogeneous decomposition of phosphine (PH3) have not yet been studied. The species PH2, PH and P2 are formed on flash photolysis of PH3 and could be identified by their absorption spectra63. There are proposals as to the mechanism of the consecutive process after the photochemical primary step, but nothing is known about the kinetic parameters of these reactions. With arsine and antimony hydride only the heterogeneous decomposition has been studied64,65. 

Nucleophilic attack. Current literature underestimates the importance of nucleophilic attack as a mechanism for the catalytic decomposition of phosphines, especially with nucleophiles such as acetate, methoxy, hydroxy and hydride (Figure 2.37). For examples of nucleophilic attack at co-ordinated phosphorus see references [36],... 

Using the above given conditions, an explosive decomposition of phosphine has never been observed. It is important, however, that no rapid change of pressure, which causes a spontaneous decomposition of phosphine into the elements, occurs because of the method of taking up of the phosphine or because of a blockage in the drying tube. 

Phosphine decomposes only at higher temperatures. The thermal decomposition of phosphine under various conditions has been examined in detail. It is found to be a first order reaction. The rate constant for the decomposition of phosphine at 500 °C is approximately 8 10 sec 57,231-233)... 

The thermal decomposition of phosphine on a glass surface can be satisfactorily described as a first order reaction using Eq. (13) ... 

The decomposition of phosphine the transformation of cyclo-propane into propylene. 

For some time the thermal decomposition of phosphine at high temperatures was believed to be a homogeneous unimolecular reaction. It was studied by Trautz and Bhandarkar, who concluded that under the conditions of their experiments, namely in a 3-litre porcelain bulb, the reaction on the walls of the vessel was negligible above 945° abs., in comparison with the homogeneous reaction. 

Many examples of this type of reaction are known the decomposition of arsine the decomposition of phosphine on surfaces of glass, f porcelain, J silica the decomposition of formic acid vapour on a variety of different surfaces— glass, platinum, rhodium, titanium oxide, and others the decomposition of nitrous oxide on the surface of gold Tf the decomposition of sulphuryl chloride on the surface of glass the decomposition of hydrogen iodide on the surface of platinum ff the decomposition of hydrogen selenide on the surface of selenium. J J A general discussion... 

H. Rose studied mainly the gaseous products and his work on the solid product was incomplete. C. F. Rammelsberg found that the gaseous products of the decomposition of hypophosphites being always a mixture of hydrogen and phosphine, the inflammability of the gas is of no importance, and seems to vary according to circumstances. The separation of phosphorus is due to the process itself, and does not depend on the decomposition of phosphine, for very often phosphorus appears at the beginning of the process, when the temp, is not sufficient for the decomposition of phosphine. 

Ex. 9 The half life periods for the thermal decomposition of phosphine at three different pressures are given below ... 

Exercise 8.4.4. The decomposition of phosphine proceeds to completion as a first order endothermic reaction with the stoichiometric equation... 

Many reactions involving heterogeneous catalysts are zero order that is rate = k. An example is the decomposition of phosphine (PH3) over tungsten... 

As mentioned above, the decomposition of phosphinous azides may yield monomers that trimerize or tetramerize. 

It was once thought that the decomposition of phosphine by heat was in... 

Hence show that kf, not h satisfies the required condition. The decomposition of phosphine is, therefore, said to be a reaction of the first order. Of course this does not prove that a reaction is really unimolecular. It only proves that the velocity of the reaction is proportional to the pressure of the gas—quite another matter. See J. W. Mellor s Chemical Statics and Dynamics. 

While investigating the rate of decomposition of phosphine, page 224, we had occasion to point out that the aotion may take place in two stages —... 

The irreversible decomposition of phosphine follows first-order kinetics at 650°C in a closed vessel ... 

The decomposition of phosphine PH3 on tungsten catalysts is first order at low pressures but zero order at high pressures. Interpret these findings. 

The problem of unimolecular reactions came to the fore with the question of how the molecules receive their activation energy. A hypothetical reaction in which rate and concentration are connected by the equation —dcjdi = kc would go half-way to completion in a time independent of the initial value of c. In a gas, therefore, this time should be the same at infinite dilution as at atmospheric pressure. The implication at one moment seemed to be that the supply of activation energy could not be dependent upon collisions, and the only alternative agency was absorbed radiation. But did any gaseous reaction follow this law At the time when this discussion arose, obvious candidates for the role, such as the decomposition of phosphine and arsine, were disqualified by their heterogeneity, so that no answer was forthcoming. 

The thermal nitration of a H-terminated Si surface and the CVD of silicon nitride were studied in situ by FTIR-IRRAS [160, 161]. The adsorption and thermal decomposition of phosphine (PH3) on a Si surface was also studied by IR absorption depending on the coverage and the exposure to the flux, PH3 adsorbs both nondissociatively and dissociatively, and the IR absorption peaks... 

The thermal decomposition of phosphine (PH3) into j S phosphorus and molecular hydrogen is a first-order reaction ... 

Ultrapure white phosphorus can be obtained by thermal decomposition of phosphine or a suitable metal phosphide (Chapter 8.1). 

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