The thermal decomposition of diethyl ether. I. Rate-pressure relations

Abstract

In the thermal decomposition of diethyl ether the first-order rate constant ( k ) varies with the pressure ( p ) of the ether itself, or that of added hydrogen, or that of various chemically inert gases according to a more complex pattern than has hitherto been supposed. In general, k increases approximately linearly with p X over a certain range: the slope of the curve then decreases as though a limit were being approached. When X refers to ether, hydrogen or certain other gases no limit is in fact reached, but k continues to increase at a considerably reduced rate. With certain gases, however, the slope of the curve becomes very small or zero. Changes in k are not explicable by variations in the chemical composition of the products. The forms of the k-p curves are qualitatively similar for the uninhibited reaction (largely a chain process) and for the nitric oxide-inhibited reaction (hypothetical molecular reaction), but the effects are quantitatively quite different. The k-p relations for the molecular reaction conform to those recently established for the decomposition of paraffins and of nitrous oxide, and may possibly be interpreted by the extended theory of unimolecular reactions proposed for these examples. The relations for the chain reactions are more complicated but the interpretation probably includes considerations similar to the above, applied to the initial molecular process by which the chains start.