Homogeneous catalysis of gaseous reactions. Part II.—The decomposition of Diethyl Ether Catalysed by Iodine

Abstract

From the analogy of the reaction C 3 H 7 .·O·C 3 H 7 =C 8 H 8 + (CH 3 ) 2 CO it was to be expected that, under the catalytic influence of iodine, diethyl ether would decompose smoothly into ethane and acetaldehyde at a temperature considerably below that at which the normal, and more profound, decomposition becomes appreciable. This anticipation was confirmed by experiment, but it was also found that the acetaldehyde itself suffered a catalytic decomposition into carbon monoxide and methane CH 3 . CH 2 · O· CH 2 CH 3 → CH 3 . CH 3 + CH 3 CHO → CH 3 CH 3 + CH 4 + CO. The kinetics of these reactions are of interest, since Glass and Hinshelwood found that, in the corresponding catalytic decomposition of isopropyl ether, almost every collision between molecules of iodine and ether in which the kinetic energy of approach exceeded the heat of activation, led to transformation. The energy of activation of the uncatalysed reaction has to be supplied from many “square terms” in the molecules, that of the catalysed reaction from two only. Thus the catalyst by a simple and effective collision brings the energy to the part of the molecule where it is required, in contrast with the wasteful and inefficient collisions between the ether molecules, which result much more rarely in transformation. This view of the matter is further substantiated by the results now to be described.