620. The effect of some additives on the oxidation rate of cyclopentane

Abstract

A study is made of the relative efficiencies of various heterogeneous additives, mainly salts, in the inhibition of cyclopentane oxidation. Inhibition occurs by destruction of peroxy-radicals, or more probably peroxide molecules.THE principal object of the present work was to investigate means of inhibiting or controlling gaseous combustion reactions. Unpublished work in this laboratory has shown that the characteristic slow start and accelerating development of these reactions depends upon the gradual accumulation of active intermediates. These are susceptible, in principle, to destruction, both by homogeneous additives and by surface reaction, whereby combustion might be suspended for a long time or even indefinitely. Homogeneous additions of an effective kind in the oxidation of cyclopentane have proved difficult to find. Small amounts of formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, or chlorine all reduce the induction period in some degree: di-t-butyl peroxide and bromine, even in amounts of less than 0*1%, completely eliminate it. Isopropyl halides, aniline, carbon tetrachloride, and carbon tetrafluoride have little or no effect on induction period or rate. The effect of nitrogen and carbon dioxide, even in large amounts, is negligible. The substances which accelerate the reaction are believed to do so by the production of free radicals through either oxidation or decomposition.Since satisfactory homogeneous additions have been difficult to find, the action of various salt and metal surfaces which are known in principle to have inhibitory effects has been investigated in more detail. Many of these markedly prolong the induction period, sometimes almost indefinitely.Pease and his co-workers: oxidising propane in a flow system at temperatures between 325" and 400°, found that coating the reaction tube with potassium chloride reduced the yield of peroxides almost to zero, without other effect on the reaction. Static experiments, on the other hand, at 270-280" with a Pyrex reaction vessel coated with potassium chloride showed a greatly lengthened induction period. Similar results have been obtained more recently by Egerton, Minkoff, and Solooja and by Walsh 3 who have studied the effect of surfaces on the oxidation of methane at about 500". Walsh divides the surfaces into three types according to their effect on the rate of oxidation, namely, (i) acidic-silicic acid, boric acid, phosphoric acid, germanium dioxide, (ii) salts in general and metallic oxides, and (iii) metals. The rates in vessels having the above types of surfaces fell in