2-Methylpropane initiated oxidation

Figure 3. Low temperature-initiated oxidation of 2-methylpropane according to Allara et al. (1)...

The mechanisms for ambient temperature oxidations become more complex as the alkyl radical R becomes more complex and as the reactions proceed. Thus, with azo-2-methylpropane (52) the pyrolysis of the tert-butoxy radical must be included, and in all but the initial stages, reactions of alkoxy radicals with products containing weak C—H bonds must be included. Numerous tertiary reactions can then occur. As with most free radical systems, useful information can be obtained only if the degree of conversion of the starting material is kept low. 

Figure 2. Product development in oxidation of 2-methylpropane at 155°C. initiated hy di-tert-butyl peroxide...

Carlier fundamental studies of autoxidations of hydrocarbons have concentrated on liquid-phase oxidations below 100 °C., gas-phase oxidations above 200°C., and reactions of alkyl radicals with oxygen in the gas phase at 25°C. To investigate the transitions between these three regions, we have studied the oxidation of isobutane (2-methylpropane) between 50° and 155°C., emphasizing the kinetics and products. Isobutane was chosen because its oxidation has been studied in both the gas and liquid phases (9, 34, 36), and both the products and intermediate radicals are simple and known. Its physical properties make both gas- and liquid -phase studies feasible at 100°C. where primary oxidation products are stable and initiation and oxidation rates are convenient. 

A log-log plot of the rates of oxidation (R0) vs. the rates of initiation (Ri) for 380 mM 2-methylpropane experiments in Table II gave a slope of 0.45 to 0.55 for the initiator dependence. [Although Figure 1 supports the same relation, the result is misleading. When we replace R0 by R0 — Ri/2a in the plot, using the liquid-phase value a = 0.091, the ordinates become smaller (solid triangles) or negative (not shown). To... 

In a dichlorodifluoromethane system, frictional wear exposed fresh metal surfaces on an aluminium compressor impellor, causing an exothermic reaction which melted much of the impellor. Later tests showed similar results, decreasing in order of intensity, with tetrafluoromethane chlorodifluoromethane bromotrifluoromethane dichlorodifluoromethane 1,2-difluorotetrafluoroethane 1,1,2-trichlorotrifluoroethane [6], In similar tests, molten aluminium dropped into liquid dichlorodifluoromethane burned incandes-cently below the liquid [7]. Aluminium bearing surfaces under load react explosively with polytrifluoroethylene greases or oils. The inactive oxide film will be removed from the metal by friction, and hot spots will initiate reaction [8]. An attempt to scale up the methylation of 2-methylpropane with chloromethane in presence of aluminium chloride and aluminium went out of control and detonated, destroying the autoclave. The preparation had been done on a smaller scale on 20 previous occasions without incident [9]. 

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