Hydrocarbons, saturated, reactions with oxygen atoms

Basic rate information permits one to examine these phenomena in detail. Leighton [2], in his excellent book Photochemistry of Air Pollution, gives numerous tables of rates and products of photochemical nitrogen oxide-hydrocarbon reactions in air this early work is followed here to give fundamental insight into the photochemical smog problem. The data in these tables show low rates of photochemical consumption of the saturated hydrocarbons, as compared to the unsaturates, and the absence of aldehydes in the products of the saturated hydrocarbon reactions. These data conform to the relatively low rate of reaction of the saturated hydrocarbons with oxygen atoms and their inertness with respect to ozone. 

The saturated hydrocarbons are relatively inert except at high temperatures. For example, sodium metal is usually stored immersed in an alkane such as kerosene (8 to 14 carbon atoms) to protect it from reaction with water or oxygen. Combustion is almost the only important chemical reaction of the alkanes. That reaction, however, makes the hydrocarbons one of the most important energy sources of our modern technology. 

It follows that oxygen atom reactions with saturated and unsaturated hydrocarbons proceed with scission of the C—C and C=C bonds, respectively. 

Besides the oxygen atom reactions discussed earlier, we studied those involving I.2-C2H4CI2,66 NH3,66 and acetylene, cyclohexane, and benzene. At first attempts were made to find an O atom reaction that would be similar and at the same time essential for all substances. This is the ease, for example, for hydrogen atoms and hydroxyl. Hydrogen reacts with saturated hydrocarbons by abstraction of the H atom, and with unsaturated hydrocarbons by addition as well. Hydroxyl is believed to react with hydrocarbons by abstraction of the H atom and formation of water. 

Analysis of all the data on O-atom reactions with squalane and consideration of the various possible reactions of ground state 0( P) and electronically-excited 0( D) lead to a qualitative summary (Fig. 16) of the initial reactions between atomic oxygen and a saturated hydrocarbon surface. The first step leading to the production of volatile reaction products is direct H-atom abstraction by 0( P). The initial OH product may... 

The design of catalysts for steam reforming of liquid hydrocarbons is dictated mainly from the need to avoid carbon formation. As illustrated in the simplified mechanism (1) in Table 2, the hydrocarbons are adsorbed on the nickel surface, and the C -species, formed by successive a-cleavage of the carbon/carbon bonds, are dehydrogenated stepwise into adsorbed carbon atoms which may dissolve in the nickel crystal. When the concentration of carbon is above saturation, a carbon whisker will nucleate. These reactions compete with the reaction of the Ci-species with adsorbed oxygen atoms to gaseous products. The concentration of adsorbed oxygen depends on the steam adsorption (and CO2 -adsorption) on the catalyst. 

Let us consider three types of interaction between (1) adsorbed hydrocarbon ion-radicals and oxygen of the gas phase (2) adsorbed oxygen and hydrocarbon of the gas phase (oxygen adsorbed both with and without dissociation) (3) adsorbed oxygen and adsorbed hydrocarbon. Saturated aldehydes and acids containing less carbon atoms than in the molecule of initial hydrocarbon, as well as carbon dioxide and water, are formed in the first case. The second type of interaction yields unsaturated aldehydes, olefine oxides, carbon monoxide, carbon dioxide, and water for the oxidation of unsaturated hydrocarbons and saturated aldehydes, carbon dioxide, carbon monoxide, and water for the oxidation of saturated hydrocarbons. The third type of reaction gives... 

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