Photooxidation of hydrocarbons

An interesting, and slightly different, autoxidation is photooxidation of hydrocarbons such as 9,10-diphenylanthracene (102) in solvents such as CS2. The light absorbed converts the hydrocarbon into the stabilised diradical (103, cf. p. 337), or something rather like it,... 

Secondly, the interaction of hindered amines with hydroperoxides was examined. At room temperature, using different monofunctional model hydroperoxides, a direct hydroperoxide decomposition by TMP derivatives was not seen. On the other hand, a marked inhibitory effect of certain hindered amines on the formation of hydroperoxides in the induced photooxidation of hydrocarbons was observed. Additional spectroscopic and analytical evidence is given for complex formation between TMP derivatives and tert.-butyl hydroperoxide. From these results, a possible mechanism for the reaction between hindered amines and the oxidizing species was proposed. 

For detailed information and bibliography on photooxidation of hydrocarbons, see Chapter 3. 

Schuck, E. A., and G. J. Doyle. Photooxidation of Hydrocarbons in Mixtures Containing Oxides of Nitrogen and Sulfor Dioxide. Report No. 29. San Marino, Calif. Air Pollution Foundation, 1959. 126 pp. 

Despite the numerous papers devoted to photooxidation of hydrocarbon polymers [21], the initiation step has not been clearly established yet even for polyethylene or polystyrene which were the most studied [22,23]. Difficulties which follow from solution of this problem consist in the necessity of analysis of small amounts of decomposing unstable structures and products which are thereby formed. Moreover, photoinitiation does not include one reaction only but the overall complex of many chemical and physical processes, which importance depends on experimental conditions. 

Examination of Carbon Monoxide Effects. Recent work (44, 50, 51) of smog photochemistry has suggested that carbon monoxide may play a role in accelerating the photooxidation of hydrocarbon/nitric oxide mixtures. The mechanism suggested is... 

Table III. Photooxidation of Hydrocarbon—NOar-CO Mixtures in Large Irradiation Chamber...

A computer model has been developed which can generate realistic concentration versus time profiles of the chemical species formed during photooxidation of hydrocarbon polymers using as input data a set of elementary reactions with corresponding rate constants and initial conditions. Simulation of different mechanisms for stabilization of clear, amorphous linear polyethylene as a prototype suggests that the optimum stabilizer would be a molecularly dispersed additive in very low concentration which can trap peroxy radicals and also decompose hydroperoxides. 

The basic mechanism of the removal of SO2 from the atmosphere is its oxidation to SO3. In the day-time, at a low relative humidity, the SO2 oxidation is prevalent in the presence of nitrogen oxides or possibly of intermediate products of the photooxidation of hydrocarbons. In the night and under conditions of high humidity, SOj is absorbed in water drops and the oxidation occurs in the liquid phase. SO3, produced during the oxidation in the gas phase reacts with the atmospheric water vapour, producing an aerosol of HjSO. The aerosol particles in the atmosphere gradually increase in size and after several days they are as large as 0.1 to... 

If it can be shown that the photooxidation of hydrocarbons in zeolites is a general method, then the shape and size-selective properties of zeolites may potentially be used to control the selectivity of specific oxidation reactions (2,3). For example, ZSM-5 is an important shape-selective catalyst in many reactions, such as the disproportionation of toluene (4). Para-xylene is the dominant product because the transport of the other isomers, ortho- and meta-xylene, is restricted due to the pore size of ZSM-5. Thus, stereochemical aspects of selective photooxidation reactions may also be influenced by the zeolite and may be used to design environmentally benign processes for the synthesis of industrially useful molecules. 

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