Azomethane, photooxidation

The experimental facts are clear that equal quantities of methanol and formaldehyde are produced in the initial stages of the oxidation of methyl radicals under many conditions,81 46 100 but recently similar amounts of methyl hydroperoxide have been determined in the photooxidation of acetone81 and it has also been detected in the photooxidation of methyl iodide87 and azomethane.7 106 122 Under some conditions,67 e.g., low pressures, the oxidation of methyl radicals appears to give more formaldehyde than methanol in the early stages, while at high temperatures (500°C.)64 little methanol is produced. 

It is interesting to note that at low conversions the yield of methyl hydroperoxide was variable and did not agree with that found by Wenger and Kutschke.181 This suggests that exact conditions are difficult to reproduce. Such behavior is common in thermal oxidation reactions and is attributed to surface reactions. It is therefore not surprising that Shahin and Kutschke107 found methyl hydroperoxide as a product of the photooxidation of azomethane even at temperatures as... 

Hanst and Calvert64 photooxidized azomethane at room temperature proceeding to about 50% decomposition. They put forward the idea that ozone was an intermediate in the oxidation and showed that it was removed rapidly only when photolysis was taking place. However, this merely proves that ozone will react with one of the radicals produced in the system. Similarly, the test which they used for ozone (tetramethyl-ethylene) was not shown to be specific to ozone and, indeed, is not likely to be. They were unable to detect methyl hydroperoxide in these experiments under conditions in which it was shown to be peculiarly stable at 200°C. for several hours. Formic acid was shown to be the major product of the prolonged further oxidation of formaldehyde in the presence of 1 atm. of oxygen (initially). 

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