The Photooxidation of Azomethane. Iii

Abstract

I t is confirmed t h a t the yields of all products in the photooxidation of azomethane a t relatively high oxygen pressure depend on conversion in a manner which would be explained if a reactive hydrogen donor were produced in the early stages of the reaction. Evidence is presented which indicates t h a t formaldehyde cannot be active as a n inhibitor in the system a t 162' C. I t is suggested that methyl radicals react with oxygen in two ways. The third order formation of methyl peroxy radicals leads to methoxy radicals and, eventually, to methanol, while the bimolecular reaction between methyl radicals and oxygen leads to a vibrationally excited state of formaldehyde. Thc latter is thought to undergo oxidization to performic acid, which acts as the inhibitor in the system. Yields of formaldehyde, of nitrogen in excess of that formed in the primary process, and of nitrous oxide are linearly related regardless of the conversion up to about 4%. Methanol is a major product of the oxidation and, if account is taken of its yield, a carbon balance of the order of 90% is obtained.

Photooxidation of Azomethane: Iv. The Role of Formaldehyde

“…Aside from that of methanol and formaldehyde the general forms of the curves in Fig. 1 agree with --those obtained earlier (2,3).…”

“…If, in addition to the assunlption above, it is also valid t o assuine (a) that nitrous oxide and secondary nitrogen arise oilly froin [2] and [3], and (b) that [2] and [3] represent the sole fates of CH2N2CH3 radicals fornled in [I], and [5] Calculations based on the data of Table I give kl/k4 = 212&10 with no obvious trend with conversion. If Al/A4 is talren a s unity approximately, this calculation indicates that El = E4 = 4-5 kcal/nlole.…”

“…Formaldehyde, nitrous oxide, and "excess nitrogen" (3) are produced a t rates which decrease with the time of exposure. These products are thought (1,3) to arise via the reactions where R is some radical in the system and [2] and [3] are written as over-all processes which might occur in stages. Provided methyl and methoxyl, or radical products of their reaction with oxygen, can function as R in [I], the elements of a chain reaction are present in the lnechanisln as appears to be required by the data (3).…”

THE OXIDATION OF DI-tertiary-BUTYL PEROXIDE

“…Considering the relatively low total pressure used in these experiments it is not unreasonable t o suggest that the present conditions would tend t o favor [4] and [5] a t the expense of [GI. This is especially so if it could be deinonstrated that D T B P were not an efficient third body, iVI.…”

“…The present study was undertaken to extend this work to !ower (<5%) coi~versioi~s and to investigate the effect of conversion on the rates of production of the inajor products. The role of formaldehyde as a hydrogen donor in the photooxidation of azomethaile has been iilvestigated previously in this laboratory (4,5,6). Experiments are reported in which formaldehyde-C13 was added to the reactailts in the present systein to investigate this point further.…”