Oxaziranes decomposition

The rupture of the oxazirane ring at the ON-bond occurring with acid treatment of the alkyl-substituted compounds is probably the result of an electronic shift initiated by the protonated oxygen (arrows as in 21). In principle, a similar rearrangement of the electronic system should also be possible initiated from the nitrogen end (22), Indeed, decomposition products similar to those of the... 

A direct attack on the oxazirane ring occurs with ferrous salts. Oxaziranes are decomposed by aqueous solutions of ferrous ammonium sulfate even at room temperature. The reaction follows a radical-chain mechanism because le.ss than stoichiometric amounts of the ferrous salt cause the decomposition, 2-icrt-Butyl-3-phenyloxazirane (9) and 1 equivalent of ferrous salt give ferf-butylbenzamide in 98%... 

In the reaction of 2,3,3-triethyloxazirane (25), three radicals are involved 26, 27, and 28. Radical 26 (Fig. 1) corresponds to the chain reaction propagating radical of the previously mentioned decomposition [Eqs. (20) and (21)]. From 26 hy fragmentation an ethyl radical (27) is formed together with the acid amide. Finally, by radical attack on the oxazirane, 29 can be formed which rearranges to the... 

Most oxaziranes withstand temperatures of 100 C for a short time, e.g., on distillation. At higher temperatures isomerization and decomposition occur. Oxaziranes derived from aromatic aldehydes are here again differentiated from the alkyl-substituted oxaziranes. 

The composition of the products is reminiscent of the decomposition of the trialkyl-oxaziranes by ferrous salts. Here also the nitrogen atom is dealkylated and the carbon atom of the oxazirane ring is found as a ketone group. 

The mechanism proposed by Emmons thus corresponds in part to the decomposition of the trialkyl-oxaziranes by ferrous salts. By radical attack on the 7V-alkyl group of the oxazirane, the radical 32 is formed which rearranges with ring opening to 33. Radical 33 propagates the chain by attack on a further molecule of oxazirane. It takes up an H-atom and is decomposed to ketone and ammonia. The aldehyde produced from the M-alkyl group is converted to tar. 

The reaction described here is probably responsible for the slow decomposition of many oxaziranes at room temperature, 2-fert-Alkyl-oxaziranes are stable at room temperature for unlimited periods radical attack on the a-C-atom of the iV-alkyl group is not possible. By contrast, oxaziranes containing a C—H group which is alpha to the N-atom are unstable at room temperature on keeping they are largely decomposed within a few weeks. 

In their thermal stability the diaziridines approximate to the oxaziranes. As with most oxaziranes, they are stable at 100° C for short periods they are decomposed by heating at 200°C 1,2-di-n-butyl-3-ri-propyldiaziridine thus eliminates butylamine. The thermal decomposition has not yet been investigated in detail. Similarly no information is available on the reaction of radical reagents on diaziridines. 

Arylnitrenes and subsequently 2-dialkylamino-3//-azepines have also been generated by the decomposition of oxaziranes (B-70MI51601) and (in almost quantitative yield) by thermolysis (100°C) of A, 0-bis(trimethylsilyl)phenyl hydroxylamine, in the presence of dialky-lamines (76JOC3381). 

As mentioned above, the oxazirane ring ha limited stability. The products of its thermal decomposition vary considerably with the structure of the oxaoirane and also with the pyrolysis conditions. The products of thermal decomposition of the 3-arytoxaziraoes are the isomeric nitrones. This is apparently a general reaction and may be conveniently accomplished by beating solutions of the oxasiraun in... 

Finally, many oxazirane decompose at room temperature over a period of days. This decomposition, although it has not been studied in detail, appears to be grossly comparable to solution deeompesitione at... 

Most oxazirancs withstand temperatures of 100 C for a short time, e.g., on distillation. At higher temperatures isomerization and decomposition occur. Oxaziranes derived from aromatic aldehydes are here again differentiated from the alkyl-substituted oxaziranes, a. Isomerization to Nitrones. 2-Cyclohexyl-3-phenyloxazirane iso-merizes on heating to 200 C. With further increase in temperature it is converted into iV-cyclohexylbenzaldoximc (70%) fEq. (24)]. ... 

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