Unimolecular decomposition carbonyl oxide

A theoretical investigation showed that the most favourable unimolecular decomposition path of primary fluorozonide is a concerted cleavage to carbonyl oxide and formyl fluoride. The secondary fluorozonide decomposition takes place most readily in a stepwise manner initiated by the 0-0 bond rupture.153 DFT calculations have shown that ozone-difluoroethylene reactions are initiated by the formation of van der Waals complexes and then yield primary ozonides, which rapidly open to carbonyl oxide compounds. The formation of primary ozonide has been predicted to be the rate-controlling step of the oxidation process.154... 

POZ). The reaction enthalpy is retained as the internal energy of the products, resulting in formation of the vibrationally excited ozonide, which subsequently undergoes unimolecular decomposition to yield a chemically activated biradical, known as the carbonyl oxide or Criegee intermediate (Cl), and an aldehyde (e.g., MVK, MACR or formaldehyde). A total of nine carbonyl oxides (methyl vinyl carbonyl oxide, derived from 1,2-ozonide isopropyl carbonyloxide, derived from... 

Equation (15) does not require an unusual reversibility of oxygen addition, direct hydrogen abstraction by oxygen, or generation and decomposition of a hydroperoxide-containing radical. It is also consistent with the observed differences between alcohols and ethers. The reported rapid unimolecular decomposition of hydroxyalkylperoxy radicals to HOO radicals and a carbonyl compound in aqueous solution under mild conditions appears to lend strong support to this proposal [25]. The production of HOO radicals has been proposed to explain inhibition in a variety of hydrocarbon oxidations [10, 27]. 

Alkoxy (RO) radicals are formed in the reaction of alkyl peroxy (R02) radicals with NO. Subsequent reactions of alkoxy radicals determine to a large extent the products resulting from the atmospheric oxidation of VOCs (Orlando et al. 2003). Alkoxy radicals react under tropospheric conditions via a variety of processes unimolecular decomposition, unimolecular isomerization, or reaction with 02. Alkoxy radicals with fewer than five carbon atoms are too short to undergo isomerization for these the competitive processes are unimolecular decomposition versus reaction with 02. The general alkoxy radical-02 reaction involves abstraction of a hydrogen atom by 02 to produce an H02 radical and a carbonyl species ... 

In acetic acid media, the oxidative decarboxylations of 2-hydroxy-carboxylic acids by Pb(OAc)i probably involve the formation of hydroxyl-bound complexes (41) with participation of the carboxyl either in a unimolecular decomposition step or in chelate formation (42) followed by decomposition in the rate-determining step. No decarboxylation is found with 3-hydroxybutyric acid, showing the importance of both OH and CO2H groups in the intermediate formation. The effect of substituents is consistent with a two-electron transfer with development of a carbonyl group from the hydroxy-group in the transition state. No radicals were detected. 

As for the reactions of vibrationally excited carbonyl oxides formed above, the formation of OH radicals by unimolecular decomposition and stabilized carbonyl oxides by collisional deactivation can be conceived. 

However, less is know about the quantitative details of these processes than is the case for the alkanes. In general, unimolecular decomposition of the alkoxy radicals [e.g., CH3CH20CH(0 )CH3 in the above reaction sequence] is more rapid than for an alkane-derived radical of similar structure. The major end product of ether oxidation is quite often an ester, the analog to the carbonyl compounds (aldehydes and ketones) generated from alkane oxidation. 

Many of the carbon compounds containing both fluorine and oxygen decompose by complex mechanisms. However, the thermal decomposition of tetrafluoro-ethylene oxide is claimed to be unimolecular over the temperature range 115-140 °C, with = 5 X 10 sec and E = 31.6 kcal.mole". The products are carbonyl fluoride and perfluoroethylene plus perfluorocyclopropane (probably formed from CF2). In a pyrex glass vessel at 40-45 °C trifluoroacetylfluoride is produced by a heterogeneous process. 

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