Peroxy carbonates, decomposition

Of the 3 possible types of peroxy carbonate esters-dialkyl monoperoxy carbonates, dialkyl diperoxycarbonates and dialkyl peroxydicarbonates-, the latter are by far the least stable group. Several of the 16 alkyl and substituted-alkyl esters prepared decomposed violently or explosively at temperatures only slightly above the temperature of preparation (0-10°C), owing to self-accelerating exothermic decomposition. Several were also explosive on exposure to heat, friction or shock [1], Amines and certain metals cause accelerated decomposition of dialkyl peroxydicarbonates by a true catalytic mechanism [2], Individually indexed compounds are ... 

On the other hand, carbon dioxide may be derived from the decomposition of the intermediates formed by the reactions of the acyl radical and oxygen, such as the acid radical, peroxy radical, or peracid-aldehyde complex. Therefore, they may be derived as follows ... 

Theoretical studies suggest reaction (71) occurs by a concerted process in which the H from H02 is transferred simultaneously to the oxygen of C=0, while the terminal oxygen of H02 adds to the carbon (Evleth et al., 1993). The forward rate constant, k7l, is 7.9 X 10 14 cm3 molecule-1 s-1, leading to a lifetime of HCHO with respect to H02 of only 7 h at [H02] = 5 X 10x radicals cm-3. However, the reverse decomposition is also fast, k 7i = 150 s-1 at 298 K. If the rate constant for the reaction of the peroxy radical formed in (71) with NO is 8 X 10-12 cm3 molecule-1 s-1,... 

To isolate acidic products which were not found by gas chromatographic analysis, the crude products were treated by ordinary methods, but only small amounts of viscous brownish red liquid products were obtained, and no adipic acid was isolated. Isolation of cyclohexene oxide was unsuccessful, however gas chromatographic analysis based on the two columns showed clearly the presence of cyclohexene oxide. Gaseous products included ethylene, 1,3-butadiene, carbon dioxide, and an unidentified C4 hydrocarbon in the ratio of 12 6 3 1. Trace amounts of other gaseous hydrocarbons were also detected, and any gaseous peroxy compound was not detected. These hydrocarbons were considered to be decomposition products of activated cyclohexene. 

The discussion above has pointed out some of the relationships between structure and concertedness in the decompositions of peroxy compounds and azo alkanes. Other structural variations have been investigated also, such as the effect of electron-donating and -withdrawing substituents and of geometry about carbon atoms at which radical character is developing. 

The most prevalent base-catalyzed reaction of an endoperoxide is the Kornblum-DeLaMare decomposition [97a] which leads to a hydroxy ketone by removal of a proton from the carbon adjacent to the peroxy linkage [9b,90b,97], The formation, in a basic solvent as acetone, of hydroxyfuranones 69 (Sch. 38) in the photo-oxygenation of a,a -unsubstituted furans might occur via a similar rearrangement [60e]. Attempts to induce asymmetry in endoperoxides with enantiotopic hydrogens or with chiral bases have led to moderate success [98]. The Et3N-catalyzed rearrangement of substituted cycloheptatriene endoperoxides 92 leads to... 

The abstraction of a hydrogen atom occurs preferentially at the tertiary carbon of the structure, leading to a polystyryl radical. This radical adds to oxygen to form a peroxy radical. By abstraction of another hydrogen atom, the peroxy radical leads to a hydroperoxide. Hydroperoxides have an IR absorption at 3450 cm-1. The decomposition of the hydroperoxide either by photolysis or by thermolysis gives an alkoxy radical that may react in several ways ... 

For monoalkyl benzenes, there is evidence of a second mechanism for hydrocarbon decomposition. Since substantial amounts of benzalde-hyde (representing a 5-25% yield) and traces (< 1% yield) of peroxy-benzoyl nitrate have been identified (10) in smog chamber experiments with aromatic hydrocarbons having at least two benzylic hydrogens, hydrocarbon oxidation apparently may occur at the a-carbon atom. Application of the usual Hammett treatment and electrophilic substituent constants (23) to any of our rate measurements for toluene, fert-butyl-benzene, and benzene indicates no linear Hammett relationship toluene... 

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 ... 

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