Dialkyl peroxide formation

Final ozonides (FOZ), 716, 717, 718 cis and trans isomers, 719, 720 dialkyl peroxide formation, 706 IR spectroscopy, 719 mass spectrometry, 690 microwave spectroscopy, 721-3 molecular model, 750 NMR spectroscopy, 724-5 ozone water disinfection, 606 X-ray crystallography, 726-30 Fireflies... 

On the other hand, the persistence of the dialkyl peroxide indicates that it must not derive from a mechanism involving such oxidants. Indeed such dialkyl peroxides are readily formed by metal-catalyzed decomposition of alkyl hydroperoxides and involve alkoxy and alkylperoxy radicals. The mechanism for dialkyl peroxide formation shown below is adapted for FeTPA from previously proposed schemes ... 

Support for this hypothesis comes from the fact that the product distributions observed depended on the nature of the catalyst (Table 1). Indeed the proportion of dialkyl peroxide formed diminished as the ligands on the iron center became more electron donating. The increased electron density at the metal center should shift the redox potential of the metal center to more negative values and disfavor the reduction of the metal catalyst in either the initiation or termination steps of the dialkyl peroxide formation mechanism. 

Reaction conditions depend on the reactants and usually involve acid or base catalysis. Examples of X include sulfate, acid sulfate, alkane- or arenesulfonate, chloride, bromide, hydroxyl, alkoxide, perchlorate, etc. RX can also be an alkyl orthoformate or alkyl carboxylate. The reaction of cycHc alkylating agents, eg, epoxides and a2iridines, with sodium or potassium salts of alkyl hydroperoxides also promotes formation of dialkyl peroxides (44,66). Olefinic alkylating agents include acycHc and cycHc olefinic hydrocarbons, vinyl and isopropenyl ethers, enamines, A[-vinylamides, vinyl sulfonates, divinyl sulfone, and a, P-unsaturated compounds, eg, methyl acrylate, mesityl oxide, acrylamide, and acrylonitrile (44,66). 

There are much fewer data for the dialkyl peroxides. The gas phase enthalpy of formation difference between the diethyl and dibutyl peroxides of about 40 kJ moH per methylene group is about twice that of the normal methylene increment of ca 21.6 kJmoH. The 219 kJmoH enthalpy of formation difference between the di-fert-butyl and di-fert-amyl peroxide is so large as to be incredible. 

FIGURE 1. Enthalpies of formation of alkyl hydroperoxides and dialkyl peroxides Vi. number of carbon atoms (Iq, kJ mol )... 

Of the five dialkyl peroxides with enthalpy of formation data, only those of unquestioned accuracy, dimethyl, diethyl and ferf-butyl peroxide, are included in the analysis. The enthalpies of the formal hydrogenolysis reaction 6 are remarkably consistent for the methyl, primary and tertiary compounds -335.0 2.9 kJmoR for the liquid (using the estimated enthalpy of vaporization for dimethyl peroxide) and -279.5 3.5 kJmoR for... 

As was the case for the alkyl hydroperoxides in reaction 4, the enthalpies of the oxy-gen/hydrocarbon double exchange reaction 8 for dialkyl peroxides are different depending on the classification of the carbon bonded to oxygen. For R = Me, Et and f-Bu, the liquid phase values are —4, 24.6 and 52.7 kJmoR, respectively, and the gas phase values are 0.1, 25.7 and 56.5 kJmoR, respectively. For the formal deoxygenation reaction 9, the enthalpies of reaction are virtually the same for dimethyl and diethyl peroxide in the gas phase, —58.5 0.6 kJ moR. This value is the same as the enthalpy of reaction of diethyl peroxide in the liquid phase, —56.0 kJ moR (there is no directly determined liquid phase enthalpy of formation of dimethyl ether). Because of steric strain in the di-ferf-butyl ether, the enthalpy of reaction is much less negative, but still exothermic, —17.7 kJmol (Iq) and —19.6 kJmol (g). 

The enthalpies of reaction 16 for solid and gaseous dibenzoyl peroxide are —45.8 and —47.3 kJmoU, respectively. These values are much smaller than those calculated for the liquid dialkyl peroxides ca —56 kJmoU ), the acyl peresters ca —70 kJmoU ) or the non-aromatic diacyl peroxides (—89 or —59 kJmol ). However, we have no reason not to accept the result. It would be futile to use this result for further calculations concerning the solid phase enthalpies of formation of bis(o-toluyl) peroxide, bis(p-toluyl) peroxide and dicinnamoyl peroxide because all the peroxide and the anhydride product enthalpy of formation data are from the same suspect source . 

About 30 years ago, an enthalpy of formation was reported for 3,3,4,4-tetramethyl-l,2-dioxetane . Both by direct microcalorimetric combustion measurements of the neat solid and by reaction calorimetry (of the solid itself, and in acetone solution to form acetone), a consensus value was derived. Now, is the enthalpy of formation plausible , notwithstanding the very large error bars Consider reaction 6 for the dioxetane that produces 2,3-dimethyl-2,3-butanediol . The liquid phase enthalpy of reaction is —329 kJmoU. It is remarkable that this value is compatible with that for the dialkyl peroxides, ca —335 kJmoU, despite the ring strain that might be expected. 

The dialkyl denomination also includes cyclic peroxides (endoperoxides). The most significant route for peroxide formation is probably that of autoxidation of organic materials, leading to their gradual degradation. Although hydroperoxides are the main products of this process, also peroxyesters are formed, as is the case, for example, of isoprostane bicyclic endoperoxides (25) mentioned in Section II.A.2.C. 

The group value of 0-(0)(C) calculated from the dialkyl peroxides gives a value of —57.1 kcal. per mole for the heat of formation of tert-BuOOH, compared with the measured value (11) of —52.3 kcal. per mole. Since the calculated value is more negative, one cannot account for the difference by the otherwise reasonable assumption that the hydroperoxide decomposed a little prior to combustion. An alternative would be that group additivity did not apply to the hydroperoxides, but Benson s... 

The reaction of Pt02(PPh3)2 with alkyl halides results in the formation of alkylperoxo complexes, presumably via an SN2 nucleophilic attack of the terminal oxygen on the carbon atom, and occurs with inversion of configuration.44 Addition of excess alkyl halide to the alkylperoxo complex results in the formation of the dialkyl peroxide (equation 4S).44... 

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