Peroxide initiators relative efficiency

The reaction of certain derivatives of oxalic acid with hydrogen peroxide in the presence of a suitable fluorescer represents an early demonstration of a relatively efficient, non-enzymatic chemiluminescent system (Rauhut, 1969). Work in this area was initiated by the report of Chandross on the chemiluminescent reaction of oxalyl chloride and hydrogen peroxide in the presence of anthracene (Chandross, 1963). While in subsequent work Rauhut... 

Ideally all reactions should result from unimolecular homolysis of the relatively weak 0-0 bond. However, unimolecular rearrangement and various forms of induced and non-radical decomposition complicate the kinetics of radical generation and reduce the initiator efficiency.46 Peroxide decomposition induced by radicals and redox chemistry is covered in Sections 3.3.2.1.4 and 3.3.2.1.5 respectively. 

Initiator decomposition studies of AIBN in supercritical C02 carried out by DeSimone et al. showed that there is kinetic deviation from the traditionally studied solvent systems.16 These studies indicated a measurable decrease in the thermal decomposition of AIBN in supercritical C02 over decomposition rates measured in benzene. Kirkwood correlation plots indicate that the slower rates in supercritical C02 emanate from the overall lower dielectric constant (e) of C02 relative to that ofbenzene. Similar studies have shown an analogous trend in the decomposition kinetics ofperfluoroalkyl acyl peroxides in liquid and supercritical C02.17 Rate decreases of as much as 30% have been seen compared to decomposition measured in 1,1,2-trichlorotrifluoroethane. These studies also served to show that while initiator decomposition is in general slower in supercritical C02, overall initiation is more efficient. Uv-visual studies incorporating radical scavengers concluded that primary geminate radicals formed during thermal decomposition in supercritical C02 are not hindered to the same extent by cage effects as are those in traditional solvents such as benzene. This effect noted in AIBN decomposition in C02 is ascribed to the substantially lower viscosity of supercritical C02 compared to that ofbenzene.18... 

Although phospholipid bilayers are better mimics of biomembranes than are micelles, there are few reliable quantitative data on flavonoid antioxidant activities in lipid bilayers. Terao and coworkers compared the antioxidant efficiency of quercetin and catechins (epicatechin and epicatechin gallate) with that of a-Toc in egg yolk PC liposomes using initiation by the water-soluble initiator, ABAP, and analysis of hydroperoxide formation and antioxidant consumption by HPLC. Based on the length of the induction periods and the profile of suppressed hydroperoxide formation, they concluded that quercetin and the catechins were more efficient antioxidants than a-Toc in these bilayers. Apparently the unique behavior of a-Toc in bUayers is responsible for these results (vide supra). In hexane and alcohols solution during suppressed peroxidation of methyl linoleate, the relative antioxidant activities reversed so that the flavonoids were 5-20 times less active... 

The effect of an efficient tin maleate stabilizer on the formation of unsaturation and peroxides in PVC is unexpected. First, the additive has no inhibitory effect on the initial formation of unsaturation in the polymer (Figure 19(c)) and relative to the control without additive (Figure 2), the unsaturation actually increases. However it markedly retards the formation of further unsaturation and it completely eliminates the initial formation of peroxide. In the latter respect it is more effective than a typical ester lubricant (Wax E), and calcium stearate which do not inhibit peroxide formation although they retard its initial rate of formation. Both lubricants reduce the initial formation of unsaturation Wax E is more effective at 170°C than at 210°C, whereas the reverse is true with... 

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