Peroxy-catalysed

Patent applications [101, 102] show accelerated compositions in which quinones such as anthraquinone, benzoquinone, 2-phenylbenzoquinone, orthoquinone and substituted benzoquinone are the preferred accelerators. This is novel because quinones are usually stabilisers in peroxy-catalysed adhesive systems. Such compositions give high adhesive strengths on PP after 3-hour curing at room temperature. Patent [103] uses chlorosulfonated PE as an accelerator. Patent [104] is Dow s first departure from exclusively... 

These materials are very easily autoxidised and often have a low autoignition temperature. It is reported that many of the less volatile liquid aldehydes will eventually inflame if left exposed to air on an absorbent surface. The mechanism is undoubtedly similar to that giving rise to easy ignition in the air-oxidation of acetaldehyde and propionaldehyde initial formation of a peroxy-acid which catalyses the further oxidation[l]. Autoignition temperatures of lower aldehydes are much reduced by pressure, but appear to depend little on oxygen content. The effect is worst in the presence of free liquid, in which initial oxidation appears to occur, possibly catalysed by iron, followed by ignition of the vapour phase [2], An acetaldehyde/rust mix exploded at room temperature on increasing the air pressure to 7 bar. 

Lipase has been employed to prepare peracids, usually in situ.m The lipase catalysed peracid production from carboxylic acids has been used for the mild epoxidation of alkenes.109 A number of immobilized lipases exist, including one from Candida Antarctica (Novozym 435), which catalyses the conversion of fatty acids to peroxy fatty acids.110... 

On the basis of theoretical studies by Bach and co-workers,17 it was found that the nucleophilic 71-bond of the alkene attacks the 0-0 cr-bond in an Sn2 fashion with displacement of a neutral carboxylic acid. There are, however, some mechanistic anomalies. For example, a protonated peracid should be a much more effective oxygen transfer agent over its neutral counterpart, but experiments have shown only modest rate enhancements for acid catalysed epoxidation. Early attempts to effect acid catalysis in alkene epoxidation where relatively weak acids such as benzoic acid were employed proved unsuccessful.18 The picture is further complicated by contradictory data concerning the influence of addition of acids on epoxidation rates.19 Trichloroacetic acid catalyses the rate of epoxidation of stilbene with perbenzoic acid, but retards the rate of a double bond containing an ester constituent such as ethyl crotonate.20 Recent work has shown that a seven-fold increase in the rate of epoxidation of Z-cyclooctene with m-chloroperbenzoic acid is observed upon addition of the catalyst trifluoroacetic acid.21 Kinetic and theoretical studies suggest that the rate increase is due to complexation of the peroxy acid with the undissociated acid catalyst (HA) rather than protonation of the peroxy acid. Ab initio calculations have shown that the free energy of ethylene with peroxy-formic acid is lowered by about 3 kcal mol-1 upon complexation with the catalyst.21... 

Figure 3.49 Acid- and base-catalysed Baeyer-Villiger oxidation of ketones with peroxy-gen compounds.

Toluene has been oxidized by the silver ion catalysed reaction with peroxy-disulfate. The reaction produces a mixture of bibenzyl, benzaldehyde and benzoic acids.299 Russian workers have described the conversion of 4-methoxy-toluene to the benzaldehyde by oxidation with peroxydisulfate in the presence of silver or copper ions and oxalic acid.300 The presence of copper salts in iron or copper catalysed peroxydisulfate oxidation is believed to suppress side-reactions.301 Phillips have patented a palladium(II)/tin(IV)/persulfate system for the oxidation of toluene derivatives.302 The reactions are carried out in carboxylic acid solvents (Figure 3.78). 

The formation of peroxides is effectively a chain termination reaction, as under most conditions these peroxides can act as effective sinks for HO . In more polluted conditions (high-NO ), peroxy radicals catalyse the oxidation of NO to NO2... 

The ultimate products of the oxidation of any hydrocarbon are carbon dioxide and water vapour, but there are many relatively stable partially oxidised organic species such as aldehydes, ketones and carbon monoxide that are produced as intermediate products during this process, with ozone produced as a by-product of the oxidation process. Figure 10 shows a schematie representation of the free radical catalysed oxidation of methane, whieh is analogous to that of a hydrocarbon. As previously discussed, the oxidation is initiated by reaction of the hydrocarbon with OH and follows a mechanism in with the alkoxy and peroxy radicals are chain propagators and OH is effectively catalytic, viz... 

Basu S. Radioimmunoassay of 8-iso-prostaglandin F2alpha an index for oxidative injury via free radical catalysed lipid peroxi- 27. dation. Prostaglandins Leukot. Essent. Fatty Acids 1998 58 319. 

The dual role of transition metals as either prodegradant or stabilizer is rationalized by the observation that the free-radical chemistry which dominates depends on the concentration of the metal ion. At low concentrations Cu I/Cu II may be a pro-oxidant, whereas at high concentrations it may be a stabilizer. The explanation lies in the complexation of hydroperoxides with transition metals (Black, 1978). Thus, taking the example of Co II/Co III, the reactions in Scheme 1.71 are recognized (Black, 1978), which together give the usual reaction for the metal-catalysed bimolecular decomposition of hydroperoxides to alkyl peroxy and alkoxy radicals. 

Both oxidation pathways, the NOs catalysed oxidation of S(IV) by molecular oxygen and the oxidation of S(IV) by peroxy nitric acid lead to the formation of sulphate anions and further studies are required to decide, which of the two pathways is the mot important (or... 

The performance of ZnDTP as an antioxidant is a complex interaction pattern involving hydroperoxides and peroxy radicals. The performance matrix is additionally influenced by other additives present in industrial or engine oil formations. In a model system comprising cumene hydroperoxide and diverse ZnDTPs, it was demonstrated that the antioxidant mechanism proceeds by an acid-catalysed ionic decomposition of the hydroperoxide. The catalyst species is (9,0 -dialkyl-hydrogendithiophosphate, (RO)2PS2H, derived from the ZnDTP, Reaction (4.57) ... 

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