Degradation metal-catalysed

In summary, the uncatalysed oxidation of hydrocarbons at temperatures of up to 120°C leads to alkylhydroperoxides, ROOH, dialkylperoxides, ROOR, alcohols, ROH, aldehydes, RCHO and ketones, RR C=0. In addition, cleavage of a dihydroperoxide II of Reaction (4.4) leads to diketones, RCO(CH2)jCOR keto-aldehydes, RCO(CH2)jCHO, hydroxy ketones, RCH(OH)-(CH2)jCOR and so forth. Under metal-catalysed conditions or at higher temperatures, considered in Sections 4.2.2 and 4.2.3, degradation leads to a complex mixture of final products. 

Acrylic, nylon and polyester are especially susceptible to hydrolysis and metals, such as iron and copper, catalyse this degradation. Metal impurities which are present as a result of the manufacturing process, or in a composite material, accelerate degradation. Many polymers are alkali and acid sensitive, and acid can cause the hydrolysis of polymer chains. Organic vapours and fumigants can dissolve or swell plastics. 

CA has been widely nsed to copy cinema film images off old supports of CA or CN. However, much of the film stock used has deteriorated severely by metal-catalysed degradation and hydrolysis of the polymer (Allen et al., 1992), the vinegar syndrome . The predicted lifetime of many CA films is c. 40 years, depending on the manufacture and storage conditions (Adelstein et al., 2002). 

Is degradation catalysed by any metals which could be present in the processing machinery ... 

The action of certain metals (e.g., copper) on unsaturated rubbers, primarily natural rubber, is to catalyse the oxidative degradation of the polymer. The metal must be in an ionic form, i.e., straightforward contact with the metal such as a seal with a copper pipe will not promote such degradation. 

Transition metals (iron, copper, nickel and cobalt) catalyse oxidation by shortening the induction period, and by promoting free radical formation [60]. Hong et al. [61] reported on the oxidation of a substimted a-hydroxyamine in an intravenous formulation. The kinetic investigations showed that the molecule underwent a one-electron transfer oxidative mechanism, which was catalysed by transition metals. This yielded two oxidative degradants 4-hydroxybenzalde-hyde and 4-hydroxy-4-phenylpiperidine. It has been previously shown that a-hydroxyamines are good metal ion chelators [62], and that this can induce oxidative attack on the a-hydroxy functionality. 

The P H HP NMR picture of CO/ethene copolymerisation in MeOH is exemplified by the sequence of variable-temperature spectra shown in Figure 7.6 relative to a reaction catalysed by [Pd(TFA)2(dppp)]. It has been observed that the intensity of the P NMR signal decreases with time, which is apparently due to the irreversible reductive degradation of Pd" species to Pd metal [5b, c]. 

The results prompted Jefford and coworkers to re-examine the iron(II) degradation of artemisinin in aqueous acetonitrile with iron(II) chloride (Scheme 10), a system they suggested was closer to the physiological conditions than iron(II) bromide in THF. They reported that iron(II) chloride catalysed isomerization of artemisinin to afford the same products identified by Posner (13 and 21), except that deoxyartemisinin 3 was not observed. When the reaction was carried out in the presence of cyclohexene, none of the expected epoxide was produced, which suggested (in sharp contrast to Posner s results) that a high-valent metal oxo species was not involved. 

Furthermore, the possibility of degradation effects should be taken into account. Oxidation reactions occurring at Cu surfaces are known to produce metal salts and complexes which are supposed to diffuse into the polymer matrix and may impair the interfacial strength [209]. Furthermore, it was suggested that Cu may induce the polymerisation of non-catalysed DGEBA [209]. Presumably, the oxides CuO and Cu20 are of major importance for these effects. 

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