Thiols, polymer-bound, oxidations

For example, the cobalt(II) complex for phthalocyanine tetrasodium sulfonate (PcTs) catalyzes the autoxidation of thiols, such as 2-mercaptoethanol (Eq. 1) [4] and 2,6-di(t-butyl)phenol (Eq. 2) [5]. In the first example the substrate and product were water-soluble whereas the second reaction involved an aqueous suspension. In both cases the activity of the Co(PcTs) was enhanced by binding it to an insoluble polymer, e.g., polyvinylamine [4] or a styrene - divinylbenzene copolymer substituted with quaternary ammonium ions [5]. This enhancement of activity was attributed to inhibition of aggregation of the Co(PcTs) which is known to occur in water, by the polymer network. Hence, in the polymeric form more of the Co(PcTs) will exist in an active monomeric form. In Eq. (2) the polymer-bound Co(PcTs) gave the diphenoquinone (1) with 100% selectivity whereas with soluble Co(PcTs) small amounts of the benzoquinone (2) were also formed. Both reactions involve one-electron oxidations by Co(III) followed by dimerization of the intermediate radical (RS or ArO ). 

Table L Oxidation of Polymer-Bound Thiols to Disulfides ...

Scheme 12.8). In the reaction, N9-substituted 2-halo-6-chloropurine 22 or 28 was captured by a resin at the C6 position. Subsequent substitution at the C2 fluoro/iodo position formed resin 24 or 30. The thiol group on 24 and 30 was then oxidized to give sulfone 25 and 31. 2,6,9-Trisubstituted purine derivatives 26 and 32 were then released by C6 substitution with amines and anilines. This approach allows diverse substitution with primary, secondary, and cyclic amines at the C2 position. With the oxidation of the thiol linker just before the cleavage, only the activated polymer-bound purine intermediates 25 and 31 will be released, thus resulting in high purity of the final product. 

Polymer-supported catalysts often have lower activities than the soluble catalysts because of the intraparticle diffusion resistance. In this case the immobilization of the complexes on colloidal polymers can increase the catalytic activity. Catalysts bound to polymer latexes were used in oxidation reactions, such as the Cu-catalyzed oxidation of ascorbic acid,12 the Co-catalyzed oxidation of tetralin,13 and the CoPc-catalyzed oxidation of butylphenol14 and thiols.1516 Mn(III)-porphyrin bound to colloidal anion exchange resin was... 

Chemical reactivity of QI is reflected in the complexity of chemical processes taking part in aging of unsaturated vulcanized rubbers [3,5,24,58], QI are oxidants and are transformed in high yields into the respective reduced formes, e.g. 11 or 83. From the point of view of the polymer stabilization, the process should be understood as regeneration of the AO/AF species. This was observed in the reaction with 2-mercaptobenzimidazole and other thiols during the vulcanization process [4,77], The majority of ArSH was bound to the arylene ring of the reduction product, e.g. in 88. 

Electrodes for voltammetry are usually made of solid or liquid metals [2, 3, 6], or from carbon [10]. Less frequently, metal oxides or polymers are used [11-15]. The primary metallic conductor may be covered with a thin film of a secondary conductor (e.g., mercury, or oxides and polymers) [9,13], or a monolayer of covalently bound foreign atoms or molecules such as thiols on gold substrate [16]. These are called chemically modified electrodes. The chemical preparation of the electrode... 

The oxidation of thiols to disulfides by dioxygen is catalyzed by cobalt phthalocyanine derivatives. The activity of cobalt phthalocyaninetetrasulfonate (66) is much higher when it is bound to a cationic polymer than it is in water. Cross-linked and soluble poly(vinylamine) added to aqueous (66) give rate enhancements by factors of 16 and 106 for oxidation of 2-mercaptoethanol. 

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