Oxidative addition photoactivated

Detailed studies of the mechanism of these reactions have been performed by Mattay and by Kochi . The former has shown that the endo/exo regiochemistry of the ring closure reaction can be controlled either by variation of the silyl group or by addition of polar molecules such as alcohols (probably the source of hydrogen in equations 37a-c). Based on solvent and salt effects, Kochi has proposed that the oxidation of enols to ketones in the presence of activated chloranil proceeds via photoactivation of chloranil which reacts with the silyl enolate through two competing pathways, namely oxidative elimination to the ketone and oxidative addition to the adduct 51 (equation 38). Non-polar solvents such as dichloromethane favour the oxidative eliminations, while polar solvents such as acetonitrile direct the reaction towards the oxidative addition. More strikingly. 

Oxidative addition to Mn(CO)j is also photoactivated. A competition study of substitution versus oxidative addition gave the results shown in Scheme 7.11. The constancy of the oxidative addition yield suggests that this path may involve an ion pair. Unfortunately, the concentration of PPh4+ was not varied to test this hypothesis. 

A more complex system which involves the photoactivated oxidative addition of benzene to Rh(PMe3)2(CO)Cl is outlined in Scheme 7.20. The system is unusual in having two photoactivated steps and the general reactions shown are based on the observations of Field and Goldman and their co-workers. The oxidative addition yields two isomers the one with the CO and Ph cis to each other is photoactivated to give CO insertion in competition with return to reactants. In the presence of CO, the acyl intermediate reacts by CO addition and reductive elimination to give benzaldehyde and the catalyst. 

Combined effect of additives—photoactivators and activators of oxidation, which together facilitate breakdown of chain... 

In addition to these principal commercial uses of molybdenum catalysts, there is great research interest in molybdenum oxides, often supported on siHca, ie, MoO —Si02, as partial oxidation catalysts for such processes as methane-to-methanol or methane-to-formaldehyde (80). Both O2 and N2O have been used as oxidants, and photochemical activation of the MoO catalyst has been reported (81). The research is driven by the increased use of natural gas as a feedstock for Hquid fuels and chemicals (82). Various heteropolymolybdates (83), MoO.-containing ultrastable Y-zeoHtes (84), and certain mixed metal molybdates, eg, MnMoO Ee2(MoO)2, photoactivated CuMoO, and ZnMoO, have also been studied as partial oxidation catalysts for methane conversion to methanol or formaldehyde (80) and for the oxidation of C-4-hydrocarbons to maleic anhydride (85). Heteropolymolybdates have also been shown to effect ethylene (qv) conversion to acetaldehyde (qv) in a possible replacement for the Wacker process. 

PO can be made degradable by means of additives. The types of additives include aromatic ketones (benzo-phenone and substituted benzophenones [47], qui-none), aromatic amines (trisphenylamine), polycyclic aromatic hydrocarbons (anthracene, certain dyes such as xanthene dyes), or transition metal organic compounds. The transition metal compounds of Fe, Co, Ni, Cr, Mn are widely used. Organo-soluble acetyl acetonates of many transition metals are photooxidants and transition metal carboxylates are also thermal pro-oxidants. Co acetylacetonate appears to be an effective catalyst for chemical degradation of PP in the marine environment. The preferred photoactivator system is ferric dibutyldithiocarbamate with a concentration range of 0.01. 1%. Scott has patented the use of organometallic compounds hke iron (ferric) dibutyldithiocarbamate or Ni-dibutyl-dithiocarbamate [48]. Cerium carboxylate [49] and carbon black are also used in such materials [50]. 

USA) own products additive system ing films, wide use anticipated photoactivators and activators of oxidation (ferric thiolates, sometimes with other metal thiolates (in polyethylene)). ... 

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