Manganese, atmospheric oxidation catalyzed

In fact, the earliest application of kinetic methods was to determine trace levels of substances exerting catalytic activity in oxidation-reduction reactions involving multiple electron transfers (1885-trace level V on its catalysis of the oxidation of aniline). For example, the reduced form of many triphenylmethane dyes is colorless , and loses two electrons on oxidation to the dye. The rate of reaction with such oxidants as 104 is relatively slow, but can be catalyzed by trace levels of transition metal ions which involve single electron transfer in their own redox steps. Thus, trace levels of manganese can be determined by the proportionality of the rate of oxidation of leuco-malachite green by iodate at less than micromolar concentrations. Similarly, trace levels of Cu ", < 10 M, can be determined from the catalytic effect on the atmospheric oxidation of ascorbic acid. Such systems can be written as a generalized redox reaction... 

The oxidation of ethylbenzene using iron-haloporphyrins in a solvent-free system under molecular oxygen at 70-110°C gives mixture of a-phenylethylhydroperoxide, methylphenylcarbinole, and acetophenone (1 1 1). The catalyst is (TPFPP=5,10,15,20-tetrakis (pentafluorophenyl) porphyrin). Ethylbenzene conversion does not more than 5%. The oxidation occurs via radical pathway [3 9]. The products of ethylbenzene oxidation with air under mild condition (T > 60°C, atmospheric pressure), catalyzed by [TPPFeJ O or [TPPMnJ O ( 0,-oxo dimeric metalloporphyrins, a,-oxo-bis(tetraphenylporphyrinato)iron (manganese)) without any additive are acetophenone and methylphenylcarbinole. The ethylbenzene oxidation is radical chain oxidation in this case also. The ketone/alcohol (mol/ mol) rations are 3.76 ([TPPMnJ O, ethylbenzene conversion - 8.08%), 2.74 ([TPPFe]20, ethylbenzene conversion - 3.73%) [40]. 

There has been recent interest in a somewhat different aspect of adsorption and reaction on metal oxides photocatalysis. The interest stems partially from that role that some transition-metal oxides can play in photochemical reactions in the atmosphere. Atmospheric aerosol particles can act as substrates to catalyze heterogeneous photochemical reactions in the troposphere. Most tropospheric aerosols are silicates, aluminosilicates and salts whose bandgaps are larger than the cutoff of solar radiation in the troposphere (about 4.3 eV) they are thus unable to participate directly in photoexcited reactions. However, transition-metal oxides that have much smaller bandgaps also occur as aerosols — the most prevalent ones are the oxides of iron and manganese — and these materials may thus undergo charge-transfer excitations (discussed above) in the pres-... 

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