Iron photochemical reaction, effects

Sun, Y. and Pignatello, J.J. (1993) Photochemical reactions involved in the total mineralization of 2,4-D by iron(3+)/hydrogen peroxide/UV. Environ. Sci. Technol. 27, 304-310 Toepfer, B., Gora, A. and Li Puma, G. (2006) Photocatalytic oxidation of multicomponent solutions of herbicides Reaction kinetics analysis with explicit photon absorption effects. Appl. Catal. B Environ. 68,171-180... 

Many common metallic impurities in paper, particularly compounds of some of the transition metals, contribute to degradation of cellulose by hydrolytic or oxidative reactions. The more important in commercial papers are iron and copper compounds, whereas some others such as magnesium compounds have been observed to exert protective effects (7). It is clearly desirable that the content of undesired metallic ions be kept low in permanent papers. Titanium dioxide, commonly used as a filler, has been observed to promote degradation by photochemical reactions. The predictive potential of metallic content in relation to permanence, however, does not allow the setting of permissible limits at the present time. 

Fig. 8 Molecular orbital depiction of the concept of band-gap energies with corresponding molecular orbital transitions for the Fe(III) oxyhydroxides. The photon action spectra [134,230] for photochemical reactions [136,141,143] of the iron oxyhydroxides (i.e., a-Fe2C>3, a-FeOOH, /S-FeOOH and y-FeOOH) indicate that the most effective electron transition leading to photocatalysis or photoreduction is the O2- to Fe3+ transition shown schematically above...

Fc2(S04)3 is one of a number of iron(III) compounds which show a partial reversible change to iron(II) ions under high pressure [9]. The change is 15% complete at 25 kbar and 49% complete at 150 kbar. Presumably the energy barrier for ligand-to-Fe " electron transfer is sufficiently small for the pressure to lower the barrier to the point where thermal excitation can effect transfer. An analogy can be drawn with the better-known photochemical reactions of iron. 

Irradiation of different types oxidize AA both in aerobic and anaerobic conditions yielding different products (Douzou and Gallon, 1956). The effect of X- and y- irradiation is better than that of ultraviolet radiation in producing DHA and hydrogen peroxide (Babin et al., 1955 Babin and Delmon, 1955 Pukhav, 1957 Douzou, 1956 1958). Presence of metal ions, especially iron as well as oxygen accelerated the photochemical reaction (Baker, 1955 Baker et al., 1955 ... 

The photochemical reaction of Group VI metal hexacarbonyls with mono-enes was studied several years ago, but only recently has the reaction of one of the hexacarbonyls, W(CO)s in fact, with conjugated dienes been investigated. The W(CO)6 proves to be an effective catalyst for cis trans isomerization of such dienes compounds of the type W(CO)6(diene), which must act as intermediates in such isomerizations, have been isolated and their reactions studied. Under normal conditions iron pentacarbonyl reacts with acetylene to produce a complicated mixture of products, but under irradiation in an argon matrix at — 256 °C the product is but-l-en-3-yne, complexed to the iron through the carbon-carbon triple bond only. This iron-alkyne-carbonyl compound is presumably an intermediate in the reaction under normal thermal conditions. In an argon matrix at — 256 C, iron pentacarbonyl reacts with ethylene to give Fe(CO)4(QH4). ... 

In 1981, the first report on the sonochemistry of discrete organometallic complexes demonstrated the effect of ultrasound on iron carbonyls in alkane solutions (174). The transition metal carbonyls were chosen for these initial studies because their thermal and photochemical reactivities have been well characterized. The comparison among the thermal, photochemical, and sonochemical reactions of Fe(CO)5 provides an excellent example of the unique chemistry which homogeneous cavitation can... 

This change, which proceeds at a measurable rate, has been utilised in quantitative determinations of the intensity of light—so-called actinometric measurements. The sensitiveness of the reaction, however, is largely dependent upon the purity of the salts, traces of iron salts increasing the sensitiveness in proportion to the amount of iron—provided the amount is very small. Indeed, there is reason to believe that if the solution were entirely free from iron no photochemical effect would be observed.1... 

Decomplexation of ArCr CO)3. The chromium carbonyl complexes of arenes are useful for activation of the aryl group to nucleophilic attack (6, 28, 125-126 7, 71-72). Decomplexation has been effected with iodine or by photochemical oxidation with destruction of the expensive Cr(CO)3 unit. A more recent method involves reflux with pyridine to form Py3-Cr(CO)3 in yields of 70-100%. The pyridine complex in the presence of BF3 can be reused for preparation of ArCr(CO)3. Isomerization of 1,3-dienes. Ergosteryl acetate (1) is isomerized by chromium carbonyl to ergosteryl 83 acetate (2) in 81% yield. Under the same conditions ergosteryl 83 acetate (3) is isomerized to ergosteryl 81 acetate (4). 80th reactions involve isomerization of a cisoid diene to a transpid diene. In contrast iron carbonyl isomerizes steroidal transoid 3,5- and 4,6-dienes to 2,4-dienes. ... 

In aspect of its toxicity, any pathway leading to abatement of chromate(VI) pollution arouse a vivid interest. One of such pathways seems to be created by cooperations between the iron and chromium photocatalytic cycles, which were reported as effectively converting chromate(Vl) into Cr(III) species. Photochemical coupling reactions between polycarboxylate Fe(III) complexes and chromate(Vl) were studied and strong collaboration between both photocatalysts was demonstrated, which was significantly affected by the oxygen concentration (16,17,95,261). On the other hand, chromium(Vl) reduction pho-toinduced by iron(lll) nitrilotriacetate accompanied by nta degradation was found to be independent of the O2 concentration, whereas the oxidation state of the chromium product depended on the pH (257). 

As mentioned above, a 1 1 stoichiometric relationship between the photooxidized donor, P700 and the reduced terminal acceptors has not yet been established for the PS-I reaction center. As previously noted, the total amount of the recognized terminal acceptors reduced at 15 K is, on average, approximately 74% of the P700 photooxidized. Even more intriguing, in the reconstituted PS-I complexes from either the Cys-14->Asp or Cys-51->Asp mutant PsaC protein, the extent of photoreduction of each intact iron-sulfur cluster at 15 K remained nearly the same as in the wild-type preparation. The presence of the other cluster that was made photochemically inactive by site-directed mutagenesis apparently had no effect on the behavior of the unaltered cluster. 

Like iron complexes, copper complexes have been shown to be an important sink for photochemically-generated superoxide in seawater and, based on the high reactivity of Cu(ii) complexed by cyanobacterial-derived ligands, it is likely that redox reactions with superoxide significantly influence Cu redox speciation in the ocean [221,222]. These reactions also have important effects on the steady state concentrations of superoxide in seawater, reducing the concentration by at least an order of magnitude compared to previous estimates that ignored the reactions with copper complexes [222]. 

Another explanation was the following. The organomontmorillonite used was a natural montmorillonite that contained iron. Chemical analysis of the clay confirmed the presence of a low amount of iron. It was recalled that iron and, in more general terms, metals are likely to induce the photochemical degradation of polymers. Iron at low concentration had a prooxidant effect that was due to the metal ion of iron that can initiate the oxidation of the polymer by the well-known redox reactions with hydroperoxides [93]. It was concluded that the transition metal ions, such as Fe, displayed a strong catalytic effect by redox catalysis of hydroperoxide decomposition, which was probably the most usual mechanism of filler accelerating effect on polymer oxidation. A characteristic of such catalytic effect was that it did not influence the steady-state oxidation rate, but it shortened the induction time. 

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