As -reducing organisms

Before the arrival of humanity, the longer-term controls were burial of carbon as carbonate, as methane hydrate in sediment, as gas, as coal, or as reduced organic matter (including charcoal). Before the Devonian, fire would have been impossible, except perhaps on lightning-hit microbial peat bogs after drought. 

Reduction of PTM radicals with ascorbic acid. It is quite remarkable that, while the radical PTM- withstands highly reactive reagents as well as reducing organic compounds such as glucose and oxalic acid, nonetheless it is converted rapidly to PTM—H with ascorbic acid (AS) in aqueous (10%) THF at room temperature (Ballester et al., 1978d M. Ballester, J. Riera and M. Casulleras, unpublished). Dehydroascorbic acid (DAS) is isolated, and the stoichiometry requires 1 mol of AS per 2 mol of PTM-. This reduction... 

Solutions of alkali metals in liquid ammonia are used in organic chemistry as reducing agents. The deep blue solutions effectively contain solvated electrons (p. 126), for example... 

Oxidation and chlorination of the catalyst are then performed to ensure complete carbon removal, restore the catalyst chloride to its proper level, and maintain full platinum dispersion on the catalyst surface. Typically, the catalyst is oxidized in sufficient oxygen at about 510°C for a period of six hours or more. Sufficient chloride is added, usually as an organic chloride, to restore the chloride content and acid function of the catalyst and to provide redispersion of any platinum agglomeration that may have occurred. The catalyst is then reduced to return the metal components to their active form. This reduction is accompHshed by using a flow of electrolytic hydrogen or recycle gas from another Platforming unit at 400 to 480°C for a period of one to two hours. 

The diffraction mechanisms in XPD and AED are virtually identical this section will focus on only one of these techniques, with the understanding that any conclusions drawn apply equally to both methods, except where stated otherwise. XPD will be the technique discussed, given some of the advantages it has over AED, such as reduced sample degradation for ionic and organic materials, quantification of chemical states and, for conditions usually encountered at synchrotron radiation facilities, its dependence on the polarization of the X rays. For more details on the excitation process the reader is urged to review the relevant articles in the Encyclopedia and appropriate references in Fadley. ... 

Prechlorination (before the clarifier) significantly improves the removal of organics as well as reducing the coagulant demand. 

A modified procedure" uses activated zinc together with dry gaseous hydrogen chloride in an organic solvent, e.g. acetic acid, as reducing agent. Under those conditions the reaction occurs at lower temperatures as with the original procedure. 

As the organic or volatile material is reduced due to the batch distillation, the steam pressure rises during the progress of the operation due to the loss of the volatile material, and the decrease of pim- When the volatile material is stripped down to a low residual concentration, then Ps approaches the total system pressure, n. When the steam saturation pressure and temperature is greater than 7t, no steam condensation will occur during the operation. 

The blue samarium diiodide solutions are stable indefinitely in the absence of water and oxygen, and Sml and Ybl2 solutions have been employed as reducing agents in organic synthesis. 

The alkali metals also release their valence electrons when they dissolve in liquid ammonia, but the outcome is different. Instead of reducing the ammonia, the electrons occupy cavities formed by groups of NH3 molecules and give ink-blue metal-ammonia solutions (Fig. 14.14). These solutions of solvated electrons (and cations of the metal) are often used to reduce organic compounds. As the metal concentration is increased, the blue gives way to a metallic bronze, and the solutions begin to conduct electricity like liquid metals. 

We cover each of these types of examples in separate chapters of this book, but there is a clear connection as well. In all of these examples, the main factor that maintains thermodynamic disequilibrium is the living biosphere. Without the biosphere, some abiotic photochemical reactions would proceed, as would reactions associated with volcanism. But without the continuous production of oxygen in photosynthesis, various oxidation processes (e.g., with reduced organic matter at the Earth s surface, reduced sulfur or iron compounds in rocks and sediments) would consume free O2 and move the atmosphere towards thermodynamic equilibrium. The present-day chemical functioning of the planet is thus intimately tied to the biosphere. 

---