Reduction-oxidation chemistry scale

Two processes, developed for the direct processing of lead sulfide concentrates to metallic lead (qv), have reached commercial scale. The Kivcet process combines flash smelting features and carbon reduction. The QSL process is a bath-smelting reactor having an oxidation 2one and a reduction 2one. Both processes use industrial oxygen. The chemistry can be shown as follows ... 

When specifically labelled compounds are required, direct chemical synthesis may be necessary. The standard techniques of preparative chemistry are used, suitably modified for small-scale work with radioactive materials. The starting material is tritium gas which can be obtained at greater than 98% isotopic abundance. Tritiated water can be made either by catalytic oxidation over palladium or by reduction of a metal oxide ... 

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid ... 

The biotransformations of sulfur compounds by microorganisms can have large-scale impacts on global chemistry. As an example, sulfate-reducing bacteria have, throughout histoiy, formed major deposits of elemental sulfur and iron sulfides on Earth, and these processes are continuing today (1). Contemporary sulfate-reduction coupled with the oxidation of reduced inorganic sulfur... 

The transformation of alcohols into aldehydes and ketones is of paramount importance in organic chemistry, both for laboratory-scale experiments and in the manufacturing processes (1). Unfortunately, the vast majority of the common oxidants have to be used at least in stoichiometric amount. Moreover, they are usually hazardous or toxic and generate large quantities of noxious by-products (2). Whilst many ecologically benign processes have been developed for the reduction of carbonyl derivatives (5), similar procedures have been far less investigated for the oxidation of alcohols (4). 

A reaction in which the oxidized or reduced form of a compound isomerizes via a first-order process on the voltammetric time-scale is common for a wide range of organometallic and organic compounds (for example Bard etal., 1973 Bond et al., 1986,1988,1992). An example from the field of organic chemistry involves the reduction of diethyl maleate to its radical anion which then isomerizes to the diethyl fumarate anion, again an overall EC mechanism (Bard et al., 1973). There is a wide range of examples of other EC mechanisms such as the reduction of the antibiotic chloramphenicol in which a nitro unit (-NO2) is reduced to a hydroxylamine (-NHOH) (E step) which rapidly converts into a nitroso (-NO) species (C step) (Kissinger and Heineman, 1983). 

The method using a diaphragm is suitable to the basic research for small-scale reactions, whereas it is not always convenient for synthetic chemistry. Anodic oxidation is often carried out without using die diaphragm, while it is gener ly necessary for cadiodic reduction. 

Robert A.W. Johnstone, Ph.D., is a full professor in the Department of Chemistry at the University of Liverpool, Liverpool, U.K. He possesses a D.Sc., a Ph.D., and a B.Sc. in chemistry. He is also a Fellow of The Royal Society of Chemistry (FRSC). An author and contributor to several books. Dr. Johnstone has published over 200 journal papers in natural product chemistry, catalysis in oxidation and reduction, and spectroscopy. His work has resulted in several new synthetic procedures in organic chemistry that are widely used and have provided some 30 full patents. Part of his research with industry led to a Queen s Award for Technological Achievement, an award not usually given to industrial and business enterprises and not normally given to university staff. The award concerned large-scale manufacture of an important ingredient of timber preservative by a new catalytic method, which produces about 30001 per annum of the product. Apart from his career... 

Excluded here are those techniques relating to tracer-level work (below weighable quantity of sample measurement by radioassay only), for the concern here will be with the determination of bulk properties of these elements. Tracer-scale studies usually reveal directly only one property of the element under investigation, that is, its relative preference for one environment over another, or more simply, its phase distribution. Nevertheless, as each new transuranium element was discovered and was available only in trace quantities, a great deal of chemistry was learned by inference from tracer-scale studies, including the identity of oxidation states, approximate values of oxidation or reduction potentials, the composition and stability of complex ions, and relative volatilities. 

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