Carbon monoxide as a reducing agent

As we saw in Section 20.2, the reduction of iron oxides is accomplished by using carbon monoxide as a reducing agent. Starting with coke in a blast furnace, the following equilibrium plays a key role in the extraction of iron ... 

The reducticn of metal oxides is often accomplished using carbon monoxide as a reducing agent. Carbon (coke) and carbon dioxide are usually present, leading to the following reaction ... 

It can be prepared by carbonylation of chromium chloride with carbon monoxide using a reducing agent such as lithium aluminium hydride (LAH). 

The sihcates formed in reactions 2 and 3 fuse with the added fluxes to form a Hquid slag at which point carbon monoxide loses its effectiveness as a reducing agent. Unreacted carbon from the fuel then becomes the predominant reductant in reducing both staimous siUcate to tin and ferrous siUcate to iron. The metallic iron, in turn, reduces tin from stannous siUcate ... 

Silicon is generally considered to be a congener of carbon and this is also reflected in the evolution of silicon as a reducing agent for metal oxides. Silicon forms a fairly stable solid oxide silica or silicon dioxide (Si02) and also a stable gaseous oxide silicon monoxide (SiO), both of which can be useful in oxide reduction reactions. 

Carbon monoxide is also useful as a reducing agent. It is used in metallurgy to obtain metals from their oxides. For example, during iron and steel production coke in a blast furnace is converted to carbon monoxide. The carbon monoxide reduces the Fe3+ in the iron (III) oxide contained in the iron ore to produce elemental iron according to the reaction Fe20... 

Formate. Sodium formate, [CAS 141-53-7]. NaCllCb, white solid, soluble, formed by reaction of NaOH and carbon monoxide under pressure at about 20(fU. Used (I) as a source of formate and formic acid, (2) as a reducing agent in organic chemistry. (3) as a mordant in dyeing. 

Here we consider carbon monoxide as a chemical reducing agent, with the oxidation product being C02 in all cases. Carbon monoxide may act as a reductant in three different ways (1) as a direct oxygen atom acceptor (2) as a two-electron reductant with water as the source of oxygen and (3) as an indirect reductant in which the reducing power of CO is used to make H2 which then carries out the desired reduction. The three ways are shown schematically as (24)-(26) (in (24) [O] represents an oxide source). Equation... 

Carbon monoxide frequently results when carbon is used as a reducing agent. For example, the reactions... 

In basic aqueous solution, coordinated carbon monoxide can act as a reducing agent with carbonate being the oxidation product for the case of a mononuclear compound undergoing a two-electron reduction (equation 39). 

In Eq. 15.7 the carbon monoxide itself is acting as a reducing agent. 

Iron is seldom found in the elemental form needed to make steel. Metallic iron must be separated and purified from iron ore—usually hematite, Fe203. This process takes place in a blast furnace in a series of redox reactions. The major reaction in which iron ore is reduced to iron metal uses carbon monoxide gas as a reducing agent. 

Carbon monoxide oxidation and reduction reactions invariably involve a change in the oxidation state of carbon. The only oxidation product of CO is COj (or carbonate if carried out in base), and it is produced in a number of different reactions which rely on CO as a reducing agent. One of these is the water gas shift (WGS) reaction, equation... 

By using pyridine as the solvent and magnesium/zinc as a reducing agent, NbCl can be carbonylated to the [Nb(CO)6] anion at room temperature and at atmospheric pressure of carbon monoxide. The method does not require the use of the hazardous alkali metals and gives better yields than the ones reported earlier. 

Et4.N)[Fe(NS3)(CO)] is also formed (Figure 4) if [Fe(acac)3] is treated with H3(NS3) in presence of tetraethylammonium acetate under an atmosphere of carbon monoxide, when the excess of H3(NS3) acts as a reducing agent. If the tetraethylammonium acetate is omitted, a complex of stoichiometry Fe3(NS3)2(CO)2 and structure [Fe(Fe(NS3)(CO) 2-5, S"] (Figure 5) with a linear trinuclear Fe3S4 core is isolated. The value of v(CO) in the spectrum of this trinuclear compound is 1938 cm The following equilibrium holds in methanol, and can be demonstrated by the reversible uptake of CO. 

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