Reduction by alkali metals

Chemical reduction by alkali metals leads to solid fullerides which are sometimes solvated. 

Side reactions can be partly cut down when the reduction by alkali metals is carried out in the presence of proton donors such as triphenylmethane, fluorene, or secondary amines ( -alkyanilines). The products of the initial... 

A rich variety of reagents and methods have been applied to generate radical ions. As illustrated above, the first methods were chemical redox reactions. Radical anions have long been generated via reduction by alkali metals. Because of the high reduction potentials of these metals, the method is widely applicable, and the reductions are essentially irreversible. 

From a synthetic objective it is unfortunate that attempts to produce the dianion of OFCOT by various reduction procedures have not resulted in a stable dianion. Although the organic decomposition products resulting from reduction by alkali metals or sodium naphthalenide are unknown, fluoride ion is produced (126). However, the nine-7t-electron radical anion has been produced at low temperatures by y irradiation of OFCOT, and electron spin resonance (ESR) spectroscopy indicates that it possesses the anticipated planar delocalized D8b structure 55 (127). The unavailability of the dianion... 

Yb 2 --r2 7 Reduction by alkali metal amalgam, FeCl3 added [96]... 

The reduction by alkali metals of Ge, Sn, and Pb salts in liquid ammonia or in the presence of hexamethylphosphoramide or cryptands has allowed the isolation of... 

Many aromatic compounds can undergo one-electron reduction by alkali metals, such as Na and Li. For example, the reaction of naphthalene with sodium in an aprotic solvent gives the naphthalene radical anion - sodium ion salt. 

The other applications are mercury reduction by sodium borohydride (NaBH4) and lead reduction by alkali metal hydride (MH). 

Reduction by Alkali Metals. This was the first reduction method successfully used it is particularly useful for reducing in liquid ammonia cyanides ( ), alkynyls (f 4 ), ammines (193) and ethylendiammines (192). The same reaction on phosphine compounds gives low yields because the reagents are insoluble in liquid ammonia (45). The zero valent nickel compounds with phosphites are obtained in good yield with the potassium graphite compound KCs (110). 

The reductive alkylation of coal, involving reduction by alkali metal naphthalenide followed by alkylation by alkyl halide, involves chemistry that is more complex than that of the reductive alkylation of simple aromatic compounds. 

Unpaired electrons can be present in ions as well as in the neutral systems that have been considered up to this point. There are many such radical cations and radical anions, and we consider some representative examples in this section. Various aromatic and conjugated polyunsaturated hydrocarbons undergo one-electron reduction by alkali metals. Benzene and naphthalene are examples. The ESR spectrum of the benzene radical anion was shown earlier in Figure 11.2a. These reductions must be carried out in aprotic solvents, and ethers are usually used for that purpose. The ease of formation of the radical anion increases as the number of fused rings increases. The electrochemical reduction potentials of some representative compounds are given in... 

Reaction with NaOR 5, 3.4.4.3.4 Reaction with Pd 8,4.8.2.2 Reduction by alkali-metal hydrides 2,... 

R2O3 Reduction by alkali metals Schleid and Meyer (1989)... 

Reduction by alkali metals for the preparation of anionic metal carbonyl derivatives is illustrated by the following equations. 

This latter reaction is similar to the gas-phase reactions between S02" and SO2. Chemical reduction by alkali metals can also be used and work with lithium suggests that the complex 8204 also dimerizes [29]. In non-aqueous solvents, the reaction of sulfur dioxide with superoxide produces the sulfur dioxide radical anion, but with an equilibrium constant of only about =1.1 [30], reaction (16) ... 

Reactions.— Nitriles can be reduced to aldehydes in aqueous media by photochemically generated hydrated electrons. The reduction of nitriles to amines by sodium borohydride is catalysed by Raney nickel. The transition metal promoted reductive decyanation of alkyl nitriles to homologous hydrocarbons with one less carbon atom is reported, and has been shown by van Tamelen to proceed by a different mechanism from that of a similar reduction by alkali metals in ammonia, where a process of stepwise two-electron transfer has been proposed. In the former reaction, where use is made of ferric acetylacetonate and sodium, the proton required for alkane production is derived exclusively from the acetylacetonate ligand, alkane being formed before a proton source is added this suggests a mechanism which involves initial co-ordination of the nitrile to iron, followed by reductive cleavage of the nitrile 1,2-carbon bond and proton transfer to this area, as pictured in Scheme 42. 

The comparative role of any particular factor of those considered in determining the stereochemistry of reactions depends in each individual case on the stereochemistry of the starting materials. In some cases, however, it is possible to give general characteristics of the individual reaction. Thus, in catalytic hydrogenation, the most important role is played by the factor of the accessibility of the reaction center, and in reduction by alkali metals by the conformational factor. 

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