Liquid ammonia redox reactions

Almost all of the reactions that the practicing inotganic chemist observes in the laboratory take place in solution. Although water is the best-known solvent, it is not the only one of importance to the chemist. The organic chemist often uses nonpolar solvents sud) as carbon tetrachloride and benzene to dissolve nonpolar compounds. These are also of interest to Ihe inoiganic chemist and, in addition, polar solvents such as liquid ammonia, sulfuric acid, glacial acetic acid, sulfur dioxide, and various nonmctal halides have been studied extensively. The study of solution chemistry is intimately connected with acid-base theory, and the separation of this material into a separate chapter is merely a matter of convenience. For example, nonaqueous solvents are often interpreted in terms of the solvent system concept, the formation of solvates involve acid-base interactions, and even redox reactions may be included within the (Jsanovich definition of acid-base reactions. 

Explosive salts such as NaNO can be prepared by the reaction of NO and liquid ammonia solutions of alkali metals. The unstable free arid, HNO, is thought to be an intermediate in many redox reactions of nitrogen compounds. 

The first divalent organolanthanide complex is prepared by the redox reaction of europium with cyclopentadienyl in liquid ammonia (Equation 8.27) [93]. Ytterbocene can be prepared in an analogous manner. 

The solvated electron in ammonia has a strong absorption band in the infrared region, and /Imax shifts from 1850 nm at 23 °C to 1410 nm at —75°C this is attributed to the effect of temperatiu-e on the orientation of the ammonia molecules in the first solvation shell [37], On the other hand, G(e am) = 0-32 pmol J remains constant over the same temperature range [37]. It is relatively straightforward, therefore, to study one-electron redox reactions in liquid ammonia by pulse radiolysis, but relatively few investigations have been made. 

CeH5)3GeNa + BrSn(CH3)3 (C6H5)3Ge-Sn(CH3)3 + NaBr Many other redox reactions have been observed in the absence of metals dissolved in liquid ammonia . Some compounds are reduced by the solvent, for example ... 

Let s recall that with ammonia, Cu + gives the deep blue cation complex hexam-mine copper(II) (cupritetrammine). In analytical toxicology, Cu° is searched for in the liquid resulting from the sulfonitric mineralization and is identified in it with ammonia. Because of its weak concentration in the mineralization liquid, Cu " " is first displaced by metallic iron, on which it deposits in the form of a red coating of metallic copper. The deposit is purely and simply the result of the following redox reaction ... 

FIGURE 2.30. Redox catalysis induction of Srn1 reactions. Cyclic voltammetry in liquid ammonia + 0.1 M KC1 at —40°C of (a) redox catalyis of the reductive cleavage of 2-chlorobenzonitrile, RX, by 4-cyanopyridine, P. The dotted reversible cyclic voltammogram corresponds to P in the absence of RX. The solid line shows the catalytic increase of the current, (b) Transformation of the voltammogram upon addition of the nucleophile PhS. Adapted from Figure 1 in reference 23, with permisison from the American Chemical Society. 

The electrochemically induced reaction of /j-chlorobenzonitrile with malononitrile anion in liquid ammonia, using 4,4 -bipyridine as a redox mediator, gave the substitution product 172 in 85% yield (equation 1 1 1)204. 

Pyrrole anion is unreactive in liquid ammonia under irradiation with PhBr or 1-chloro-naphthalene. However, the reactions of aryl chlorides (p-chlorobenzonitrile, 3- and 4-chloropyridines and 4-chlorodiphenyl sulphone) with 2,5-dimethylpyrrole anion under electrochemical inducement in the presence of a redox mediator gave the C3-substituted product in moderate yields (35-40%) (equation 120)225. The rate constant of the coupling reaction between this nucleophile and aryl radicals is about 5-8 x 109 M"1 s 1 determined by electrochemical methods225. 

Chemical reagents can also be used to carry out redox intercalation reactions. Alkali metals in liquid ammonia and organometallic reagents such as n-butylhthium were among the earliest used. Other chemical reagents can be used to provide different effective activities of the alkali metal relative to the pure metal. A convenient sununary, developed for comparison of the reduction potentials for some common lithium reagents and common host lattices, is shown in Figure S. ... 

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