Radical anions potassium

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

The ESR spectrum of the pyridazine radical anion, generated by the action of sodium or potassium, has been reported, and oxidation of 6-hydroxypyridazin-3(2//)-one with cerium(IV) sulfate in sulfuric acid results in an intense ESR spectrum (79TL2821). The self-diffusion coefficient and activation energy, the half-wave potential (-2.16 eV) magnetic susceptibility and room temperature fluorescence in-solution (Amax = 23 800cm life time 2.6 X 10 s) are reported. 

On treatment with potassium metal, cij-bicyclo[6.1.0]nona-2,4,6-triene gives a mono-cyclic dianion. The trams isomer under similar conditions gives only a bicyclic monoanion (radical anion). Explain how the stereochemistry of the ring junction can control the course of these reductions. 

Various other observations of Krapcho and Bothner-By are accommodated by the radical-anion reduction mechanism. Thus, the position of the initial equilibrium [Eq. (3g)] would be expected to be determined by the reduction potential of the metal and the oxidation potential of the aromatic compound. In spite of small differences in their reduction potentials, lithium, sodium, potassium and calcium afford sufficiently high concentrations of the radical-anion so that all four metals can effect Birch reductions. The few compounds for which comparative data are available are reduced in nearly identical yields by the four metals. However, lithium ion can coordinate strongly with the radical-anion, unlike sodium and potassium ions, and consequently equilibrium (3g) for lithium is shifted considerably... 

A particular case of a [3C+2S] cycloaddition is that described by Sierra et al. related to the tail-to-tail dimerisation of alkynylcarbenes by reaction of these complexes with C8K (potassium graphite) at low temperature and further acid hydrolysis [69] (Scheme 24). In fact, this process should be considered as a [3C+2C] cycloaddition as two molecules of the carbene complex are involved in the reaction. Remarkable features of this reaction are (i) the formation of radical anion complexes by one-electron transfer from the potassium to the carbene complex, (ii) the tail-to-tail dimerisation to form a biscarbene anion intermediate and finally (iii) the protonation with a strong acid to produce the... 

Figure 2.3 ESR spectrum of the potassium salt of pyrazine radical anion simulated using hyperfine couplings from ref. 2.

The sonochemistry of the other alkali metals is less explored. The use of ultrasound to produce colloidal Na has early origins and was found to greatly facilitate the production of the radical anion salt of 5,6-benzo-quinoline (225) and to give higher yields with greater control in the synthesis of phenylsodium (226). In addition, the use of an ultrasonic cleaning bath to promote the formation of other aromatic radical anions from chunk Na in undried solvents has been reported (227). Luche has recently studied the ultrasonic dispersion of potassium in toluene or xylene and its use for the cyclization of a, o-difunctionalized alkanes and for other reactions (228). 

PMR) trends that correspond to relative rates.179 From an examination of the displacement of chloride from l-chloro-5-nitrofuran by potassium iodide in acetic acid or by sodium sulfide in water it was concluded that the substitution need not be a true nucleophilic substitution. Initially there could be a transfer of one electron from the nucleophile to the furan nucleus the resultant radical anion loses chloride to form a furyl radical and product.179... 

Other selected examples include tris(tetramethylethylene diamine-sodium)-9,9-dianthryl 143,154 alkali metal salts of 9,10-bis(diisopropylsilyl)anthracene 144,155 as well as the closely related naked 9,10-bis(trimethylsilyl)anthra-cene radical anion 145.156 This chemistry is further extended to the solvent-shared and solvent-separated alkali metal salts of perylene radical anions and dianions 146, 147,156 while other examples focus on alkali metal salts of 1,2-diphenylbenzene and tetraphenylethylene derivatives, where reduction with potassium in diglyme afforded contact molecules with extensive 7r-bonding, [l,2-Ph2C6H4K(diglyme)] 148.157 Extensive 7r-coordination is also observed in (1,1,4,4 tetraphenylbutadiene-2,3-diyl)tetracesiumbis(diglyme)bis(methoxyethanolate) 149.158... 

The radical anions 1, anti-2, anti,anti-3, and anti,anti,anti-4 were generated by the reduction of the corresponding ladder polysilanes with potassium (Scheme 8). When the ladder poly silanes were treated with potassium in tetrahydrofuran (THF) at ca. — 70 °C, the solutions were immediately colored 1, purple anti-2, brown anti,anti-3, blue and anti,anti,anti-4, black. In the UV-visible-NIR spectra, several absorption bands appeared (Fig. 15). The intense absorption of anti,anti-3 and anti,anti,anti-4 in the near-infrared region is noted because it has been... 

In contrast to 51, hexacyano[3]radialene (50) proved difficult to obtain in pure form. Freshly prepared samples are bright-yellow, but mm brown on exposure to air and blue on contact with many solvents. Potassium bromide and sodium iodide reduce 50 to the radical anion and the dianion, respectively24. 

The redox chemistry of [4]radialenes shows similarities as well as differences with respect to [3]radialenes (see elsewhere1 for a more detailed comparison). The simplest [4]radialene for which a redox chemistry in solution is known appears to be octa-methyl[4]radialene (94). It has been converted into the radical anion 94 (with potassium, [2.2.2]cryptand, THF, 200 K) and into the radical cation 94 + (with AICI3/CH2CI2, 180 K)82. Both species are kinetically unstable, but the radical cation is less stable than the radical anion and disappears even at 180 K within 2 hours, probably by polymerization. For the success of the oxidation of 94 with the one-electron transfer system... 

Radical anions have also been obtained recently from the tin equivalents of the alkynes, the distannynes (see Section 3.14.24.6). Reduction of 2,6-di(2,4,6-triisopropylphenyl)phenyltin(ll) chloride (ArSnCl) with potassium in THF gave [ArSnSnAr] K+, which showed g= 2.0069, (117Sn) = 0.83 mT, (119Sn) = 0.85 mT, and in the crystal, the radical anion adopts a tram-bent structure. The 2,6-di(2,6-diisopropylphenyl)phenyltin analog behaves similarly.533 534... 

In recent years, the first distannynes have been obtained. Reduction of 2,6-di(2,6-diisopropylphenyl)phenyltin(ll) chloride (Ar SnCl) or 2,6-di(2,4,6-triisopropylphenyl)phenyltin(n) chloride (ArSnCl) with sodium or potassium has given not only the stannynes Ar Sn=SnAr and ArSn=SnAr, but also the radical anion [ArSn=SnAr, and the dianions [ ArSn=SnAr] and [Ar Sn=SnAr ]=.534 The properties of the Ar compounds are as shown in Table 11. 

Reduction of the distannynes with sodium or potassium gives the radical anions. [Ar Sn=SnAr ] has the trans-bent geometry given in Table 11, and shows an ESR spectrum with g= 2.0691, (ll7Sn) 0.83 mT and (117Sn) = 0.85 mT, indicating a very low unpaired spin density on tin. The main line is about 0.6mT wide, and no proton coupling is resolved. 

Radical anions of acyclic vicinal oligo-ketones with up to five CO units, generated by reduction of the parent compounds with potassium in the presence of Kryptofix 222, were shown to be extended rr-systems by ESR measurements. ... 

An early electrochemical study of corannulene revealed the presence of two well-defined polarographic waves with half-wave potentials of-1.88 and -2.36 V (r-butylammonium perchlorate in acetonitrile). The first wave represented a reversible, one-electron reduction leading to radical anion formation (emerald green solution) further characterized by UV-VIS and ESR. The second wave was reported to be associated with the formation of a bright red species which is not paramagnetic, but it is not believed to be the dianion, but rather some decay product of it. Treatment of THF solutions of 8 with sodium and potassium metals also led to the formation of the same species. ... 

Electron-transfer initiation from other radical-anions, such as those formed by reaction of sodium with nonenolizable ketones, azomthines, nitriles, azo and azoxy compounds, has also been studied. In addition to radical-anions, initiation by electron transfer has been observed when one uses certain alkali metals in liquid ammonia. Polymerizations initiated by alkali metals in liquid ammonia proceed by two different mechanisms. In some systems, such as the polymerizations of styrene and methacrylonitrile by potassium, the initiation is due to amide ion formed in the system [Overberger et al., I960]. Such polymerizations are analogous to those initiated by alkali amides. Polymerization in other systems cannot be due to amide ion. Thus, polymerization of methacrylonitrile by lithium in liquid ammonia proceeds at a much faster rate than that initiated by lithium amide in liquid ammonia [Overberger et al., 1959]. The mechanism of polymerization is considered to involve the formation of a solvated electron ... 

Other methods that use 55 anions as precursor for the synthesis of fullerene-derivatives usually involve chemical formation of the anion. Alkylation of 55 has been accomplished, e.g. by reduction with propanethiol and potassium carbonate in DMF [91,92], sodium methanethiolate in acetonitrile [93], the naphthalene radical anion in benzonitrile[94], potassium naphthalide [95] or simply with zinc [96]. 

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