Naphthalene radical anion, reactivity

The styryl radical anion species is much more reactive than the naphthalene radical anion, and rapidly couples to form a dimeric dianion, the source of the red color and the reason for the disappearance of the ESR signal (Eq. 22.40). The dimeric dianion is a double-ended anionic propagating species useful for the initiation of a number of valuable homopolymerizations (Eq. 22.41). 

A similarly reactive Mg powder is formed from the Na naphthalene radical-anion ... 

The opposite is true for naphthalene where the radical anion is faster than the anion in reaction with primary chloride. The difference arises from disparate reactivity of the respective radical anions and shows the danger in extrapolating from one radical anion-anion pair to another. Another point of interest is the much greater reactivity of naphthalene radical anion ys. anthracene, which suggests alternate mechanisms for the electron transfer step, again raising the possibility for the existence of RX7 for the naphthalene system. 

Since different reactivity is observed for both the stoichiometric and the catalytic version of the arene-promoted lithiation, different species should be involved in the electron-transfer process from the metal to the organic substrate. It has been well-established that in the case of the stoichiometric version an arene-radical anion [lithium naph-thalenide (LiCioHg) or lithium di-ferf-butylbiphenylide (LiDTBB) for using naphthalene or 4,4 -di-ferf-butylbiphenyl (DTBB) as arenes, respectively] is responsible for the reduction of the substrate, for instance for the transformation of an alkyl halide into an alkyllithium . For the catalytic process, using naphthalene as the arene, an arene-dianion 2 has been proposed which is formed by overreduction of the corresponding radical-anion 1 (Scheme 1). Actually, the dianionic species 2 has been prepared by a completely different approach, namely by double deprotonation of 1,4-dihydronaphthalene, and its X-ray structure determined as its complex with two molecules of N,N,N N tetramethylethylenediamine (TMEDA). ... 

Dianions, [ArH] "2 Li (ArH = naphthalene, anthracene or PhPh), with PhjCH and Ph2CH2 also give PhjCLi and Ph2CHLi, respectively, and are more reactive than the radical anions. Metallation by [ArH] 2 Li is faster in THF than in Et20. 

Another approach, recently described, consists in the electrochemical preparation of a very active zinc with the use of a mediator3. This zinc is able to react with low reactive organic halides. This electrochemical process is analogous to the chemical reaction developed by Rieke in which the naphthalene anion radical is used to activate metals such as zinc4. 

The Alkylation Reaction. Ether solvents and naphthalene often are employed in the Sternberg alkylation reaction. Inasmuch as these substances are reactive in strongly basic solution, concern has been expressed about their polymerization reactions and about their incorporation into the alkylation product. In view of these potential problems we examined the reaction of potassium with carefully purified tetrahydrofuran at 25 C. The results shown in Figure 1, Curve A, indicate that the reaction is insignificant. On the other hand, the results shown in Figure 1, Curve B, indicate that potassium reacts rapidly with naphthalene to form naphthalene anion radical and naphthalene dianion. The reduction to the dianion is about 80% complete after 4.5 hr. 

In radical substitution, an even AH is converted to an intermediate odd AH radical and in nucleophilic substitution to the corresponding anion. Since these differ from the corresponding electrophilic intermediate only in the number of nonbonding electrons, the energies of reaction should be the same in all three cases. The relative reactivities of different even AHs and the orientation of substitution in a given AH, should therefore be the same for all reagents. This is the case. Thus naphthalene substitutes mainly in the 1 position both with electrophiles (e.g., nitration) and with radicals (e.g., phenylation by phenyl radicals, as in the Gomberg reaction) and with nucleophiles (e.g., amination by sodamide, the Chichibabin reaction) i.e.. 

In the early work on aromatic anion radicals, Paul, Lipkin, and Weissman (1) correlated the reactivities of these radicals with electron affinities derived from their spectra. Bank and Bockrath ( ) compared the rates of protonation of naphthalene and anthracene anion radicals and concluded that the higher rate for naphthalene was in contradiction to their prediction from molecular orbital localization energy calculations. Fry and Schuettenberg (5) correlated the rates of protonation of various aromatic... 

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