Naphthalenes, 1,7-dimethoxy metalation

Naphthalenes, 1,7-dimethoxy-, metalation 16, 839 Naphthalenes, 1,4,5,6,7,8-hexahydro-2-methoxy-... 

The initiation step is normally fast in polar solvents and an initiator-free living polymer of low molecular weight can be produced for study of the propagation reaction. The propagation step may proceed at both ends of the polymer chain (initiation by alkali metals, sodium naphthalene, or sodium biphenyl) or at a single chain end (initiation by lithium alkyls or cumyl salts of the alkali metals). The concentration of active centres is either twice the number of polymer chains present or equal to their number respectively. In either case the rates are normalized to the concentration of bound alkali metal present, described variously as concentration of active centres, living ends or sometimes polystyryllithium, potassium, etc. Much of the elucidation of reaction mechanism has occurred with styrene as monomer which will now be used to illustrate the principles involved. The solvents commonly used are dioxane (D = 2.25), oxepane (D = 5.06), tetrahydropyran D = 5.61), 2-methyl-tetrahydrofuran (D = 6.24), tetrahydrofuran (D = 7.39) or dimethoxy-ethane D = 7.20) where D denotes the dielectric constant at 25°C. 

As implied by the above treatment, the conversion of A into A7, Met+ is never quantitative. For example, reduction of naphthalene in tetrahydrofaran by sodium yields about 95% of its radical anions at ambient temperature, whereas the yield in diethyl ether is very low, less than 1%. The sodium reduction of biphenyl, a hydrocarbon of lower electron affinity than naphthalene, results only in about 20% conversion in tetrahydrofaran, although nearly 100% reduction may be accomplished in dimethoxy-ethane. Since these processes lead to equilibria, it is immaterial whether they take place on the surface of the metal, being followed by desorption of the product, or whether they proceed homogeneously in a solution saturated by metal atoms and their ionization products, these being replenished from the bulk of the solid metal as the reduction proceeds. 

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