Anthracene reaction with alkali metal

Electron transfer reactions involving alkali metals are heterogeneous, and for many purposes it is desirable to deal with a homogeneous electron transfer system. It was noticed by Scott39 that sodium and other alkali metals react rapidly with aromatic hydrocarbons like diphenyl, naphthalene, anthracene, etc., giving intensely colored complexes of a 1 to 1 ratio of sodium to hydro-... 

The complex mechanism of the protonation of anion radicals in DMF may have some bearing upon the mechanism proposed for the reaction of perylene radical anion with alcohols (Levin et a/., 1972) and anthracene radical anion with t-butyl alcohol (Rainus et a ., 1973). The disproportionation mechanism was proposed for these reactions in ethereal solvents with alkali-metal counter-ions. The principal evidence for the mechanism was the observation of rate laws of the form of (77) where was suggested to be... 

No difficulty is experienced in effecting reaction between alkali metals and conjugated hydrocarbons provided that reaction (a) is run such that the equilibrium favors the products rather than the reactants, and provided that the products are stable under these conditions. Selecting these conditions is the chief experimental problem. In reactions of benzene, biphenyl, naphthalene, and anthracene with alkali metals, theory and practice agree that the electron affinities are benzene < biphenyl < naphthalene < anthracene. What conditions are most favorable for each hydrocarbon ... 

Catalysts and reaction conditions used are generally similar to those used for olefin isomerization. Catalysts reported are sodium-organosodium catalysts prepared in situ by reaction of a promoter such as o-chloro-toluene or anthracene with sodium 19-24), alkali metal hydrides 20,21), alkali metals 22), benzylsodium 26), and potassium-graphite 26). These catalysts are strong bases that can react with alkylaromatics to replace a benzylic hydrogen [Reaction (2)]. 

The reaction involves the transfer of an electron from the alkali metal to naphthalene. The radical nature of the anion-radical has been established from electron spin resonance spectroscopy and the carbanion nature by their reaction with carbon dioxide to form the carboxylic acid derivative. The equilibrium in Eq. 5-65 depends on the electron affinity of the hydrocarbon and the donor properties of the solvent. Biphenyl is less useful than naphthalene since its equilibrium is far less toward the anion-radical than for naphthalene. Anthracene is also less useful even though it easily forms the anion-radical. The anthracene anion-radical is too stable to initiate polymerization. Polar solvents are needed to stabilize the anion-radical, primarily via solvation of the cation. Sodium naphthalene is formed quantitatively in tetrahy-drofuran (THF), but dilution with hydrocarbons results in precipitation of sodium and regeneration of naphthalene. For the less electropositive alkaline-earth metals, an even more polar solent than THF [e.g., hexamethylphosphoramide (HMPA)] is needed. 

Sodium and potassium are the two most frequently used alkali metals in side-chain alkylation. Sodium usually requires a promoter (o-chlorotoluene, anthracene) to form an organosodium intermediate that is the true catalyst of the reaction. A temperature range of 150-250°C is usually required for alkylation with monoolefins, whereas dienes and styrenes are reactive at lower temperatures. 

The addition product, C QHgNa, called naphthalenesodium or sodium naphthalene complex, may be regarded as a resonance hybrid. The ether is more than just a solvent that promotes the reaction. Stabihty of the complex depends on the presence of the ether, and sodium can be Hberated by evaporating the ether or by dilution using an indifferent solvent, such as ethyl ether. A number of ether-type solvents are effective in complex preparation, such as methyl ethyl ether, ethylene glycol dimethyl ether, dioxane, and THF. Trimethjlamine also promotes complex formation. This reaction proceeds with all alkali metals. Other aromatic compounds, eg, diphenyl, anthracene, and phenanthrene, also form sodium complexes (16,20). 

CHROMIUM TRIHYDROXIDE (308-14-1) CrH204 A powerful oxidizer. Violent reaction with many materials, including reducing agents (explosion) hydrides, nitrides, and sulfides acetic acid, acetic anhydride acetone, alcohols, alkalis, alkali metals, ammonia, anthracene, arsenic, combustible materials dimethylformamide, ethers, ethyl alcohol fumes (ignition) finely divided metals hydrogen sulfide sulfuric acid organic matter peroxyformic acid, phosphorus, pyridine, selenium, sodium, sulfur, and other oxidizable materials. 

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