Phenyllithium from benzene preparation

Optimum Conditions for Preparing Phenyllithium from Benzene. The optimum procedure for metalation of an aromatic compound in high yield was to use the aromatic compound itself as the solvent. The alkyl-lithium compound used mainly in this study was n-butyllithium because it was convenient and economical. 

Other reactions typical of aromatic systems, such as nitration and bromination, arc not feasible with metallocenes because of their sensitivity to oxidation.,h- However. many of the derivatives that would be produced in these types of reactions can be made indirectly by means of another reaction typical of aromatic systems mctalla-lion. Just as phenyllithium can be obtained from benzene, analogous ferrocene compounds can be prepared ... 

Recently methyltriphenylammonium tetrafluoroborate was prepared from triphenylamine and trimethyloxonium fluoroborate. Demethylation was affected by butyllithium in hexane or methylene chloride and with phenyllithium in benzene or ether. No evidence for biphenyl or diphenyl-methylamine was noted and only triphenylamine was characterized. In demethylation reactions with potassium methoxide in methanol-O-d, no exchange of methyl hydrogen for deuterium was observed. Thus, no proton abstraction processes occurred in these decompositions 114>. 

Ethereal phenyllithium, prepared from lithium and bromo-benzene,3 may be standardized by adding an aliquot to water and titrating with standard sulfuric acid. 

Methylene triphenylarsorane (//, 31, 34, 39) has been prepared in situ from the salt in ether (34, 39), benzene (34, 39, 60), tetrahydrofuran (31), or dimethyl sulfoxide (II) by reaction with butyl- or phenyllithium (34, 39), sodium hydride (31), methylsulfinylcarbanion (II), or sodamide (102). Ethylidene triphenylarsorane has been prepared by reaction with methylsulfinylcarbanion (II) whereas fluorenylidene-(9)-trimethyl- and fluor-enylidene-(9)-dimethylbenzylarsorane (101) have been made using phenyllithium in ether. Sodium methoxide in methanol has been used successfully (41, 47, 48, 94) to generate ylides from their corresponding salts when R is an electron-withdrawing group (e.g., COOR, COR, or CN). 

There are several recent methods for the reduction of azobenzene to hydrazobenzene in near-quantitative yield. Samarium(II) iodide reduces azobenzene to hydrazobenzene rapidly at room temperature. Hydrogen telluride, generated in situ from aluminum telluride and water, reduces both azobenzene and azoxybenzene to hydrazobenzene a mixture of phenyllithium and tellurium powder has been used to reduce azobenzene. A complex of the coenzyme dihydrolipoamide and iron(II) is also effective for the reduction of azo- and azoxy-benzene to hydrazobenzene the reduction probably involves coordination of the azobenzene to iron(II) as shown in structure (1). Electrochemical reduction has been used to prepare a number of hydrazobenzenes from the corresponding azobenzenes. In the presence of an acylating agent a diacylhydrazine (e.g. the pyridazinedione derivative 2) can be isolated from the electrochemical reduction of azobenzene. 

A procedure better adapted to operation on a large scale is described by Bavin. A solution of 1 mole of fluorene in 500 ml. of ether is added with stirring under reflux to an ethereal solution of phenyllithium prepared from 1.5 moles of bromo-benzene. After 1 hr. more the orange solution of metallated hydrocarbon is poured as rapidly as possible into powdered dry ice which has been slurried with ether. The mixture is acidified, the solvent removed by steam distillation, and the solid is dissolved in aqueous potassium carbonate solutioa Clarification with Norit gives a pale yellow solution which is poured into excess 30% hydrochloric acid. The colorless, crystalline product on reaction with methanol and hydrogen chloride gave the pure methyl ester, m.p. 64-65°. The yield was generally over 70% and occasionally reached 90%. ... 

Optimum Conditions for Preparing Benzyllithium from Toluene. Both the TMEDA and TED complexes of benzyllithium were investigated. Toluene metalation proceeds much faster than does benzene metalation under similar conditions. The benzyllithium complexes were more soluble in hydrocarbon solvents than were the corresponding phenyllithium complexes. This method of preparation of benzyllithium is the most convenient of the few literature procedures available. Other procedures described are the cleavage of benzyl methyl ether with lithium... 

An ethereal soln. of Fe-pentacarbonyl added slowly at -40° to a stirred soln. of phenyllithium prepared from bromobenzene and lithium, stirring continued 3 hrs., benzyl bromide in ether added, kept 2 hrs. at -40°, benzene added, and stirred with slow warming to 50° benzyl phenyl ketone. Y 57%. F. e. s. Y. Sawa, M. Ryang, and S. Tsutsumi, Tetrah. Let. 1969, 5189. 

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