[1623-99-0] · C6H5Na · Phenylsodium · (MW 100.10)
Physical Data: amorphous, infusible solid.
Solubility: insol hydrocarbons and reacts with ethers; can be solubilized as complexes, e.g. with N,N,N´,N´´,N´´-Pentamethyldiethylenetriamine.3 Also forms more soluble complexes, but with modified reactivity, with phenyllithium, diphenylmagnesium, and magnesium 2-ethoxyethoxide.4
Preparative Methods: usually by reaction of chlorobenzene with Sodium dispersion; also by metalation of benzene with alkylsodium compounds (e.g. as a one-pot process by reaction of 1-chloropentane with sodium dispersion in benzene); by reaction of Phenyllithium with sodium t-butoxide;3 and by transmetalation of Diphenylmercury, e.g. with sodium.5
Purification: the reagent is normally prepared and used in situ. Its composition, and therefore its properties, may depend on the method of preparation.
Handling, Storage, and Precautions: reacts explosively with air and violently with water; hydrolysis gives benzene (carcinogen) and sodium hydroxide (corrosive). It must be handled in an inert atmosphere under strictly anhydrous conditions.
Despite a considerable amount of early work,1a phenylsodium has been underutilized as a reagent for metalation. While it is probably less
superbasic than, for example, butylpotassium, it is certainly more basic than most organolithium compounds. For example, reaction of phenylsodium with acetophenone results in enolate formation and nucleophilic addition in a ratio of 2:1, whereas with Phenyllithium the ratio is 1:23.6 Some examples of its use, chosen with the emphasis on reactions where it differs from organolithium compounds, are shown in the following equations.
Eq 1 represents a convenient synthesis of benzylsodium, via the preparation of phenylsodium in situ in toluene.7 Toluene is metalated by n-Butyllithium only in the presence of e.g. N,N,N´,N´-Tetramethylethylenediamine.
In contrast to eq 2,8 reaction of benzyldimethylamine with butyllithium leads mainly to ortho metalation.
Both 2- and 4-alkylpyridines may be metalated with phenylsodium as an alternative to Sodium Amide or organolithium compounds (eq 3).9
Phenylsodium resembles phenyllithium in its reactions with carbonyl compounds (including a,b-unsaturated carbonyl compounds, where 1,2-addition predominates), Carbon Dioxide, Iodomethane, oxirane (Ethylene Oxide), etc.,1b,c but generally offers no significant advantage (except possibly cost). Indeed, its higher basicity may be a disadvantage when the substrate contains a-hydrogens, as in its reaction with acetophenone noted above.
A less routine example involves both nucleophilic ring-opening and addition to a carbon-nitrogen double bond (eq 4).10 In this case also, phenyllithium gave a similar yield of phenol, though a lower yield of the sulfonamide.
Early studies on the polymerization of dienes and styrene initiated by phenylsodium2 have not been extensively followed up or exploited, although various patents listed in Chem. Abstr. include the use of phenylsodium.
Andrea J. Dawson & Basil J. Wakefield
University of Salford, UK