Structrure and Reactivity of Lithium Amides. Role of Aggregates, Mixed Aggregates, Monomers, and Free Ions on the Rates and Selectivities of N-Alkylation and E2 Elimination

Article abstract of DOI:10.1021/ja00224a042

Rate studies of the N-alkylation of lithium diphenylamide with n-butyl bromide in THF/hydrocarbon mixtures (THF=tetrahydrofuran) are described.Dramatic induction periods observed for the N-alkylation at low THF concentrations are described to the intervention of reactive mixed dimers of lithium diphenylamide and lithium bromide.In the presence of 1.0 equiv. of added lithium bromide, the alkylation rate exhibits a first-order dependence on both the mixed aggregate and n-butyl bromide concentration, indicating the contribution of an additional, highly solvent dependentalkylation pathway.This latter pathway exhibits fractional-order dependence on the amide concentration, approximate first order dependence on the n-butyl bromide concentration, and a seventh-order dependence on the THF concentration.Common ion rate inhibitions by lithium perchlorate and lithium tetraphenylborate, a significant dependence on dielectric effects, and the observed reaction orders implicate a mechanism involving predissociation of free lithium ions.The appearence of competitive eliminations of n-alkyl bromides to form 1-alkenes coincides with the appearence of the free ion alkylation pathway.