Nonhydrated Anion Transfer from the Aqueous to the Organic Phase: Enhancement of Nucleophilic Reactivity in Phase-Transfer Catalysis

Article abstract of DOI:10.1021/jo00133a006

A systematic study of how the nature and concentration of the inorganic salt affect hydration and reactivity of anions transferred into the organic phase under conditions of phase-transfer catalysis (PTC) has been performed.The inorganic salt concentration in the aqueous phase up to saturated solution (= or > 6 M), does not affect the hydration and hence the reactivity of the anion in aliphatic nucleophilic substitutions.On the other hand, in concentrated aqueous alkaline solutions (50percent NaOH or 60percent KOH) unhydrated anions are transferred from the aqueous to the organic phase.The anionic reactivity thus becomes identical with that found under anhydrous homogeneous conditions, the rate enhancement being 13.0, 4.0, 2.6, and 1.4 times for Cl(1-), N3(1-), Br(1-), and I(1-), respectively.The same dehydrating effect was not observed with less concentrated alkaline solutions or with 50percent aqueous NaF.These data show the unique property of OH(1-) in producing conditions of virtually null water activity under PTC conditions.