Electron-transfer to and protonation of the diphenylacetylene radical-anions

Abstract

The mechanism of the reaction of sodium salt of diphenyl acetylene radical-ion (DPA^–, Na⁺) with sodium biphenylide (B^–, Na⁺) or naphthalide (N^–, Na⁺) in tetrahydrofuran (THF) was elucidated. The slow protonation be THF of the disodium salt of the dianion, PhC : CPh = DPA^2–, is the rate-determining step; the latter is maintained at exceedingly low concentration by the unfavourable electron-transfer equilibrium, DPA^–., Na⁺+ B^–., Na⁺(or N^–., Na⁺)⇌DPA^2–,2Na⁺+ B(or N). The retardation of the overall process by the parent hydrocarbon (B or N) conclusively proves that the electron-transfer equilibrium, and not a slow electron-transfer as proposed by previous workers, is governing the reaction. The identification of the product, PhCH: CPh, Na⁺ provides additional evidence in favour of the proposed mechanism.