Reactions of radical anions. Part VI. The transfer of an electron to the tolan radical anion

Abstract

When tolan is added to an excess of alkali metal hydrocarbon using tetrahydrofuran as solvent, an electron is added to tolan, at a rate too fast to measure, to form the monomer radical anion (I) which may dimerise to form the dianion (II) or may accept an electron from the excess of alkali metal hydrocarbon to form the monomer dianion (III). When lithium is the gegenion, reaction (3) is much faster than (2), and too fast for us to measure. When potassium is the gegenion, reaction (3) is too slow to observe, and all the monomer radical anion formed in reaction (1) dimerises according to (2). When sodium is the gegenion, reaction (3) is competitive in rate with (2), and the thermodynamic constants obtained for reaction (3) at 0° are: sodium phenanthrene, ΔG₃^‡= 13·5 kcal. mole^–1, ΔH₃^‡= 19·5 kcal. mole^–1, and ΔS₃^‡= 22 cal. mole^–1 deg.^–1; sodium naphthalene, 13·5,14·5, and 4, respectively. PhCCPh + M⁺ArH^–→(PhCCPh)[graphic omitted]M⁺(I)(yellow-green)+ ArH (1), 2(PhCCPh)[graphic omitted]M⁺→ Ph[graphic omitted]CPh–CPh[graphic omitted]Ph (II)(green)(2), (PhCCPh)[graphic omitted]M⁺+ M⁺ArH^–→ Ph[graphic omitted]Ph (III)(red)+ ArH (3)

When an excess of tolan is mixed with an alkali metal hydrocarbon, reaction (3) does not occur, but there is a slower reaction of the tolan dimer dianion (II) with the tolan monomer to give a blue product (λ_max, 600 mµ). The results at 0° for this reaction are k₄= 6·7 × 10^–3 I. mole^–1 sec.^–1, ΔG₄^‡= 18·6 kcal. mole^–1, ΔH₄^‡= 16·0 kcal. mole^–1, and ΔS₄^‡=–9·5 cal. mole^–1 deg.^–1, when Na⁺ is the gegenion.