Phenanthrene–silver ion complexes in trifluoroacetic acid, and their influence on the rates of detritiation of [9-3H]phenanthrene in the presence of silver trifluoroacetate

Abstract

Silver trifluoroacetate has a marked inhibiting effect on detritiation of [9-³H]phenanthrene, P, in trifluoroacetic acid at 100°. A rough analysis of the rates of detritiation at various concentrations of hydrocarbon and silver salt in the light of equilibrium constants for the several complexes deduced from spectroscopic studies at 20° indicates that the [P·Ag]⁺ complex is only a few times less reactive than free phenanthrene, and is more reactive than the [2P·Ag]⁺ complex.

Detritiation of [1-³H]phenanthrene is retarded by silver trifluoroacetate by about the same factor as that for [9-³H]phenanthrene. Silver trifluoroacetate inhibition of detritiation decreases in the sequence [9-³H]phenanthrene < [1-³H]naphthalene < [2-³H]-p-xylene, in line with the decreasing strength of the complexes with silver ion.

The electronic spectrum of phenanthrene in the presence of silver trifluoroacetate has been analysed on the assumption that 1:1, 1:2, and 2:1 complexes are formed between phenanthrene and silver ion. The degree of complex formation is much greater than that in aqueous solutions at corresponding concentrations, and the following equilibrium constants (at 20 °C) have been derived: K₁₁= 5·1 × 10⁴ l mol^–1, K₁₂= 1·4 × 10⁷ l² mol^–2, and K₂₁= 3·3 × 10⁶ l² mol^–2. For the 1:1 complex there is a small shift of the first phenanthrene absorption band to lower frequencies and a small increase in intensity. The first absorption band of the 2:1 complex has much greater intensity, suggesting that there is an exciton interaction between the two phenanthrene molecules.