Acidity of dibasic acids I: the second acidity constant of 9,10-dihydroanthracene and its 9,10-substituted derivatives: effect of substituent and counter ion

Abstract

The second equilibrium ion pair acidity constants (pK₂) of 9,10-dihydroanthracene, 9-phenyl-9,10-dihydroanthracene, 9,10-diphenyl-9,10-dihydroanthracene and 9-cyano-9,10-dihydroanthracene with sodium, potassium and rubidium have been determined in tetrahydrofuran (THF) at 25 °C in the concentration range l0^–5–10^–2 mol dm^–3. Equilibria were monitored by UV–VIS and ¹H NMR spectroscopies and the spectra of the dimetallic and monometallic salts reported. The dimetallic salts of all the dibasic carbon acids studied behave as contact ion pairs in THF. The pK₂ of 9,10-dihydroanthracene is insensitive to substituent effect but is strongly dependent on the cation.