Effects of electron donors on the photodecomposition of menadione in aqueous solution. IV. Charge transfer absorption bands of the complexes between menadione and either caffeine of ethyl p-aminobenzoate.

Abstract

In previous papers, it was reported that menadione formed complexes with various electron donrs in aqueous systems, and that the driving force of the complex formation was due to the charge transfer force. However, the charge transfer absorption bands of the complexes were not recognized completely in the above systems. In the present paper, the charge transfer absorption bands of the complexes between menadione and either caffeine or ethyl p-aminobenzoate were determined in chloroform, and energies of the charge transfer absorption bands were compared with those between better electron donors and menadione, or between better electron acceptors and either caffeine or ethyl p-aminobenzoate. Consequently, it was concluded that the indistinct charge tranfser absorption bands of the complexes between menadione and either caffeine or ethyl p-aminobenzoate in aqueous system are responsible for lower electronic affinity of menadione, for higher ionization potentials of caffeine or ethyl p-aminobenzoate and for lower solubilities of caffeine or ethyl p-aminobenzoate.