Physico-chemical properties of isomeric forms of luminol in aqueous solutions

Two luminol isomers, 2,4-diaminoisoindoline-1,3-dione and 8-amino-4-hydroxyphthalazin-1(2H)-one, have been obtained and described, their physical and chemical properties studied. Using UV-spectroscopy and fluorescence data, it has been shown that, in aqueous solutions, 2,4-diaminoisoindoline-1,3-dione isomerize into 8-amino-4-hydroxyphthalazin-1(2H)-one, with the speed of transition depending on the pH values. Thermodynamic dissociation constants for the 2,4-diaminoisoindoline-1,3-dione and 8-amino-4-hydroxyphthalazin-1(2H)-one luminol isomers have been determined.