Adducts of an anion of an oxa acid and a keto compound, process for the preparation of said adducts, and process for the determination of the concentration of the anions of oxa acids using said keto compounds

Claim 1

An adduct of an anion of an oxa acid and a keto compound having the formula II ##STR23## wherein the radicals Ar and Ar' are selected independently from the following ring systems containing at least one aromatic nucleus: (a) aromatic systems selected from the group consisting of substituted or unsubstituted benzene, substituted or unsubstituted naphthalene, substituted or unsubstituted anthracene; and (b) substituted and unsubstituted heterocyclic systems selected from the group consisting of substituted or unsubstituted thiophene, substituted or unsubstituted furane, substituted or unsubstituted pyrrole, substituted or unsubstituted indole, substituted or unsubstituted benzofurane, substituted or unsubstituted benzothiophene, substituted or unsubstituted pyridine, substituted or unsubstituted quinoline, substituted or unsubstituted pyrazine, and substituted or unsubstituted triazine; in which ring systems the substituents are selected from the group consisting of hydrogen, halo, nitro, thiol, azo, ether, carboxylic acid ester, hydroxy, amino, alkylamino, dialkylamino, arylamino, diarylamino, cycloalkylamino, dicycloalkylamino, alkyl, alkenyl, alkinyl, cycloalkyl, and aryl; and X 1 , X 2 and X 3 are selected independently from the group consisting of hydrogen, alkyl, alkenyl, alkinyl, aryl, fluorine, chlorine, bromine, iodine and nitro, provided that at least one of X 1 , X 2 and X 3 is fluorine, chlorine, bromine or nitro, further provided that the keto compound is capable of interacting with an anion of an oxa acid to shift the light absorption in the visible or ultraviolet range of the adduct compared with the light absorption in the visible or ultraviolet range of the corresponding free carbonyl group of formula II.