Synthesis of Quaternized Thiazoloquinazolinium Triiodide and Its Application as an Active Substance for Potentiometric Sensor

For the first time, the synthesis, isolation, and identification of angular triiodide, 1,2,4,5-tetrahydro-4-ethyl-1-(iodomethyl)-1-methyl-5-oxothiazolo[3,2-a]quinazolin-10-ium, have been achieved. The formation of the triiodide was confirmed by elemental analysis, and its structure was approved by NMR spectra containing signals from the fused thiazolonine ring. The cyclization process was confirmed by the change in signal multiplicity from singlets (thioether) to doublets (thiazole) and a shift to a weaker field in the spectrum of the methyl group from 1.83 ppm to 2.15 ppm. Optimal reaction conditions for the synthesis of thiazolochinazolinium triiodide were found using a double excess of iodine in chloroform at room temperature for 24 hours, yielding 84%. The obtained thiazolochinazolinium triiodide product was utilized as an active substance for a PVC plasticized triiodide selective potentiometric sensor. The sensor exhibited a super-Nernstian response of 75 mV/pC with a detection limit of 5 10-6 mol/L I3- and a lifetime exceeding 4 months. The pH working range of the sensor was found to be within pH 2-10, with a response time of 15-30 s. The sensor is selective to anions and exhibits some sensitivity to molecular iodine and iodide. The sensor was used as an indicator electrode for the direct potentiometric titration of ascorbic acid using a solution of KI3 in intensely colored fruit juices and vitamin preparations. The accuracy was confirmed by the added-found method and HPLC analysis.