New chemical markers based on mixtures of individual phthaleins were developed. These markers are characterized by high level of secrecy in use, good transferability to contacting persons, enhanced retention on the objects marked, and reliable identification of phthaleins by expert investigation. The experimental studies of the markers obtained show that the synthesized mixture of three phthalein homologs contains the previously unknown phthalein with unsymmetrical phenolic substituents, o-cresolphenolphthalein 3-(3'-methyl-4'-hydroxyphenyl)-3-(4aEuro(3)-hydroxyphenyl)phthalide, which decreases the probability of the marker falsification. Quantum-chemical calculations of the reaction of the o-cresolphthalein synthesis show that the overall reaction is characterized by small positive changes in the enthalpy and Gibbs free energy, and the second and third steps occur with negative changes in the Gibbs energy. The optimum structure of the transition state was calculated.
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