Poređenje teorijskog i eksperimentalnog ispitivanja procesa protonacije nekih tionova u kiselim medijima

Mirjana Jankulovska,Ilinka Spirevska,Vesna Dimova,Milena Jankulovska

doi:10.5937/zasmat2101009j

Abstract

PM3 semiempirical method was used for quantum chemical investigation in order to investigate the electronic properties and to determine the protonation centre in 1,2,4-triazoline-3-thione molecule. Confirmation of protonation center in acid media of investigated compounds was made using the values of atomic charges, as well as, proton affinity values. The results from semiempirical calculations indicated that the protonation center in the thione molecule was the sulphur atom. The behavior of thiones was investigated in mineral acid media using UV spectroscopy. The influence of the strength of the acid and its anion on the protonation process was discussed using three different mineral acids (perchloric, hydrochloric and phosphoric acid) for protonation. The protonation process in perchloric and hydrochloric acid took place in one step, while in phosphoric acid was not finished even when its concentration was to the highest degree. The dissociation constants of protonated forms (pKBH + ) and the solvation parameter m* values were calculated in accordance with "excess acidity" function method (Cox and Yates) using the absorbance data from the experimental and reconstructed spectra (Characteristic Vector Analysis (CVA)). The determined pKBH + values in hydrochloric acid had more negative value than those obtained in perchloric acid media. The pKBH + values were in agreement with the literature data for this class of compounds.

Highlights

Heterocycles are an important class of compounds which are present in a wide variety of drugs, most vitamins, many natural products, biomolecules, and biologically active compounds
In our previous works the pKBH+ values of the compounds that we present in this paper were determined in sulfuric acid mediaand their dissociation constants in sodium hydroxide media [16,17].Because of the influence of the acidity of the media on biological activity of these compounds we were interested to extend our investigations in other mineral acids
First step in our study was theoretical investigation of protonation process of studied triazole-3-thione compounds applying PM3 semiempirical method in order to determine the possible center of protonation

Summary

Introduction

Heterocycles are an important class of compounds which are present in a wide variety of drugs, most vitamins, many natural products, biomolecules, and biologically active compounds. They are significant structural unit in synthetic pharmaceuticals and agrochemicals. The derivatives of 1,2,4-triazole belong to the nitrogen heterocyclic class of compounds which possess aromatic characteristics [1]. In the literature there are a lot of data about synthesis and wide application of compounds that contain triazole ring in their molecule [2,3]. The biological and antiviral activity of these compounds is the result of –NH–C(S)– NH– group in their molecule [4].

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Conclusion