Vol. 24 No. 2 (2026): Issue in Progress

Imidazo[1,5-a]pyridine carboxylic acids are useful building blocks for medical chemistry, but their synthesis scale-up and isolation depend strongly on pH. For zwitterion-prone representatives, a direct titration of acids does not always reveal the basicity of the heteroaromatic center, which is critical for their further use. Therefore, a series of acids, their corresponding esters, and hydrochlorides were analyzed by the potentiometric titration together with ¹H/¹³C NMR, HPLC, LCMS, and HRMS. The acids showed apparent pK_a values of 5.13-6.11, while the esters exposed the basic-center pK_a values in the range of 2.75-4.64. NMR data indicate close electronic similarity within the acid/ester pairs, supporting the use of esters as models for acids with masked basicity.

Hierarchical titanosilicate zeolites of the MFI structural type (zeolites with the MFI framework topology according to the classification of the International Zeolite Association) showed a high catalytic activity in the synthesis of cyclic carbonate from styrene in the presence of tert-butyl hydroperoxide as an oxidant. It has been shown that the combination of the redox properties of titanium centers with the acid-base characteristics of the zeolite matrix ensures the efficient implementation of the tandem process within a single reaction medium. The results obtained confirm the potential of titanium-containing zeolites as an effective platform for creating heterogeneous catalysts for the direct conversion of olefins into cyclic carbonates.

Pentafluorophenyl iodine(III) diacetate (F₅-PIDA) is an electron-deficient hypervalent iodine(III) reagent with growing utility in modern synthetic methodology, including iodine(III)-mediated ring-expansion chemistry. However, its application as a stoichiometric reagent requires reliable access to preparative amounts. This article describes a practical chromatography-free protocol for the preparation of F₅-PIDA on a ca. 300 g scale by the oxidation of pentafluoroiodobenzene with sodium hypochlorite pentahydrate in acetic acid. The product was isolated by a simple slurry trituration in the hexane/MTBE mixture giving F₅-PIDA in the yield of 65% and the purity of ≥ 98%. The thermogravimetry-differential thermal analysis has shown that F₅-PIDA is stable up to approximately 100-110 °C, while the rapid decomposition occurs above this temperature range. The protocol developed provides a reliable preparative access to high-purity F₅-PIDA and practical thermal data for its safe use.

Cyclic voltammetry was applied to a series of substituted bis(2-nitrophenyl)disulfides in acetonitrile containing tetraethylammonium tetrafluoroborate under unified experimental conditions. Seven compounds were initially considered (S01-S07). One of them (S07) proved practically insoluble in acetonitrile and was excluded from further analysis. As a result, the electrochemical study was performed for six compounds (S01–S06). Among them, three compounds had voltammograms suitable for semiquantitative treatment, including the comparison of cathodic peak currents, whereas the remaining three compounds provided only qualitative electrochemical information due to their limited solubility and attenuated current response. The multistage cathodic behavior was observed in all cases suitable for analysis. The comparison with nitrobenzene measured under identical conditions indicated a nitro-related reduction process in the region of approximately –1.1 V vs Ag/AgCl and a stronger cathodic process near –1.7 V, which was consistent with the cleavage of the disulfide bond and might overlap with a deeper nitro-related reduction. Substituent effects were evident both in peak potentials and, for the more soluble subset, in the cathodic current value. The results show that cyclic voltammetry is a useful screening tool for substituted aromatic nitrodisulfides, even when the solubility prevents the uniform quantitative comparison across the whole series.