Equilibrium constants of the sorption of pyridinecarboxylic acids by polystyrene type sulfocationite

The processes of sorption of pyridine-3-carboxylic (nicotinic) and pyridine-4-carboxylic (isonicotinic) acids by sulfonic acid cation exchangers of the polystyrene type (CU-2-4 and CU-2-8) from aqueous solutions with different pH values were studied. Analysis of the FTIR spectra of isonicotinic acid, isonicotinic acid sulfate, and CU-2-8 sulfonic cation exchanger filled with isonicotinic acid showed that pyridinecarboxylic acid is in the protonated form in the polymer phase. Experimental data of the equilibrium distribution of acids in the aqueous solution-cation exchange system have been obtained. The values of the equilibrium constants for ion exchange and ligand sorption processes involving various forms of pyridinecarboxylic acid, sulfonic cation exchanger, and protons were calculated. The equilibrium constants for the ion exchange of sulfocationite protons by pyridinecarboxylic acid cations from solution are in the range 3.3-4.4. The selectivity of sulfonic cation exchangers to cations increases in the sequences proton < nicotinic acid cation < isonicotinic acid cation. The values of the equilibrium constant for ligand sorption of molecules are 195-220 dm3/mol for isonicotinic acid and reach 320-330 dm3/mol for nicotinic acid, i.e. the sorption activity of the H-form of the cation exchanger is higher in relation to nicotinic acid molecules. A change in the amount of a crosslinking agent (from 4% to 8% divinylbenzene) in a polystyrene type sulfonic cation exchanger does not significantly affect its sorption activity towards pyridinecarboxylic acids.

Synthesis of cobalt doped mesoporous silica by using the rice husks as both silicon source and template with its catalytic oxidation of 2-methyl pyridine

Cobalt doped mesoporous silica (Co-SiO2) was prepared using the rice husks as both silicon source and template. Structural characterization of the catalysts was done by various techniques, such as Xray diffraction, FT-IR, N2 adsorption/desorption, and scanning electron microscopy. Co-SiO2 was used as a catalyst for the oxidation of 2-methyl pyridine and exhibited high substrate conversion (94.6%) and good product (2-pyridinecarboxylic acid) selectivity (92.4%). It even exhibited higher selectivity than Co-MTiO2, Co-MCM-41, Co-SBA-15. Fast hot catalyst filtration experiment proved that the catalyst acted as a heterogeneous one and it can be reused with almost the same activity.

Chromatography of Hedysarum extracts on modified Sepharose CL sorbents

Aim. To study the chromatographic efficiency of modified Sepharose CL-4B sorbents for separation, purification, and preparation of major components from Hedysarum theinum Krasnob. and Hedysarum neglectum Ledeb. root extracts.Materials and Methods. Sorption capacity of the native and modified sepharose was evaluated in both isocratic and gradient elution modes. 4-pyridinecarboxylic acid derivative [(4-hydroxy-3-methoxyphenyl)methylene]hydrazide (ftivazide) was used as a sorbent modifier ligand. We studied chromatographic properties of Sepharose CL-4B, Sepharose CL-6B, and azoepoxyadsorbent Sepharose CL-4B-DEP-p-nitrobenzohydrazide-ftivazide, a chemically modified analogue of Sepharose CL-4B.Results. Sepharose CL-4B and Sepharose CL-4B-DEP-p-nitrobenzohydrazide-ftivazide were found efficient carriers for liquid column chromatography of water-ethanol Hedysarum extracts. Complete elution of bioactive substances has been achieved exclusively by using sodium tetraborate as an eluent. We were able to identify flavonoids and tannins of different condensation in chromatographic fractions.Conclusion. Comparative chromatography of bioactive substances from Hedysarum root extracts is more efficient if employing Sepharose CL-4B instead of Sepharose CL-6B as a sorbent. Sepharose CL-4B-DEP-p-nitrobenzohydrazide-ftivazide demonstrates excellent separation capacity for tannins and flavonoids.