Thermal and spectral properties of alkali metal complexes of vitamin K3 analogue phthiocol

Abstract

Hydroxynaphthoquinones, alkali, and alkali metal salts were used to synthesize several biologically important molecules. As hydroxynaphthoquinones act also as potential ligands, it is possible that alkali metal complexes may be formed as intermediates in such reactions. To ensure this, the reactions of 2-hydroxy-3-methyl-1,4-naphthoquinone (phthiocol, a vitamin K3 analogue) with sodium metal, alkali such as NaOH and KOH, and alkali metal salts such as CH3COONa, Na2CO3 and K2CO3 were studied in the present investigation. The products were characterized by various analytical techniques, namely elemental analysis, FT-IR, 1H NMR, UV–Vis, thermogravimetric (TG) analysis, GC–MS, and DSC studies. 100 % reduction of the ligand was observed in Phth-1 with sodium metal as reducing agent. The solution of CH3COONa, NaOH, KOH, and K2CO3 in methanol facilitates the reduction of phthiocol ligand. The reduction of the ligands may be probably due to disproportionate reaction of the ‘catechol’ form and the fully oxidized naphthoquinone form of the ligand. The radical signatures of the ligands in complexes were detected by EPR studies and also by carbonyl frequencies in FT-IR spectra. Non-isothermal TG studies confirm the presence of adsorbed and coordinated water molecules. Residue formed after complete decomposition was observed to be 1/2 Na2O in Phth-1 to Phth-3, K2O in Phth-4, and 1/2 K2O in Phth-5. Based on GC–MS and TG studies, three decomposition mechanisms are being proposed for all complexes.