This work presents the synthesis of six derivatives 3-thioether of 2-hydroxy-1,4-naphthoquinone in a thia-Mannich type reaction with a greener and more effective procedure in comparison to the literature, using an aqueous solution of formalin as the methylene source and formic acid as an activator and co-solvent, giving good yields. A new procedure was standardized with a Michael type reaction for the synthesis of five bis-thioether products with 2,3-dichloro-1,4-naphthoquinone and 3 new bis-thioether products with 6,7-dichloro-5,8-quinolinquinone, using the “cesium effect” with Cs2CO3 as the base and 1,2-dimethoxyethane as solvent, with moderate to good reaction yields. The compounds were fully characterized with spectroscopic techniques. All the compounds were screening for biological activity, with only the 6,7-bis(t-butylthio)-5,8-quinolinquinone shows a promising activity against Staphylococcus aureus and Candida albicans, compared to vancomycin and ketoconazole. Solvatochromic effect was observed and quantified in seven of the compounds, with a maximum value of Δλ: 22 nm (ΔE: 12.08 kJ/mol). No correlation was found with several polarity parameters to help explain the solvatochromic behaviour. Thermochromic effect was observed for 2,3-bis(1-dodecylthio)-1,4-naphthoquinone. The results of several meassurements lead to the hypothesis that this phenomena arise from a shift in the HOMO-LUMO absorbtion band between the aromatic π-system of one molecule and the σ* C-S of an adjacent molecule.

Synthesis, characterization, and chromic properties of thio-ether derivatives of 1,4-naphthoquinones

2019 Spring National Meeting

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