Conformational analysis on protonation and deprotonation of calmagite in protic solvents and its reactivity through Fukui function

In the present work a systematic theoretical study on 1-(1-hydroxy-4-methyl-2-phenylazo)-2-naphthol-4-sulfonic acid was performed. All possible protonation and deprotonation degrees were analyzed. The use of solvents in calculations affect in a direct way the stability of azo and hydrazone tautomers. This is the first systematic theoretical study, from electronic structure point of view, on this widely used azodye. Additionally, local reactivity utilizing the Fukui function was obtained. Interestingly, reactivity of the molecule undergoes no significant changes despite azo–hydrazone tautomerism, since the Fukui functions are not modified in a significant way in both tautomers. It is worth mentioning that results presented here are important in studies about degradation of this kind of azodyes, in studies when calmagite forms complex compounds with metallic and lanthanide atoms or in photoabsorption studies since spectrum depends on protonation and deprotonation degree and on the most stable conformers in the sample.

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