J. J. Nué-Martínez, I. Alkorta, C. Dardonville
Jun 13, 2021
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Journal
Arkivoc
Abstract
The reported two-step synthesis of 2-isopropoxy-4-nitrobenzoic acid from 2-hydroxy-4-nitrobenzoic acid, using iodopropane/K2CO3 and subsequent hydrolysis of the isopropyl 2-isopropoxy-4-nitrobenzoate intermediate with 45% NaOH/THF-EtOH at 80 °C, was reconsidered. (Z)-1,2-bis(4-carboxy-3isopropoxyphenyl)diazene-1-oxide derivative (3), which was isolated as main product (92%) of the reaction, was characterized by IR, H, C, and N NMR spectroscopy. The N chemical shifts were consistent with the trans-configuration for this azoxybenzene derivative. As an alternative, synthesis of 2-isopropoxy-4nitrobenzoic acid was accomplished in high yield (82%) working at room temperature and using lithium hydroxide instead of concentrate NaOH. Incorrect reaction temperature report or measurement in the published protocol (J. Org. Chem. 2011, 76, 7040) probably accounts for the discrepancies with our findings.