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Robust Cationic Quaternary Ammonium Surfactant-Catalyzed Condensation Reaction for (E)‑3-Aryl-1-(3-alkyl-2-pyrazinyl)-2-propenone Synthesis in Water at Room Temperature

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journal contribution
posted on 05.08.2013, 00:00 by Bheru S. Kitawat, Man Singh, Raosaheb K. Kale
An efficient, convenient, and environmentally benign method for synthesis of novel (E)-3-aryl-1-(3-alkyl-2-pyrazinyl)-2-propenone in aqueous micellar medium at room temperature has been developed. Initially, the reaction between 2-acetyl-3-methylpyrazine (1a; 1 mmol) and 4-bromobenzaldehyde (2c; 1 mmol) was separately conducted with 10 mol % cationic quaternary ammonium surfactants (CQAS), namely, methyltrioctylammonium chloride (MTOAC), methyltrioctylammonium bromide (MTOAB), cetylpyridinium chloride (CPC), cetylpyridinium bromide (CPB), dodecyltrimethylammonium bromide (DTAB), and hexadecyltrimethylammonium bromide (CTAB). An 89.0% maximum yield was noted with DTAB due to higher a catalyzing effect on the reaction. The other surfactants used for the same reaction have produced only 50–86% yield. DTAB was found to be a most efficient catalyst because of the higher yield in the reaction. Therefore, applying DTAB, the various reaction conditions such as effect of concentration (2.5–20 mol %), temperature (rt-reflux), and reusability of aqueous micellar medium were investigated. Thus, the 15 mol % DTAB used for synthesis of a series (3a3l) of compounds at room temperature produced a 78–94% yield. The method using DTAB allows for the preparation of a variety of aryl propenones with better yield and purities, making any further purification unnecessary. DTAB is also considered environmentally benign and may lead to developing a new option of synthesis in green chemistry. The structures were confirmed by FTIR, 1H NMR, 13C NMR, LCMS (Q-TOF), and elemental analysis.