| Synthesis and Characterization of a Novel Crowned Schiff Base Ligand Linked to Ionic Liquid and Application of Its Mn(III) Complex in the Pyrazole synthesis |
| کد مقاله : 1226-ICOC |
| نویسندگان |
|
reza sandaroos *1، sanaz naderi2 1عضو هیات علمی 2Chemistry department, University of Birjand, Birjand, Iran |
| چکیده مقاله |
| A homogeneous ionic liquid–based catalyst was synthesized (Scheme 1). A novel Schiff base ligand functionalized with an ionic liquid and a crown ether moiety was prepared and subsequently coordinated to Mn(III). Finally, the catalyst was fully characterized by FT-IR spectroscopy, TGA, ICP, CHN elemental analysis, and XRD techniques [1].The manganese complex was used, in the presence of the oxidant hydrogen peroxide, in the synthesis of pyrazoles via the oxidation of benzylic alcohols. Various reaction parameters were systematically investigated, and the highest efficiency was achieved at 50 °C using 0.004 g of catalyst and 0.3 mmol of oxidant under aqueous (H₂O) conditions. The effect of aromatic substituents on benzylic alcohols was evaluated during the optimization studies of pyrazole synthesis. In this reaction, benzyl alcohols bearing electron-donating substituents such as 2-hydroxybenzyl alcohol, 2-methoxybenzyl alcohol, and 3-methoxybenzyl alcohol increase the yield to about 85%, while stronger resonance-donating groups in the para position, namely 4-hydroxybenzyl alcohol and 4-methoxybenzyl alcohol, provide the highest yields of around 90%. Substrates with neutral or weakly influencing groups, including benzyl alcohol, 4-chlorobenzyl alcohol, 2-chlorobenzyl alcohol, and 4-methylbenzyl alcohol, show yields close to 80%, indicating that these substituents exert only a limited effect on the oxidation and cyclization steps. In contrast, the compound containing a strongly electron-withdrawing group, 4-nitrobenzyl alcohol, exhibits the lowest yield (40%) due to significant reduction of electron density at the benzylic position, which makes the oxidation step markedly more difficult. Attaching the crown ether ring to the Schiff base brings the oxidant closer to the catalyst’s central metal and increases its oxygen affinity, resulting in faster and more efficient alcohol oxidation. Additionally, the crown ether and ionic liquid moieties enhance the complex’s solubility in water, allowing the reaction to be performed under green conditions using H₂O₂ in an aqueous medium. |
| کلیدواژه ها |
| Ionic liquid, Crown ether, Manganese complex, Pyrazole synthesis |
| وضعیت: پذیرفته شده |