Green Synthetic Methods for a Schiff Base from 2-Aminopyridine and 4-Ethoxybenzaldehyde

Abstract

The novel Schiff base was acquired from the reaction between 2-aminopyridine and 4-ethoxybenzaldehyde using three (3) techniques; refluxing in ethanol for 2 hours, stirring in ethanol and an ethanol-water (1:1) mixture at room temperature for an hour. The synthesis of the 2-aminopyridine-4-ethoxybenzaldehyde Schiff base produced dark yellow crystals with melting point range of 95-97^oC. The reaction in ethanol under reflux produced the highest yield of 88.2% while the reaction in ethanol and ethanol-water (1:1 v/v) mixture at room temperature gave 69.2% and 43.5% yield of the compound respectively. The IR spectrum showed the following bands; 1681cm^-1 (C=N), 1595cm^-1 (aromatic C=C stretch), 2981cm^-1 (aromatic C-H stretch), 1509cm^-1 (aromatic C=N stretch), 1155cm^-1 (aliphatic C-C stretch), 1036 (aromatic C-O stretch), 2825 (aliphatic C-H stretch). The ¹³C NMR spectrum showed the following chemical shifts (δppm); 158.48 (C=N, imino), 154.98 and 150.18 (C-N of aromatic pyridine moiety), 121.44 – 137.53 (aromatic carbons), 158.68 (aromatic C-O), 63.88 (aliphatic C-O), 15.22 (aliphatic C). The ¹H NMR spectral data (δppm) for the compound gave the following results; 7.06-7.91, m (8H) (Ar-H), 9.71, s (1H) (HC=N-), 4.10, q (2H) and 1.32, t (3H) (OCH₂CH₃). The spectral data was in agreement to the predicted structure of the Schiff base.