Synthesis of Schiff Bases Compounds from Oxamic Hydrazide: Spectroscopic Characterization, X–ray Diffraction Structure and Antioxidant Activity Study

The compounds (E)–2–amino–N'–(1–(2–hydroxyphenyl)ethylidene)–2–oxoacetohydrazide (I) and (E)–N'–(2–hydroxy–3–methoxybenzylidene)–2–amino–2–oxoacetohydrazide (II) were synthetized by the 1:1 ratio condensation reaction of oxamic hydrazide and 2–hydroxyacetophenone or o–vanillin respectively. The two compounds were characterized by physico–chemical analyses, elemental analysis, FTIR, 1H and 13C NMR spectroscopies techniques. The structure of the compound (I) was determined by single–crystal X–ray diffraction study. The compound (I) (C10H11N3O3) crystallises in the triclinic space group P–1 with the following unit cell parameters: a = 7.0399 (5) A, b = 8.6252 (8) A, c = 9.5474 (9) A, a = 81.730 (3)°, b = 72.738 (3)°, g = 67.450 (3)°, V = 510.99 (8) A3, Z = 2, T = 173 (2) K, m = 0.11 mm–1, Dcalc = 1.438 g/cm3, Rint = 0.028, Rsigma = 0.073. The oxamic hydrazide moiety of the molecule is slightly twisted as reflected by the torsion angles values of 177.2 (2)° [N1–N2–C9–C10], –171.3 (3)° [N2–C9–C10–N3], –4.6 (4)° [O2–C9–N2–N1] and 8.4 (4)° [O3–C10–C9–N2]. The intramolecular hydrogen bond O1(phenol)–H1•••N1(hydrazide) which close in S (6) ring stabilized the conformation. The intermolecular hydrogen bonds, C3–H3•••O1i(phenol) (i: −x+1, −y, −z+1), N3(amide)–H3A•••O3ii(amide) (ii: −x+1, −y+2, −z) and N3(amide)–H3B•••O2iii(hydrazide) (iii: −x+1, −y+1, −z) lead to the formation of sheets parallel to ac plane. Compounds (I) and (II) showed antioxidant activities less than 10% inhibition of DPPH.