Synthesis, Characterization of Some Hydroxamic Acids and Their Complexes

Abstract

This work dealt with the synthesis, characterization of four hydroxamic acid and their complexes. The hydroxamic acids Ligands synthesized were (nitrobenzo hydroxamic (l1), N-p-tolyl nitrobenzohydroxamic acid (l2), N-phenylb-nitrobenzo hydroxamic acid (l3) and di.Phenyloxalo- hydroxamic acid (l4).There were prepared using (Esterifiaction and coupling method) according to the action of an alkaline solution of hydroxylamine on the sodium salt of methyl-nitrobenzoate in aqueous medium. All synthesized ligands were solid, air stable and of high yield. The synthesized acids were characterized by melting point and spectroscopic techniques, vis FT-IR, UV- vis spectroscopy, (1H and 13C) NMR, and mass spectroscopy. All ligands show an IR spectrum absorption in the 1315- 1348 cm_1 which were assigned to 𝜈 C-N stretching mode of hydroxamic acids. The IR stretching vibration bands at 1691cm-1 ,1695cm-1,1693cm-1 and 1635cm-1 correspond to the 𝜈 C=O group function of L1, L2 , L3 and L4 respectively. The ranges of 3112-3442cm-1 correspond to 𝜈 O-H stretching vibration of hydroxyl group (vibration of O-H in L4 is higher than the first three ligands, L4 have two functional group of hydroxyl). A group of bands observed in the range 918-941cm-1 may be due to the (N-O) stretching vibrations. The electronic impact mass spectra of L1, L2 and L3 hydroxamic acid (ligands) showed molecular ion (M+) peaks at m/z = 182 a.m.u, m/z = 274 a.m.u and m/z = 259 a.m.u, corresponding to the [C7H7 N2 O4]+, [C14H16N2O4]+ and [C13H13N2O4]+ respectively. Their 1H NMR spectra exhibiting proton signals in the range 5.8 – 8.8 ppm was assigned to (L1), while the singlet at 2.60 – 3.43 ppm, to hydroxyl group, a signal at 2.38ppm is due to an aromatic methyl group(L2), the multiplet at (7.43 – 7.70) ppm assigned to protons(L3). The 13C NMR spectrum show signals vi due to carbonyl (C=O) nearly 167.02 ppm. The chemical shifts of aromatic carbons appear in the region (119.60 – 150.47) ppm. Beside these signals, a signal nearly 16 ppm appeared which corresponding to atom of the Alkyl group. The NMR spectra of each analogue showed the general characteristic bands associated with hydroxamic acids. 1- (3-4ppm) due to Ar-OH 2-(7.21-832ppm) due to Ar-H 3- (2.38ppm) due to aromatic methyl group. Hydroxamic acids have a high binding affinity to a range of transition metal ions, particularly Fe (III), V (V) and Cu (II). The ligands have useful application in coordination chemistry. In this context this thesis had focused on the complexation reactions mainly in aqueous solutions. Complexation between synthesis ligands and metals were done by UV-vis Spectro-photometric method (four hydroxamic acids (L1, L2, L3 and L4) with Fe (III), V (V) and Cu (II). The colored products showed absorption band at λmax 420, 410, 520nm respectively for Fe(III), Cu (II), and V (V) with L1, 410, 435,510nm respectively for Fe(III), Cu (II), and V (V) with L2, 415, 425, 520nm respectively for Fe (III), Cu (II), and V (V) with L3, 420,410,520nm respectively for Fe (III), Cu (II), and V (V) with L4. The parameters of (pH, Molar ratio, time) that affect the formation of complexes were studied. The Molar ratio of complexes was (1:1) Metal: Ligand for all complexes. The electronic spectra of all the complexes showed that the inter-ligand transitions were shifted coordination of ligands to metal ions. The molar ratio for metal: ligand complexes using the continuous variation method, the ratio of the four ligands with the three metals were found to 1:1, 1:2, 1:3, and 1:4 measured at different pH values.