Study of some Ortho Hydroxy Acetophenoximes as Spectrometric Reagents

Abstract

In the course of this research work, two ortho hydroxy acetophenoxime compounds namely 2,5-dihydroxy acetophenoxime and 5-Chloro-2-hydroxy- 3-methyl acetophenoxime were synthesised and purified by recrystallization several times. Their purities were confirmed by the method of thin layer chromatography with the aid of UV absorption spectroscopy and elemental analysis. Structural elucidation of these two synthesised oximes were also studied by infrared absorption spectrometry, proton and carbon 13 nuclear magnetic resonance spectroscopy. Metallochromic properties of the synthesised oximes were primarily investigated at various pH. Among the investigated metal ions, nickel (II) showed green coloured pricipitate in slightly alkaline solution with the two oximes whereas copper (II) showed buff coloured precipitate in acidic solution. The other metal ions, Fe (III), Mn (II) and Co (II) gave dark coloured soluble complexes in acidic and basic medium. Solvent extraction spectrometric method was used for determining the amount of Ni (II) by extracting the precipitate of Ni-oxime complex with chloroform. Experimentally, it was found that the performance of 5-chloro-2-hydroxy-3-methyl acetophenoxime as spectrometric reagent was satisfactory whereas the complex of Ni-2,5-dihydroxy acetophenoxime was partially extractable into chloroform layer and gave very small sensitivity for Ni detection. In the chloroform extraction spectrometric study of Ni-5- chloro-2-hydroxy-3-methyl acetophenoxime complex, it was found that at pH 8, the green precipitate of 1:2 mole ratio complex was readily extracted into chloroform and stable for at least 24 hours. The efficiency of the extraction between water and chloroform determined by atomic absorption spectroscopic method was reported to be over 98 %.The solubility of the complex in chloroform was 0.195 g per litre. At 607.0 ran, the conformity to Beer's law as in the range of 0-20 ppm of Ni with the molar absorptivity 1.6 X 10² L mol ⁻¹cm \ equivalent to the specific absorptivity 2.73 X 10 ⁻³mL g⁻¹cm and Sandell sensitivity 0.3663 µg cm ⁻². The effect of coexisting ions was also investigated. 5-Choro-2-hydroxy-3-methyl acetophenoxime was also used as complexometric reagent for determination of Fe(III) by the method of direct titration with EDTA using it as end point indicator. At the end point, the colour change was form dark brown to yellow. The titration sensitivity for Fe(III) determination was in the range 5 to 30 mg with the accuracy of ±1.0 %. The following ions, Pb(II), Zn(II), Co(II), Mn(II), Cu(II), Ni (II), P0₄³⁻, W0₄²- C₂0₄²- and M0O₄²- interfered seriously. The titration method could be applied comparatively for the determination of iron in iron ores, cements and barite sample.