新显色剂2-(2-咪唑偶氮)-苯甲酸的合成及其与钴的显色反应研究

Synthesis of 2 (2 imidazolylazo) benzoic Acid and Its Color Reaction with Cobalt

合成了新显色剂２（２咪唑偶氮）苯甲酸（简称ＩＡＢＡ），分子式Ｃ１０Ｈ８Ｎ４Ｏ２，分子量２１６．２０，熔点２１３℃，各级酸离解常数ｐＫａ１为３．２，ｐＫａ２为９．８，研究了它的性质及其与钴显色反应的条件。在ｐＨ７的ＮＨ４Ａｃ介质中，试剂与钴形成紫红色络合物，λｍａｘ为５４６ｎｍ，试剂的λｍａｘ为４６２ｎｍ，Δλ为８４ｎｍ，Ｃｏ２＋与试剂络合比为１∶２，摩尔吸光系数１．６１×１０４Ｌ·ｍｏｌ－１·ｃｍ－１，Ｃｏ２＋在０～０．８ｍｇ／Ｌ遵守比尔定律。所拟方法直接测定了工业废水及ＶＢ１２中痕量钴，结果与原子吸收法相符，加标回收率为１０１．３％～１０２．２％，ＲＳＤ（ｎ＝６）在２．０％～２．７％。

The synthesis of a new reagent 2 (2 imidazolylazo) benzoic acid (IABA) and the condition of color reaction with Co 2+ are reported in this paper. The results from UV spectrometric, IR spectroscopic and 1HNMR spectroscopic analysis show that its structure formula is COOH NN[LJ(H,S(1)W(3,4,5)] N NH [JJ3,LX,X,2;5,Z,1*3/7;1,Z] with molecular formula C 10 H 8N 4O 2, molecular weight 216.20, m.p. 213℃, dissociation constants pKa 1 3.2, pKa 2 9.8. It is a red brown crystalline powder and easy to be dissolved in polar solvent. The new reagent reacts with cobalt to form a stable red complex (1∶2) in pH 7.0 NH 4Ac buffer solution with λ max =546 nm. The apparent molar absorptivity is 1.61×10 4 L·mol -1 ·cm -1 . Beer's law is obeyed in the range of 0～0.8 mg/L for Co 2+ . The interferences from numerous cations and anions on the determination of Co 2+ were examined. The results show that the maximum tolerance for foreign irons on determination of 20 μg of Co are K +, Na +, NH + 4,Cl -, Br -, I -, SO 2- 4, NO - 3, PO 3- 4, CO 2- 3, Ca 2+ , Mg 2+ 10 mg; Sr 2+ , Ba 2+ 4 mg; Cr 3+ 2 mg; As(Ⅲ) 1 mg; Mn 2+ , Zn 2+ , Sb 3+ , Pb 2+ , Hg 2+ , Ag + 0.5 mg; UO 2+ 2 0.2 mg, Sn(Ⅳ), Ni 2+ 0.5 mg; Fe 3+ , Cu 2+ 1.5 mg; V(Ⅴ) 0.01 mg; Bi 3+ 0.3 mg; Cd 2+ 0.005 mg; NH 4F, thiourea 500 mg, citric acid 2 mg; tartaric acid 100 mg. The method has been applied to the direct determination of trace Co 2+ in VB 12 , waste water samples with satisfactory results. The recovery of standard addition is 101.3%～102.2% with precision of 2.0%～2.7% RSD( n =6).