Formation of Palladium(II)-4-(2-Pyridylazo)resorcinol Complexes and lts Application to the Extraction Spectrophotometric Determination of Palladium(II)

Abstract

Palladium(II) formed four kinds of stable 1:1 chelates with 4-(2-pyridylazo)resorcinol(PAR or II2R), i'e.at pH 4, a green chelate [Pd(H2R)OH2]2 (e=1.75x10' at 440 nm and e=8.63x103 at 580 nm), at pH 4N7 two kinds of red chelates [Pd(HR)OHa] (e=2.68x10' at 515 nm) and [Pd(R)OH2]e (e=2.89x10' at 525 nm) and at pH 8-11 a red chelate [Pd(R)OH]- (e=3.40x10' at 520 nm), (Fig. 1 and 4). The acid dissociation constants of the chelates were estimated as Kai=, Pd(HR)OH2 (H+)/[Pd(H3R)OH22 ]= 14 ss ho 5 and Kaa= [Pd(R)OH2 H+]/(Pd(HR) OH, ')=10-536 e5 in 5Q% aqueous dioxane solution at 25C, , ec=O.1 (Fig. 5 and 6)
At pH 6.vll, Pd(U)-PAR chelates reacted with tetradecyldimethylbenzylammonium chloride (Zephiramih, Zeph eCl-) to form an iorvassociation complex which was easily extracted into chloroform and had a maximal absorbance at 540 nm with molar absorptivity of 3.29x10 (Fig. 2).
Beer's law was confirmed over a range of Ov20 ptg Pd2/10 ml CHCIs and sensitivity which gave the absorbance of O. OOI was O.0032 ptg Pd2/cm2. Pd(II)-PAR chelate was more stable thanPd(II)-EDTA chelate so' that EDTA could be used as a masking agent for hindering metal ions. Among twenty kinds of diverse metal ions, only Fe(II II)and C (III)ions seriously interfered with the determination (Table 1). The role of EDTA was not restricted only as a masking agent, but also as an agent which accelerated the rate of the PAR chelate formationby preventing the hydrolysis of Pd2 ion.