Solvent Extraction and Indirect Spectrophotometric Determination of Cyanate, Thiocyanate and Selenocyanate Anions with the Copper(II) Complex of Di-2-pyridylmethanone 2-Quinolylhydrazone

Abstract

The extraction of cyanate, thiocyanate or selenocyanate ions with the copper(II) complex of di-2-pyridylmethanone 2-quinolylhydrazone (DPQH) into benzene has been investigated spectrophotometrically at 25° C and μ=0.1. Copper(II) reacts with DPQH in a weakly acidic solution to form a dipositively charged mono complex (Cu(HL)²⁺) with the formation constant of log β_Cu(HL)=9.47. This complex undergoes deprotonation to a highly colored CuL⁺ species in the higher pH range, the proton dissociation constant having been determined to be pK_ac=4.53. In the presence of the above-mentioned anions both complex species can be extracted into benzene as a highly colored ternary complex, Cu(L)A (A=NCO⁻, NCS⁻ or NCSe⁻). The extraction constant, defined as K_ex=[Cu(L)A]_o/[Cu(L)⁺][A⁻] (the subscript (o) denotes the organic phase), is found to be 4.96 for NCO⁻, 6.15 for NCS⁻ and 5.56 for NCSe⁻ in logarithmic units. On the basis of the above observations, a sensitive spectrophotometric method for the determination of up to 3×10⁻⁵ M of the anions has been developed by measuring the absorbance of the organic phase at 540 nm.