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

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 logβCu(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 pKac=4.53. In the presence of the abovementioned 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 Kex=[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 3×10-5M of the anions has been developed by measuring the absorbance of the organic phase at 540nm.