Collect. Czech. Chem. Commun. 1984, 49, 1360-1366

5-Methyl-1,3,4-thiadiazolylazo-resorcinol as a new metallochromic indicator for complexometric titration of lead

Juan Cachoa, Cristina Nerinb and José Romeroa

a Departamento de Quimica Analitica, Facultad de Ciencias, Universidad de Zaragoza, Espana
b Departamento de Quimica, Escuela Tecnica Superior de Ingenieros Industriales, Universidad de Zaragoza, Espana


The synthesis, characteristics and analytical reactions of 5-methyl-1,3,4-thiadiazolylazo-resorcinol (MTDAR) are described. Their dissociation constants of OH groups in ortho and para position are respectively pK1 = 8.09 ± 0.01 and pK2 = 5.72 ± 0.02. For the Pb-MTDAR complex, the molar absorptivity is 2.0 . 104 l mol-1 cm-1 at 525 nm and pH = 8.0. The complex of ML type is formed. Beer`s law is obeyed between 0 and 9 ppm of Pb. The formation constant is 7.9 . 105. The studied reagent can be employed as a metallchromic indicator in chelometric titrations with visual and photometric indication. The interferences and their elimination are studied, too. The triestimul coordinates to chromatic transition are determined. This transition is increased by adding indigo carmine as an inert dyestuff.