New, high sensitive organic reagents for cobalt

Abstract

Heterocyclic azo dyestuffs, 5-(2-pyridylazo)-2, 4-diaminotoluene(PADAT) and its analogs have been prepared, and their possible use as spectrophotometric reagents has been investigated. Cobalt(II) and PADAT in a slightly acid, neutral or alkaline medium form a yellowish brown complex. This complex, on addition of mineral acid, changes into a species of a deep violet color. The reagent itself and the violet complex are very stable even in strongly acid solutions, and the system follows Beer's law; the optimal range for measurements in a 1-cm cell is 0.0010.4 ppm cobalt in 27 N hydrochloric acid. The yellowish complex which is formed at pH 411 can be extracted with 3-methyl-butanol or n-butyl phosphate. The reagent blank is also negligiable at an absorption peak of the violet complex. Common anions and cations do not interfere. The molar absorption coefficient of 5-[ (3-benzyloxy-2-pyridyl) azo]-2, 4-diaminotoluene (3-Benzyloxy-PADAT), PADAT, 5-[(5-chloro-2-pyridyl) azo]-2, 4-diaminotoluene (5-Cl-PADAT), 5-[ (5-bromo-2-pyridyl) azo]-2, 4-diaminotoluene (5-Br-PADAT) and 5-[(3, 5-dichloro-2-pyridyl)azo]-2, 4-diaminotoluene (3, 5-diCl-PADAT) are 1.10×105, 1.16×105, 1.26×105, 1.30×105 and 1.38×105 cm2mol-1 at 591, 561, 573, 574 and 590 nm, respectively.