New reagent for spectrophotometric determination of salicylic acid

In 6M hydrochloric acid solution, salicylic acid reacts with pentachloronitrosyliridate [Ir(NO)Cl(5)](-) to form a new 1:1 complex giving two absorption maxima at 369 and 446 nm with molar absorptivities both of 1.1 x 10(4) l.mole(-1) cm(-). The reaction is second order with apparent energy, E(a), of 16.8 kJ/mole. At constant temperature, the apparent rate constant k increases to a maximum when the concentration of hydrogen ion is decreased to 4-5M and the concentration of chloride ion is kept at approximately 6M. The mechanism of the reaction is also discussed. In alkaline solution, the absorption maxima shift to 381 and 506 nm with molar absorptivities of 6.0 x 10(3) and 2.4 x 10(4) l.mole(-1) cm(-1), respectively. Salicylic acid can be determined spectrophotometrically with high sensitivity and precision. Benzoic and boric acids do not interfere.