The acetylsalicylic acid-bromine system for multicomponent kinetic determinations.

When acetylsalicylic acid (ASA) is added to a bromine solution, slow decay of the bromine concentration occurs. Hydrolysis of ASA yields salicylic acid (SA) slowly, and bromine reacts rapidly with SA but not with ASA. Simulated reaction profiles based on a two-step reaction scheme agree closely with the experimental profiles. This behaviour can be used to develop kinetic methods for resolution of mixtures of ASA and a second component that reacts rapidly with bromine. A remarkable practical feature of these methods is that the faster the reaction between bromine and the second component, the simpler and easier the analytical method. The reaction between hydroquinone (HQ) and bromine is rapid and a very simple analytical method is proposed. Mean validation errors of 2.8% for HQ and 7.2% for ASA have been found with concentration ratios [ASA]:[HQ] ranging between 0.32 and 19.4. The reaction between paracetamol (AAP) and bromine is not so fast and more complicated calibration methods are required. After use of a calibration plane mean validation errors of 2.7% for AAP and 8.1% for ASA have been found with concentration ratios ranging between 1.28 and 77.5. Similar kinetic approaches should be possible with many other mixtures of ASA and a second fast-reacting component, because bromine reacts with many inorganic and organic species by oxidation-reduction, substitution, and addition reactions.