The mechanism of Hager's test for glucose

Abstract

There are several colour tests for glucose detection, not being the case for glucose estimation. Thus, the quantitative test for glucose due to Hager is fairly important. The test is based on an oxide reduction process. It employs mercury oxide, sodium chloride, and sodium acetate in a slightly acidic medium (2.5% acetic acid). In the presence of glucose, this reagent precipitates the very insoluble dimercury dichloride which is related to glucose content and concentration. Since the reaction route has not been described, and less the reaction mechanism, both are provided in this communication. Each step is fully commented and the electron flow is given. The reactive intermediate is H-O-Hg+ which reacts with nucleophilic species. This way hydroxymercury glucose-enolate is formed, as well as, chloromercury hydroxide. Proteolysis of both intermediates and reaction with chloride ions gives the two key intermediates, chloromercury glucose-enolate and the cation Cl-Hg+. A bimolecular reaction between these intermediates occurs via a concerted mechanism (redox reaction). The oxidation product is 2-ketoglucose (Glucosone), whereas the reduced compound is dimercury dichloride.