The chemistry of the Baeyer and Hoppe-Seyler test for glucose in urine

Glucose is an analyte and has drawn the attention of researchers for a long time. Baeyer accomplished several synthesis for indigo. The one under study was adapted by Hoppe-Seyler for detection of glucose in urine. The blue colour observed in the test is due to the formation of indigo. The reagent used in the test is o-nitrophenylpropiolic acid. However the route from the starting compound to indoxyl has not been cleared out. There are missing intermediates or inadequate ones have been proposed. In this communication we provide the route and the reaction mechanism involved in each step. This is in accordance with experimental data and the chemical deportment of the involved compounds.