Kinetics and Mechanism of Oxidative Conversion of 5-Hydroxyindole to 2-Oxo-5-hydroxyindole by Chloramine-B in Basic Solutions

The conversion of 5-hydroxyindole (Indole) to 2-oxo-5-hydroxyindole is an important oxidative transformation in synthetic organic and biochemistry. Under pseudo first-order conditions of[Indole]o >>[chloramine-B or CAB]o, the indole oxidation reaction in a basic solution follows the following experimental rate law: rate = k‘[CAB]o[Indole]o[OH-]x/[BSA]y, where BSA represents benzenesulfonamide and x and y are fractional orders. The retarding effect of BSA on the rate indicates its involvement in a fast pre-equlibrium in the mechanism of oxidation. Activation parameters have been determined. The variation of[OH-] at constant[BSA] was performed to evaluate the equilibrium and decomposition constants. Based on the mechanism proposed, a rate law has been derived. Furthermore, the methodology developed could be adopted in the synthesis of 2-oxo-5-hydroxyindole. Advantages of the method include: mild reaction conditions, short reaction time, ease of isolation of products, cost effectiveness, and the use of eco friendly reagents.