Decomposition and Stabilization of Drugs. VII. Stability of Norphenylephrine in Aqueous Solution

A kinetic study was made on norphenylephrine in aqueous solution. The decomposition rate of norphenylephrine depended on the rate constants of three dissociated ionic species, kA, kB and kC, and hydronium ion [H3O]+ or hydroxyl ion [OH]- have no catalytic activity. It was found that the most stable pH region for norphenylephrine in aqueous solution is pH 2-5, only one stable ionic species existing in this range. Arrhenius parameters were determined by plotting the decomposition rate constants of three ionic species against temperature, and activation energies were calculated.