Stability of aqueous solutions of pirbuterol

The hydrolytic degradation of pirbuterol was investigated under saturated oxygen conditions over a wide range of pH values and at different temperatures. Two of the five observed breakdown products were positively identified. The first-order decomposition rate appeared to depend on the rate constants of the four dissociated ionic species. The most stable region for the drug was pH 1-2, where the diprotonated molecule predominated; appropriate thermodynamic parameters were calculated.