Bromide and Hydrobromide Salts: Showing a Significant Difference in the Pharmaceutical Sciences through a Colorful Chemical Demonstration

In organic chemistry, nomenclature is often one of the topics that is least enjoyable for students. In the pharmaceutical field, solid knowledge of nomenclature is essential to appropriately manipulating and using chemicals or drugs. To illustrate the importance of this topic, a demonstration using two well-known drugs with closely related names, scopolamine hydrobromide and N-butyl-scopolamine bromide, is proposed. This original extractability experiment uses lipophilic ion pairs, which are generated by the interaction between the cationic form of the drug and the anionic form of Bromophenol Blue, the counterion. The latter makes it easy to visualize the interaction between the cation and counterion by coloring the organic solvent, thereby differentiating between the amine and the quaternary ammonium functional groups. This may help students improve their knowledge of physicochemical properties of amines and quaternary ammoniums, not only in the context of organic chemistry but also in other subjects examined later in their study program. Indeed, due to having different bioavailabilities, the activity of these compounds is very different in terms of their toxicity and targeted tissues. It is therefore important to emphasize, for future daily pharmaceutical activity, the necessity of using the correct product, as drug mix-up may have serious consequences for patients. Unlike the classical extractability procedure, the experiments presented in this demonstration illustrate the permanent ionization of quaternary ammonium, demonstrating the difference in the chemical properties between quaternary ammonium and amine salts.