Unimolecular nucleophilic substitution (S N 1): Structural reactivity evidenced by colored acid-base indicators

Abstract

The different reactivities between 1°, 2°, and 3° butyl chlorides by the unimolecular nucleophilic substitution (S N 1) mechanism were easily observed at 60 °C by a solvolysis reaction in ethanol with ether formation. The hydrogen ion from the byproduct HCl reacted with an acid-base indicator such as methyl red to induce a color change. At room temperature, the addition of AgNO 3 was used to detect the released chloride ion by AgCl precipitation. The reactivity order (3° > 2° ≫1°) was visually confirmed by both a color change in an indicator and precipitate formation by these safe, quick, and easy assays.