S_N2: Synthesis of 1-bromobutane

Introduction

Alkyl halides can be prepared from their corresponding alcohols via an acid catalyzed substitution reaction. The mechanism of these acid catalyzed substitution reactions are labeled as S_N1 (substitution, nucleophilic, unimolecular) and S_N2 (substitution, nucleophilic, bimolecular). Tertiary alcohols follow the S_N1 route, primary alcohols follow the S_N2, route and secondary alcohols can follow either path.

The S_N2 reaction for converting 1-butanol to 1-bromobutane involves rapid protonation of the alcohol along with a concerted step where the nucleophile attacks the carbon, displacing water. The backside attack by the nucleophile is favored for primary substrates and less ideal for secondary and tertiary substrates.

The product will be verified by gas chromatography by comparing the chromatograms of the starting material, 1-bromobutane standard, and your product. Confirmation of your product, 1-bromobutane can also be performed by reacting the product with a solution of sodium iodide in acetone. The primary alkyl halide will react by means of an S_N2 mechanism with the sodium iodide to form an insoluble precipitate. The appearance of a precipitate indicates a positive result suggesting the presence of a primary alkyl halide.

Objectives

In this experiment, you will

• Synthesize tert-butyl chloride via an S_N1 reaction.
• Confirm the presence of a tertiary alkyl halide using the silver nitrate test.
• Verify the product by gas chromatography.