Dehydration and Dehydrobromination

DEHYDRATION OF 1-BUTANOL AND 2-BUTANOL

DEHYBROMINATION OF 1-BROMOBUTANE AND 2-BROMOBUTANE

Abstract

By conducting four elimination reactions, alkenes were produced through E1 and E2 mechanisms. The dehydration was performed on the molecules 1-butanol and 2-butanol, and was found to be preferred by the 2-butanol, due to its secondary substrate, which had the favorable product of trans-2-butene. Of the two-dehydrobromination reactions that were performed on the molecules 1-bromobutane and 2-bromobutane, it was found to be preferred by the 2-bromobutane also due to the secondary positioning of the substrate with a preferred product of trans-2-butene.

Introduction

Elimination is an organic reaction in which two substituents are removed from a molecule and double bond is formed in the by-product molecules. There are two type of elimination reactions, one-step mechanism is known as the E2 reaction, and the two-step mechanism is known as E2 reaction. E1 is 1st order reaction, the carbocation intermediate is formed after the leaving group leaves and it can rearrange to more stable position by hydride or alkyl shift. Because this is two-step mechanism, so it require only weak base. Tertiary carbocation is more favorable and polar protic solvent is required. E2 is 2nd order reaction. Its rate depends on both substrate and base. Because everything happens at the same time, so the strong base is required. The H abstracted must be anticoplanar to the leaving group. Similar to the E1 mechanism, tertiary substrate is preferred. The E2 reaction will be sped up if high temperature and polar protic solvent, which slows down the base, are applied. The set of reactions of dehydration of 1-butanol and 2-butanol is considered E1 mechanism because concentrated phosphoric acid and concentrated sulfuric acid act as weak base. Dehydrobromination reaction follow an E2 mechanistic pathway because it is conducted in the presence of potassium hydroxide, which is strong base, dissolved...