Preparation of Cyclohexene from Cyclohexanol.

EXPERIMENT 1

Preparation of cyclohexene from cyclohexanol.

Abstract:

A secondary alcohol undergoes dehydration in the presence of a strong acid by an E1 mechanism to form an alkene. Dehydration is the elimination of two hydrogen atoms and an oxygen atom (H2O) from an alcohol and results in the formation of π-bonds. In this experiment, cyclohexene was synthesized from cyclohexanol with water as the leaving group. The acid used in this experiment is 85% phosphoric acid. The elimination reaction involves the loss of a hydroxyl group (-OH) from one carbon and a hydrogen atom (-H) from an adjacent carbon. The reaction is carried out in a fractional distillation apparatus to prevent the alkene formed in the dehydration reaction from reforming the alcohol. The aim of this experiment is to illustrate the acid catalyzed dehydration reaction by synthesizing cyclohexene from cyclohexanol.

INTRODUCTION:

A hydrocarbon is any chemical compound that consists only of the elements carbon (C) and hydrogen (H). There are four major classes of hydrocarbons: (1) alkanes, (2) alkenes, (3) alkynes and (4) aromatic hydrocarbons. The alkanes contain only carbon and hydrogen connected by single (sigma) bonds exclusively. Alkanes are the least reactive class. Alkenes differ from the alkanes by the presence of one or more double (pi) bonds. The presence of these pi- bonds makes alkenes more reactive than the alkanes. There are a number of simple tests, based upon the reactivity of alkenes with a variety of reagents and varied conditions that may be used to differentiate alkanes from alkenes. These tests employ the reagents and conditions to which the alkanes are insensitive. Cyclohexanol, an alcohol, has a higher boiling point than cyclohexene, an alkene. In the presence of a strong acid, an alcohol can form an alkene by dehydration. The dehydration reaction involves the elimination of water (H2O) from the alcohol. The phosphoric acid is a catalyst and as such increases the...