Chemistry Experiment 12: Dehydration of Cyclohexanol

Questions and Answers

What is the purpose of dehydrating cyclohexanol in this experiment?

To form cyclohexene in an elimination reaction.

What occurs in the first step of the dehydration reaction?

The -OH is protonated to form a protonated alcohol.

What are azeotropes?

Mixtures of two liquids that have a single sharp boiling point.

What indicates a positive bromine test?

The bromine color is discharged rapidly without the evolution of hydrogen bromide. Signup and view all the answers

What is observed in the permanganate test for alkenes and alkynes?

The deep purple color of permanganate disappears and a brown precipitate of manganese dioxide is formed. Signup and view all the answers

What should you do if concentrated acid is spilled during the experiment?

Neutralize the spill with sodium bicarbonate. Signup and view all the answers

Which of the following are true statements about bromine (Br2)? (Select all that apply)

Causes skin burns Signup and view all the answers

What should you do if your skin comes in contact with HCl?

Tell the TA immediately and wash the affected area with copious amounts of water. Signup and view all the answers

Match the density of the following solvents from most to least dense:

Chloroform = Most dense Dichloromethane = Less dense than chloroform Water = Less dense than dichloromethane Diethyl ether = Less dense than water Hexanes = Least dense Signup and view all the answers

What indicates the presence of an alkane in the bromine test?

The reddish color of the bromine will disappear. Signup and view all the answers

How can you determine whether a reaction has occurred in the experiment?

The product separates forming layers. Signup and view all the answers

Why is concentrated HCl a poor choice as the acid catalyst for the dehydration of cyclohexanol?

The chlorine ion would attack the carbocation to form a bond, preventing double bond formation. Signup and view all the answers

What type of reaction do bromine and permanganate undergo with cyclohexene?

They both react by addition. Signup and view all the answers

Why is the reaction of cyclohexene with HBr not useful for characterization?

HBr does not show a color change, making it difficult to determine if a double bond is present. Signup and view all the answers

What does a 'dry' distilling flask mean for the experiment?

It means there should be nothing in the flask at all. Signup and view all the answers

Why is acetone not suitable as a solvent for extraction from water?

Acetone and water are miscible. Signup and view all the answers

Which of the following statements about E2 reactions are true? (Select all that apply)

E2 reactions are stereospecific Signup and view all the answers

What should you do if you spill sulfuric acid on your hand?

Wash it with cold water and apply a 0.6 M sodium bicarbonate solution. Signup and view all the answers

Which of the following is used for the treatment of reagent spills in the laboratory?

Sodium bicarbonate Signup and view all the answers

What is the rate-determining step of the dehydration of cyclohexanol?

The formation of the carbocation when the protonated alcohol loses water. Signup and view all the answers

What is the similarity between E2 elimination and SN2 substitution?

The concentration of the nucleophile affects the rate of the reactions. Signup and view all the answers

What occurs during the formation of 3-chloro-3,7-dimethyloctane from 3,7-dimethyl-3-octanol?

The alcohol is protonated and a water molecule is produced in the reaction. Signup and view all the answers

What solution should be used after rinsing sulfuric acid from the skin?

Sodium bicarbonate. Signup and view all the answers

Study Notes

Dehydration of Cyclohexanol

Cyclohexanol is dehydrated using acid catalysis to produce cyclohexene through an elimination reaction, specifically an E1 mechanism.
Water is lost during the reaction, creating a carbon-carbon π-bond.

Reaction Steps

Protonation: The hydroxyl group (-OH) of cyclohexanol is protonated, forming a better leaving group (water).
Carbocation Formation: The protonated alcohol undergoes dehydration, losing water and forming a carbocation. The rate of this step determines the reaction rate.
Deprotonation: The carbocation rapidly loses a proton to yield cyclohexene.

Azeotropes

Azeotropes are mixtures with a distinct boiling point that cannot be separated by distillation.
Multiple-component mixtures (three or four compounds) can also form azeotropes.

Bromine Test

A positive bromine test for unsaturation occurs when the reddish color of bromine is rapidly discharged, indicating the presence of alkenes.

Permanganate Test (Baeyer's Test)

For alkenes and alkynes, a deep purple color from permanganate disappears, forming brown manganese dioxide as a precipitate.

Spill Protocols

Concentrated acid spills should be neutralized with sodium bicarbonate.
Immediate reporting and washing with copious amounts of water is crucial if there’s contact with HCl.

Density and Solvent Properties

Density ranking: chloroform > dichloromethane > water > diethyl ether > hexanes.
Acetone is unsuitable for extracting organic materials from water due to its miscibility.

Safety Measures

Bromine is hazardous: causes skin burns and may be fatal if inhaled; gloves are required for handling.
Rinse sulfuric acid spills with cold water followed by sodium bicarbonate solution.

Reaction Characteristics

E2 reactions are stereospecific; strong bases enhance elimination reactions.
Formation of 3-chloro-3,7-dimethyloctane from 3,7-dimethyl-3-octanol involves initial protonation leading to water release.

Comparisons

Both E2 eliminations and SN2 substitutions are influenced by nucleophile concentration.
Concentrated HCl is suboptimal for cyclohexene formation due to potential carbocation bond formation instead of double bond formation.

Distillation Practices

Distillation should not be continued until the flask is completely dry, meaning lacking all materials, not just water.

Indicators for Reaction Occurrence

Successful dehydration is indicated by the separation of product layers — cyclohexene forms the top layer while the aqueous layer remains below.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

In this quiz, you will explore the dehydration of cyclohexanol to cyclohexene through an acid-catalyzed elimination reaction. This process involves the formation of a carbon-carbon π-bond via an E1 mechanism. Test your understanding of the concepts and steps involved in this chemical reaction.