Dehydration of Alcohols

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Chemical Reactions of Alkanes and Alkenes

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Presentation transcript:

Dehydration of Alcohols

Elimination Reactions Y C - C X To make C=C need to eliminate X, Y.

3 ways to break 2 bonds 1. Concerted (x and y leave same time) C - C X 3 ways to break 2 bonds 1. Concerted (x and y leave same time) 2. X leaves first 3. Y leaves first

Leaving Group

E1 Reaction R-X R+ + X- Alkene + H+

E1 1 bond at a time Elimination

R+ SN1 E1 Rearrangement Substitution Elimination

SN1 E1

Dehydrohalogenation X C - C H Strong base

C-D bond stronger than C-H bond. What is the mechanism of dehydrohalogentation? C-D bond stronger than C-H bond.

Isotope Effect NaOEt NaOEt kH/kD = 7

Isotope effect shows that C-H bond broken in the transition state.

Element Effect Change Element I > Br > Cl

SYN vs. ANTI Elimination Same Side Opposite Side

Transition State Energy Starting Material Product

E 2 2 Bonds at a time Elimination

Procedure

Put cyclohexanol and sulfuric acid in round bottom flask Fractional Distillation (steam distillation) collect distillate 80-85o Dry product with K2CO3 4. Distill

Distil immiscible liquids PT = PA + PB (Steam Distillation)

Baeyer Unsaturation Tests Potassium Permanganate KMnO4

Bromine and Cyclohexene