Experiment # 7 Preparation of Cyclohexene from Cyclohexanol

volatile, flammable & irritant liquid

cyclohexanol

Sodium chloride does what

decreases the solubility of cyclohexene in water layer

anhydrous calcium chloride does what

dehydrating agent it removes traces of water

H2O loss from a molecule is called

dehydration

what type of rxn is the conversion of alcohol to an alkene

elimination rxn

Cyclohexene has a strong pungent smell, always work in the

fume hood

irritant e.g.

sodium sulfate

When more than one elimination product can be formed, the major product is

the more substituted alkene

Test for unsaturation

-Bromination test -Baeyer (cold KMnO4) test -Reaction with cold sulphuric acid

Types of mechanism for dehydration reaction.

-E1 mechanism (elimination unimolecular) -E2 mechanism (elimination bimolecular)

Cyclohexanol is dehydrated to cyclohexene involving these process:

-OH group = very poor leaving group, an alcohol can undergo dehydration only if its -OH group is converted into a better leaving group. -to convert an OH group into a good group is to protonate it. -1st step of dehydration reaction = protonation = changes the very poor leaving group -OH into a good leaving group -OH2 + -2nd step= H2O departs, leaving behind a carbocation. -3rd step = the base HSO4- removes a proton from the carbon adjacent to the +vely charged carbon, forming an alkene -regenerating the acid catalyst H2SO4. -cyclohexene has lower boiling point than the cyclohexanol = cyclohexene can be distilled as it forms.

most used acid catalysts

-Sulfuric acid (H2SO4) -phosphoric acid (H3PO4)

strongly corrosive & toxic

-Sulfuric acid (H2SO4) -phosphoric acid (H3PO4)

In many cases alcohol dehydration requires

-acid catalyst -heat

from what is alkene prepared from & how is it separated?

-alcohol by an acid-catalyzed dehydration rxn -alkene is removed from the reaction by simple distillation

more substituted alkene is obtained by

-by removing a proton from the adjacent carbon that has fewer hydrogens.

what does the elimination reaction involve?

-loss of an -OH from 1 carbon & an -H from an adjacent carbon. -i.e., elimination of a H2O molecule, resulting in a pi-bond formation of an alkene

The more substituted alkene is the major product because

it is the more stable alkene

Sodium carbonate solution does what

neutralizes any traces of acid

H2O loss and H+ can occur in one step if the alcohol is

primary