2 Dehydration

Reaction of Alcohols with Dehydrating Agents Dehydration Reaction: removal of a water molecule from a molecule Reaction: Alcohol  Alkene Reagents: Concentrated Sulphuric or Phosphoric acids Conditions: warm (under reflux) Role of reagent: dehydrating agent/catalyst Type of reaction: acid catalysed elimination C C + H2O H H H C H H H propan-1-ol Propene Some 2o and 3o alcohols can give more than one product, when the double bond forms between different carbon atoms C H C H C H H H C H H H O H H C C C C H H H H H H H H C H H C C C H H H H H H Butan-2-ol can form both alkenes although more but-2-ene would be formed Butan-2-ol But-1-ene But-2-ene But-2-ene could also exist as E and Z isomers Producing alkenes from alcohols provides a possible route to polymers without using monomers derived from oil C O H H H C H H C H H H CH3CH2CH2OH  CH2=CHCH3 + H2O : H3C C CH3 O H H H3C C CH3 O + H H H C C + CH3 H H H H H+ H+ C C CH3 H H H Acid catalysed elimination mechanism The H+ comes from the conc H2SO4 or conc H3PO4