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Reactions of Alcohols & Ethers 1

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Reactions of Alcohols & Ethers 1 REACTIONS OF ALCOHOLS & ETHERS 1. Combustion (Extreme Oxidation) alcohol + oxygen carbon dioxide + water 2 CH3CH2OH + 6 O2 4 CO2 + 6 H2O 2. Elimination (Dehydration) ° alcohol H 2 S O 4/ 1 0 0 C alkene + water H2SO4/100 ° C CH3CH2CH2OH CH3CH=CH2 + H2O 3. Condensation ° excess alcohol H 2 S O 4 / 1 4 0 C ether + water H2SO4/140 ° C 2 CH3CH2OH CH3CH2OCH2CH3 + H2O 4. Substitution Lucas Reagent alcohol + hydrogen halide Z n C l2 alkyl halide + water ZnCl2 CH3CH2OH + HCl CH3CH2Cl + H2O • This reaction with the Lucas Reagent (ZnCl2) is a qualitative test for the different types of alcohols because the rate of the reaction differs greatly for a primary, secondary and tertiary alcohol. • The difference in rates is due to the solubility of the resulting alkyl halides • Tertiary Alcohol→ turns cloudy immediately (the alkyl halide is not soluble in water and precipitates out) • Secondary Alcohol → turns cloudy after 5 minutes • Primary Alcohol → takes much longer than 5 minutes to turn cloudy 5. Oxidation • Uses an oxidizing agent such as potassium permanganate (KMnO4) or potassium dichromate (K2Cr2O7). • This reaction can also be used as a qualitative test for the different types of alcohols because there is a distinct colour change. dichromate → chromium 3+ (orange) → (green) permanganate → manganese (IV) oxide (purple) → (brown) Tertiary Alcohol not oxidized under normal conditions CH3 KMnO4 H3C C OH NO REACTION K2Cr2O7 CH3 tertbutyl alcohol Secondary Alcohol ketone + hydrogen ions H O KMnO4 H3C C CH3 + K2Cr2O7 C + 2 H H3C CH3 OH propanone 2-propanol Primary Alcohol aldehyde + water carboxylic acid + hydrogen ions O KMnO4 O H H KMnO H H 4 + CH3CH2CH2OH C C C H C C C H + 2 H K2Cr2O7 + H2O K Cr O H H H 2 2 7 HO H H 1-propanol propanal propanoic acid 6. Acid-Base Reactions • Like water, alcohols can act as an acid or base, depending on what it is reacting with. • When they react as an acid, the alkyl oxide ion - (R-CH2O ) is formed. ethanol + sodium ethoxide ion + sodium ion + hydrogen - + 2 CH3CH2OH + 2 Na 2 CH3CH2O + 2 Na + H2 • When they react as a base, the alkyl oxonium ion + (R-CH2OH2 ) is formed ethanol + sulfuric acid ethyloxonium ion + bisulfate ion + - CH3CH2OH + H2SO4 CH3CH2OH2 + HSO4 Preparation of Alcohols 1. Hydration of an Alkene H SO / 100 °C alkene + water 2 4 alcohol H H SO / 100 °C H H H C CHCH + H O 2 4 2 3 2 H C C C H H OH H 2. Oxidation of an Alkene • This reaction uses an oxidizing agent like KMnO4 or K2Cr2O7 to produce a “diol”. KMnO alkene + water 4 "diol" K2Cr2O7 KMnO H H H H C CHCH + H O 4 2 3 2 H C C C H K2Cr2O7 OH OH H Reactions of Ethers 1. Ethers do not react with oxidizing or reducing agents. 2. Combustion ether + oxygen carbon dioxide + water CH3-O-CH3 + 3 O2 2 CO2 + 3 H2O 3. Reaction with Concentrated Binary Acids ether + 2 binary acid 2 alkyl halides + water CH3OCH2CH3 + 2 HCl H3CCl + ClCH2CH3 + H2O 4. Reaction with Atmospheric Oxygen • This is a slow reaction in which highly unstable peroxides are formed ether + oxygen peroxide CH3OCH2CH3 + O2 H3COOCH2CH3 HOMEWORK • Pg 44 # 7-9 • Pg 48 # 12, 13 of Practice • Pg 48 # 2-4, 6 of Section.
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