Exam

• Alcohols


  Compounds containing the hydroxyl (-OH) functional group bonded to an alkyl, R
• Classification of alcohols


  • Primary Alcohol (1ª)
  • Secondary Alcohol (2º)
  • Tertiary Alcohol (3ª)
• Primary alcohols


  • n-propyl alcohol
  • 1-propanol
• Secondary alcohols


  • sec. butyl alcohol
  • 2-butanol
• Tertiary alcohols


  • tert. butyl alcohol
  • 2-methyl-2-propanol

  
• Classification of alcohols by number of OH groups

  • Monohydroxy alcohols
  • Polyhydroxy alcohols
• Polyhydroxy alcohols


  • Ethylene glycol
  • Glycerol / 1,2,3-propanetriol

  
• Reactivity of alcohols


  Mainly attributed to the -OH group
• • OH group


  Has an inherent acid character shown when the hydrogen is released from the -OH bond

  
• Protonation of -OH group

  Weakens the C-O bond so that the whole group may be cleaved off as water and subsequently replaced in the molecule
• Removal of -OH group


  Dependent upon the relative polarization of the -OH bond
• Ethyl alcohol


  Most commonly known primary alcohol
• Ethanol


  Alcohol present in alcoholic beverages, obtained from the fermentation of sugars and starches catalyzed by the enzyme zymase

  
• Fermentation of sugars and starches

  C6-CH12-O6 + Zymase

  
• Chromic acid test


  Used to distinguish primary and secondary alcohols from tertiary alcohols
• Chromic acid


  Oxidizes primary alcohols to carboxylic acids, oxidizes secondary alcohols to ketones, oxidizes aldehydes to ketones

  
• Tertiary alcohols


  Not readily oxidized by chromic acid due to the absence of alpha hydrogen
• Lucas test


  Used to further distinguish different classes of alcohols

  
• Tertiary alcohols


  React immediately with Lucas reagent (HCl in the presence of ZnCl2) to form an immiscible upper layer of alkyl chloride

  
• Secondary alcohols


  Cloudiness appears after 5 minutes with Lucas reagent
• Primary alcohols


  Do not react with Lucas reagent under these conditions
• SN1 reaction mechanism


  Involved with tertiary and secondary alcohols
• Glycerol


  Most important triol, obtained as a by-product from the manufacture of soap, used as a moisturizing agent in cosmetic formulations, tobacco products, and foods
• Dehydration of glycerol


  When heated with KHSO4, forms propenal (acrolein) which has a pungent odor
• Iodoform test


  Used to identify aldehydes or ketones
• Positive iodoform reaction


  Molecule has a carbon attached to an OH and to both a methyl group and hydrogen atom

  
• Iodoform test procedure


  Add iodine solution and sodium hydroxide to the alcohol, observe color change and precipitate formation
• Negative iodoform test


  Color of the solution disappears
• Positive iodoform test


  Lighter and brown, yellow or yellow and cloudy color, produces a solid yellow precipitate of triiodomethane with an antiseptic smell
• Acrolein test


  Used to detect the presence of glycerol or fat
• Acrolein and propenal


  Unsaturated aldehydes with a disagreeable burned fat odor
• Fats and oils


  Concentrated sources of energy, triesters of glycerol and higher fatty acids
• Fats


  Solids at ordinary temperature
• Oils


  Liquids at ordinary temperature
• Propan-2-ol + 10% Iodine + 2M NaOH


  Pale yellow precipitate with an antiseptic smell
• Alcohols may be classified based on the number of OH groups
• Types of alcohols

  • Monohydroxy alcohols
  • Polyhydroxy alcohols
• Polyhydroxy alcohols


  • Ethylene glycol
  • Glycerol/1,2,3-propanetriol

  
• Glycerol


  • Most important triol
  • Obtained as a by-product from the manufacture of soap
  • Used as a moisturizing agent in cosmetic formulations, tobacco products, and foods
  • Detected by the acrolein test
  • Undergoes dehydration when heated with KHSO4 to form propenal (acrolein) which has a pungent odor
• Acrolein and Propenal


  • Unsaturated aldehyde
  • Smells of burned fat
  • Used to detect presence of glycerol or fat