Module 7 Thiols

• Thiols can be defined as a sulfur analog of alcohols
• Thiols is also referred as mercaptan containing a sulfhydryl group
• Properties of Thiol

  Odor: Strong smell – onion and garlic odor

  Furan-2-yl methanethiol - responsible for the beautiful aroma of roasted coffee
• Thiol: Hydrogen Bonding

  Weaker intermolecular forces - Less dipole moment
• Thiol Physical Properties

  • Non polar covalent
  • Low boiling point
  • water insoluble
• Thiol - BP

  Methanethiol - 6

  Ethanethiol - 35

  1-butanethiol - 98
• Alcohol - BP

  Methanol - 65

  ethanol - 78

  1-butanol - 117
• Thiol: Acidity

  Hydrogen sulfide is stronger acid than water

  Thiols are stronger acids than alcohols
• Thiols are sufficiently strong acids that, when dissolved in aqueous sodium hydroxide, they are converted completely to alkylsulfide salts
• Oxidation of thiols and sulfides

  • Unlike alcohols, thiols don’t generally oxidize to give double bounded compounds
  • One oxidation that does happen is formation of disulfides
  • Other oxidants can result in sulfides being oxidized to sulfoxides or sulfones
• The oxidation of thiols to disulfides has important biological implications. The important amino acid cysteine contains a thiol group and disulfide bonds are responsible for the tertiary structures of proteins
• Alkoxides vs thiolate

  • thiolate are less basic than alkoxides
  • Thiols are more nucleophillic than alcohols
  • Thiolates are more nucleophilic than alkoxides
• Lead Acetate Test

  This test is specific for sulphur containing amino acids

  (Cysteine, Cystine and Methionine)
• Virtual Lab: Thiols

  • Thiols and Thioethers smell bad.
  • Hydrogen sulfide (H2S) is responsible for the smell of rotten eggs and bad breath, among other unpleasant things.
  • Thiols contribute to the smell of skunks and “skunky” beer.
• Example of Smelly Thiols:

  Hydrogen sulfide (rotten eggs, bad breath)

  3-methyl-1 butanethiol (skunk odor)

  3-methyl-2-butene-1-thiol (skunky beer)