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Thiols

Thiols. Thiols are less polar than alcohols. Methanol. Methanethiol. bp: 65°C. bp: 6°C. 1. low molecular weight thiols have foul odors 2. hydrogen bonding is much weaker in thiols than in alcohols 3. thiols are stronger acids than alcohols

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Thiols

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  1. Thiols

  2. Thiols are less polar than alcohols Methanol Methanethiol bp: 65°C bp: 6°C

  3. 1. low molecular weight thiols have foul odors 2. hydrogen bonding is much weaker in thiols than in alcohols 3. thiols are stronger acids than alcohols 4. thiols are more easily oxidized than alcohols; oxidation takes place at sulfur Properties of Thiols

  4. 1) analogous to alcohols, but suffix is -thiol rather than -ol 2) final -e of alkane name is retained, not dropped as with alcohols CH3CHCH2CH2SH CH3 Nomenclature of Thiols 3-Methyl-1-butanethiol

  5. have pKas of about 10; can be deprotonated in aqueous base – •• •• •• •• OH H H OH RS •• •• •• •• •• Thiols are stronger acids than alcohols – + + RS •• stronger acid(pKa = 10) weaker acid(pKa = 15.7)

  6. C6H5S H Cl H (75%) C6H5SNa SN2 KSH Br SH SN2 (67%) RS– and HS – are weakly basic and good nucleophiles

  7. thiol-disulfide redox pair is important in biochemistry other oxidative processes place 1, 2, or 3 oxygen atoms on sulfur •• •• •• RS RS SR H •• •• •• Oxidation of thiols take place at sulfur thiol (reduced) disulfide (oxidized)

  8. •• •• •• RS RS SR H •• •• •• – •• O •• •• •• + RS RS OH OH •• •• Oxidation of thiols take place at sulfur thiol disulfide – •• O •• •• 2+ RS OH O •• •• •• – sulfenic acid sulfinic acid sulfonic acid

  9. O O Example: sulfide-disulfide redox pair SH HSCH2CH2CH(CH2)4COH O2, FeCl3 S S a-Lipoic acid (78%) (CH2)4COH

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