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Thiols Thiols are less polar than alcohols Methanol Methanethiol bp: 65°C bp: 6°C Properties of Thiols 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 Nomenclature of Thiols 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 3-Methyl-1-butanethiol Thiols are stronger acids than alcohols have pKas of about 10; can be deprotonated in aqueous base •• RS •• – •• H + •• OH stronger acid (pKa = 10) •• •• – RS •• •• + H •• OH •• weaker acid (pKa = 15.7) RS– and HS – are weakly basic and good nucleophiles C6H5S H H Cl C6H5SNa (75%) SN2 KSH Br SN2 SH (67%) Oxidation of thiols take place at sulfur •• RS •• H thiol (reduced) •• RS •• •• SR •• disulfide (oxidized) thiol-disulfide redox pair is important in biochemistry other oxidative processes place 1, 2, or 3 oxygen atoms on sulfur Oxidation of thiols take place at sulfur •• RS •• H thiol •• RS •• •• SR •• disulfide •• – •• O •• •• RS •• OH sulfenic acid + RS OH •• sulfinic acid •• – •• O •• 2+ RS OH •• O •• •• – sulfonic acid Example: sulfide-disulfide redox pair SH O HSCH2CH2CH(CH2)4COH O2, FeCl3 S S O (CH2)4COH a-Lipoic acid (78%)
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