Thiols

Thiols are less polar than alcohols MethanolMethanethiol 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 4. thiols are more easily oxidized than alcohols; oxidation takes place at sulfur Properties of Thiols

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 CH 3 CHCH 2 CH 2 SH CH 3 3-Methyl-1-butanethiol

have pK a s of about 10; can be deprotonated in aqueous base stronger acid (pK a = 10) weaker acid (pK a = 15.7) Thiols are stronger acids than alcohols H RS OHOHOHOH –RS H OHOHOHOH – ++

RS – and HS – are weakly basic and good nucleophiles HClH C6H5SC6H5SC6H5SC6H5S C 6 H 5 SNa SN2SN2SN2SN2 (75%) KSH SN2SN2SN2SN2 (67%) BrSH

Oxidation of thiols take place at sulfur thiol (reduced) disulfide (oxidized) RS H RS SR 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 thioldisulfide sulfinic acid sulfonic acid RS H RS SR sulfenic acid RS OH RS OH O –+ RS OH O – 2+ O –

HSCH 2 CH 2 CH(CH 2 ) 4 COH SHSHSHSH O 2, FeCl 3 (CH 2 ) 4 COH  -Lipoic acid (78%) Example: sulfide-disulfide redox pair O OS S