alcohol
compounds containing -OH (hydroxyl)
thiol
compounds containing -SH (sulfhydrol)
structure of Alchohols
the hydroxyl functional group is bonded to an sp3 hybridized carbon and the oxygen is sp3 hybridized, thus a sigma bond connects them
physical properties of Alcohols
- polar due to -OH interactions
- have dipole dipole interactions and hydrogen bonding
- have relatively high boiling points
- polar alcohols are more soluble in water
acidity and basicity of alcohols
-OH can function as both a weak acid and weak base
reactions of alcohols with active metals
alcohols react with Li, Na and K to liberate H2 and form the corresponding metal alkoxides, which are reasonably strong bases
reaction with phophorus tribromide
- alternative way to make bromoalkanes from primary and secondary alcohols
- mild reaction conditions required and rearrangements are not as typical as with HBr
reaction with thionyl chloride (SOCl2) and thionyl bromide (SOBr2)
- common alternative to making chloroalkanes and bromoalkanes from primary and secondary carbons
- mild reaction conditions required and rearrangements are rare
- non nucleophilic base is typically added to (i) generate a small amount of the more reactive alkoxide to accelerate the reaction or (ii) neutralize the HCl or HBr that is generated during the reaction to prevent side reaction
- SN2 mechanism leads to inversion of chiral secondary alcohols
formation of aryl and alkyl sulfonates
- similar to the reaction with SOCl2 that forms chlorosulfanites, are reactions with sulfonyl chlorides
- this turns an alcohol into an excellent leaving group, because the sulfate anion that leaves is very stable
dehydration
elimination of water; a way to transform an alcohol to an alkene in the presence of acid and heat
pinacol rearrangement
a particular acid-catalyzed dehydration with rearrangement that transforms vicuna diols into carbonyl functional groups
oxidation
loss of electrons/hydrogens or gain of oxygen
-used to transform primary alcohols into aldehydes and carboxylic acids and secondary alcohols into ketones
chromic acid oxidation
(H2CrO4)
- transforms primary alcohols into carboxylic acids
- transforms secondary alcohols into ketones
- tertiary alcohols do not oxidize
pyridinium chlorochromate (PCC)
- transforms primary alcohols into aldehydes
- transforms secondary alcohols into ketons
swern oxidation
- less toxic alternative to chromium based oxidation
- transforms primary alcohols into aldehydes
- transforms secondary alcohols into ketons
- stops at aldehyde
- reagents: 1. oxalyl chloride((COCL)2) + dimethyl sulfoxide (DMSO), 2. R-OH (alcohol), 3. tertiary amine (Et2N =TEA)
Dess Martin Oxidation
- less toxic alternative procedure to chromium based oxidation
- transforms primary alcohols into aldehydes
- transforms secondary alcohols into ketones
- reagents: dess martin period inane (DMP; hypervalent iodine = breaks octet rule)
periodic acid oxidation of glycols
-method for transforming a glycol into two carbonyl groups using periodic acid (HIO4)
thiols structure
- contains -SH
- more p character in thiols than alcohols
physical properties of thiols
-they stink
S-H bond is less polar than the O-H bond and thus exhibits much weaker H bonding
-lower boiling points for thiols than alcohols
preparation of thiols
- the hydrosulfide anion is a strong nucleophile due to the polarizability of sulfur and is used to generate thiols via SN2
- thiolates are a stronger nucleophiles but weaker bases compared to alkoxides and thus prefer SN2 over E2
acidity of thiols
thiols are more acidic than alcohols due to polarizability
oxidation
the sulfur atoms of a thiol is easily oxidized to higher oxidation states
