Download Reactions of Alcohols

CH21 –AY 2013-2014 SEM II -- R.D. A. Bolinas

By protonating –OH in acid,
we get an oxonium –OH2+
that can leave as H2O

E1/E2 depends on the nature
of ROH, but usually E1
prevails, except for 1°
alcohols (E2)

Predict the major product. Remember
Zaitsev’s rule!

Predict the major product. Remember
Zaitsev’s rule!


E1cB occurs in biological systems:
the -OH group is two carbons away from a
carbonyl (C=O) group

We use oxidizing agents:
 periodinane (with Iodine in +5 oxidation state)
 PRIMARY R-OH TO ALDEHYDE ONLY

We use oxidizing agents:
 Acidic CrO3/CrO42- (with Chromium in +6 oxidation
state)
 PRIMARY R-OH TO CARBOXYLIC ACID

Secondary alcohols will give ketones with
either reagent
Periodinane


Ethers (R-O-R)
SN2 reaction between R-X and R-O-


SN2 reaction between R-X and R-OWE NEED TO CONSIDER STERIC
HINDERANCE. This might lead to E2!
Backside attack is
not favorable!
Methoxide is also a
very strong base.

Practice:

Practice:


CANNOT: be dehydrated with acid, convert
into halides with HX
CAN: convert to ether via Williamson ether
synthesis, react via EArS (review)
The aromatic ring allows the H+ to
leave easily, making phenols ACIDIC.

Because they don’t have a hydrogen on the COH carbon, phenols become quinones

Quinones easily change form into
hydroquinones


Ethers are unreactive to most common
reagents
Only strong acids can usually react with
them: HI/HBr via SN1 or SN2


Ethers are unreactive to most common
reagents
Only strong acids can usually react with
them: HI/HBr via SN1 or SN2
SN1



Epoxides come from alkenes + peroxy acids
High angular strain induces reactivity.
SN2 attacks with H3O+ or HX lead to trans-diol
or trans-halohydrins, other nucleophiles work
too.

SN2 attacks with H3O+ or HX lead to trans-diol
or trans-halohydrins, other nucleophiles
work too.
beta-blocker that is used for treatment of cardiac
arrhythmias, hypertension, and heart attacks
SN2 Synthesis:
Williamson thioether synthesis
http://b.vimeocdn.com/ts/147/230/147230470_640.jpg
http://delight.spslinfotechpvtl.netdnacdn.com/media/catalog/product/cache/1/image/650x650/9df78eab3
3525d08d6e5fb8d27136e95/r/e/rebonding.jpg
For rebonding:
(1) Thioglycolate (acid-like) to convert
disulfide bonds in hair protein to
thiolates
(2) Hydrogen peroxide to oxidize the
thiolates back to disulfides.
(3) Reforming the disulfides helps re-align
amino acids and make hair straight
http://delight.spslinfotechpvtl.netdnacdn.com/media/catalog/product/cache/1/image/650x650/9df78eab3
3525d08d6e5fb8d27136e95/r/e/rebonding.jpg
“antioxidant”
because it protects
your cells from
oxidative
degradation.
http://b.vimeocdn.com/ts/147/230/147230470_640.jpg
E
A
B
C
D
1. H2SO4 2. H2/Pd
H2SO4
KMnO4
CrO3
1.
conc’d H2SO4
NaBH4, H3O+
PBr3
Periodinane
1.
2.
2.
Ph-CH2-MgBr
2. H3O+
Convert to
Grignard
(Mg/ether)
add CH2=O then
acid