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CH21 –AY 2013-2014 SEM II -- R.D. A. Bolinas. 8.4 Reactions of Alcohols. Alcohols can undergo E1/E1cB/E2 reactions to form alkenes. By protonating –OH in acid , we get an oxonium –OH 2 + that can leave as H 2 O - PowerPoint PPT Presentation
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8.4 Reactions of AlcoholsCH21 –AY 2013-2014 SEM II -- R.D. A. Bolinas
Alcohols can undergo E1/E1cB/E2 reactions to form alkenes
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)
Alcohols can undergo E1/E1cB/E2 reactions to form alkenes
Alcohols can undergo E1/E1cB/E2 reactions to form alkenes
Predict the major product. Remember Zaitsev’s rule!
Alcohols can undergo E1/E1cB/E2 reactions to form alkenes
Predict the major product. Remember Zaitsev’s rule!
Alcohols can undergo E1/E1cB/E2 reactions to form alkenes
E1cB occurs in biological systems: the -OH group is two carbons away
from a carbonyl (C=O) group
Alcohols can be oxidized into carbonyls…
Alcohols can be oxidized into carbonyls… We use oxidizing agents:
periodinane (with Iodine in +5 oxidation state)
PRIMARY R-OH TO ALDEHYDE ONLY
Alcohols can be oxidized into carbonyls… We use oxidizing agents:
Acidic CrO3/CrO42- (with Chromium in +6
oxidation state) PRIMARY R-OH TO CARBOXYLIC ACID
Alcohols can be oxidized into carbonyls… Secondary alcohols will give ketones
with either reagent
Alcohols can be oxidized into carbonyls…
Alcohols can be oxidized into carbonyls…
Periodinane
The Williamson Ether synthesis uses an alkoxide and alkyl halide…
Ethers (R-O-R) SN2 reaction between R-X and R-O-
The Williamson Ether synthesis uses an alkoxide and alkyl halide…
SN2 reaction between R-X and R-O- WE NEED TO CONSIDER STERIC
HINDERANCE. This might lead to E2!
Backside attack is not favorable!
Methoxide is also a very strong base.
The Williamson Ether synthesis uses an alkoxide and alkyl halide…
Practice:
The Williamson Ether synthesis uses an alkoxide and alkyl halide…
Practice:
Phenols can sometimes react like alcohols in forming ethers.
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.
Oxidation of phenols gives us QUINONES Because they don’t have a hydrogen
on the C-OH carbon, phenols become quinones
Oxidation of phenols gives us QUINONES Quinones easily change form into
hydroquinones
Quinones are biologically significant redox facilitators
Ethers generally undergo only acidic cleavages. Ethers are unreactive to most
common reagents Only strong acids can usually react
with them: HI/HBr via SN1 or SN2
Ethers generally undergo only acidic cleavages. Ethers are unreactive to most
common reagents Only strong acids can usually react
with them: HI/HBr via SN1 or SN2
SN1
Cyclic ethers are also generally as unreactive, except for EPOXIDES.
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.
Cyclic ethers are also generally as unreactive, except for EPOXIDES.
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
Sulfur analogs of alcohols and ethers are called thiols and sulfides.
Thiols can be made via SH- and RX, and can react via Williamson mechanismSN2 Synthesis:
Williamson thioether synthesis
Disulfides are formed via oxidation. Reduction to thiols can occur as well.
http://delight.spslinfotechpvtl.netdna-cdn.com/media/catalog/product/cache/1/image/650x650/9df78eab33525d08d6e5fb8d27136e95/r/e/rebonding.jpg
http://b.vimeocdn.com/ts/147/230/147230470_640.jpg
Disulfides are formed via oxidation. Reduction to thiols can occur as well.
http://delight.spslinfotechpvtl.netdna-cdn.com/media/catalog/product/cache/1/image/650x650/9df78eab33525d08d6e5fb8d27136e95/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
Disulfides are formed via oxidation. Reduction to thiols can occur as well.
http://b.vimeocdn.com/ts/147/230/147230470_640.jpg
“antioxidant” because it protects your cells from oxidative degradation.
Propose a synthetic route from 2-phenylethanol to make:
AB C D
E
Propose a synthetic route from 2-phenylethanol to make:
H2SO4 Pe
riod
inan
eCrO3
KMnO4
1. H2SO4 2. H2/Pd
Problems
Problems
More synthetic routes
More synthetic routes
More synthetic routes: propose reagents for each step!
More synthetic routes: propose reagents for each step!
NaBH4, H3O+
PBr3
1. Convert to Grignard (Mg/ether)
2. add CH2=O then acid
1. Ph-CH2-MgBr 2. 2. H3O+
Periodinane
conc’d H2SO4