ch.10-chem212
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Chapter 10
Dr.Abdulaziz Ajlouni
Organic Chemistry, 7th Edition
L. G. Wade, Jr.
Structure and Synthesis
of Alcohols
Chapter 10 2
Structure of Water and Methanol
• Oxygen is sp3 hybridized and tetrahedral.
• The H—O—H angle in water is 104.5°.
• The C—O—H angle in methyl alcohol is 108.9°.
Chapter 10 3
Classification of Alcohols
• Primary: carbon with —OH is bonded to
one other carbon.
• Secondary: carbon with —OH is bonded
to two other carbons.
• Tertiary: carbon with —OH is bonded to
three other carbons.
• Aromatic (phenol): —OH is bonded to a
benzene ring.
Chapter 10 4
Examples of Classifications
C H 3 C
C H 3
C H 3
O H *
C H 3 C H
O H
C H 2 C H 3
* C H 3 C H
C H 3
C H 2 O H *
Primary alcohol Secondary alcohol
Tertiary alcohol
Chapter 10 5
IUPAC Nomenclature
• Find the longest carbon chain containing the
carbon with the —OH group.
• Drop the -e from the alkane name, add -ol.
• Number the chain giving the —OH group the
lowest number possible.
• Number and name all substituents and write
them in alphabetical order.
Chapter 10 6
Examples of Nomenclature
2-methyl-1-propanol
2-methylpropan-1-ol
2-methyl-2-propanol
2-methylpropan-2-ol
2-butanol
butan-2-ol
C H 3 C
C H 3
C H 3
O H
C H 3 C H
C H 3
C H 2 O H C H 3 C H
O H
C H 2 C H 3
3 2 1 1 2 3 4
2 1
Chapter 10 7
• Enol:
End the name in –ol, but also specify that there is a double bond by using the ending –ene before -ol
4-penten-2-ol
pent-4-ene-2-ol
C H 2 C H C H 2 C H C H 3
O H
5 4 3 2 1
OH
Br
Cl
OH
• Trans-2-Bromocyclohexanol
• (Z)-4-chloro-3-buten-2-ol
Or
(Z)-4-chlorobut-3-en-2-ol
Chapter 10 8
Naming Priority
1. Acids
2. Esters
3. Aldehydes
4. Ketones
5. Alcohols
6. Amines
7. Alkenes
8. Alkynes
9. Alkanes
10. Ethers
11. Halides
Highest ranking
Lowest ranking
Chapter 10 9
Hydroxy Substituent
• When —OH is part of a higher priority class of
compound, it is named as hydroxy.
4-hydroxybutanoic acid
also known as g-hydroxybutyric acid (GHB)
C H 2 C H 2 C H 2 C O O H
O H carboxylic acid
4 3 2 1
Chapter 10 10
Common Names
• Alcohol can be named as alkyl alcohol.
• Useful only for small alkyl groups.
isobutyl alcohol sec-butyl alcohol
C H 3 C H
C H 3
C H 2 O H C H 3 C H
O H
C H 2 C H 3
Chapter 10 11
Naming Diols
• Two numbers are needed to locate the two
—OH groups.
• Use -diol as suffix instead of -ol.
hexane-1,6- diol
1 2 3 4 5 6
Chapter 10 12
Glycols
• 1, 2-diols (vicinal diols) are called glycols.
• Common names for glycols use the name of the
alkene from which they were made.
ethane-1,2- diol
ethylene glycol propane-1,2- diol
propylene glycol
Chapter 10 13
Give the systematic (IUPAC) name for the following alcohol.
The longest chain contains six carbon atoms, but it does not contain the carbon bonded to the hydroxyl
group. The longest chain containing the carbon bonded to the —OH group is the one outlined by the
green box, containing five carbon atoms. This chain is numbered from right to left in order to give the
hydroxyl-bearing carbon atom the lowest possible number.
The correct name for this compound is 3-(iodomethyl)-2-isopropylpentan-1-ol.
Solved Problem 1
Solution
Chapter 10 14
Physical Properties
• Most of the common alcohols, up to about 11-
12 carbons are liquids at R.T
• Alcohols have high boiling points due to
hydrogen bonding between molecules.
• Small alcohols are miscible in water, but
solubility decreases as the size of the alkyl
group increases.
Chapter 10 15
Boiling Points of alcohols
• Alcohols have higher boiling points than ethers and alkanes because alcohols can form hydrogen bonds.
• The stronger interaction between alcohol molecules will require more energy to break them resulting in a higher boiling point.
• Dipole-Dipole attraction also contributes to the relatively high boiling points due to polarized C-O,O-H bonds and the nonbonding electrons on oxygen.
Chapter 10 16
Solubility in Water
Small alcohols are miscible in water, but
solubility decreases as the size of the
alkyl group increases.
In chemistry, the hydroxyl group is
called hydrophilic, meaning “water
loving” and the alkyl group is called
hydrophobic, meaning “water hating”
Chapter 10 17
Methanol1 • “Wood alcohol”
• Industrial production from synthesis gas
• Common industrial solvent
• Toxic Dose: 100 mL methanol
• Used as fuel engine at Indianapolis 500 (1965-2006)
Fire can be extinguished with water
High octane rating
Low emissions
Lower energy content
Invisible flame
Can damage the optic nerve
3C + 4 H2OHigh Temp
CO2 + 2CO + 4H2
CO + H2
400 C, 300 atm H2
CuO-ZnOCH3OH
Chapter 10 18
Ethanol • Fermentation of sugar and starches in grains such as
corn, wheat and barley resulting in “grain alcohol”.
• 12–15% alcohol result, then yeast cells die
• Distillation increase the alcohol concentration and produces “hard” liquors.
• Azeotrope: 95% ethanol at lower temp (78.3) by constant boiling
• Denatured alcohol is ethanol that contain impurites, therefore can be used as solvent only
• Gasahol: 10% ethanol in gasoline and used since 2006
• Methanol is about twice toxic as ethanol,Toxic dose: 200 mL
C6H12O6
yeast enzyme2 CH3OH + 2 CO2
Chapter 10 19
Acidity of Alcohols • pKa range: 15.5–18.0 (water: 15.7)
• Acidity decreases as the number of carbons increase
bcs alkyl group inhibits solvation of alkoxide ion and
therefore decrease the stability of the alkoxide ion
• Halogens and other electron withdrawing groups
increase the acidity, it helps stabilize the alkoxide ion.
ROH
alcohol alkoxide ion
RO
Chapter 10 20
Table of Ka Values
Chapter 10 21
Formation of Alkoxide Ions
• Since alcohols are weak acids, therefore NaOH is not strong enough to for alkoxide ion
• Ethanol reacts with sodium or potassium metal to form sodium ethoxide (NaOCH2CH3), a strong base commonly used for elimination reactions.
• Oxidation-Reduction reaction.
• More hindered alcohols like 2-propanol or tert-butanol react faster with potassium(more reactive) than with sodium.
• Alternative reagents is sodium hydride (NaH).
Chapter 10 22
Formation of Phenoxide Ion
The aromatic alcohol phenol is more acidic than
aliphatic alcohols by around 100 million times due to
the ability of aromatic rings to delocalize the negative
charge of the oxygen within the carbons of the ring.
Chapter 10 23
Charge Delocalization on the
Phenoxide Ion
• The negative charge of the oxygen can be delocalized over four atoms of the phenoxide ion.
• There are three other resonance structures that can localize the charge in three different carbons of the ring.
• The true structure is a hybrid between the four resonance forms.
Chapter 10 24
Synthesis of Alcohols (Review)
• 1.Alcohols can be synthesized by nucleophilic
substitution of alkyl halide.(Ch.6)
• 2. from Alkene
• 1.Hydration of alkenes also produce alcohols(Ch.8)
Acid-catalyzed hydration
H3CH2C
H CH3
BrKOH
R
HO
H CH3
CH2CH3
S
SN2
RR
RH
H2O, H+
RR
RH
OH H
Markonikove
25
Indirect Hydration • 2. Oxymercuration-Demercuration
Markovnikov product formed
Anti addition of H-OH
No rearrangements
• 3.Hydroboration Anti-Markovnikov product formed
Syn addition of H-OH
CH3
CH3
H
BH2
CH3
H
OH
H2O2
NaOHBH3 THF
Chapter 10 26
Synthesis of Vicinal Diols 4. Vicinal diols can be synthesized by two different
methods:
• A)Syn hydroxylation of alkenes
Osmium tetroxide,
hydrogen peroxide
Cold, dilute, basic
potassium permanganate
B) Anti Dihydroxylation: Peroxy acid
CH3COOH
O
OH
H
OH
H
Chapter 9 27
3. Nucleophilic Addition to Carbonyl
Compounds
• Nucleophiles can attack the carbonyl carbon
forming an alkoxide ion which on protonation
will form an alcohol.
Chapter 10 28
Organometallic Reagents
• Carbon is negatively charged so it is
bonded to a metal (usually Mg or Li).
• It will attack a partially positive carbon.
C—X
C═O
• Good for forming carbon–carbon bonds.
Chapter 10 29
Grignard Reagents
• Formula R—Mg—X (reacts like R:- +MgX).
• Ethers are used as solvents to stabilize the complex.
• RI > RBr > RCl > > RF
• May be formed from any halide.
Chapter 10 30
Reactions with Grignards
Br
+ Mgether
MgBr
CH3CHCH2CH3
Clether
+ Mg CH3CHCH2CH3
MgCl
Chapter 10 31
Organolithium Reagents • Formula R—Li (reacts like R:- +Li)
• Can be produced from alkyl, vinyl, or aryl halides, just
like Grignard reagents.
• Ether not necessary, wide variety of solvents can be
used.
Reactivity: alkyl > aryl, Cl < Br < I etc
Commercial synthesis: mostly from chlorides
In laboratory: usually from alkyl bromides/iodides
(easier to start)
In apolar or weakly polar solvents
RX + 2Li Li X + RLi
X = Cl, Br, I
Chapter 10 32
Limitations of Grignard
• Grignards are good nucleophiles but in
the presence of acidic protons it will
acts as a strong base.
• No water or other acidic protons like
O—H, N—H, S—H, or terminal alkynes.
• No other electrophilic multiple bonds,
like C═N, CN, S═O, or N═O.
33
Organolithium and Organomagnesium Compounds
as Brønsted Bases - Grignard reagents (M = MgX) and
organolithium reagents (M = Li) are very strong bases.
R-M + H2O R-H + M-OH
Hydrocarbons are very weak acids; their conjugate bases are
very strong bases.
C CR H H3C-H2C-H2C-H2C-Li
terminal
acetylene
(pKa ~ 26)
+ C CR Li H3C-H2C-H2C-H2C-H+THF
butyllithium lithiumacetylide
pKa > 60
C CR H H3C-H2C-MgBr+ C CR MgBr H3C-H2C-H+THF
magnesiumacetylide
ethylmagnesiumbromide
Chapter 10 34
Reaction with Carbonyl
Chapter 10 35
Formation of Primary Alcohols
Using Grignard Reagents
• Reaction of a Grignard with formaldehyde will
produce a primary alcohol after protonation.
Chapter 10 36
Synthesis of 2º Alcohols
• Addition of a Grignard reagent to an aldehyde followed by protonation will produce a secondary alcohol.
Chapter 10 37
Synthesis of 3º Alcohols
• Tertiary alcohols can be easily obtained by
addition of a Grignard to a ketone followed by
protonation with dilute acid.
Chapter 10 38
Show how you would synthesize the following alcohol from compounds containing no more than five
carbon atoms.
Solved Problem 2
Solution
Chapter 10 39
Grignard Reactions with
Acid Chlorides and Esters
• Use two moles of Grignard reagent.
• The product is a tertiary alcohol with
two identical alkyl groups.
• Reaction with one mole of Grignard
reagent produces a ketone
intermediate, which reacts with the
second mole of Grignard reagent.
Chapter 10 40
Reaction of Grignards with
Carboxylic Acid Derivatives
Chapter 10 41
Mechanism
C
CH3
Cl
OR MgBr C
CH3
RO
+ MgBrCl
C O
C l
H 3 C
M g B r R M g B r C
C H 3
C l
O R
Step 1: Grignard attacks the carbonyl forming the tetrahedral
intermediate.
Step 2: The tetrahedral intermediate will reform the carbonyl and form
a ketone intermediate.
Chapter 10 42
Mechanism continued
H O H C
C H 3
R
O H R C
C H 3
R
O R M g B r
C
C H 3
R O
R M g B r + C
C H 3
R
O R M g B r
Step 3: A second molecule of Grignard attacks the carbonyl of the
ketone.
Step 4: Protonation of the alkoxide to form the alcohol as the product.
Chapter 10 43
Addition to Ethylene Oxide
• Grignard and lithium reagents will attack epoxides (also called oxiranes) and open them to form alcohols.
• This reaction is favored because the ring strain present in the epoxide is relieved by the opening.
• The reaction is commonly used to extend the length of the carbon chain by two carbons.
Chapter 10 44
Limitations of Grignard
• Grignards are good nucleophiles but in
the presence of acidic protons it will
acts as a strong base.
• No water or other acidic protons like
O—H, N—H, S—H, or terminal alkynes.
• No other electrophilic multiple bonds,
like C═N, CN, S═O, or N═O.
45
Organolithium and Organomagnesium Compounds
as Brønsted Bases - Grignard reagents (M = MgX) and
organolithium reagents (M = Li) are very strong bases.
R-M + H2O R-H + M-OH
Hydrocarbons are very weak acids; their conjugate bases are
very strong bases.
C CR H H3C-H2C-H2C-H2C-Li
terminal
acetylene
(pKa ~ 26)
+ C CR Li H3C-H2C-H2C-H2C-H+THF
butyllithium lithiumacetylide
pKa > 60
C CR H H3C-H2C-MgBr+ C CR MgBr H3C-H2C-H+THF
magnesiumacetylide
ethylmagnesiumbromide
Chapter 10 46
Reduction of Carbonyl
• Reduction of aldehyde yields 1º alcohol.
• Reduction of ketone yields 2º alcohol.
• Reagents:
Sodium borohydride, NaBH4
Lithium aluminum hydride, LiAlH4
Raney nickel
Chapter 10 47
Sodium Borohydride • NaBH4 is a source of hydrides (H-)
• Hydride attacks the carbonyl carbon, forming
an alkoxide ion.
• Then the alkoxide ion is protonated by dilute
acid.
• Only reacts with carbonyl of aldehyde or
ketone, not with carbonyls of esters or
carboxylic acids.
• Takes place with wide variety of solvents:
alcohol, ether, water
Chapter 10 48
Mechanism of Hydride Reduction
• The hydride attacks the carbonyl of the aldehyde or
the ketone.
• A tetrahedral intermediate forms.
• Protonation of the intermediate forms the alcohols.
Chapter 10 49
Lithium Aluminum Hydride • LiAlH4 (LAH) is source of hydrides (H-)
• Stronger reducing agent than sodium
borohydride, but dangerous to work with.
• Reduces ketones and aldehydes into the
corresponding alcohol.
• Converts esters and carboxylic acids to 1º
alcohols.
• LAH and water are incompatibile. An explosion
and fire would result from the process
Chapter 10 50
Reduction with LiAlH4
• The LiAlH4 (or LAH) will add two hydrides to
the ester to form the primary alkyl halide.
• The mechanism is similar to the attack of
Grignards on esters.
Chapter 10 51
Reducing Agents
• NaBH4 can reduce
aldehydes and
ketones but not
esters and
carboxylic acids.
• LiAlH4 is a stronger
reducing agent and
will reduce all
carbonyls.
Chapter 10 52
Catalytic Hydrogenation
• Raney nickel is a hydrogen rich nickel powder that is more reactive than Pd or Pt catalysts.
• This reaction is not commonly used because it will also reduce double and triple bonds that may be present in the molecule.
• Hydride reagents are more selective so they are used more frequently for carbonyl reductions.
O
H2
SELECTIVE HYDROGENATIONS O
Pd/C easy 20O C
1 atm
+
HOH
Ni 40O C
2 atm
more
difficult
O
HOH
PtO2 100o C
5 atm most
difficult
HOH
?
Hydride
reagents
Conditions will vary
with the specific
compound.
Chapter 10 54
Thiols (Mercaptans)
• Sulfur analogues of alcohols are called thiols.
• The —SH group is called a mercapto group.
• Named by adding the suffix -thiol to the
alkane name.
• They are commonly made by an SN2 reaction
so primary alkyl halides work better.
• The odor of thiols is their strongest
characterstics. Shunk scent is 3-
methylbutane-1-thiol. Ethanethiol added to
natural gas to give it “gassy” odor
Thiols - Nomenclature • IUPAC names are derived in the same manner
as are the names of alcohols
Retain the final -e of the parent alkane and add the
suffix -thiol
Common names for simple thiols are derived by
naming the alkyl group bonded to -SH and adding the word "mercaptan"
CH3CH2SH
CH3
CH3CHCH2SH
Ethanethiol(Ethyl mercaptan)
2-Methyl-1-propanethiol(Isobutyl mercaptan)
Chapter 10 56
Synthesis of Thiols
• The thiolate will attack the carbon displacing the halide.
• This is an SN2 reaction so methyl halides will react faster than primary alkyl halides.
• To prevent dialylation use a large excess of sodium hydrosulfide with the alkyl halide.
Reactions of Thiols
• Thiols are weak acids (pKa~10), and are
comparable in strength to phenols
thiols react with strong bases such as
NaOH to form water-soluble thiolate salts
CH3 CH2 SH NaOHH2 O
CH3 CH2 S-Na
+H2 O+
Ethanethiol(pKa 10)
+
Sodiumethanethiolate
Chapter 10 58
Thiol Oxidation
Thiols can be oxidized (by Zn/HCl) to form disulfides. The
disulfide bond
can be reduced back to the thiols with a reducing agent.
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