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Chapter 12
Alcohols, Phenols, Thiols, and
Ethers
Denniston
Topping
Caret
5th Edition
12.1 Alcohols: Structure and
Physical Properties
• An organic compound containing a hydroxyl
group attached to an alkyl group
• Alcohols have the general formula R-OH
12.1 Structure and
Physical Properties
Physical Properties
• R-O-H has a structure similar to that of water
• Hydroxyl group is very polar
• Hydrogen bonds can form readily
12.1 Structure and
Physical Properties
Alcohol Boiling Points
• Alcohols have abnormally high boiling points
relative to their molecular weights due to their
ability to hydrogen bond
Hydrogen bonds in Ethane
CH3
CH2 H
O
CH3CH
H Hydrogen bonds
2O
H
O CH2 CH3
12.1 Structure and
Physical Properties
Trends in Alcohol Boiling Points
CH3CH2CH3 bp -42
oC
bp -23
oC
CH3O CH3
o
bp
+78.5
C
CH3CH2OH
12.1 Structure and
Physical Properties
Solubility
• Low molecular weight alcohols (up to 5-6
carbons) are soluble in water
– Very polar
– Hydrogen bond with the water molecule
• CH3CH2OH very soluble
• CH3OCH3 barely soluble
• CH3CH2CH2CH2OH, 7 g per 100 mL
–
HOCH2CH2CH2CH2OH is very soluble
(two OH groups)
12.1 Structure and
Physical Properties
High Molecular Weight Alcohol
Solubility
• As molecular weight increases, alcohols
become insoluble in water
– Still polar
– Ratio of hydroxyl groups to carbons in the
chain determines solubility
• Diols and triols are more soluble than those with
only a single hydroxyl group
12.2 Alcohols: Nomenclature
• IUPAC: based on the longest chain
containing the OH carbon
• The -e of the alkane name is replaced with
-ol
• The chain is numbered from the end giving
the -OH carbon the lower number
• The name is prefixed with the number
indicating the position of the OH group
• For cyclic alcohols, the OH is at C-1
12.2 Alcohols:
Nomenclature
Naming Alcohols
CH3
CH3CH CH CH3
OH
1. Name the parent compound – 4 carbons = butane
2. Replace the –e with –ol = butanol
3. Number the parent chain to minimize number of carbon
with the –OH group = number from right to left
4. Identify, name, and number all substituents = methyl on C-3
3-methyl-2-butanol
Naming Alcohols
12.2 Alcohols:
Nomenclature
CH3
3-methylcyclohexanol
OH must be at C-1
OH
1. Name the parent compound – 6 carbon ring = cyclohexane
2. Replace the –e with –ol = cyclohexanol
3. Number the ring to minimize number of carbon with the
–OH group = number counterclockwise
4. Identify, name, and number all substituents = methyl on C-3
12.2 Alcohols:
Nomenclature
Common Names of Alcohols
CH3
CH3 C CH3 CH3CH CH3
OH
OH
t-butyl alcohol
isopropyl alcohol
The common names for alcohols consist of the alkyl
group name, a space, and the word alcohol
12.3 Medically Important
Alcohols
• Methanol
–
–
–
–
Colorless and odorless liquid
Used as a solvent
Toxic, can cause blindness and death if ingested
Can be used as a fuel
12.3 Medically Important
Alcohols
Ethanol
• An odorless and colorless liquid
• Widely used as a solvent
• The alcohol in alcoholic beverages
– Derived from fermentation of
carbohydrates
– Beverage produced varies with the starting
material and the fermentation process
12.3 Medically Important
Alcohols
2-Propanol
•
•
•
•
Colorless, but has a slight odor
Commonly called rubbing alcohol
Toxic when ingested
Used as a:
– Disinfectant
– Astringent
– Industrial solvent
12.3 Medically Important
Alcohols
1,2-Ethanediol
• Used as automobile antifreeze
• Has a sweet taste, but is extremely
poisonous
• Added to water
– Lowers the freezing point
– Raises the boiling point
HO CH2CH2OH
ethylene glycol
(antifreeze)
12.3 Medically Important
Alcohols
1,2,3-Propanetriol
•
•
•
•
•
Very viscous, thick
Has a sweet taste
OH
Non-toxic
H
O
CH
CH
CH
OH
2
2
Highly water soluble
glycerol
Used in:
(in fats,
a moisturizer)
• Cosmetics
• Pharmaceuticals
• Lubricants
• Obtained as a by-product of fat hydrolysis
12.4 Classification of Alcohols
• Alcohols, depending on the number of alkyl
groups attached to the carbinol carbon, are
classified as:
– Primary
– Secondary
– Tertiary
• Carbinol carbon is the carbon bearing the
hydroxyl group
12.4 Classification of
Alcohols
Structures of Different Alcohol
Categories
12.4 Classification of
Alcohols
Classify the Alcohols
a.
b.
c.
d.
Carbinol carbon has 2 other alkyls attached
Carbinol carbon has 3 other alkyls attached
Carbinol carbon has 1 other alkyl attached
Carbinol carbon has 2 other alkyls attached
12.5 Reactions Involving Alcohols
Preparation of Alcohols
• Hydration
– Addition of water to the carbon-carbon double bond of
an alkene produces an alcohol
– A type of addition reaction called hydration
– Requires a trace of acid as a catalyst
12.5 Reactions Involving
Alcohols
Preparation of Alcohols
• Hydrogenation
– Addition of water to the carbon-oxygen double bond
of an aldehyde or ketone produces an alcohol
– A type of addition reaction
– Also considered a reduction reaction
– Requires Pt, Pd, or Ni as a catalyst
12.5 Reactions Involving
Alcohols
Dehydration of Alcohols
• Alcohols dehydrate with heat in the presence of strong acid
to produce alkenes
• Dehydration is a type of elimination reaction
– A molecule loses atoms or ions from its structure
– Here –OH and –H are removed / eliminate from adjacent carbon
atoms to produce an alkene and water
– A reversal of the hydration reaction that forms alcohols
12.5 Reactions Involving
Alcohols
Zaitsev’s Rule
• Some alcohol dehydration reactions produce a
mixture of products
• Zaitsev’s rule states that in an elimination reaction
the alkene with the greatest number of alkyl
groups on the double bonded carbon is the major
product of the reaction
CH3
OH
warm
H2SO4 or
H3PO4
CH3
major product:
more substituted
alkene
12.5 Reactions Involving
Alcohols
Predict the Product of Dehydration
• What are the major and minor products when 3methyl-2-butanol is dehydrated?
• Zaitsev’s rule states that in an elimination reaction the
alkene with the greatest number of alkyl groups on the
double bonded carbon is the major product of the reaction
12.5 Reactions Involving
Alcohols
Oxidation Reaction of Primary
Alcohols
• Primary alcohols usually oxidize to carboxylic
acids
• With some care (using CrO3 as the reagent) an
aldehyde may be obtained
12.5 Reactions Involving
Alcohols
Oxidation Reaction of Secondary
Alcohols
• Secondary alcohols oxidize to ketones
– This reaction is also an elimination of 2H
• The usual oxidizing agent is a Cr(VI) species
• Tertiary alcohols do not oxidize as there is no H
on the carbonyl carbon to remove
12.6 Oxidation and Reduction in
Living Systems
• Oxidation
– loss of electrons
• Reduction
– gain of electrons
• These changes are easily detected in inorganic
systems with formation of charged ions
• In organic systems it is often difficult to determine
whether oxidation or reduction has taken place as
there might be no change in charge
12.6 Oxidation and
Reduction in Living Systems
Organic Oxidation and Reduction
• In organic systems changes may be tracked:
– Oxidation
• gain of oxygen
• loss of hydrogen
– Reduction
• loss of oxygen
• gain of hydrogen
More oxidized form
H
R C H
H
Alkane
H
H
R C OH R C O
H
Alcohol
Aldehyde
More reduced form
OH
R C O
Acid
12.6 Oxidation and
Reduction in Living Systems
Biological OxidationReduction
• Oxidoreductases catalyze biological
redox reactions
• Coenzymes (organic molecules) are
required to donate or accept hydrogen
• NAD+ is a common coenzyme
-
COO
COO
H O C H Malate
C O
CH2 dehydrogenase CH
2 COO
COO
+ NADH + H+
+ NAD+
12.7 Phenol
• Phenols are compounds in which the hydroxyl group is
attached to a benzene ring
– Polar compounds due to the hydroxyl group
– Simpler phenols are somewhat water soluble
– Components of flavorings and fragrances
• Phenols have the formula Ar-OH
– Ar must be an aromatic ring (e.g., Benzene)
Phenol Derivatives
12.7 Phenols
• Widely used in healthcare as:
– Germicides
– Antiseptics
– Disinfectants
12.7 Phenols
Phenol Reactivity
OH
+ NaOH
ONa
+ H2O
• Phenols are acidic, but not as acidic as
carboxylic acids
• They react with NaOH to give salt and
water
12.8 Ethers
• Ethers have the formula R-O-R
– R can be aliphatic or aromatic
• Ethers are slightly polar due to the polar C=O
bond
• Do not hydrogen bond to one another as there are
no –OH groups
12.8 Ethers
Ether Physical Properties
• Ethers have much lower boiling points than
alcohols due to the lack of hydrogen bonding
12.8 Ethers
Common Names of Ethers
• Common names for ethers consist of the names of
the two groups attached to the O listed in
alphabetical order (or size) and followed by
‘ether’
• Each of the three parts is a separate word
• Name:
CH3CH2
CH3
O
CH3 CH O CH3
Isopropyl methyl ether Ethyl phenyl ether
12.8 Ethers
IUPAC Nomenclature of Ethers
• The IUPAC names for ethers are based on the
alkane name of the longest chain attached to the
oxygen
• The shorter chain is named as an alkoxy
substituent
– Alkane with the -ane replaced by -oxy
– e.g., CH3CH2O = ethoxy
CH3CH2CH2CH2CH2-O-CH3
1-methoxypentane
Reactivity of Ethers
12.8 Ethers
• Chemically, ethers are moderately inert
– Do not normally react with reducing agents or bases
– Extremely volatile
– Highly flammable = easily oxidized in air
• Symmetrical ethers may be prepared by
dehydrating two alcohol molecules
– Requires heat and acid catalyst
CH3 CH2OH
HO CH2 CH3
H+ (H3PO4)
warm
CH3 CH2O CH2 CH3
12.8 Ethers
Medical Uses of Ethers
• Ethers are often used as anesthetics
• Accumulate in the lipid material of nerve cells
interfering with nerve impulse transmission
• Today halogenated ethers are used routinely as
general anesthetics
– Less flammable
– Safer to store and to work with
F Cl
CH3 CH2O CH2 CH3 CH3O C C
Diethyl ether First successful
general anesthetic
F Cl
Penthrane
H
12.9 Thiols
• Thiols have the formula R-SH
• Similar in structure to alcohols with S replacing O
• Disulfides have the formula R-S-S-R
– R may be aliphatic or aromatic
• Name is based on longest alkane chain with the
suffix –thiol position indicated by number
CH3
CH3 CH CH2 CH2
SH
3-methy-1-butanethiol
Thiols and Scent
12.9 Thiols
• Thiols, as many other sulfur-containing
compounds can have nauseating aromas
– Defensive spray of North American striped skunk
– Onions and garlic
• Compare with pleasant scents below
Naming Thiols
12.9 Thiols
• Write the IUPAC name for the thiols shown
12.9 Thiols
Disulfide Formation
• The thiol-disulfide
redox pair controls a
critical factor in protein
structure called a
disulfide bridge
– Two cysteine molecules
(amino acids) can
undergo oxidation to
form cystine
– Forms a new bond
called a disulfide bond
12.9 Thiols
Disulfide Formation and Insulin
Structure
Reaction Schematic
Alkene
Hydration
Reduction
Alcohol
Carbonyl
Oxidation
+ H+ and heat
If tertiary
Dehydration
NO REACTION
If primary
If secondary
Aldehyde
Ketone
Summary of Reactions
1. Preparation of Alcohols
a. Hydration of Alkenes
b. Reduction of Aldehyde or Ketone
2. Reactions of Alcohols
a. Dehydration
b. Oxidation
i. Primary alcohol to aldehyde
ii. Secondary alcohol to ketone
iii. Tertiary alcohol does not react
3. Dehydration Synthesis of an Ether
Summary of Reactions