Chapter4alcoholsphenolsandethers 151111010603-lva1-app6892

Chapter 4
Alcohols, Phenols and
Ethers
General, Organic, and Biological Chemistry,Fifth Edition
H. Stephen Stoker
Brroks/Cole Cengage Learning. Permission required for reproduction or display.
Prepared by:
GIZEL R. SANTIAGO

3
Chapter 3 Topics
• Bonding Characteristics of Oxygen Atoms in Organic
Compounds
• Structural Characteristics of Alcohols
• Nomenclature for Alcohols
• Isomerism for Alcohols
• Important Commonly Encountered Alcohols
• Physical Properties of Alcohols
• Preparation of Alcohols
• Classiﬁcation of Alcohols
• Chemical Reactions of Alcohols
• Polymeric Alcohols

4
Chapter 3 Topics
• Structural Characteristics of Phenols
• Nomenclature for Phenols
• Physical and Chemical Properties of Phenols
• Occurrence of and Uses for Phenols
• Structural Characteristics of Ethers
• Nomenclature for Ethers
• Isomerism for Ethers
• Physical and Chemical Properties of Ethers 4
• Cyclic Ethers
• Sulfur Analogs of Alcohols
• Sulfur Analogs of Ethers

5
Bonding Characteristics of Oxygen Atoms
in Organic Compounds
Normal bonding behavior for oxygen atoms
in such functional groups is the formation of
two covalent bonds. Oxygen is a member of
Group VIA of the periodic table and thus
possesses six valence electrons. To complete
its octet by electron sharing, an oxygen atom
can form either two single bonds or a double
bond.

6

7
Thus, in organic chemistry, carbon forms four
bonds, hydrogen forms one bond, and oxygen
forms two bonds.

8
A hydrocarbon derivatives containing a single
oxygen atom with the generalized formula:
R-OH
Structural Characteristics of Alcohols
An alcohol is an organic compound in which an
—OH group is bonded to a saturated carbon
atom. A saturated carbon atom is a carbon
atom that is bonded to four other atoms.

9

10
The —OH group, the functional group that is
characteristic of an alcohol, is called a hydroxyl
group. A hydroxyl group is the —OH functional
group. Examples of structural formulas for alcohols
include

11
Alcohols may be viewed structurally as being
alkyl derivatives of water in which a hydrogen
atom has been replaced by an alkyl group.

12
Alcohols may also be viewed structurally as
hydroxyl derivatives of alkanes in which a
hydrogen atom has been replaced by a
hydroxyl group.

13
Nomenclature for Alcohols
Common names exist for alcohols with
simple (generally C1 through C4) alkyl
groups. To assign a common name:
Rule 1: Name all of the carbon atoms
of the molecule as a single alkyl group.

14
Rule 2: Add the word alcohol,
separating the words with a space.

15
IUPAC rules for naming alcohols that
contain a single hydroxyl group follow.
Rule 1: Name the longest carbon chain to
which the hydroxyl group is attached. The
chain name is obtained by dropping the
ﬁnal -e from the alkane name and adding
the sufﬁx -ol.

16
Rule 2: Number the chain starting at the end
nearest the hydroxyl group, and use the
appropriate number to indicate the position of
the —OH group. (In numbering of the longest
carbon chain, the hydroxyl group has priority
over double and triple bonds, as well as over
alkyl, cycloalkyl, and halogen substituents.)

17
Rule 3: Name and locate any other
substituents present.
Rule 4: In alcohols where the —OH
group is attached to a carbon atom in
a ring, the hydroxyl group is assumed
to be on carbon 1.

23
Alcohols with More Than One Hydroxyl
Group
Polyhydroxy alcohols—alcohols that possess more
than one hydroxyl group—can be named with only a
slight modiﬁcation of the preceding IUPAC rules. An
alcohol in which two hydroxyl groups are present is
named as a diol, one containing three hydroxyl
groups is named as a triol, and so on. In these
names for diols, triols, and so forth, the ﬁnal -e of
the parent alkane name is retained for
pronunciation reasons.

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Group

25
Group
The ﬁrst two of the preceding compounds
have the common names ethylene glycol
and propylene glycol. These two alcohols
are synthesized, respectively, from the
alkenes ethylene and propylene; hence the
common names.

26
Isomerism for Alcohols
Constitutional isomerism is possible for alcohols
containing three or more carbon atoms. As with
alkenes, both skeletal isomers and positional
isomers are possible. For monohydroxy
saturated alcohols, there are two C3 isomers,
four C4 isomers, and eight C5 isomers. The
three pentanols are positional isomers as are
the four methylbutanols.

28
Important Commonly Encountered
Alcohols
Commonly encountered alcohols are
methyl, ethyl, and isopropyl alcohols
(all monohydroxy alcohols), ethylene
glycol and propylene glycol (both
diols), and glycerol (a triol).

29
Alcohols
Methyl Alcohol (Methanol)
Methyl alcohol, with one carbon atom and
one —OH group, is the simplest alcohol. This
colorless liquid is a good fuel for internal
combustion engines. Since 1965 all racing cars
at the Indianapolis Speedway have been
fueled with methyl alcohol.

30
Alcohols
(Methyl alcohol ﬁres are easier to put out
than gasoline ﬁ res because water mixes
with and dilutes methyl alcohol.) Methyl
alcohol also has excellent solvent
properties, and it is the solvent of choice
for paints, shellacs, and varnishes.

31
Alcohols
Methyl alcohol is sometimes called wood
alcohol, terminology that draws attention
to an early method for its preparation—the
heating of wood to a high temperature in
the absence of air. Today, nearly all methyl
alcohol is produced via the reaction
between H2 and CO.

32
Alcohols

33
Alcohols
Drinking methyl alcohol is very dangerous. Within
the human body, methyl alcohol is oxidized by the
liver enzyme alcohol dehydrogenase to the toxic
metabolites formaldehyde and formic acid.

34
Alcohols
Formaldehyde can cause blindness (temporary or
permanent). Formic acid causes acidosis. Ingesting
as little as 1 oz (30 mL) of methyl alcohol can
cause optic nerve damage.

35
Alcohols
Ethyl Alcohol (Ethanol)
Ethyl alcohol, the two-carbon monohydroxy
alcohol, is the alcohol present in alcoholic
beverages and is commonly referred to simply
as alcohol or drinking alcohol. Like methyl
alcohol, ethyl alcohol is oxidized in the human
body by the liver enzyme alcohol
dehydrogenase.

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Alcohols

37
Alcohols
Acetaldehyde, the ﬁrst oxidation product, is
largely responsible for the symptoms of
hangover. The odors of both acetaldehyde and
acetic acid are detected on the breath of
someone who has consumed a large amount of
alcohol. Ethyl alcohol oxidation products are
less toxic than those of methyl alcohol.

38
Alcohols
Long-term excessive use of ethyl alcohol may
cause undesirable effects such as cirrhosis of
the liver, loss of memory, and strong
physiological addiction. Links have also been
established between certain birth defects and
the ingestion of ethyl alcohol by women during
pregnancy (fetal alcohol syndrome).

39
Alcohols
Ethyl alcohol can be produced by yeast
fermentation of sugars found in plant extracts.
The synthesis of ethyl alcohol from grains such
as corn, rice, and barley, is the reason why ethyl
alcohol is often called grain alcohol.

40
Alcohols
Fermentation is the process by which ethyl alcohol for
alcoholic beverages is produced. The maximum
concentration of ethyl alcohol obtainable by fermentation
is about 18% (v/v), because yeast enzymes cannot
function in stronger alcohol solutions. Alcoholic beverages
with a higher concentration of alcohol than this are
prepared by either distillation or fortiﬁcation with alcohol
obtained by the distillation of another fermentation
product.

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Alcohols

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Alcohols

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Alcohols

44
Alcohols
Denatured alcohol is ethyl alcohol that has been rendered
unﬁt to drink by the addition of small amounts of toxic
substances (denaturing agents). Almost all of the ethyl
alcohol used for industrial purposes is denatured alcohol.
Most ethyl alcohol used in industry is prepared from
ethene via a hydration reaction

45
Alcohols
The reaction produces a product that is 95% alcohol and
5% water. In applications where water does interfere with
its use, the mixture is treated with a dehydrating agent to
produce 100% ethyl alcohol. Such alcohol, with all traces
of water removed, is called absolute alcohol.

46
Alcohols
Isopropyl Alcohol (2-Propanol)
Isopropyl alcohol is one of two three-carbon
monohydroxy alcohols; the other is propyl alcohol. A 70%
isopropyl alcohol–30% water solution is marketed as
rubbing alcohol. Isopropyl alcohol’s rapid evaporation rate
creates a dramatic cooling effect when it is applied to the
skin, hence its use for alcohol rubs to combat high body
temperature. It also ﬁnds use in cosmetics formulations
such as after-shave lotion and hand lotions.

47
Alcohols
Isopropyl alcohol has a bitter taste. Its toxicity is
twice that of ethyl alcohol, but it causes few
fatalities because it often induces vomiting and thus
doesn’t stay down long enough to be fatal. In the
body it is oxidized to acetone.
Large amounts (about 150 mL) of ingested isopropyl
alcohol can be fatal; death occurs from paralysis of
the central nervous system.

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Alcohols

49
Alcohols
Ethylene Glycol (1,2-Ethanediol) and Propylene
Glycol (1,2-Propanediol)
Ethylene glycol and propylene glycol are the
two simplest alcohols possessing two —OH
groups. Besides being diols, they are also
classiﬁed as glycols. A glycol is a diol in which
the two —OH groups are on adjacent carbon
atoms.

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Alcohols

51
Alcohols
Both of these glycols are colorless, odorless,
high-boiling liquids that are completely
miscible with water. Their major uses are as
the main ingredient in automobile “year-
round” antifreeze and airplane “de-icers” and
as a starting material for the manufacture of
polyester ﬁbers.

52
Alcohols
Ethylene glycol is extremely toxic when ingested.
In the body, liver enzymes oxidize it to oxalic
acid. Oxalic acid, as a calcium salt, crystallizes in
the kidneys, which leads to renal problems.

53
Alcohols
Propylene glycol, on the other hand, is
essentially nontoxic and has been used as a
solvent for drugs. Like ethylene glycol, it is
oxidized by liver enzymes; however, pyruvic acid,
its oxidation product, is a compound normally
found in the human body, being an intermediate
in carbohydrate metabolism.

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Alcohols

55
Alcohols
Glycerol (1,2,3-Propanetriol)
Glycerol, which is often also called glycerin, is a
clear, thick liquid that has the consistency of honey.
Its molecular structure involves three —OH groups
on three different carbon atoms.

56
Alcohols
Glycerol is normally present in
the human body because it is a
product of fat metabolism. It is
present, in combined form, in
all animal fats and vegetable
oils. In some Arctic species,
glycerol functions as a
“biological antifreeze”.

57
Alcohols
Because glycerol has a great afﬁnity for water vapor
(moisture), it is often added to pharmaceutical preparations
such as skin lotions and soap. Florists sometimes use
glycerol on cut ﬂowers to help retain water and maintain
freshness. Its lubricative properties also make it useful in
shaving creams and in applications such as glycerol
suppositories for rectal administration of medicines. It is
used in candies and icings as a retardant for preventing
sugar crystallization.

58
Physical Properties of Alcohols
Alcohol molecules have both polar and nonpolar
character. The hydroxyl groups present are polar, and
the alkyl (R) group present is nonpolar.
The physical properties of an alcohol depend on
whether the polar or the nonpolar portion of its
structure “dominates.” Factors that determine this
include the length of the nonpolar carbon chain
present and the number of polar hydroxyl groups
present.

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Boiling Points and Water Solubilities
The boiling point for 1-alcohols, unbranched-chain
alcohols with an —OH group on an end carbon,
increases as the length of the carbon chain
increases. This trend results from increasing London
forces with increasing carbon chain length. Alcohols
with more than one hydroxyl group present have
signiﬁcantly higher boiling points (bp) than their
monohydroxy counterparts.

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The boiling-point trend is related to increased
hydrogen bonding between alcohol molecules.

63
Small monohydroxy alcohols are soluble in water in all
proportions. As carbon chain length increases beyond
three carbons, solubility in water rapidly decreases
because of the increasingly nonpolar character of the
alcohol. Alcohols with two —OH groups present are more
soluble in water than their counterparts with only one —
OH group. Increased hydrogen bonding is responsible for
this. Diols containing as many as seven carbon atoms show
appreciable solubility in water.

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Alcohols and Hydrogen Bonding
A comparison of the properties of alcohols
with their alkane counterparts:
1.Alcohols have higher boiling points than
alkanes of similar molecular mass.
2.Alcohols have much higher solubility in
water than alkanes of similar molecular
mass.

67
The differences in physical properties between
alcohols and alkanes are related to hydrogen
bonding. Because of their hydroxyl group(s),
alcohols can participate in hydrogen bonding,
whereas alkanes cannot. Hydrogen bonding
between alcohol molecules is similar to that which
occurs between water molecules.

68
Extra energy is needed to overcome alcohol–
alcohol hydrogen bonds before alcohol
molecules can enter the vapor phase. Hence
alcohol boiling points are higher than those for
the corresponding alkanes (where no
hydrogen bonds are present).

69
Extra energy is needed to overcome alcohol–
alcohol hydrogen bonds before alcohol molecules
can enter the vapor phase. Hence alcohol boiling
points are higher than those for the corresponding
alkanes (where no hydrogen bonds are present). As
the alcohol chain length increases, alcohols become
more alkane-like (nonpolar), and solubility
decreases.

70

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Preparation of Alcohols
A general method for preparing alcohols—the hydration
of alkenes. Alkenes react with water (an unsymmetrical
addition agent) in the presence of sulfuric acid (the
catalyst) to form an alcohol. Markovnikov’s rule is used
to determine the predominant alcohol product.

73
Another method of synthesizing alcohols
involves the addition of H2 to a carbon–
oxygen double bond (a carbonyl group). A
carbonyl group behaves very much like a
carbon–carbon double bond when it
reacts with H2 under the proper
conditions. As a result of H2 addition, the
oxygen of the carbonyl group is converted
to an —OH group.

75
Alcohols are classiﬁed as primary (10), secondary
(20), or tertiary (30) depending on the number of
carbon atoms bonded to the carbon atom that bears
the hydroxyl group.

76
A primary alcohol is an alcohol in which the
hydroxyl-bearing carbon atom is bonded to only
one other carbon atom. A secondary alcohol is
an alcohol in which the hydroxylbearing carbon
atom is bonded to two other carbon atoms. A
tertiary alcohol is an alcohol in which the
hydroxyl-bearing carbon atom is bonded to
three other carbon atoms.

77
Increasing the number of R groups around the
carbon atom bearing the OH group decreases
the extent of hydrogen bonding. This effect,
called stearic hindrance, becomes particularly
important when the R groups are large. Thus, 10
alcohols are best able to hydrogen-bond and 30
alcohols are least able to hydrogen-bond.

80
Chemical Reactions of Alcohols
Combustion
Hydrocarbons of all types undergo combustion in air to
produce carbon dioxide and water. Alcohols are also
ﬂammable; as with hydrocarbons, the combustion
products are carbon dioxide and water. Methyl alcohol is
the fuel of choice for racing cars. Oxygenated gasoline,
which is used in winter in many areas of the United States
because it burns “cleaner,” contains ethyl alcohol as one of
the “oxygenates.”

81
Intermolecular Alcohol Dehydration
At a lower temperature (1400C) than that
required for alkene formation (1800C), an
intermolecular rather than an intramolecular
alcohol dehydration process can occur to
produce an ether—a compound with the
general structure R—O—R.

82

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A condensation reaction is a chemical
reaction in which two molecules combine
to form a larger one while liberating a small
molecule, usually water. Two alcohol
molecules combine to give an ether and
water.

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85

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Oxidation
Organic redox reactions use the following set of
operational rules instead of oxidation numbers.
1. An organic oxidation is an oxidation that increases the
number of C—O bonds and/ or decreases the number
of C—H bonds.
2. An organic reduction is a reduction that decreases the
number of C—O bonds and/or increases the number
of C—H bonds.

87
Some alcohols readily undergo oxidation with mild
oxidizing agents; others are resistant to oxidation
with these same oxidizing agents. Primary and
secondary alcohols, but not tertiary alcohols,
readily undergo oxidation in the presence of mild
oxidizing agents to produce compounds that
contain a carbon–oxygen double bond (aldehydes,
ketones, and carboxylic acids).

88
A number of different oxidizing agents can be used for
the oxidation, including potassium permanganate
(KMnO4), potassium dichromate (K2Cr2O7), and
chromic acid (H2CrO4).

89
The net effect of the action of a mild oxidizing
agent on a primary or secondary alcohol is
the removal of two hydrogen atoms from the
alcohol. One hydrogen comes from the —OH
group, the other from the carbon atom to
which the —OH group is attached. This H
removal generates a carbon–oxygen double
bond.

90
Primary and secondary alcohols, the two
types of oxidizable alcohols, yield different
products upon oxidation. A 10 alcohol
produces an aldehyde that is often then
further oxidized to a carboxylic acid, and a
20 alcohol produces a ketone.

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Primary alcohol oxidation

94
Secondary alcohol oxidation

95
Tertiary alcohols do not undergo oxidation with mild
oxidizing agents. This is because they do not have
hydrogen on the —OH-bearing carbon atom.

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Halogenation
Alcohols undergo halogenation reactions in which a
halogen atom is substituted for the hydroxyl group,
producing an alkyl halide. Alkyl halide production in this
manner is superior to alkyl halide production through
halogenation of an alkane because mixtures of products
are not obtained. A single product is produced in which
the halogen atom is found only where the —OH group
was originally located.

99
Several different halogen-containing reactants,
including phosphorus trihalides (PX3; X is Cl or Br),
are useful in producing alkyl halides from alcohols.

100

101

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Polymeric Alcohols
It is possible to synthesize polymeric alcohols with
structures similar to those of substituted polyethylenes.
One of the simplest such compounds is poly(vinyl alcohol)
(PVA).

103
Polymeric Alcohols
Poly(vinyl alcohol) is a tough, whitish polymer that can be
formed into strong films, tubes, and fi bers that are highly
resistant to hydrocarbon solvents. Unlike most organic
polymers, PVA is water-soluble. Water-soluble fi lms and
sheetings are important PVA products. PVA has oxygen-
barrier properties under dry conditions that are superior
to those of any other polymer. PVA can be rendered
insoluble in water, if needed, by use of chemical agents
that cross-link individual polymer strands.

104
Structural Characteristics of Phenols
A phenol is an organic compound in which an —OH
group is attached to a carbon atom that is part of an
aromatic carbon ring system.

105
The general formula for phenols is Ar–OH,
where Ar represents an aryl group. An aryl
group is an aromatic carbon ring system
from which one hydrogen atom has been
removed.
A hydroxyl group is thus the functional
group for both phenols and alcohols.

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Nomenclature for Phenols
Phenol is also the IUPAC-approved name for the
simplest member of the phenol family of
compounds.

108
Phenol is also the IUPAC-approved name for the
simplest member of the phenol family of
compounds.

109
The name phenol is
derived from a
combination of the
terms phenyl and
alcohol.

110
The IUPAC rules for naming phenols are simply
extensions of the rules used to name benzene
derivatives with hydrocarbon or halogen substituents.
The parent name is phenol. Ring numbering always
begins with the hydroxyl group and proceeds in the
direction that gives the lower number to the next
carbon atom bearing a substituent. The numerical
position of the hydroxyl group is not speciﬁed in the
name because it is 1 by deﬁnition.

112
Methyl and hydroxy derivatives of phenol have IUPAC-
accepted common names. Methylphenols are called
cresols. The name cresol applies to all three isomeric
methylphenols.

113
For hydroxyphenols, each of the three isomers
has a different common name.

114
Physical and Chemical Phenols
Phenols are generally low-melting solids or oily
liquids at room temperature. Most of them are
only slightly soluble in water. Many phenols
have antiseptic and disinfectant properties. The
simplest phenol, phenol itself, is a colorless
solid with a medicinal odor. Its melting point is
410C, and it is more soluble in water than are
most other phenols.

115
The similarities and differences between
these two reaction chemistries are as
follows:
1. Both alcohols and phenols are
ﬂammable.
2. Dehydration is a reaction of alcohols but
not of phenols; phenols cannot be
dehydrated.

116
3. Both 10 and 20 alcohols are oxidized by mild
oxidizing agents. Tertiary (30) alcohols and phenols
do not react with the oxidizing agents that cause 10
and 20 alcohol oxidation. Phenols can be oxidized by
stronger oxidizing agents.
4. Both alcohols and phenols undergo halogenation
in which the hydroxyl group is replaced by a
halogen atom in a substitution reaction.

117
Acidity of Phenols
One of the most important properties of phenols is their
acidity. Unlike alcohols, phenols are weak acids in
solution. As acids, phenols have Ka values of about 10-10.
Such Ka values are lower than those of most weak
inorganic acids (10-5 to 10-10). The acid ionization reaction
for phenol itself is

118
Acidity of Phenols
The negative ion produced from the ionization is called
the phenoxide ion. When phenol itself is reacted with
sodium hydroxide (a base), the salt sodium phenoxide is
produced.

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Occurrence of and Uses for Phenols
Dilute (2%) solutions of phenol have
long been used as antiseptics.
Concentrated phenol solutions,
however, can cause severe skin burns.
Today, phenol has been largely
replaced by more effective phenol
derivatives such as 4-hexylresorcinol.
The compound 4-hexylresorcinol is an
ingredient in many mouthwashes and
throat lozenges.

120
The phenol derivatives o-
phenylphenol and 2-benzyl-4-
chlorophenol are the active
ingredients in Lysol, a disinfectant
for walls, ﬂoors, and furniture in
homes and hospitals.

121

122
A number of phenols possess antioxidant activity. An
antioxidant is a substance that protects other
substances from being oxidized by being oxidized
itself in preference to the other substances. An
antioxidant has a greater afﬁnity for a particular
oxidizing agent than do the substances the
antioxidant is “protecting”; the antioxidant,
therefore, reacts with the oxidizing agent ﬁrst.

123
Many foods sensitive to air are protected
from oxidation through the use of
phenolic antioxidants. Two commercial
phenolic antioxidant food additives are
BHA (butylated hydroxy anisole) and BHT
(butylated hydroxy toluene).

124

125
A naturally occurring phenolic antioxidant that is
important in the functioning of the human body is
vitamin E.

126
A number of
phenols found in
plants are used
as ﬂavoring
agents and/or
antibacterials.
Included among
these phenols
are

127

128
Certain phenols exert profound physiological
effects. For example, the irritating
constituents of poison ivy and poison oak are
derivatives of catechol. These skin irritants
have 15-carbon alkyl side chains with varying
degrees of unsaturation (zero to three double
bonds).

129

130
Structural Characteristics of Ethers
An ether is an organic compound in which an oxygen
atom is bonded to two carbon atoms by single
bonds. In an ether, the carbon atoms that are
attached to the oxygen atom can be part of alkyl,
cycloalkyl, or aryl groups.

131
All ethers contain a
C—O—C unit,
which is the ether
functional group.

132
Generalized formulas for ethers, which
depend on the types of groups attached to
the oxygen atom (alkyl or aryl), include R—
O—R, R—O—R’ (where R’ is an alkyl group
different from R), R—O—Ar, and Ar—O—
Ar.

133
An ether can be visualized as a derivative
of water in which both hydrogen atoms
have been replaced by hydrocarbon
groups. Note that unlike alcohols and
phenols, ethers do not possess a hydroxyl
(—OH) group.

134

135

136
Nomenclature for Ethers
Common names are almost always used for
ethers whose alkyl groups contain four or
fewer carbon atoms. There are two rules, one
for unsymmetrical ethers (two different alkyl/
aryl groups) and one for symmetrical ethers
(both alkyl/aryl groups the same).

137
Rule 1: For unsymmetrical ethers, name
both hydrocarbon groups bonded to the
oxygen atom in alphabetical order and
add the word ether, separating the words
with a space. Such ether names have
three separate words within them.

139
Rule 2: For symmetrical ethers, name the alkyl
group, add the preﬁx di-, and then add the word
ether, separating the words with a space. Such ether
names have two separate words within them.

140
Ethers with more complex alkyl/aryl groups are
named using the IUPAC system. In this system, ethers
are named as substituted hydrocarbons. The smaller
hydrocarbon attachment and the oxygen atom are
called an alkoxy group, and this group is considered a
substituent on the larger hydrocarbon group. An
alkoxy group is an —OR group, an alkyl (or aryl)
group attached to an oxygen atom.

142
The general symbol for an alkoxy group is
—O—R (or —OR). The rules for naming an
ether using the IUPAC system are
Rule 1: Select the longest carbon chain
and use its name as the base name.

143
Rule 2: Change the -yl ending of the other
hydrocarbon group to -oxy to obtain the
alkoxy group name; methyl becomes
methoxy, ethyl becomes ethoxy, etc.
Rule 3: Place the alkoxy name, with a
locator number, in front of the base chain
name.

146
The simplest aromatic ether involves a methoxy
group attached to a benzene ring. This ether goes
by the common name anisole.

149
The ether MTBE (methyl tert-butyl ether) has
been a widely used gasoline additive since the
early 1980s.

150
As an additive, MTBE not only raises octane levels
but also functions as a clean-burning “oxygenate”
in EPA-mandated reformulated gasolines used to
improve air quality in polluted areas. The amount
of MTBE used in gasoline is now decreasing in
response to a growing problem: contamination of
water supplies by small amounts of MTBE from
leaking gasoline tanks and from spills.

151
MTBE in the water supplies is not a health-and
safety issue at this time, but its presence does
affect taste and odor in contaminated supplies.
Compounds with ether functional groups occur in
a variety of plants. The phenolic ﬂavoring agents
eugenol, isoeugenol, and vanillin are also ethers;
each has a methoxy substituent on the ring.

152
Isomerism for Ethers
Ethers contain two carbon chains (two alkyl groups),
unlike the one carbon chain found in alcohols.
Constitutional isomerism possibilities in ethers depend
on
(1) the partitioning of carbon atoms between the two
alkyl groups and
(2) isomerism possibilities for the individual alkyl groups
present. Isomerism is not possible for a C2 ether
(two methyl groups) or a C3 ether (a methyl and an
ethyl group).

153
For C4 ethers, isomerism arises not only from
carbon atom partitioning between the alkyl groups
(C1—C3 and C2—C2) but also from isomerism
within a C3 group (propyl and isopropyl). There are
three C4 ether constitutional isomers.
For C5 ethers, carbon partitioning possibilities are
C2—C3 and C1—C4. For C4 groups there are four
isomeric variations: butyl, isobutyl, sec-butyl, and
tert-butyl.

155
Functional Group Isomerism
Ethers and alcohols with the same number of
carbon atoms and the same degree of saturation
have the same molecular formula. The simplest
manifestation of this phenomenon involves
dimethyl ether, the C2 ether, and ethyl alcohol, the
C2 alcohol. Both have the molecular formula
C2H6O.

156

157
Functional group isomers are constitutional isomers that
contain different functional groups. When three carbon
atoms are present the ether–alcohol functional group
isomerism possibilities are

158

159
Physical and Chemical Properties of
Ethers
The boiling points of ethers are similar to those of alkanes
of comparable molecular mass and are much lower than
those of alcohols of comparable molecular mass.

160
Ethers

161
Ethers
Ethers, in general, are more soluble in water
than are alkanes of similar molecular mass
because ether molecules are able to form
hydrogen bonds with water. Ethers have water
solubilities similar to those of alcohols of the
same molecular mass.

162
Ethers
Diethyl ether and butyl alcohol have the same
solubility in water. Because ethers can also
hydrogen-bond to alcohols, alcohols and ethers
tend to be mutually soluble. Nonpolar substances
tend to be more soluble in ethers than in alcohols
because ethers have no hydrogen-bonding
network that has to be broken up for solubility to
occur.

163
Ethers
Two chemical properties of ethers are especially
important.
1. Ethers are flammable. Special care must be
exercised in laboratories where ethers are used.
Diethyl ether, whose boiling point of 350C is only a
few degrees above room temperature, is a
particular fl ash-fire hazard.

164
Ethers
Two chemical properties of ethers are especially
important.
2. Ethers react slowly with oxygen from the air to
form unstable hydroperoxides and peroxides.

165
Ethers

166
Ethers
Such compounds, when concentrated,
represent an explosion hazard and must be
removed before stored ethers are used. Like
alkanes, ethers are unreactive toward acids,
bases, and oxidizing agents. Like alkanes, they
do undergo combustion and halogenation
reactions.

167
Ethers
The general chemical unreactivity of ethers,
coupled with the fact that most organic
compounds are ether-soluble, makes ethers
excellent solvents in which to carry out
organic reactions. Their relatively low boiling
points simplify their separation from the
reaction products.

168
Ethers
The intermolecular dehydration of a primary
alcohol will produce an ether.

169
Cyclic Ethers
Cyclic ethers contain ether functional groups as
part of a ring system. Some examples of such cyclic
ethers, along with their common names, follow.

170
Cyclic Ethers
Ethylene oxide has few direct uses. Its
importance is as a starting material for the
production of ethylene glycol, a major
component of automobile antifreeze.
THF is a particularly useful solvent in that it
dissolves many organic compounds and yet is
miscible with water.

171
Cyclic Ethers
Many cyclic structures that are polyhydroxy
derivatives of the ﬁve-membered (furan) and six-
membered (pyran) cyclic ether systems. These
carbohydrate derivatives are called furanoses and
pyranoses.
Vitamin E and THC, the active ingredient in
marijuana, have structures in which a cyclic ether
component is present.

172
Cyclic Ethers
Cyclic ethers are our ﬁrst encounter with
heterocyclic organic compounds. A
heterocyclic organic compound is a cyclic
organic compound in which one or more of the
carbon atoms in the ring have been replaced
with atoms of other elements. The hetero
atom is usually oxygen or nitrogen.

173
Cyclic Ethers
Cyclic ethers—compounds in which the ether
functional group is part of a ring system—exist.
Cyclic alcohols—compounds in which the alcohol
functional group is part of a ring system—do not
exist.
To incorporate an alcohol functional group into a
ring system would require an oxygen atom with
three bonds, and oxygen atoms form only two
bonds.

175
Sulfur Analogs of Alcohols
Many organic compounds containing
oxygen have sulfur analogs, in which a
sulfur atom has replaced an oxygen atom.
Sulfur is in the same group of the periodic
table as oxygen, so the two elements have
similar electron conﬁgurations.

176
Thiols, the sulfur analogs of alcohols, contain
—SH functional groups instead of —OH
functional groups. The thiol functional group
is called a sulfhydryl group. A sulfhydryl group
is the —SH functional group. A thiol is an
organic compound in which a sulfhydryl group
is bonded to a saturated carbon atom. An
older term used for thiols is mercaptans.

177

178
Nomenclature for Thiols
Thiols are named in the same way as
alcohols in the IUPAC system, except that
the -ol becomes -thiol. The preﬁx thio-
indicates the substitution of a sulfur atom
for an oxygen atom in a compound.

179

180
As in the case of diols and triols, the -e at the
end of the alkane name is also retained for
thiols.
Common names for thiols are based on use of
the term mercaptan, the older name for
thiols. The name of the alkyl group present
(as a separate word) precedes the word
mercaptan.

181

182

183

184
Properties of Thiols
Two important properties of thiols are lower boiling
points than alcohols of similar size (because of lack of
hydrogen bonding) and a strong, disagreeable odor. The
familiar odor of natural gas results from the addition of a
low concentration of methanethiol (CH3—SH) to the gas.
The exceptionally low threshold of detection for this thiol
enables consumers to smell a gas leak long before the
gas, which is itself odorless, reaches dangerous levels.
The scent of skunks is due primarily to two thiols.

186
Thiols are easily oxidized but yield different products than
their alcohol analogs. Thiols form disulﬁdes. Each of two
thiol groups loses a hydrogen atom, thus linking the two
sulfur atoms together via a disulﬁde group, —S—S—.

187
Reversal of this reaction, a reduction process, is also
readily accomplished. Breaking of the disulﬁde bond
regenerates two thiol molecules.

188
These two “opposite
reactions” are of biological
importance in the area of
protein chemistry. Disulﬁde
bonds formed from the
interaction of two —SH
groups contribute in a major
way to protein structure.

190
Sulfur Analogs of Ethers
Sulfur analogs of ethers are known as
thioethers (or sulﬁdes). A thioether is an
organic compound in which a sulfur atom is
bonded to two carbon atoms by single
bonds. The generalized formula for a
thioether is R—S—R. Like thiols, thioethers
(or sulﬁdes) have strong characteristic odors.

191
Thioethers are named in the same way as ethers,
with sulﬁde used in place of ether in common
names and alkylthio used in place of alkoxy in
IUPAC names.

192
Thiols and thioethers are functional group isomers
in the same manner that alcohols and ethers are
functional group isomers.

193
1-propanethiol and the thioether
methylthioethane both have the molecular
formula C3H8S.

End of Chapter 4
Alcohols, Phenols and
Ethers
General, Organic, and Biological Chemistry,Fifth Edition
H. Stephen Stoker
Brroks/Cole Cengage Learning. Permission required for reproduction or display.

Chapter4alcoholsphenolsandethers 151111010603-lva1-app6892

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