Transcript Chapter Fourteen

Fundamentals of General, Organic,
and Biological Chemistry
5th Edition
Chapter Fourteen
Some Compounds with
Oxygen, Sulfur, or a Halogen
James E. Mayhugh
Oklahoma City University
2007 Prentice Hall, Inc.
Outline
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14.1 Alcohols, Phenols, and Ethers
14.2 Some Common Alcohols
14.3 Naming Alcohols
14.4 Properties of Alcohols
14.5 Reactions of Alcohols
14.6 Phenols
14.7 Acidity of Alcohols and Phenols
14.8 Ethers
14.9 Thiols and Disulfides
14.10 Halogen-Containing Compounds
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14.1 Alcohols, Phenols, and Ethers
An alcohol has an –OH bonded to an alkyl group; a
phenol has an –OH bonded directly to an aromatic ring;
and an ether has an O bonded to two organic groups.
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► Ethyl alcohol, dimethyl ether, and propane have
similar molecular weights, yet ethyl alcohol boils
more than 100° higher than the other two.
► The high boiling points of ethyl alcohol and water
are due to hydrogen bonding.
► Alkanes and ethers do not have hydroxyl groups and
cannot form hydrogen bonds. As a result, they have
lower boiling points. Ethers, in fact, resemble
alkanes in many of their properties.
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14.2 Some Common Alcohols
► Simple alcohols are very common organic chemicals.
They are useful as solvents, antifreeze agents, and
disinfectants, and they are involved in the metabolic
processes of all living organisms.
► Methyl alcohol is commonly known as wood alcohol
because it was once prepared by heating wood in the
absence of air. Today it is made in large quantities by
reaction of carbon monoxide with hydrogen.
► Methanol is used to make formaldehyde
and methyl tert-butyl ether (MTBE), an
octane booster added to gasoline. Methyl
alcohol is colorless, miscible with water,
and toxic to humans when ingested.
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► Ethyl alcohol produced by fermentation is called grain
alcohol; with methyl alcohol, camphor, or kerosene
added it is called denatured alcohol. Industrially, most
ethanol is made by hydration of ethylene. Absolute
alcohol is 100% ethyl alcohol. Gasohol is a blend of
ethyl alcohol and gasoline.
► Isopropyl alcohol, or rubbing alcohol, is used for
rubdowns, as a solvent, as a sterilant for instruments,
and as a skin cleanser before drawing blood or giving
injections. Less toxic than methyl alcohol, isopropyl
alcohol is more toxic than ethyl alcohol.
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► Ethylene glycol, a diol, is: a toxic, colorless liquid,
miscible with water and insoluble in nonpolar solvents.
Its two major uses are as antifreeze and as a material for
making polyester.
► The triol, glycerol or glycerin, is: a nontoxic, colorless
liquid that is miscible with water. It is used as a
sweetener, a moisturizer, in plastics manufacture, in
antifreeze and shock-absorber fluids, and as a solvent.
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14.3 Naming Alcohols
► Common names of many alcohols identify the alkyl
group and then add the word “alcohol.” In the
IUPAC system:
► STEP 1: Name the parent compound. Find the
longest chain that has the hydroxyl substituent
attached, and name the chain by replacing the -e
ending of the corresponding alkane with -ol:
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► STEP 2: Number the carbon atoms in the main
chain. Begin at the end nearer the hydroxyl group,
ignoring the location of other substituents:
► If the compound is a cyclic alcohol, add the -ol
ending to the name of the parent cycloalkane. In a
cyclic alcohol, begin with the carbon that bears the
–OH group and proceed in a direction that gives the
other substituents the lowest possible numbers.
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STEP 3: Write the name, placing the number that
locates the hydroxyl group immediately before the
parent compound name. Number the positions of all
other substituents, and list them alphabetically. Note
that in a cyclic alcohol, it is not necessary to use the
number “1” to specify the location of the –OH group.
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► Dialcohols, or diols, are often called glycols.
► Ethylene glycol is the simplest glycol; propylene
glycol is often used as a solvent for medicines that
need to be inhaled or rubbed onto the skin.
► Numbering starts from the end closer to an –OH
group, and the -diol name ending is used.
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► Alcohols are classified as primary, secondary, or
tertiary according to the number of carbon
substituents bonded to the hydroxyl-bearing carbon.
► Alcohols with one substituent are said to be
primary, those with two substituents are secondary,
and those with three substituents are tertiary.
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14.4 Properties of Alcohols
► Alcohols are much more polar than hydrocarbons.
Hydrogen bonding also occurs and has a strong
influence on alcohol properties.
► Straight-chain alcohols with up to 12 C’s are liquids,
and each boils at a considerably higher temperature
than the related alkane.
► Alcohols with a small organic part resemble water.
Methanol and ethanol are miscible with water and they
can dissolve small amounts of many salts.
► Alcohols with a large organic part are more like
alkanes. 1-Heptanol is nearly insoluble in water and
can’t dissolve salts but does dissolve alkanes.
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Alcohols with 2 or more –OH groups can form more than
one hydrogen bond. They are higher boiling and more
water soluble than similar alcohols with one –OH group.
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14.5 Reactions of Alcohols
► Alcohols undergo loss of water (dehydration) on
treatment with a strong acid catalyst.
► The –OH group is lost from a C, and an –H is lost
from an adjacent C to yield an alkene product:
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► When more than one alkene can result from
dehydration of an alcohol, a mixture of products is
usually formed.
► A good rule of thumb is that the major product has
the greater number of alkyl groups attached to the
double-bond carbons.
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► Primary and secondary alcohols are converted into
carbonyl-containing compounds on treatment with
an oxidizing agent. A carbonyl group is a functional
group that has a C=O. The symbol [O] will indicate
a generalized oxidizing agent.
► An organic oxidation is one that increases the
number of C-O bonds and/or decreases the number
of C-H bonds.
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Primary alcohols are converted either into aldehydes
if carefully controlled conditions are used, or into
carboxylic acids if an excess of oxidant is used.
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Secondary alcohols are converted into ketones on
treatment with oxidizing agents.
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Tertiary alcohols do not normally react with
oxidizing agents because they do not have a
hydrogen on the carbon atom to which the –OH
group is bonded.
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14.6 Phenols
► Phenol is the name both of a specific compound,
hydroxybenzene, and of a family of compounds.
► Phenols are usually named with the ending -phenol
rather than -benzene even though their structures
include a benzene ring.
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► Phenol is a medical antiseptic first used by Joseph
Lister in 1867. Lister showed that the occurrence of
postoperative infection dramatically decreased when
phenol was used to cleanse the operating room and
the patient’s skin.
► The medical use of phenol is now restricted because
it can cause burns and is toxic. Only solutions with
<1.5% phenol or lozenges with <50 mg of phenol are
now allowed in nonprescription drugs. Many
mouthwashes and throat lozenges contain alkylsubstituted phenols such as thymol as active
ingredients for pain relief.
► Alkyl-phenols such as the cresols are common as
disinfectants in hospitals. Antiseptics safely kill
microorganisms on living tissue, disinfectants
should only be used on inanimate objects.
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14.7 Acidity of Alcohols and Phenols
Alcohols and phenols are weakly acidic. They
dissociate slightly in water and establish equilibria
between neutral and anionic forms:
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► Methanol and ethanol are about as acidic as water,
with Ka  10-15. Their aqueous solutions are neutral.
► An alkoxide ion, or anion of an alcohol, is as strong
a base as hydroxide ion.
► Phenols are considerably more acidic than water.
Phenol itself has Ka = 1.010-10. Phenols react with
dilute aqueous sodium hydroxide to give an anion.
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14.8 Ethers
Ethers, compounds with two organic groups bonded
to the same O atom, are named by identifying the
two organic groups and adding the word ether.
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Compounds that contain the oxygen atom in a ring
are classified as cyclic ethers and are often given
common names.
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► An –OR group is referred to as an alkoxy group;
-OCH3 is a methoxy group, -OCH2CH3 is an ethoxy
group, and so on.
► These names are used when the ether functional
group is present in a compound that also has other
functional groups.
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► Ethers are polar but do not form hydrogen bonds to
one another. Simple ethers are higher boiling than
comparable alkanes but lower boiling than alcohols.
► Dimethyl ether is soluble and diethyl ether is partially
soluble in water.
► Ethers with large organic groups are insoluble in water.
Ethers are alkane-like and do not react with most acids,
bases, or other reagents.
► The simple ethers are highly flammable. On standing
in air, many ethers form explosive peroxides,
compounds that contain an O-O bond.
► Diethyl ether acts quickly and effectively as an
anesthetic, but it has a long recovery time and induces
nausea so it has now been replaced by safer anesthetics
such as enflurane and isoflurane.
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14.9 Thiols and Disulfides
Thiols, or mercaptans, are sulfur analogs of alcohols.
Skunk scent is caused by the two thiols shown below
center and right. The systematic name of a thiol is
formed by adding -thiol to the parent name.
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► Thiols (R-SH) react with mild oxidizing agents to yield a
disulfide (R-S-S-R).
► The reverse reaction (R-S-S-R  2R-SH) occurs when a
disulfide is treated with a reducing agent.
► Hair protein is rich in S-S and –SH groups. When hair is
“permed,” some disulfide bonds are broken and new ones are
formed, giving hair a different shape.
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14.10 Halogen-Containing
Compounds
Alkyl halides, R-X, have an alkyl group, R, bonded
to a halogen, X. Their common names consist of the
name of the alkyl group followed by the halogen
name with an -ide ending. Systematic names
consider the halogen atom as a substituent on a
parent alkane.
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► Halogenated organic compounds have a variety of
medical and industrial uses:
-Anesthetics
-Solvents, propellants, degreasing agents
-Fire extinguishers
-Herbicides, fungicides, insecticides
► Despite the enormous benefits of halogenated
organic compounds, their use has been restricted,
and sometimes banned altogether because:
-They persist in the environment and are not
broken down rapidly.
-They accumulate in some animals to harmful
levels.
-They can damage the ozone layer.
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► Halogen-containing organic compounds are important
in marine organisms; few are significant in human
biochemistry. One exception is thyroxine, an iodinecontaining hormone secreted by the thyroid gland.
► A deficiency of iodine in the diet
leads to a low thyroxine level, which
causes a swelling of the thyroid
gland called goiter. To ensure
adequate iodine in the diet KI is
sometimes added to table salt.
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Chapter Summary
► An alcohol has an –OH group bonded to a saturated,
alkane-like carbon atom; a phenol has an –OH group
bonded directly to an aromatic ring; and an ether has
an oxygen atom bonded to two organic groups.
► Phenols are notable for their use as disinfectants and
antiseptics; ethers are used primarily as solvents.
► Thiols are sulfur analogs of alcohols, with unpleasant
odors. Thiols are found in proteins.
► Alkyl halides contain a halogen atom bonded to an
alkyl group. Halogenated compounds are widely used
in industry as solvents and in agriculture as herbicides,
fungicides, and insecticides.
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Chapter Summary Cont.
► Alcohols are named using the -ol ending, and
phenols are named using the -phenol ending. Ethers
are named by identifying the two organic groups
attached to oxygen, followed by the word ether.
Thiols use the name ending -thiol, and alkyl halides
are named as halo-substituted alkanes.
► Both alcohols and phenols are like water in their
ability to form hydrogen bonds. As the size of the
organic part increases, alcohols become less soluble
in water. Ethers do not hydrogen-bond and are more
alkane-like in their properties.
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Chapter Summary Cont.
► Alcohols and phenols are weak acids that can donate
H+ to a strong base. Alcohols and water have similar
acidity; phenols are more acidic than water.
► Alcohols dehydrate to yield alkenes when treated with
a strong acid, and they undergo oxidation to yield
compounds that contain a carbonyl group. Primary
alcohols are oxidized to yield either aldehydes or
carboxylic acids, secondary alcohols are oxidized to
yield ketones and tertiary alcohols are not oxidized.
► Thiols react with mild oxidizing agents to yield
disulfides (RSSR), a reaction of importance in protein
chemistry. Disulfides can be reduced back to thiols.
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End of Chapter 14
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