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12.3 Alcohols
,67
rigid, like plastic milk containers. Polypropylene is prepared by polymerization of propene.
CH"
f"'
t-
-+
ICH:CH,
+CH-CH|+*
Propene
{propylene)
Pollpropylene
Polypropylene makes a stiffer polymer than polyethylene, and it is used
extensivelyin utensils and containers.
Polystyreneis preparedby the po\rmerization of styrene (vinyl benzene):
<-\
ttl
>.'
rCH2:CH
*
Styrene
(vinyl benzene)
Figure12.5
polymersplayan imporSynthetic
tantrolein ourdailylives.
-FCHz-CH+"
Polysty'rene
Polystyreneis a poor heat conductor when produced as a foam. It is used to
insulate homes and in the manufacture of molded items such as coffee
cups and coolers.
Polyisopreneis the polyrner that constitutes natural rubber. It is used in
the manufacture of boots, tires, and rubber tubing. The polyisoprene molecule contains cls double bonds:
+c{,
,rCHr:6611:CH2
I
CHs
-------
C:C
H"c/
Isoprene
/,cH2+"
tu,
Polyisoprene
Figure 12.3shows a small selection of the wide variety of articles made from
polyrners.
12.5Alcohols
AIMS: Tonome ond drow structuresof olcohols,glycols,ond
phenols.Toidentify on olcoholos being primory
secondoryor teftiory. Toidentify fhe usesof some
commonolcohols.
Focus
Alcohols are organic derivatives
of water.
Alcohols are compounds in which one hydrogen of the water molecule is
replacedby a hydrocarbon chain or ring. Thefunctional group - OH in alcohok is called a hydro:ry function or hydroryl Soup. In organic chemistry,
the symbol R is often used to represent any carbon chains or carbon rings.
Therefore,the generalformula of an alcohol can be written as ROH.
o
HH
Watermolecule
"/
o9
/
/ ,-"
hvdroxyl
group
RH
Alcoholmolecule
568
CHAPTER12 Halocarbons,
Alcohols,and Ethers
Chemists often arrange aliphatic alcohols into structural categories
according to the number of R groups attached to the carbontl-ntis bonded
to the hydroxyl group. The R groups in a molecule may be the same or may
be different. Only one R group and two hydrogens are attached to the
C-OH of a primary (abbreviated l') alcohol. Two R groups and one hydrogen are attached to the C-OH of a secondary (2") alcohol. A tertiary (3")
alcohol has three R groups and no hydrogens attached to the C-OH.
H
I
R-C
I
OH
R
I
R-C-OH
R-C-OH
H
R
| 2.5
EXAri[PLE
I
I
I
H
Primary (f ') alcohol
R
(2")alcohol
Secondary
Tertiary (3') alcohol
Determining'whetfter
an,'alcoholis primary secondatyioilertiary ' ,, , - ,,,:.' ,..,.
Identiff each of the following compounds as a primary, secondary or tertiary alcohol.
CHq
cH3cH2cH2oH
I
CH3CHCH2OH
CH.
t-
CH3-C-CH2OH
I
CHs
sotuTtoN
The alcohols in this example have increasingly complex hydrocarbon
chains. However, it is the number of alkyl groups bonded to the carbon in
C-OH that determines whether an alcohol is primary, secondary or tertiary: A primary alcohol has one R group and two hydrogens attached, a
secondary alcohol has two R groups and one hydrogen attached, and a tertiary alcohol has three R groups and no hydrogens attached. In each ofthe
examples,the carbon bonded to the hydroxyl group has only one R group
and two hydrogens attached. Therefore, each of these alcohols is a primary
alcohol.
Naming
alcohols
To name straight-chain and substituted alcohols by the IUPAC system, we
drop the -eending of the name of the parent alkane and add the ending -ol.
The parent alkane is the longest continuous chain of carbons that includes
the carbon attached to the hydroxyl group. In numbering the longest continuous chain, we give the position of the hydroxyl group the lowest possible number. Alcohols containing two, three, and four -OH substituents
are named diols, triols, and tetrols, respectively. Common names of
aliphatic alcohols are written in the same way as those for the halocarbons.
The altcylgroup-methyl, for example-is named and followed by the word
alcohol, as in methyl alcohol. Compounds with more than one -OH sub-
12.5 Alcohols
569
stituent are called glycok. Here are some simple irliphatic alcohols along
with their IUPAC and common niunes:
cH3-oH
CH3-CHr-OH
CH3-CH2-CH2-OH
CH3-CH-CH3
OH
Methanol
(methyl
alcohol)
1-Propanol
(propyl
alcohol)
Ethanol
(ethyl
alcohol)
CH"
t-
cH3-c-cHs
?".
GH3-CH2-CH-CH3
OH
2-Propanol
(isopropyl
alcohol)
CI{3-CH-CH2-OH
OH
2-Methyl-2-propanol
(tert-butyl alcohol)
2-Butanol
(sec-butyl alcohol)
2-Methyl-1-propanol
(isobutyl alcohol)
OH
/)
\-j
Cyclohexanol
(cycloheryl alcohol)
Hr9-9H,
CH3-CH-CH2
lttl
OH
OH
OH
OH
l,2-Ethanediol
l,2-Propanediol
(ethylene glycol)
(tlre common narlrehas arr -ene
ending but the molecule
contains no double bond)
PRACTICE
EXERCISE
I2.5
Name the following alcohols.
(a) CH,CH,CI{2CH,OH (b) CH,
cI{3cHoH
oH
cH2-cH-cH2
tll
OH
OH OH
1,2,3-Propanetriol
(glycerol)
(c) CHsCHzfHCH2oH
CHt
?".
(e)CrLfoH
CH3
':.
PRACTICE
EXERCISE
12.6
,:
Classify each of the alcohols in Practice Exercise 12.5 as primary,
::r: secondary, or tertiary.
Uses of alcohols
Many aliphatic alcohols are used in the laboratory, in the health sciences,
and in industry. Isopropyl alcohol, a colorless, nearly odorless liquid (bp
82 'C), is the rubbing alcohol used for massages.It is also used as a base for
perfumes, creams,lotions, and other cosmetics.Ethylene glycol (bp 197 .C)
is the principal ingredient of antifreeze.Its advantagesover other high-boiling liquids are its solubility in water and a freezing point of -IT.4"C.If
T70
Alcohols,and Ethers
t2 Halocarbons,
CHAPTER
water is added to ethylene glycol, the mixture freezesat an even lower temperature-a 50To (vlv) aqueous solution of ethylene glycol freezes at
-36 'C. Glycerolis a viscous,sweet-tasting,water-solubleliquid. It is used
as a lubricant in suppositories and as a moistening agent in cosmetics,
foods, and drugs.Glycerolis also an important component of fats and oils.
Ethanol (bp 78.5 'C) is the most important alcohol. Also called grain
alcohol, much ethanol is produced byyeast fermentation of sugar.Archaeological evidenceindicates that cave dwellers had produced alcoholic beveragesby using fermentation. Since those early times, people have pursued
and perfected that art. Virtually every grain, fruit, or vegetablehas been fermented: corn, wheat, r1r€,rice, grapes,tomatoes,dandelions,elderberries,
cherries,potatoes, and even cactus pulp. The proofof an alcoholic beverage
is twice the alcohol content. For example, 100 proof spirits contain 50%
ethanol. Ethanol itself is tastelessand odorless.The differencesin taste
among alcoholic beveragesare the result of other products formed during
the fermentation process.Among these products are the fusel oils, which
include propyl, isopropyl, and other straight- and branched-chain aliphatic
alcohols.Fusel oils are often toxic and are one causeof the hangover effects
of excessivedrinking.
Most ethanol is produced by the fermentation of corn starch and cane
sugar.Ethanol is an alternative fuel for use in automobiles. It is mixed with
gasolineto form gasohol.At a concentrationof 10%ethanol,gasoholcan be
used in a standardautomobile engine.
Ethanol is a hypnotic or sleep-inducingdrug. Its abuseis a seriouspublic health problem. Someexpertsestimatethat one in nine adultAmericans
have a drinking problem of some kind. There is no evidencethat moderate
drinking is harmful.
Ethanol for industrial use is often denatured. Denatured alcohol ls
ethanol that contains an added substanceto make it toxic. Methanol, sometimes called wood alcoholbecausebefore 1925it was preparedby the distillation of wood, is often the denaturant.The inability to remember the difference between grain alcohol and wood alcohol has spelled tragedy for
many people.Wood alcohol is extremelytoxic: l0 mL has been reported to
causepermanent blindness-and as little as 30 mL, death. Someundenatured ethanol is used in laboratories under careful supervision. Pure
ethanol is labeled absolutealcohol.A preparation containing 5Towater is
also available.Nobody should ever attempt to drink laboratory alcohol.
Phenols
Phenols are compounds in which a hydroxyl group is attached directly to an
aromatic ring. Many phenolic compounds are found in nature. Shown
below are phenol, the parent compound, and some natural and qmthetic
derivatives.
c(cH3)3
;-*4t*
I
ll
cHi\'/
CHa
BHT
Th1.rnol
'cH.
1 2 . 5A l c o h o l s
,71
Phenol was formerly used as an antiseptic in hospitals (seeA closer Look:
Phenolic Antiseptics and Disinfectants).A synthetic derivative of phenol,
burylated hydroxy toluene (BHT), is widely used as a food preservative.
BHT is often put in food wrappers rather than in the food itself to keep it
from imparting a rather antisepticflavor to the product.
PhenolicAntisepticsand
Disinfectants
Phenol, also called carbolic acid,wasfirst used as
a medical antiseptic in 1867by Ioseph Lister. He
demonstrated that the incidence of infections
after surgical procedures was dramatically
reduced when solutions of phenol were used to
clean the surgical instruments, the operating
room, and the patient's skin. Today'suse of phenol for medicinal purposesis more limited. \il/hen
phenol is absorbedthrough the skin, ingested,or
inhaled, it is toxic. It also can causeseverechemical burns. However,it is available as an antiseptic in aqueousor alcoholic solutions that contain
a maximum of 1.5Vophenol. Phenol is an ingredient in a variety of throat lozengesthat can contain up to 50 mg phenol per lozenge.It is a useful
topical drug for treating sore throats because it
numbs the inflamed area.
A number of derivativesof the parent phenol
are used today as antiseptics. Many mouthwashesand throat lozengesinclude alkyl-substituted phenols as their uciive ingredients for pain
relief (seefigure). The compound 4-hexylresorcinol has a superior antibacterial action to that of
phenol. It is also much less toxic. Therefore,it is
an ingredient of choice in mouthwashes and
throat lozenges.
around the home. Disinfectants are formulated
for use on inanimate objects, not living tissues.
Phenol's germicidal properties result because
these chemicals have the ability to disrupt the
microorganisms'cell wall permeabiliry.
The naturally occurring phenol eugenol is
found in clovesand is used in dentistry to relieve
toothaches. Methyl salicylate, another phenol
derivative commonly known as oil of wintergreen, is a flavoring agent and is used in liniments to relieve sore muscles.Another derivative
of phenol, thymol, is used as an antiseptic in
mouthwashpreparations.
OH
cH2cH2cH2cH2CH2CH3
4-hexylresorcinoi
Phenols and methyl phenols {cresols) are
commonly used as disinfectants in hospitals and
Phenoland its derivativesare the activeingredientsin
many of the preparationsused for oral hygiene.