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14.5 Physical Properties of Alcohols, Phenols, and Ethers
14.6 Reactions of Alcohols
Chapter 14 Alcohols, Phenols, Ethers, and Thiols
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Boiling Points of Alcohols
Alcohols contain a strongly electronegative O in the OH groups.
Thus, hydrogen bonds form between alcohol molecules.
Hydrogen bonds contribute to higher boiling points for alcohols compared to alkanes and ethers of similar mass.
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Boiling Points of Ethers
Ethers have an O atom, but there is no H attached.
Thus, hydrogen bonds cannot form between ether molecules.
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Solubility of Alcohols and Ethers in Water
Alcohols and ethers are more soluble in water than alkanes because the oxygen atom can hydrogen bond with water.
Alcohols with 1-4 C atoms are soluble, but alcohols with 5 or more C atoms are not.
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Alcohols undergo combustion with O2 to produce CO2 and H2O.
2CH3OH + 3O2 2CO2 + 4H2O + Heat Dehydration removes H- and -OH from adjacent
carbon atoms by heating with an acid catalyst. H OH
| | H+, heatH—C—C—H H—C=C—H + H2O
| | | | H H H H
alcohol alkene
Reactions of Alcohols
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Formation of Ethers
Ethers form when dehydration takes place at low temperature.
H+
CH3—OH + HO—CH3 CH3—O—CH3 + H2O
Two Methanol Dimethyl ether
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Oxidation and Reduction In organic chemistry, oxidation is a loss of
hydrogen atoms or a gain of oxygen. In an oxidation, there is an increase in the
number of C-O bonds. Reduction is a gain of hydrogen or a loss of
oxygen. The number of C-O bonds decreases.
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In the oxidation [O] of a primary alcohol, one H is lost from the –OH and another H from the carbon bonded to the OH.
[O] Primary alcohol Aldehyde
OH O | [O] ||
CH3—C—H CH3—C—H + H2O |
H Ethanol Ethanal (ethyl alcohol) (acetaldehyde)
Oxidation of Primary Alcohols
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The oxidation of a secondary alcohol removes one H from –OH and another H from the carbon bonded to the –OH.
[O] Secondary alcohol Ketone OH O
| [O] || CH3—C—CH3 CH3—C—CH3 + H2O |
H 2-Propanol Propanone (Isopropyl alcohol) (Dimethylketone; Acetone)
Oxidation of Secondary Alcohols
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Tertiary alcohols are resistant to oxidation.[O]
Tertiary alcohols no reaction OH | [O] CH3—C—CH3 no product | CH3 no H on the C-OH to oxidize 2-Methyl-2-propanol
Oxidation of Tertiary Alcohols
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Ethanol: Acts as a depressant. Kills or disables more
people than any other drug. Is metabolized at a rate of
12-15 mg/dL per hour by a social drinker.
Is metabolized at a rate of 30 mg/dL per hour by an alcoholic.
Ethanol CH3CH2OH
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Enzymes in the liver oxidize ethanol. The aldehyde produced impairs coordination. A blood alcohol level over 0.4% can be fatal.
O ||
CH3CH2OH CH3CH 2CO2 + H2OEthyl alcohol acetaldehyde
Oxidation of Alcohol in the Body
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Oxidation of alcohols in liver
CH3CH2OH CH3C
O
HCH3C
O
OH
CO2 + H2O
ethyl alcoholethanol
acetaldehydeethanal
acetic acidethanoic acid
alcoholdehydrogenase
CH3OH HCO
H
alcoholdehydrogenase
metyl alcoholmethanol
formaldehydemethanal
reacts with proteins causing denaturationgreat toxicity to humansnot toxic to horses and rats
HCO
OH
formic acidmethanoic acid
acetaldehydedehydrogenase
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Breathalyzer test
K2Cr2O7 (potassium dichromate) This orange colored solution is used in the
Breathalyzer test (test for blood alcohol level) Potassium dichromate changes color when it is
reduced by alcohol K2Cr2O7 oxidizes the alcohol
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Breathalyzer reaction orange-red green
8H++Cr2O72-+3C2H5OH→2Cr3++3C2H4O+7H2O
dichromate ethyl chromium (III) acetaldehyde
ion alcohol ion
(from K2Cr2O7)
H3C C H
H
OH[O]
H3C C
O
H
+ H2O
ethylalcohol
acetaldehyde
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% Ethanol Product
50% Whiskey, rum, brandy
40% Flavoring extracts
15-25% Listerine, Nyquil, Scope
12% Wine, Dristan, Cepacol
3-9% Beer, Lavoris
Alcohol Contents in Common Products
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The proof of an alcohol The proof of an alcoholic beverage is merely twice the
percentage of alcohol by volume. The term has its origin in an old seventeenth-century
English method for testing whiskey. Dealers were often tempted to increase profits by adding
water to booze. A qualitative method for testing the whiskey was to pour
some of it on gunpowder and ignite it. If the gunpowder ignited after the alcohol had burned
away, this was considered “proof” that the whiskey did not contain too much water.
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Production of ethanol from grain by fermentation Grain seeds are grounded and cooked → mash Malt (the dried sprouts of barley) or special mold is added
→ source of the enzyme diastase that catalyzes the conversion of starch to malt sugar, maltose
diastase
(C6H10O5)2x + H2O → x C12H22O11
starch maltose Pure yeast culture is addedC12H22O11 + H2O → 2 C6H12O6
maltose glucose
C6H12O6 → 2 CH3CH2OH + 2 CO2
glucose ethanol carbon dioxide
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Preparation of alcohols Ethanol is made by hydration of ethylene (ethene)
in the presence of acid catalyst
C C
H
H
H
H
+ HOH[H+]
C C H
OH
HH
H
H
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Isopropyl is produced by addition of water to propylene (1-
propene)
H3CHC CH2 + HOH
[H+]H3C
HC CH3
OH
(Markovnikov's rule)
CH3CH2CH2OHpropyl alcohol is never formed
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Oxidation of Thiols. Mild oxidizing agens remove two hydrogen
atoms from two thiol molecules. The remaining pieces of thiols combine to
form a new molecule, disulfide, with a covalent bond between two sulfur atoms.
R – S – H H – S – R+I2 → RS – SR+2HI
2 RSH + H2O2 → RS – SR + 2 H2O
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The chemistry of the “permanent” waving of hair. Hair is protein, and it is held in shape by disulfide linkages between adjacent
protein chains. The first step involves the use of lotion containing a reducing agent such as
thioglycolic acid, HS – CH2 – COOH. The wave lotion ruptures the disulfide linkages of the hair protein. The hair is then set on curles or rollers and is treated with a mild oxidizing
agent such as hydrogen peroxide (H2O2). Disulfide linkages are formed in new positions to give new shape to the hair. Exactly the same chemical process can be used to straighten naturally curly
hair. The change in hair style depends only on how one arranges the hair after the
disulfide bonds have been reduced and before the reoxidation takes place. Permanent Hair Wave (http://www.elmhurst.edu/~chm/vchembook/
568hairwave.html)