C22 09/17/2013 11:27:34 Page 319 CHAPTER 22 ALCOHOLS, ETHERS, PHENOLS, AND THIOLS SOLUTIONS TO REVIEW QUESTIONS 1. The question allows great freedom of choice. These shown here are very simple examples of each type. (a) an alkyl halide CH 3 CH 2 Cl (b) a phenol OH (c) an ether CH 3 CH 2 OCH 2 CH 3 (d) (e) (f) a carboxylic acid CH 3 COOH (g) (h) a thiol CH 3 CH 2 SH 2. Alkenes are almost never made from alcohols because the alcohols are almost always the higher value material. This is because recovering alkenes from hydrocarbon sources in an oil refinery (primarily catalytic cracking) is a relatively cheap process. 3. Oxidation of primary alcohols yields aldehydes. Further oxidation yields carboxylic acids. Examples: 4. 1,2-Ethanediol is superior to methanol as an antifreeze because of its low volatility. Methanol is much more volatile than water. If the radiator leaks gas under pressure (normally steam), it would primarily leak methanol vapor so you would soon have no antifreeze. Ethylene glycol has a lower volatility than water, so it does not present this problem. - 319 -
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C22 09/17/2013 11:27:34 Page 319
C H A P T E R 2 2
ALCOHOLS, ETHERS, PHENOLS, AND THIOLS
SOLUTIONS TO REVIEW QUESTIONS
1. The question allows great freedom of choice. These shown here are very simple examples of each type.
(a) an alkyl halide CH3CH2Cl
(b) a phenol OH
(c) an ether CH3CH2OCH2CH3
(d)
(e)
(f) a carboxylic acid CH3COOH
(g)
(h) a thiol CH3CH2SH
2. Alkenes are almost never made from alcohols because the alcohols are almost always the higher value
material. This is because recovering alkenes from hydrocarbon sources in an oil refinery (primarily
catalytic cracking) is a relatively cheap process.
3. Oxidation of primary alcohols yields aldehydes. Further oxidation yields carboxylic acids. Examples:
4. 1,2-Ethanediol is superior to methanol as an antifreeze because of its low volatility. Methanol is much
more volatile than water. If the radiator leaks gas under pressure (normally steam), it would primarily
leak methanol vapor so you would soon have no antifreeze. Ethylene glycol has a lower volatility than
water, so it does not present this problem.
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5. Oxidation of alcohols affects the hydroxyl carbon in two ways: (1) the carbon adds a new bond to
oxygen; (2) the carbon loses a bond to hydrogen. When the hydroxyl carbon is not directly bonded to
hydrogen (as in tertiary alcohols), oxidation is difficult.
6. Dietary polyphenols have a variety of health benefits. They protect cells from oxidation by acting as
antioxidants. Perhaps more importantly polyphenols can serve as cellular signaling compounds. They
can decrease the risk of coronary heart disease by impacting arterial cells. By interacting with brain
cells, polyphenols can decrease cognitive loss. Current research suggests that polyphenols have a
beneficial impact on many cell types.
7. The liver oxidizes ingested methanol, first to methanal (formaldehyde) and then to methanoic acid
(formic acid). Methanoic acid is much more toxic than methanol. This acid causes metabolic acidosis
and inhibition of central energy metabolism that can lead to death.
8. The following classes of organic compounds can be easily formed from alcohols: aldehydes, ketones,
and carboxylic acids by oxidation; alkenes and ethers by dehydration; esters by esterification.
9.
10. Some common phenols include (a) hydroquinone, a photographic reducer and developer, (b) vanillin, a
flavoring, (c) eugenol, used to make artificial vanillin, (d) thymol, used as an antiseptic in mouthwashes,
(e) butylated hydroxytoluene (BHT), an antioxidant, and, (f) the cresols, used as disinfectants.
11. Low molar mass ethers present two hazards. They are very volatile and their highly flammable vapors
form explosive mixtures with air. They also slowly react with oxygen in the air to form unstable
explosive peroxides.
12. Ethanol (molar mass¼ 46.07) is a liquid at room temperature because it has a significant amount of
hydrogen bonding between molecules in the liquid state, and thus has a much higher boiling point than
would be predicted from molar mass alone. Dimethyl ether (molar mass¼ 46.07) is not capable of
hydrogen bonding to itself, so has low attraction between molecules, making it a gas at room
temperature.
13. Alcohols form strong intermolecular hydrogen bonds while thiols do not. Ethanol hydrogen bonding
makes for a higher boiling point than that for ethanethiol which does not hydrogen bond.
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14. At the boiling point of diethyl ether (35�C) the vapor pressure of diethyl ether must equal the
atmospheric pressure.
15. Benzyl alcohol is a primary alcohol. It can be oxidized to form an aldehyde or a carboxylic acid.
CH2OH
[O]
[O]
CH
COH
O
O
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SOLUTIONS TO EXERCISES
1. (a)
CH3CHCH3
OH (d)
CH3 C CHCHCH2 3
CH3 CH3
OH
(b)
CH2
CH
CH2 OH
OH
OH(e)
OH
(c)
CH3 CHCHCH2 2 OHCHCH 2
CH3 CH3(f) CH3CH2OH
2. (a)OH
(d) CH3CHCH2CH2OH
OH
(b) CH3CCH2CH3
OH
CH3
(e)
CH2
CH
CH2 OH
OH
OH
(c) CH3 CHCHC 2CH2CH3
CH3
CH3
OH
(f) CH3 CCHC 2CH3
OH
CH3
CH3
CH3
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3. There are only five isomers:
CH3 CHCCH 22 OH
CH3
CH3
CH2CH3 CCH2OH
CH3
CH33
CH3CHCHCH2OH
CH3
CH3
CH3CHCCH3
H C 3
CH3
OH
CH3CHCCH
CH3
CH
3
HO
4. There are only eight isomers:
CH3 CHCCH 2 CH32
CH3
OH
CH3CHCHCH2CH3
CH3
OH
CH3 CCH2CH3CH2
CH3
OH
CH3CHCHCH2CH3
CH3
OH
CH 22 CHCH CH 2CH3
CH3
HO
CH2 CHCHCH 2CH3
CH3
HO
CH3 CHCHCHCH 32
CH3 OH
2
CH3 CHCHCH 2CH2
CH3
OH2
5. (a) primary alcohols (where the hydroxyl carbon is bonded to one other carbon): b, c, f;
(b) secondary alcohols (where the hydroxyl carbon is bonded to two other carbons): a, b, e;
(c) tertiary alcohols (where the hydroxyl carbon is bonded to three other carbons): d; diol (where the
compound contains two hydroxyl groups): none; triols (where the compound contains three hydroxyl
groups): b.
6. (a) primary alcohols (where the hydroxyl carbon is bonded to one other carbon): d, e;
(b) secondary alcohols (where the hydroxyl carbon is bonded to two other carbons): a, c, d, e;
(c) tertiary alcohols (where the hydroxyl carbon is bonded to three other carbons): b, f; diol (where the
compound contains two hydroxyl groups): d; triols (where the compound contains three hydroxyl
groups): e.
7. The names of the compounds are:(a) 1-butanol (butyl alcohol) (e) 2-methyl-2-butanol