ALCOHOLS, ETHERS, PHENOLS, AND THIOLS

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1 C22 09/17/ :27:34 Page 319 APTER 22 ALCLS, ETHERS, PHENLS, AND THILS SLUTINS T REVIEW QUESTINS 1. The question allows great freedom of choice. These shown here are very simple examples of each type. (a) an alkyl halide 2 Cl a phenol an ether 2 2 (d) (e) (f) a carboxylic acid C (g) (h) a thiol 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. xidation 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

2 C22 09/17/ :27:34 Page xidation 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 Some common phenols include (a) hydroquinone, a photographic reducer and developer, vanillin, a flavoring, 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 mass ¼ 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 mass ¼ 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

3 C22 09/17/ :27:34 Page 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. [] 2 [] C

4 C22 09/17/ :27:34 Page 322 SLUTINS T EXERCISES 1. (a) (d) 2 C 2 (e) 2 (f) (a) (d) C 2 (e) 2 C 2 2 (f) C C

5 C22 09/17/ :27:35 Page There are only five isomers: H C 3 C 22 2 C H C C 2 4. There are only eight isomers: H C H C 2 5. (a) primary alcohols (where the hydroxyl carbon is bonded to one other carbon): b, c, f; secondary alcohols (where the hydroxyl carbon is bonded to two other carbons): a, b, e; 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; secondary alcohols (where the hydroxyl carbon is bonded to two other carbons): a, c, d, e; 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) 2-propanol (isopropyl alcohol) 2-methyl-3-phenyl-l-propanol (d) oxirane (ethylene oxide) (e) 2-methyl-2-butanol (f) 2-methylcyclohexanol (g) 2,3-dimethyl-1,4-butanediol

6 C22 09/17/ :27:35 Page The names of the compounds are (a) ethanol (ethyl alcohol) 2-phenylethanol 3-methyl-3-pentanol (d) 1-methylcyclopentanol (e) 3-pentanol (f) 1,2-propanediol (g) 4-ethyl-2-hexanol 9. Chief product of dehydration (a) 2 2-pentene cyclohexene 10. Chief product of dehydration (a) 1-methylcyclopentene 2 butene 11. (a) cyclopentanol methylcyclohexanol 2-methyl-1-butanol

7 C22 09/17/ :27:35 Page (a) 1,2-dimethylcyclohexanol pentanol H C 3 4,4-dimethy1-1pentanol 13. Primary alcohols oxidize to carboxylic acids; secondary alcohols oxidize to ketones; tertiary alcohols don t easily oxidize. (a) C 2 butanone HC ethylpentanoic acid (d) C NR 2 acetone, propanone 14. Primary alcohols oxidize to carboxylic acids; secondary alcohols oxidize to ketones; tertiary alcohols don t easily oxidize. (a) HC, methanoic acid, formic acid NR C, ethanoic acid, acetic acid (d) 2 C hexanone 15. Upon ester hydrolysis, the alcohol forms from the alkyl group and oxygen bonded to the C. (a) butanol 2 ethanol

8 C22 09/17/ :27:35 Page propanol 16. Upon ester hydrolysis, the alcohol forms from the alkyl group and oxygen bonded to the C. (a) cyclopentanol H 2 methanol 2-methyl-1-propanol 17. (a) Br 2-bromopropane Br bromocyclohexane (cyclohexyl bromide) 18. (a) (a) 2 2 þ H 2 S 4! C þ H 2 diethyl ether þ H 2 S 4! C 3 2 þh 2 propene (d)

9 C22 09/17/ :27:35 Page (a) 2 2 þ 2Na! 2 2 Na þ þ H 2 (d) 21. (a) 22. (a) methanol, 23. (a) methanol 2-methyl-1-propanol cyclohexanol

10 C22 09/17/ :27:36 Page (a) cyclopentanol 2-propanol 2-methyl-2-propanol 25. (a) o-methylphenol m-dihydroxybenzene 26. (a) p-nitrophenol 2,6-dimethylphenol H 3 C N 2 o-dihydroxybenzene 27. (a) phenol 2-ethyl-5-nitrophenol m-methylphenol (d) 4-bromo-2-chlorophenol 28. (a) p-dihydroxybenzene (hydroquinone) 2,4-dinitrophenol 2,4-dimethylphenol (d) m-hexylphenol 29. rder of increasing solubility in water [c (lowest), a, b, d (highest)] ð1þ ðþ 2 2 ð3þ (a) ð2þ (d) ðþðþ 2 ð4þ 30. rder of decreasing solubility in water: [a (highest), d, c, b (lowest)] (a) ðþðþ 2 ð1þ ð3þ (d) ðþ 2 2 ð2þ 2 2 ð4þ

11 C22 09/17/ :27:36 Page The three compounds have about the same molar mass but differ with respect to hydrogen bonding and polarity. Compound (1-propanethiol) does not hydrogen bond, is nonpolar, and so, has the lowest boiling point. Compound (diethyl ether) is polar but does not hydrogen bond to itself. It has a higher boiling point than compound. Compound a (1,2-propanediol) hydrogen bonds to itself and has the highest boiling point. 32. The three compounds have about the same molar mass but differ with respect to hydrogen bonding and polarity. Compound (pentane) does not hydrogen bond, is nonpolar, and so, has the lowest boiling point. Compound (diethyl ether) is polar but does not hydrogen bond to itself. It has a higher boiling point than Compound. Compound (a) (2-butanol) hydrogen bonds to itself and has the highest boiling point ethyl methyl ether propanol Each of these molecules has about the same molar mass. In this case, differences in boiling point arise because of differences in intermolecular attractive forces. 1-propanol can hydrogen bond to itself while ethyl methyl ether can not. Thus, ethyl methyl ether will have the lower boiling point. boiling point for ethyl methyl ether ¼ 8 C boiling point for 1-propanol ¼ 97.4 C ethyl isopropyl ether pentanol Each of these molecules has about the same molar mass. In this case, differences in boiling point arise because of differences in intermolecular attractive forces. 1-pentanol can hydrogen bond to itself while ethyl isopropyl ether cannot. Thus, ethyl isopropyl ether will have the lower boiling point. boiling point for ethyl isopropyl ether ¼ 54 C boiling point for 1-pentanol ¼ 138 C 35. (a) common, isopropyl methyl ether; IUPAC, 2-methoxypropane common, ethyl phenyl ether; IUPAC, ethoxybenzene common, butyl ethyl ether; IUPAC, 1-ethoxybutane 36. (a) common, ethyl methyl ether; IUPAC, methoxyethane common, ethyl isobutyl ether; IUPAC, l-ethoxy-2-methylpropane common, ethyl phenyl ether; IUPAC, ethoxybenzene 37. There are three isomeric saturated ethers with the formula, C 4 H methyl propyl ether (1-methoxypropane) diethyl ether (ethoxyethane) methyl isopropyl ether (2-methoxypropane)

12 C22 09/17/ :27:37 Page Six isomeric ethers: C 5 H n-butyl methyl ether (1-methoxybutane) ethyl n-propyl ether (1-ethoxypropane) 39. Possible combinations of reactants to make the following ethers by the Williamson synthesis: (a) 2 Na þ 2 Cl or 2 Na þ Cl Na ± 2 Cl or 2 Cl ± 2 Na 40. Possible combinations of reactants to make the following ethers by the Williamson synthesis: (a) Na þ 2 2 Cl

13 C22 09/17/ :27:37 Page 331 cannot be made by the Williamson synthesis. Cannot use secondary RX. 41. IUPAC names (a) 2-methyl-2-butanethiol cyclohexanethiol 2-methyl-2-propanethiol (d) 2-methyl-3-pentanethiol 42. IUPAC names (a) 2-methylcyclopentanethiol 2,3-dimethyl-2-pentanethiol 2-propanethiol (d) 3-ethyl-2,2,4-trimethyl-3-pentanethiol hexylresorcinol or 4-hexyl-1,3-dihydroxybenzene ( 2 ) 4 cis-1,2-cyclopentanediol trans-1,2-cyclopentanediol 45. The phenol compound (3-methylphenol) is more acidic than the alcohol compound (benzyl alcohol) but is less acidic than carbonic acid. 46. The name catecholamine is built of two pieces, catechol and amine. A catechol is a phenol derivative that contains an additional hydroxyl group (o-hydroxyphenol). H 2 N (An amine is a NH 2 functional group.)

14 C22 09/17/ :27:37 Page xidation products from ethylene glycol include H 2 HC H 2 C HCC HC C 48. In each compound, the most oxidized carbon will have the most positive oxidation number and, commonly, the most bonds to oxygen. In contrast, the most reduced carbon will have the most negative oxidation number and, commonly, the most bonds to hydrogen. The most reduced carbon has been circled while an asterisk has been placed by the most oxidized carbon. oxidation number = 1, two bonds to hydrogen oxidation number = +1, two bonds to oxygen 2 HC * oxidation number = 3, three bonds to hydrogen ( 2 ) 16 oxidation number = +3, three bonds to oxygen * C oxidation number = 3, three bonds to hydrogen C oxidation number = +3, three bonds to oxygen * C ribose (a sugar) stearic acid (a fat) pyruvic acid (a metabolite) 49. (a) 2 2 þ 2NaðmetalÞ! 2 2 Na þ H 2 (d) (e)

15 C22 09/17/ :27:37 Page 333 (f) A simple chemical test to distinguish between: (a) ethanol and dimethyl ether. Ethanol will react readily with potassium dichromate and sulfuric acid to make acetaldehyde. Visibly, the orange color of the dichromate changes to green. Ethanol reacts with metallic sodium to produce hydrogen gas. Dimethyl ether does not react with either of these reagents. 1-pentanol and 1-pentene. 1-pentene will rapidly decolorize bromine as it adds to the double bond. 1-pentanol does not react. p-methylphenol has acidic properties so it will react with sodium hydroxide. Methoxybenzene does not have acidic properties and will not react with sodium hydroxide. 52. Isomers of C 8 H

16 C22 09/17/ :27:38 Page nly compound (a) will react with Na. 54. rder of increasing boiling points. 1-pentanol < 1-octanol < 1,2-pentanediol 138 C 194 C 210 C All three compounds are alcohols. 1-pentanol has the lowest molar mass and hence the lowest boiling point. 1-octanol has a higher molar mass and therefore a higher boiling point than 1-pentanol. 1,2- pentanediol has two groups and therefore forms more hydrogen bonds than the other two alcohols which causes its higher boiling point. 55. (a) The primary carbocation that is formed first is unstable. Thus, the primary carbocation shifts to a much more stable, tertiary carbocation It is this intermediate that goes on to form the major product, 2-methyl-2-butene. Hydration will not form 2-methyl- 1-butanol because the double bond lies between the middle two carbons in 2-methyl-2-butene. By Markovnikov s rule, the H will add to the double bonded carbon that already has a hydrogen. Thus, 2-methyl-2-butanol will be the major product