681 24.12 (a) The compound is named as a derivative of phenol. The substituents(ethyl and nitro) are cited n alphabetical order with numbers assigned in the direction that gives the lowest number at the first point of difference OH CH,CH3 (b) An isomer of the compound in part(a) is 4-ethyl-3-nitrophenol CH3 (c) The parent compound is phenol. It bears, in alphabetical order, a benzyl group at C-4 and a chlorine at C-2 (d) This compound is named as a derivative of anisole, C6HsOCH3 Because multiplicative pre- H-C CH (e) The compound is an aryl ester of trichloroacetic acid. The aryl group is 2, 5-dichlorophenyl Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
24.12 (a) The compound is named as a derivative of phenol. The substituents (ethyl and nitro) are cited in alphabetical order with numbers assigned in the direction that gives the lowest number at the first point of difference. (b) An isomer of the compound in part (a) is 4-ethyl-3-nitrophenol. (c) The parent compound is phenol. It bears, in alphabetical order, a benzyl group at C-4 and a chlorine at C-2. (d) This compound is named as a derivative of anisole, C6H5OCH3. Because multiplicative pre- fixes (di, tri-, etc.) are not considered when alphabetizing substituents, isopropyl precedes dimethyl. (e) The compound is an aryl ester of trichloroacetic acid. The aryl group is 2,5-dichlorophenyl. 2,5-Dichlorophenyl trichloroacetate Cl Cl 1 2 3 4 5 6 OCCCl3 O 4-Isopropyl-2,6- dimethylanisole OCH3 H3C CH3 CH(CH3)2 1 2 3 4 5 6 Cl HO CH2 1 2 3 4 6 5 4-Benzyl-2-chlorophenol OH NO2 CH2CH3 1 2 3 4 5 6 4-Ethyl-3-nitrophenol 3-Ethyl-4-nitrophenol OH CH2CH3 NO2 1 2 3 4 5 6 PHENOLS 681 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
682 PHENOLS 24.13(a)The reaction is an acid-base reaction. Phenol is the acid; sodium hydroxide is the base. (ONa+ Ho Pheno Sodium Sodium phenoxide (weaker acid) (b) Sodium phenoxide reacts with ethyl bromide to yield ethyl phenyl ether in a Williamson reaction. Phenoxide ion acts as a nucleophile C6H ONa CH CH, Br CHOCH CH NaBr Sodium Ethyl phenyl ether Sodi (c) p-Toluenesulfonate esters behave much like alkyl halides in nucleophilic substitution reac tions. Phenoxide ion displaces p-toluenesulfonate from the primary carbor H_ ONa CH3CH,CH, CH,O C6H-OCH, CH, CH, CH3 NaoS SycH Sodium Butyl p-toluenesulfonate Butyl phenyl ether Sodium p-toluenesulfonate (d) Carboxylic acid anhydrides react with phenoxide anions to yield aryl esters CH,ONa CH, COCCH C.HOCCH,+CH,CONa Sodium Acetic anhydride Phenyl acetate Sodium (e) Acyl chlorides convert phenols to aryl esters CC t HCl o-cresol Benzoyl chloride 2-Methylphenyl benzoate Hydrogen (f) Phenols react as nucleophiles toward epoxides. CH H, C +H2C—CH DCH,CH,OH m-cresol 2-(3-Methylphenoxy )ethanol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
24.13 (a) The reaction is an acid–base reaction. Phenol is the acid; sodium hydroxide is the base. (b) Sodium phenoxide reacts with ethyl bromide to yield ethyl phenyl ether in a Williamson reaction. Phenoxide ion acts as a nucleophile. (c) p-Toluenesulfonate esters behave much like alkyl halides in nucleophilic substitution reactions. Phenoxide ion displaces p-toluenesulfonate from the primary carbon. (d ) Carboxylic acid anhydrides react with phenoxide anions to yield aryl esters. (e) Acyl chlorides convert phenols to aryl esters. ( f ) Phenols react as nucleophiles toward epoxides. CH3 OH m-Cresol Ethylene oxide H2C CH2 O 2-(3-Methylphenoxy)ethanol H3C OCH2CH2OH OH OC HCl CH3 CH3 CCl O O o-Cresol Benzoyl chloride 2-Methylphenyl benzoate Hydrogen chloride C6H5ONa C CH3COCCH3 6H5OCCH3 CH3CONa Sodium phenoxide Acetic anhydride Phenyl acetate Sodium acetate O O O O C6H5ONa C CH3CH2CH2CH2OS 6H5OCH2CH2CH2CH3 NaOS Sodium phenoxide Butyl p-toluenesulfonate Sodium Butyl phenyl ether p-toluenesulfonate O O O O CH3 CH3 C CH3CH2Br 6H5ONa C 6H5OCH2CH3 NaBr Sodium phenoxide Sodium bromide Ethyl bromide Ethyl phenyl ether OH NaOH ONa H2O Phenol (stronger acid) Water (weaker acid) Sodium hydroxide (stronger base) Sodium phenoxide (weaker base) 682 PHENOLS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
683 The reaction as written conforms to the requirements of the problem that a balanced equation be written. Of course, the reaction will be much faster if catalyzed by acid or base, but the cat- all (g) Bromination of the aromatic ring of 2, 6-dichlorophenol occurs para to the hydroxy group. The more activating group(Oh) determines the orientation of the product. Cl 2. 6-Dichlorophenol Bromine (h) In aqueous solution bromination occurs at all the open positions that are ortho and para to the hydroxyl group. Br H,O 2Br 2HBr p-Cresol Bromine 2, 6-Dibromo-4. Hydrogen (i Hydrogen bromide cleaves ethers to give an alkyl halide and a phenol. OCH(CH3)2+ HBr OH + CH,)2 CHBr Isopropyl phenyl ether Phenol 24. 14(a) Strongly electron-withdrawing groups, particularly those such as-NO2, increase the acidity of phenols by resonance stabilization of the resulting phenoxide anion. Electron-releasing substituents such as-CH3 exert a very small acid-weakening effect. ON NO 2,4, 6-Trinitrophenol, 2,4, 6-Trimethylphenol more acidic less acidic (K2=3.8×10-1,pKa=04) (K2=1.3×10-1,pK2=10.9) Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
The reaction as written conforms to the requirements of the problem that a balanced equation be written. Of course, the reaction will be much faster if catalyzed by acid or base, but the catalysts do not enter into the equation representing the overall process. (g) Bromination of the aromatic ring of 2,6-dichlorophenol occurs para to the hydroxy group. The more activating group (GOH) determines the orientation of the product. (h) In aqueous solution bromination occurs at all the open positions that are ortho and para to the hydroxyl group. (i) Hydrogen bromide cleaves ethers to give an alkyl halide and a phenol. 24.14 (a) Strongly electron-withdrawing groups, particularly those such as GNO2, increase the acidity of phenols by resonance stabilization of the resulting phenoxide anion. Electron-releasing substituents such as GCH3 exert a very small acid-weakening effect. OH H3C CH3 CH3 2,4,6-Trimethylphenol, less acidic (Ka 1.3 1011, pKa 10.9) OH O2N NO2 NO2 2,4,6-Trinitrophenol, more acidic (Ka 3.8 101 , pKa 0.4) Hydrogen bromide HBr Isopropyl phenyl ether OCH(CH3)2 Isopropyl bromide (CH3)2CHBr Phenol OH heat OH CH3 CH3 Br Br 2Br 2HBr 2 OH p-Cresol 2,6-Dibromo-4- Bromine methylphenol Hydrogen bromide H2O OH Br Br HBr 2 Cl Cl OH Cl Cl 2,6-Dichlorophenol Bromine 4-Bromo-2,6- dichlorophenol Hydrogen bromide PHENOLS 683 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
684 PHENOLS Picric acid (2, 4, 6-trinitrophenol) is a stronger acid by far than 2, 4, 6-trimethylphenol All three nitro groups participate in resonance stabilization of the picrate anion O O (b) Stabilization of a phenoxide anion is most effective when electron-withdrawing groups are present at the ortho and para positions, because it is these carbons that bear most of the nega rge in phenoxide 2, 6-Dichlorophenol is therefore expected to be(and is)a stronger acid than 3, 5-dichloro- OH 2, 6-Dichlorophenol, more acidic 3. 5-Dichlorophenol, less acidic (K2=1.6×10-7,pK=68) NO2 (K2=4.1×10-9,pK=84) Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
Picric acid (2,4,6-trinitrophenol) is a stronger acid by far than 2,4,6-trimethylphenol. All three nitro groups participate in resonance stabilization of the picrate anion. (b) Stabilization of a phenoxide anion is most effective when electron-withdrawing groups are present at the ortho and para positions, because it is these carbons that bear most of the negative charge in phenoxide anion. 2,6-Dichlorophenol is therefore expected to be (and is) a stronger acid than 3,5-dichlorophenol. (c) The same principle is at work here as in part (b). A nitro group para to the phenol oxygen is directly conjugated to it and stabilizes the anion better than one at the meta position. OH NO2 4-Nitrophenol, stronger acid (Ka 1.0 108 , pKa 7.2) OH NO2 3-Nitrophenol, weaker acid (Ka 4.1 109 , pKa 8.4) OH Cl Cl 3,5-Dichlorophenol, less acidic (Ka 6.5 109 , pKa 8.2) OH Cl Cl 2,6-Dichlorophenol, more acidic (Ka 1.6 107 , pKa 6.8) O O O O N N O O O O O O N O N N O O O O O O N O N N O O O O O N O O N N O O O O O N O O 684 PHENOLS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website