CHAPTER 24 PHEN○LS SOLUTIONS TO TEXT PROBLEMS 4.1 (b) A benzyl group(CH-CH2)is ortho to the phenolic hydroxyl group in o-benzylphenol (c) Naphthalene is numbered as shown. 3-Nitro-1-naphthol has a hydroxyl group at C-1 and a nitro group at C-3 (d) Resorcinol is 1, 3-benzenediol. 4-Chlororesorcinol is therefore 676 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
676 CHAPTER 24 PHENOLS SOLUTIONS TO TEXT PROBLEMS 24.1 (b) A benzyl group (C6H5CH2G) is ortho to the phenolic hydroxyl group in o-benzylphenol. (c) Naphthalene is numbered as shown. 3-Nitro-1-naphthol has a hydroxyl group at C-1 and a nitro group at C-3. (d) Resorcinol is 1,3-benzenediol. 4-Chlororesorcinol is therefore OH Cl OH OH NO2 Naphthalene 3-Nitro-1-naphthol 5 4 8 1 3 2 6 7 OH CH2C6H5 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
PHENOLS 677 4.2 Intramolecular hydrogen bonding between the hydroxyl group and the ester carbonyl can occur when these groups are ortho to each other. Methyl salicylate Intramolecular hydrogen bonds form at the expense of intermolecular ones, and intramolecularly hydrogen-bonded phenols have lower boiling points than isomers in which only intermolecular hydrogen-bonding is possible 24.3(b) A cyano group withdraws electrons from the ring by resonance. A p-cyano substituent is con- jugated directly with the negatively charged oxygen and stabilizes the anion more than does an m-cyano substituent p-Cyanophenol is slightly more acidic than m-cyanophenol, the Ka values being 1.0 X 10 and 2. X 10, respectively (c) The electron-withdrawing inductive effect of the fluorine substituent will be more pronounced at the ortho position than at the para. o-Fluorophenol(a=1.9 x 10)is a stronger acid han p-fluorophenol(K=1.3 10) 24.4 The text points out that the reaction proceeds by the addition-elimination mechanism of nucleophilic aromatic substitution Under the strongly basic conditions of the reaction, p-toluenesulfonic acid is first converted to its H,C HOH alfonic acid Hydroxide Toluenesulfonate ion Water Nucleophilic addition of hydroxide ion gives a cyclohexadienyl anion intermediate. OH C SO,+ OH H,C p-Toluenesulfonate ion Hydroxide Cyclohexadienyl anion Loss of sulfite ion(SO 2)gives p-cresol gC OH SO Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
24.2 Intramolecular hydrogen bonding between the hydroxyl group and the ester carbonyl can occur when these groups are ortho to each other. Intramolecular hydrogen bonds form at the expense of intermolecular ones, and intramolecularly hydrogen-bonded phenols have lower boiling points than isomers in which only intermolecular hydrogen-bonding is possible. 24.3 (b) A cyano group withdraws electrons from the ring by resonance. A p-cyano substituent is conjugated directly with the negatively charged oxygen and stabilizes the anion more than does an m-cyano substituent. p-Cyanophenol is slightly more acidic than m-cyanophenol, the Ka values being 1.0 108 and 2.8 109 , respectively. (c) The electron-withdrawing inductive effect of the fluorine substituent will be more pronounced at the ortho position than at the para. o-Fluorophenol (Ka 1.9 109 ) is a stronger acid than p-fluorophenol (Ka 1.3 1010). 24.4 The text points out that the reaction proceeds by the addition–elimination mechanism of nucleophilic aromatic substitution. Under the strongly basic conditions of the reaction, p-toluenesulfonic acid is first converted to its anion. Nucleophilic addition of hydroxide ion gives a cyclohexadienyl anion intermediate. Loss of sulfite ion (SO3 2) gives p-cresol. p-Cresol H3C OH SO3 2 Cyclohexadienyl anion H3C SO3 OH OH p-Toluenesulfonate ion Hydroxide H3C SO3 Cyclohexadienyl anion H3C SO3 OH H3C SO O O H p-Toluenesulfonic acid H3C SO O O p-Toluenesulfonate ion OH Hydroxide ion HOH Water O CN O C N OCH3 O O C H Methyl salicylate PHENOLS 677 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
PHENOLS It is also possible that the elimination stage of the reaction proceeds as follows + ho H,C- OH Cyclohexadienyl anion H H OH H C so,+ H,o p-Methylphenoxide ion 24.5 The text states that the hydrolysis of chlorobenzene in base follows an elimination-addition mechanism H + Ho+c Chlorobenzene -OH Benzyne 24.6 (b) The reaction is Friedel-Crafts alkylation. Proton transfer from sulfuric acid to 2-methyl- propene gives tert-butyl cation. Because the position para to the hydroxyl substituent already bears a bromine, the tert-butyl cation attacks the ring at the position ortho to the sOa B 2-Methylpropene methylphenol (c) Acidification of sodium nitrite produces nitrous acid, which nitrosates the strongly activated aromatic ring of phenols H HC HC 2-lsopropyl-5-methylphenol 2-Isopropyl-5-methyl-4-nitrosophenol isolated yield, Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
678 PHENOLS It is also possible that the elimination stage of the reaction proceeds as follows: 24.5 The text states that the hydrolysis of chlorobenzene in base follows an elimination–addition mechanism. 24.6 (b) The reaction is Friedel–Crafts alkylation. Proton transfer from sulfuric acid to 2-methylpropene gives tert-butyl cation. Because the position para to the hydroxyl substituent already bears a bromine, the tert-butyl cation attacks the ring at the position ortho to the hydroxyl. (c) Acidification of sodium nitrite produces nitrous acid, which nitrosates the strongly activated aromatic ring of phenols. CH(CH3)2 OH H3C NaNO2 HCl, H2O CH(CH3)2 OH N O H3C 2-Isopropyl-5-methylphenol 2-Isopropyl-5-methyl-4-nitrosophenol (isolated yield, 87%) H2SO4 (CH3)2C OH CH3 CH2 Br (CH3)3C OH CH3 Br 4-Bromo-2- methylphenol 4-Bromo-2-tert-butyl- 6-methylphenol (isolated yield, 70%) 2-Methylpropene OH OH Phenol OH Benzyne H2O OH H2O Cl H Cl Chlorobenzene Benzyne H2O Cyclohexadienyl anion intermediate H3C SO3 OH H H3C SO3 O H H H SO3 2 H2O OH H3C H H O OH p-Methylphenoxide ion H3C O HO Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
PHENOLS 679 (d) Friedel-Crafts acylation occurs ortho to the hydroxyl group CCHCH Ch3CHaCCI H3 p-Cresol 1-(2-Hydroxy-5-methylpher 24.7(b) The hydroxyl group of 2-naphthol is converted to the corresponding acetate ester OH OCCH CH3COCCH3 CH CONa 2-Naphthol Acetic anhydride 2-Naphthyl acetate Sodium acetate (c) Benzoyl chloride acylates the hydroxyl group of phenol CCI t HCl Phenol Benzoyl chloride Phenyl benzoate 24.8 Epoxides are sensitive to nucleophilic ring-opening reactions. Phenoxide ion attacks the less hin- dered carbon to yield l-phenoxy-2-propanol ④“政mm OCH-CHCH Phenoxide ion 1, 2-Epoxypropane l-Phenoxy-2-propanol 24.9 The aryl halide must be one that is reactive toward nucleophilic aromatic substitution by the addition-elimination mechanism. p-Flt trobenzene is far more reactive than fluorobenzene The reaction shown yields p-nitrophenyl phenyl ether in 92%o yield. p-Nitrophenyl phenyl ether 24.10 Substituted allyl aryl ethers undergo a Claisen rearrangement similar to the reaction described in text Section 24.13 for allyl phenyl ether. 2-Butenyl phenyl ether rearranges on heating to give o-(1 meth oH enolization 2-Butenyl phenyl Methyl-2 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(d ) Friedel–Crafts acylation occurs ortho to the hydroxyl group. 24.7 (b) The hydroxyl group of 2-naphthol is converted to the corresponding acetate ester. (c) Benzoyl chloride acylates the hydroxyl group of phenol. 24.8 Epoxides are sensitive to nucleophilic ring-opening reactions. Phenoxide ion attacks the less hindered carbon to yield 1-phenoxy-2-propanol. 24.9 The aryl halide must be one that is reactive toward nucleophilic aromatic substitution by the addition–elimination mechanism. p-Fluoronitrobenzene is far more reactive than fluorobenzene. The reaction shown yields p-nitrophenyl phenyl ether in 92% yield. 24.10 Substituted allyl aryl ethers undergo a Claisen rearrangement similar to the reaction described in text Section 24.13 for allyl phenyl ether. 2-Butenyl phenyl ether rearranges on heating to give o-(1- methyl-2-propenyl)phenol. O H OH o-(1-Methyl-2-propenyl)- phenol rearrangement enolization 2-Butenyl phenyl ether O OK Potassium phenoxide F NO2 p-Fluoronitrobenzene O NO2 p-Nitrophenyl phenyl ether 150C OCH2CHCH3 OH 1-Phenoxy-2-propanol O Phenoxide ion HO, H2O 1,2-Epoxypropane H2C O CHCH3 Phenyl benzoate OC O Phenol OH Benzoyl chloride O CCl Hydrogen chloride HCl NaOH 2-Naphthyl acetate OCCH3 O 2-Naphthol OH Sodium acetate CH3CONa O Acetic anhydride CH3COCCH3 O O AlCl3 OH CH3 O CH3CH2CCl p-Cresol Propanoyl chloride CCH2CH3 OH CH3 O 1-(2-Hydroxy-5-methylphenyl)- 1-propanone (isolated yield, 87%) PHENOLS 679 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
680 PHENOLS 24.11 (a) The parent compound is benzaldehyde Vanillin bears a methoxy group(CH O)at C-3 and a hydroxyl group(HO)at C-4 Vanillin (b, c) Thymol and carvacrol differ with respect to the position of the hydroxyl group CH(CH3) CH(CH) (2-isopropyl-5-methylphenol) (5-isopropyl-2-methylphenol) (d) An allyl substituent is-CH, CH=CH, OCH CHCH=CH Eugenol (e) Benzoic acid is CHCO, H. Gallic acid bears three hydroxyl groups, located at C-3, C-4, and C-5 COH HO allic acid (3, 4, 5-trihydroxybenzoic Benzyl alcohol is CsHS CH,OH. Salicyl alcohol bears a hydroxyl group at the ortho position Salicyl alcohol (o-hydroxybenzyl alcohol) Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
24.11 (a) The parent compound is benzaldehyde. Vanillin bears a methoxy group (CH3O) at C-3 and a hydroxyl group (HO) at C-4. (b, c) Thymol and carvacrol differ with respect to the position of the hydroxyl group. (d) An allyl substituent is GCH2CH?CH2. (e) Benzoic acid is C6H5CO2H. Gallic acid bears three hydroxyl groups, located at C-3, C-4, and C-5. (f ) Benzyl alcohol is C6H5CH2OH. Salicyl alcohol bears a hydroxyl group at the ortho position. Salicyl alcohol (o-hydroxybenzyl alcohol) CH2OH OH Gallic acid (3,4,5-trihydroxybenzoic acid) CO2H HO OH OH 1 2 3 4 5 6 OH OCH3 CH2CH CH2 1 2 3 4 5 6 Eugenol (4-allyl-2-methoxyphenol) HO CH3 CH(CH3)2 3 2 1 6 5 4 Thymol (2-isopropyl-5-methylphenol) HO CH3 CH(CH3)2 3 2 1 6 5 4 Carvacrol (5-isopropyl-2-methylphenol) OCH3 C O H OH 3 2 1 6 5 4 Vanillin (4-hydroxy-3-methoxybenzaldehyde) 680 PHENOLS Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website