CHAPTER 22 AMINES SOLUTIONS TO TEXT PROBLEMS 22.1 (b) The amino and phenyl groups are both attached to C-1 of an ethyl group C6HSCHCH H,C=CHCH,NH, 2-propen-1-amin 22.2 N, N-Dimethylcycloheptylamine may also be named as a dimethyl derivative of cycloheptanamine. N(CH3)2 22.3 Three substituents are attached to the nitrogen atom; the amine is tertiary In alphabetical order, the substituents present on the aniline nucleus are ethyl, isopropyl, and methyl. Their posi pecified as N-ethyl, 4-isopropyl, and N-methyl (CH3)2CH- N一CH2CH3 N-Ethyl-4-isopropyl-N-methylaniline 604 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
CHAPTER 22 AMINES SOLUTIONS TO TEXT PROBLEMS 22.1 (b) The amino and phenyl groups are both attached to C-1 of an ethyl group. (c) 22.2 N,N-Dimethylcycloheptylamine may also be named as a dimethyl derivative of cycloheptanamine. 22.3 Three substituents are attached to the nitrogen atom; the amine is tertiary. In alphabetical order, the substituents present on the aniline nucleus are ethyl, isopropyl, and methyl. Their positions are specified as N-ethyl, 4-isopropyl, and N-methyl. (CH3)2CH CH2CH3 CH3 N N-Ethyl-4-isopropyl-N-methylaniline N(CH3)2 N,N-Dimethylcycloheptanamine H2C CHCH2NH2 Allylamine, or 2-propen-1-amine C6H5CHCH3 NH2 1-Phenylethylamine, or 1-phenylethanamine 604 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
AMINES 605 22.4 The electron-donating amino group and the electron-withdrawing nitro group are directly conjugated in p-nitroaniline. The planar geometry of p-nitroaniline suggests that the delocalized resonance form shown is a major contributor to the structure of the compoun NH NH 22.5 The pk, of an amine is related to the equilibrium constant kb by Kb The pk, of quinine is therefore pKb=-log(1×10-6)=6 the values of Kb and pk, for an amine and Ka and pKa of its conjugate acid are given by KXK=1×10 The values of K and pK for the conjugate acid of quinine are therefore 10-141×10 Ka 1×10 pKb=14-6 22.6 The Henderson-Hasselbalch equation described in Section 19.4 can be applied to bases such as amines, as well as carboxylic acids. The ratio [CH, NH,"I/[CH, NH, is given by CHNH3_田 The ionization constant of methylammonium ion is given in the text as 2 X 10. At pH =7 the hydrogen ion concentration is 1 X10-.Therefore CHaNH3]_1×107 CH3NH22×10-=5×103 22.7 Nitrogen is attached directly to the aromatic ring in tetrahydroquinoline, making it an arylamine, and the nitrogen lone pair is delocalized into the T system of the aromatic ring. It is less basic than tetrahydroisoquinoline, in which the nitrogen is insulated from the ring by an sp-hybridized NH (an alkylamine): more basic, (an arylar K25×10-3(pk46) kb1.0 See Learning By Modeling for the calculated charges on nitrogen Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
AMINES 605 22.4 The electron-donating amino group and the electron-withdrawing nitro group are directly conjugated in p-nitroaniline. The planar geometry of p-nitroaniline suggests that the delocalized resonance form shown is a major contributor to the structure of the compound. 22.5 The pKb of an amine is related to the equilibrium constant Kb by pKb log Kb The pKb of quinine is therefore pKb log (1 106 ) 6 the values of Kb and pKb for an amine and Ka and pKa of its conjugate acid are given by Ka Kb 1 1014 and pKa pKb 14 The values of Ka and pKa for the conjugate acid of quinine are therefore Ka 1 108 and pKa 14 pKb 14 6 8 22.6 The Henderson–Hasselbalch equation described in Section 19.4 can be applied to bases such as amines, as well as carboxylic acids. The ratio [CH3NH3 ][CH3NH2] is given by The ionization constant of methylammonium ion is given in the text as 2 1011. At pH 7 the hydrogen ion concentration is 1 107 . Therefore 5 103 22.7 Nitrogen is attached directly to the aromatic ring in tetrahydroquinoline, making it an arylamine, and the nitrogen lone pair is delocalized into the system of the aromatic ring. It is less basic than tetrahydroisoquinoline, in which the nitrogen is insulated from the ring by an sp3 -hybridized carbon. See Learning By Modeling for the calculated charges on nitrogen. N H Tetrahydroquinoline (an arylamine): less basic, Kb 1.0 109 (pKb 9.0) NH Tetrahydroisoquinoline (an alkylamine): more basic, Kb 2.5 105 (pKb 4.6) 1 107 2 1011 [CH3NH3 ] [CH3NH2] [H ] Ka [CH3NH3 ] [CH3NH2] 1 1014 1 106 1014 Kb NH2 NH2 N O O O O N Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
606 AMINES 22.8 (b) An acetyl group attached directly to nitrogen as in acetanilide delocalizes the nitrogen lone pair into the carbonyl group. Amides are weaker bases than amines CCH CCH (c) An acetyl group in a position para to an amine function is conjugated to it and delocalizes the C CH3 22.9 The reaction that leads to allylamine is nucleophilic substitution by ammonia on allyl chloride H, C=CHCH,CI+ 2NH H,C=CHCH,NH, NHC Allyl chloride Allyl chloride is prepared by free-radical chlorination of propene( see text page 371) 40°C H,C=CHCH3 CI H, C=CHCH,CI+ HCl allyl chloride Hydrogen 22.10 (b) Isobutylamine is(CH3),CHCH,NH, It is a primary amine of the type RCH,NH, and can be prepared from a primary alkyl halide by the gabriel synthesis (CH3), CHCH, Br CH, CH(CH3)2 Isobutyl bromide -Potassiophthalimide (CH3),CHCH,NH2+ Isobutylamine Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
606 AMINES 22.8 (b) An acetyl group attached directly to nitrogen as in acetanilide delocalizes the nitrogen lone pair into the carbonyl group. Amides are weaker bases than amines. (c) An acetyl group in a position para to an amine function is conjugated to it and delocalizes the nitrogen lone pair. 22.9 The reaction that leads to allylamine is nucleophilic substitution by ammonia on allyl chloride. Allyl chloride is prepared by free-radical chlorination of propene (see text page 371). 22.10 (b) Isobutylamine is (CH3)2CHCH2NH2. It is a primary amine of the type RCH2NH2 and can be prepared from a primary alkyl halide by the Gabriel synthesis. Isobutyl bromide (CH3)2CHCH2Br N-Potassiophthalimide NK O O N-Isobutylphthalimide NCH2CH(CH3)2 O O Phthalhydrazide Isobutylamine (CH3)2CHCH2NH2 H2NNH2 O O NH NH Cl2 Chlorine H2C CHCH3 Propene H2C CHCH2Cl Allyl chloride HCl Hydrogen chloride 400C 2NH3 Ammonia H2C CHCH2Cl Allyl chloride H2C CHCH2NH2 Allylamine NH4Cl Ammonium chloride O H2N C CH3 O H2N C CH3 O N H CCH3 O N H CCH3 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
AMINES 607 (c) Although tert-butylamine( CH3)3CNH, is a primary amine, it cannot be prepared by the Gabriel method, because it would require an SN2 reaction on a tertiary alkyl halide in the first step. Elimination occurs instead. ( CH3)2 CBr (CH3),C=CH,+ KBr 2-Methylpropene Phthalimide (d) The preparation of 2-phenylethylamine by the Gabriel synthesis has been described in the chemical literature C6HsCH, CH, Br+ NCH,CH, CSH 2-Phenylethyl bromide N-Potassiophthalimide N-(2-Phenylethyl)phthalimide CHCHChNh+ 2-Phenylethylamine Phthalhydrazide (e) The Gabriel synthesis leads to primary amines; N-methylbenzylamine is a secondary amine and cannot be prepared by this method. CH,一N nitrogen; a secondary amine) (f) Aniline cannot be prepared by the Gabriel method. Aryl halides do not undergo nucleophilic substitution under these conditions no reaction Bromobenzene N-Potassiophthalimide Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(c) Although tert-butylamine (CH3)3CNH2 is a primary amine, it cannot be prepared by the Gabriel method, because it would require an SN2 reaction on a tertiary alkyl halide in the first step. Elimination occurs instead. (d) The preparation of 2-phenylethylamine by the Gabriel synthesis has been described in the chemical literature. (e) The Gabriel synthesis leads to primary amines; N-methylbenzylamine is a secondary amine and cannot be prepared by this method. ( f ) Aniline cannot be prepared by the Gabriel method. Aryl halides do not undergo nucleophilic substitution under these conditions. Br Bromobenzene no reaction N-Potassiophthalimide NK O O CH2 CH3 H N N-Methylbenzylamine (two carbon substituents on nitrogen; a secondary amine) 2-Phenylethyl bromide C6H5CH2CH2Br N-Potassiophthalimide NK O O N-(2-Phenylethyl)phthalimide NCH2CH2C6H5 O O Phthalhydrazide 2-Phenylethylamine C6H5CH2CH2NH2 H2NNH2 O O NH NH tert-Butyl bromide (CH3)2CBr N-Potassiophthalimide NK O O KBr Potassium bromide Phthalimide NH O O 2-Methylpropene (CH3)2C CH2 AMINES 607 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
608 AMINES 22.11 For each part of this problem, keep in mind that aromatic amines are derived by reduction of the corresponding aromatic nitro compound. Each synthesis should be approached from the standpoint of how best to prepare the necessary nitroaromatic compound. Ar—NH, NO, Ar-H (Ar substituted aromatic ring) (b) The para isomer of isopropylaniline may be prepared by a procedure analogous to that used for its ortho isomer in part(a) CH(CH3) CH(CH3) CH(CH3h2 NO Benzene Isopropylbenzene O-lsopropylnitro. p-Isopropylnitro- After separating the ortho, para mixture by distillation, the nitro group of p-isopropyl benzene is reduced to yield the desired CH(CH3)2 CH(CH3)2 NO NH (c) The target compound is the reduction product of 1-isopropyl-2, 4-dinitrobenzene CH(CH3)2 CH(CHi)2 reduce I-Isopropyl-2, 4- 4-1sopropyl-1, 3- dinitrobenzene This reduction is carried out in the same way as reduction of an arene that contains only a single nitro group. In this case hydrogenation over a nickel catalyst gave the desired product in 90% yield The starting dinitro compound is prepared by nitration of isopropylbenzene CH(CHa) CH(CH3)2 HNO.H Isopropylbenze 1-lsopropyl-2,4- Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
22.11 For each part of this problem, keep in mind that aromatic amines are derived by reduction of the corresponding aromatic nitro compound. Each synthesis should be approached from the standpoint of how best to prepare the necessary nitroaromatic compound. (b) The para isomer of isopropylaniline may be prepared by a procedure analogous to that used for its ortho isomer in part (a). After separating the ortho, para mixture by distillation, the nitro group of p-isopropylnitrobenzene is reduced to yield the desired p-isopropylaniline. (c) The target compound is the reduction product of 1-isopropyl-2,4-dinitrobenzene. This reduction is carried out in the same way as reduction of an arene that contains only a single nitro group. In this case hydrogenation over a nickel catalyst gave the desired product in 90% yield. The starting dinitro compound is prepared by nitration of isopropylbenzene. 80C HNO3, H2SO4 Isopropylbenzene CH(CH3)2 1-Isopropyl-2,4- dinitrobenzene (43%) CH(CH3)2 NO2 NO2 reduce CH(CH3)2 NH2 NH2 4-Isopropyl-1,3- benzenediamine CH(CH3)2 NO2 NO2 1-Isopropyl-2,4- dinitrobenzene H2, Ni; or 1. Fe, HCl; 2. HO or 1. Sn, HCl; 2. HO CH(CH3)2 NH2 CH(CH3)2 NO2 (CH3)2CHCl AlCl3 HNO3 H2SO4 CH(CH3)2 NO2 p-Isopropylnitrobenzene CH(CH3)2 NO2 o-Isopropylnitrobenzene CH(CH3)2 Benzene Isopropybenzene Ar NH2 Ar NO2 Ar H (Ar substituted aromatic ring) 608 AMINES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website