University:
Kentucky State University
Course:
CHE 102 | Organic Chemistry II
Academic year:

2024
Views:

430

Pages:

31
Author:

sagsag236gx

Amines – Organic Nitrogen Compounds • Organic derivatives of ammonia, NH3, • Nitrogen atom with a lone pair of electrons, making amines both basic and nucleophilic • Occur in plants and animals 2 Naming Amines • Alkyl-substituted (alkylamines) or aryl-substituted (arylamines) • Classified: • 1° (RNH2) primary amine • 2° (R2NH) secondary amine • Tertiary amine 3° (R3N) H N R N H R H R Primary Secondary R N R R Tertiary 3 Quaternary Ammonium Ions • A nitrogen atom with four attached groups is positively charged • Compounds are quaternary ammonium salts R X R N R R 4 IUPAC Names – Simple Amines • For simple amines, the suffix -amine is added to the name of the alkyl substituent H 2N NH 2 2-M ethylpropan-2-am ine N H 2N 1,4-butandiam ine cyclohexanam ine N NH 2 H 3C N H N,N-Dim ethyl-4-am inopyridine N-M ethyl-Cyclohexanam ine 5 IUPAC Names – “-amine” Suffix • The suffix -amine can be used in place of the final -e in the name of the parent compound NH2 4,4-Dimethylcyclohexanamine 6 IUPAC Names – Amines With More Than One Functional Group • Consider the NH2 as an amino substituent on the parent molecule 7 IUPAC Names – Multiple Alkyl Groups • Symmetrical secondary and tertiary amines are named by adding the prefix di- or tri- to the alkyl group 8 IUPAC Names – Multiple, Different Alkyl Groups • Named as N-substituted primary amines • Largest alkyl group is the parent name, and other alkyl groups are considered N-substituents 9 Common Names • Alkylamines do not have common names unless they are biological molecules • Simple arylamines have common names 10 Common Names of Heterocyclic Amines • If the nitrogen atom occurs as part of a ring, the compound is designated as being heterocyclic • Each ring system has its own parent name 11 Physical properties - Amines Form H-Bonds • Amines with fewer than five carbons are watersoluble • Primary and secondary amines form hydrogen bonds, increasing their boiling points 12 Structure and Bonding in Amines • Bonding to N is similar to that in ammonia • N is sp3-hybridized • C–N–C bond angles are close to 109° tetrahedral value 13 Basicity of Amines • The lone pair of electrons on nitrogen makes amines basic and nucleophilic • They react with acids to form acid–base salts and they react with electrophiles 14 Relative Basicity • Amines are stronger bases than alcohols, ethers, or water • Amines establish an equilibrium with water in which the amine becomes protonated and hydroxide is produced • The most convenient way to measure the basicity of an amine (RNH2) is to look at the acidity of the corresponding ammonium ion (RNH3+) 15 Basicity of Substituted Arylamines • The N lone-pair electrons in arylamines are delocalized by interaction with the aromatic ring  electron system and are less able to accept H+ than are alkylamines 16 General Patterns of Basicity • Most simple alkylammmonium ions have pKa's of 10 to 11 • Arylamines and heterocyclic aromatic amines are considerably less basic than alkylamines (conjugate acid pKa 5 or less) 17 Amides • Amides (RCONH2) in general are not proton acceptors except in very strong acid • The C=O group is strongly electron-withdrawing, making the N a very weak base • Addition of a proton occurs on O but this destroys the double bond character of C=O as a requirement of stabilization by N 18 Substituted Arylamines • • • Can be more basic or less basic than aniline Electron-donating substituents (such as CH3, NH2, OCH3) increase the basicity of the corresponding arylamine Electron-withdrawing substituents (such as Cl, NO2, CN) decrease arylamine basicity 19 Amines, syntheses: 1. Reduction of nitro compounds Ar-NO2 + H2,Ni  Ar-NH2 2. Ammonolysis of 1o or methyl halides R-X + NH3  R-NH2 3. Reductive amination R2C=O + NH3, H2, Ni  R2CHNH2 4. Reduction of nitriles R-CN + 2 H2, Ni  RCH2NH2 Amines, syntheses: 1. Reduction of nitro compounds Ar-NO2 + H2,Ni  Ar-NH2 2. Ammonolysis of 1o or methyl halides R-X + NH3  R-NH2 3. Reductive amination R2C=O + NH3, H2, Ni  R2CHNH2 4. Reduction of nitriles R-CN + 2 H2, Ni  RCH2NH2 1. Reduction of nitro compounds: NH2 NO2 metal + acid; then OHor H2 + Ni, Pt, or Pd R NO2 $$$ Chiefly for primary aromatic amines. R NH2 CH3 HNO3,H2SO4 CH3 + orthoNO2 H2,Ni CH3 NH2 p-toluidine 2. Ammonolysis of 1o or methyl halides. NH3 R-X RNH2 R-X R2NH o 1o 2 R-X R3N 3o R-X R-X must be 1o or CH3 R4N+X4o salt CH3CH2CH2CH2Br NH3 CH3CH2CH2CH2NH2 n-butylamine CH3CH2CH2NH2 n-propylamine NH2 CH3Cl CH3CH2CH2NHCH3 methyl-n-propylamine 2 CH3CH2Br aniline Et N Et N,N-diethylaniline (xs) CH3I H2 C NH2 benzylamine H2 CH3 C N CH3 CH3 I benzyltrimethylammonium iodide 3. Reductive amination: O + N H H 2, N i 3 o r L iA lH O O + + C H N H R N H R 2N H C H N H R o r L iA lH o a m in e 2 o a m in e 4 H 2, N i o r L iA lH 1 4 H 2, N i 2 2 C H N R 4 2 3 o a m in e Reductive amination via the imine. O C N H H C N H 3 2 H 2, N i O H C N H - H 2O 2 C N H im in e H 3C O C N H 3 , H 2 /N i CH3 is o p ro p yla m in e a c e to n e O C C H 2C H 3 + C H 3C H 2N H 2 p ro p io p h e n o n e O cy c lo h e xa n o n e NH2 C H 3C H C H 3 C H 2C H 3 NH C H C H 2C H 3 L iA lH 4 1 -(N -e th yla m in o )-1 -p h e n y lp ro p a n e N H 3 , H 2 /N i NH2 c yc lo h e xy la m in e SN2 Reactions of Alkyl Halides • Ammonia and other amines are good nucleophiles 29 4. Reduction of nitriles R-CN + 2 H2, catalyst  R-CH2NH2 1o amine R-X + NaCN  R-CN  RCH2NH2 primary amine with one additional carbon (R must be 1o or methyl) CH2Br benzyl bromide NaCN CH2C N 2 H2, Ni CH2CH2NH2 1-amino-2-phenylethane Amines, syntheses: 1. Reduction of nitro compounds Ar-NO2 + H2,Ni  Ar-NH2 2. Ammonolysis of 1o or methyl halides R-X + NH3  R-NH2 3. Reductive amination R2C=O + NH3, H2, Ni  R2CHNH2 4. Reduction of nitriles R-CN + 2 H2, Ni  RCH2NH2 Reactions of Amines • Alkylation and acylation have already been presented 32

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