Amines -

Amines -

1 340 Chem 1st 1439 Amines 2 Outline Structure and Classification Nomenclature Physical Properties Preparation Reaction 340 Chem 1st 1439 Structure and Classification 3 Amines are organic derivatives of ammonia in which one or more hydrogens are replaced with alkyl or aryl groups. Amines are further divided into aliphatic and aromatic amines. It has high degree of biological activity, many amines are used as drugs and medicines. 340 Chem 1st 1439 Amines are classified as primary, secondary, or tertiary,

depending on the number of carbon atoms bonded directly to nitrogen. In a heterocyclic amine, the nitrogen atom is part of an aliphatic or aromatic ring. 4 Nomenclature of amines A.Common Name of amines Common Names are formed from the names of the alkyl groups bonded to nitrogen, followed by the suffix -amine. The prefixes di-, tri-, and tetra- are used to describe two, three, or four identical substituents. H N CH3 H3C N CH3 H3C NH2 Methylamine 340 Chem 1st 1439 Benzyl methyl amine Trimethyl amine 5 B. IUPAC nomenclature of amines

The IUPAC nomenclature for amines is similar to that for alcohols. The longest continuous chain of carbon atoms determines the root name. The -e ending in the alkane name is changed to -amine, and a number shows the position of the amino group along the chain. Other substituents on the carbon chain are given numbers, and the prefix N- is used for each substituent on nitrogen. NH2 NH2 O OH OH 5-Methyl-3-hexanamine 5-Aminoheptanoic acid NH2 CH3 CH2 CH 2-Butanamine 340 Chem 1st 1439 CH3

CH3 CH2 NH CH3 CH CH3 N-methyl-2-butanamine H2N 3-Amino-2-butanol H2N CH2 CH2OH 2-Aminoethanol 6 Naming Of Aromatic Amines Some common arylamines have the following names:

Aniline (benzenamine) o-Toluidine 340 Chem 1st 1439 m-Aminophenol p-Anisidine (4methoxybenzenamine) 7 Physical Properties of Amines Solubility Amines are strongly polar because the large dipole moment of the lone pair of electrons adds to the dipole moments of the C-N and H-N bonds. Primary and secondary amines have N-H bonds, allowing them to form hydrogen bonds. Pure tertiary amines cannot engage in hydrogen bonding because they have no N-H bonds. They can, however, accept hydrogen bonds from molecules having O H or N H bonds. 340 Chem 1st 1439 8 Boiling point Because nitrogen is less electronegative than oxygen, the N-H bond is less polar than the O-H bond. Therefore, amines form weaker hydrogen bonds than do alcohols of similar molecular

weights. Primary and secondary amines have boiling points that are lower than those of alcohols, yet higher than those of ethers of similar molecular weights. With no hydrogen bonding, tertiary amines have lower boiling points than primary and secondary amines of similar molecular weights. 340 Chem 1st 1439 9 Basicity of Amines: Amine Salts Amines are relatively weak bases. Most are stronger bases than water but are far weaker bases than hydroxide ions, alkoxide ions, and alkanide anions. Aromatic amines less basic than aliphatic amines Electron donating (releasing) groups on N atom increase the basicity Electron withdrawing groups decrease the basicity H3C N CH3 >

H3C NH2 > > O2N H3C Most basic NH2 340 Chem 1st 1439 NH2 NH2 H NH2 > > Least basic

NH2 NO2 10 Amines syntheses Reduction of nitro compounds Ar-NO2 + H2,Ni Ar-NH2 Ammonolysis of 1o or methyl halides R-X + NH3 R-NH2 Reductive amination R2C=O +

NH3, H2, Ni R2CHNH2 Reduction of nitriles R-CN + 2 H2, Ni RCH2NH2 Hofmann degradation of amides RCONH2 340 Chem 1st 1439 + KOBr RNH2 11

1. Reduction of nitro compounds NH2 NO2 metal + acid; then OHor H2 + Ni, Pt, or Pd metal + acid; then OHR NO2 340 Chem 1st 1439 or H2 + Ni, Pt, or Pd R NH2 CH3 12 HNO3,H2SO4 CH3 + orthoNO2 H2,Ni CH3 NH2 p-toluidine 340 Chem 1st 1439

13 2. Ammonolysis of 1o or methyl halides NH3 R-X RNH2 R-X R2NH 2o 1o R-X R3N 3o R-X R-X must be 1o or CH3 R4N+X4o salt CH3CH2CH2CH2Br 340 Chem 1st 1439

NH3 CH3CH2CH2CH2NH2 n-butylamine 14 CH3CH2CH2NH2 n-propylamine NH2 CH3Cl CH3CH2CH2NHCH3 methyl-n-propylamine 2 CH3CH2Br aniline Et N,N-diethylaniline (xs) CH3I H2 C NH2 benzylamine 340 Chem 1st 1439

N Et H2 CH3 C N CH3 CH3 I benzyltrimethylammonium iodide 15 Ammonolysis of alkyl halides is an SN2 reaction. The alkyl halide must be primary or methyl. If the alkyl halide is secondary or tertiary, then an E2 reaction will take place and the product will be an alkene! Br NH2 + NH3 2o RX 340 Chem 1st 1439 16 SN2 Reactions of Alkyl Halides Ammonia and other amines are good nucleophiles

340 Chem 1st 1439 17 3. Reductive amination O + NH3 O + RNH2 O + R2NH 340 Chem 1st 1439 H2, Ni or NaBH3CN H2, Ni or NaBH3CN H2, Ni or NaBH3CN CH NH2 1o amine CH NHR 2o amine CH NR2

3o amine 18 340 Chem 1st 1439 19 Reductive amination via the imine. O C NH3 H2,Ni H C NH2 H2, Ni OH C NH2 - H2O C NH imine

340 Chem 1st 1439 20 H3C O C NH3, H2/Ni CH3 NH2 CH3CHCH3 isopropylamine acetone O CCH2CH3 + CH3CH2NH2 propiophenone O cyclohexanone 340 Chem 1st 1439 NaBH3CN CH2CH3 NH

CHCH2CH3 1-(N-ethylamino)-1-phenylpropane NH3, H2/Ni NH2 cyclohexylamine 21 4. Reduction of nitriles R-CN + 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 340 Chem 1st 1439 NaCN CH2C N 2 H2, Ni CH2CH2NH2 1-amino-2-phenylethane

22 340 Chem 1st 1439 Examples 23 5. Hofmann degradation of amides O R C NH2 KOBr R-NH2 Removes one carbon! CH3 O CH3C C CH3 NH2 OBr 2,2-dimethylpropanamide 340 Chem 1st 1439 CH3 CH3C NH2

CH3 tert-butylamine 24 Outline possible laboratory syntheses for each of the following amines, starting with toluene. Use a different method for each compound. NH2 H3C aniline p-toluidine CH2CH2NH2 1-amino-2-phenylethane CH2NH2 benzylamine 340 Chem 1st 1439 NH2 H3C NH2 CHCH3

1-amino-1-(p-tolyl)ethane 25 Hofmann and Curtius Rearrangements Carboxylic acid derivatives can be converted into primary amines with loss of one carbon atom by both the Hofmann rearrangement and the Curtius rearrangement 340 Chem 1st 1439 26 Hofmann rearrangement 1. deprotonation of the amide by the base to form an anion which then attacks the halogen to form a N-haloamide. R O OH NH2 R

R N H NH2 R N H Br OH R OH2 N Br R N C O Isocyanate O O R

R-NH2 + CO2 H2O O O Br-Br NaOH, Br2 prim amide 2. deprotonation by the base provides an anion that rearranges to an isocyanate intermediate and releases a halide anion. O O N H 3. The isocyanate is attacked by water which after a series of proton transfer step results in a zwitterionic intermediate, containing an ammonium cation and a carboxylate anion. 4. Thermal conditions result in the explosion of carbon dioxide gas and quenching of the ammonium cation to the amine product R Br

N Br O H H2N R - CO2 O N H R carbamic acid instable 340 Chem 1st 1439 27 Curtius rearrangement O R R O

N3 R Cl OH2 N N acyl halide H2O, heat acyl azide acyl azide O N3 R N C O N Isocyanate R-NH2 - CO2 O

R N N N Mechanistic. related to Hofmann rearrang. O O R NH2 R N Br O R 340 Chem 1st 1439 N Br OH2 R N C O

Isocyanate - CO2 R-NH2 R-NH2 + CO2 + N2 Amine Reactions 28 Reaction as Bases: Salt Formation HCl R-NH2 R-NH3Cl Amide Formation O O R C

340 Chem 1st 1439 Cl + ` R-NH 2 Reaction with Nitrous Acid R C ` NHR 29 Amine Reactions with Nitrous Acid Primary amines: Diazotization Secondary Amines: Nitrosamine formation Tertiary Amines: C-nitroso com

RNH2 HONO o 0 C ArNH2 HONO o 0 C R2NH or ArNHR + R N N alkyl diazonium salt unstable + Ar N N Nu +R N2

+ Ar Nu aryl diazonium salt stable at low temp. HONO o 0 C R Ar R N N or O R N N O Nitrosamines NR2

HONO o 0 C O N NR2 Aromatic C-nitroso compound 340 Chem 1st 1439 + N2 30 340 Chem 1st 1439 Mechanism of Diazonium salt formation 1 31 340 Chem 1st 1439 Mechanism of Diazonium salt

formation 2 32 Diazonium Salt Reactions HO N N an azo dye I KI H2O Phenol + heat CN N N Cl CuCN CuCl CuBr

H3PO2 1.HBF4 2. heat Br H 340 Chem 1st 1439 OH F

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