Amines are organic derivatives of ammonia, NH3 Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.1 Introduction Amines are organic derivatives of ammonia, NH3 Classification of Amines Primary amines Secondary amines Tertiary amines

Classify the following amines: Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.1 Classify the following amines: 1° 2° Aliphatic amines 3° 2° 1° Aromatic amines 3°

Chapter 19 : Amines 19.1 : Introduction 19.4 : Preparation 19.2 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.2 IUPAC Nomenclature In primary amines, the suffix ‘amine’ replaces the ‘e’ in the name of the parent alkane propan e amine e 3 2 1 Secondary and tertiary amines are named as N-substituted derivatives of primary amines 2° N-methyl ethan e amine e 2 1

N-ethyl-N-methyl ethanamine Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.2 Examples: Structure IUPAC Name Methanamine 2-propanamine Cyclopentanamine N-methylpentanamine N-ethyl-N-methyl ethanamine

Chapter 19 : Amines 19.1 : Introduction 19.4 : Preparation 19.2 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.2 IUPAC Nomenclature When multiple functional groups are present and the –NH2 group does not take priority, it is named as an “amino” substituent Examples: 2-amino ethanoic acid 2 1 4 1 2,4-diamino phenol 3 2

Aromatic amines are named as derivatives of aniline Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.2 IUPAC Nomenclature Aromatic amines are named as derivatives of aniline N-ethyl-N-methylaniline

Most primary amines are named as alkylamines Structure IUPAC Name Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.2 Common Name Most primary amines are named as alkylamines Structure IUPAC Name methylamine ethylamine propylamine dimethylamine methylethylamine

Tertiary amines cannot form hydrogen bonds to each other. Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.3 (i) Boiling Point Both primary and secondary amines can form intermolecular hydrogen bonds. Boiling point Solubility Basicity 1° amines 3° amines 2° amines Tertiary amines cannot form hydrogen bonds to each other.

Relative molecular mass Examples: The table below compares the boiling points of isomeric amines. Amines Class Relative molecular mass Boliling points/oC CH3CH2CH2NH2 1° 59 49 CH3CH2-NH-CH3 2° 37 CH3 | CH3-N-CH3 3° 4 Boiling Point : CH3CH2CH2NH2 > CH3CH2NH(CH3) > (CH3)3N

intermolecular hydrogen bonding Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.3 (i) Boiling Point Amines have higher boiling points than alkanes or haloalkanes of similar relative molecular mass due to Boiling point Solubility intermolecular hydrogen bonding Example Basicity Amines have lower boiling points than alcohols or carboxylic acids of comparable molecular weight because H- bond in RNH2 is weaker than the H- bond in ROH and RCOOH (Nitrogen is less electronegative than the Oxygen)

Relative molecular mass Examples: The table below compares the boiling points of organic compounds of comparable relative molecular mass. Amines Type Relative molecular mass Boliling points/oC CH3CH2CH2CH3 butane CH3CH2Cl chloroethane CH3CH2CH2NH2 1-propanamine Alkane 58 -0.5 64.5 12.5 Haloalkane 59 48.6 Amine

intermolecular hydrogen bonding Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.3 (i) Boiling Point Amines have higher boiling points than alkanes or haloalkanes of similar relative molecular mass due to Boiling point Solubility intermolecular hydrogen bonding Example Basicity Amines have lower boiling points than alcohols or carboxylic acids of comparable molecular weight because H- bond in RNH2 is weaker than the H- bond in ROH and RCOOH (Nitrogen is less electronegative than the Oxygen) Example

Relative molecular mass Examples: The table below compares the boiling points of organic compounds of comparable relative molecular mass. Amines Type Relative molecular mass Boiling points/oC CH3CH2CH2CH3 butane CH3CH2Cl chloroethane CH3CH2CH2NH2 1-propanamine Alkane 58 -0.5 64.5 12.5 Haloalkane CH3CH2CH2NH2 1-propanamine 59 48.6 Amine CH3CH2CH2OH 1-propanol Alcohol 60 97.2 CH3COOH ethanoic acid Carboxylic acid 60 118 Boiling Point : Carboxylic acid > Alcohol > Amine > Haloalkane > Alkane

Chapter 19 : Amines 19.1 : Introduction 19.4 : Preparation 19.3 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.3 (ii) Solubility Boiling point All amines including tertiary amines, are capable of forming hydrogen bonds with water molecules. Thus simple amines (amines of fewer than 5 carbons) are generally water soluble and dissolve to form basic aqueous solutions Solubility Basicity

Comparison the solubility between 1°,2° and 3°amine 3° < 2 ° < 1 ° Increasing solubility : hydrogen bonds 3 hydrogen bonds per a 1° amine molecule 2 hydrogen bonds per a 2° amine molecule 1 hydrogen bond per a 3° amine molecule

Chapter 19 : Amines 19.1 : Introduction 19.4 : Preparation 19.3 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.3 Basicity An amine is a nucleophile (a Lewis base) because its lone pair of non-bonding electrons on nitrogen Boiling point Solubility Basicity Ammonia Ammonium ion

Basicity – (i) Inductive effect An alkyl group is electron donating Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.3 Basicity – (i) Inductive effect An alkyl group is electron donating group, and it stabilises the alkylammonium ion by dispersing its positive charge Boiling point Solubility Basicity 1° Amine alkylammonium ion Stabilised by the alkyl group Stronger base

Increasing Chapter 19 : Amines 19.1 : Introduction 19.4 : Preparation 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.3 Boiling point Solubility 1° Amine alkylammonium ion Basicity 2° Amine alkylammonium ion Strength as a base : Methyl, 1°, 2° Increasing

Basicity – (ii) Resonance effect Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.3 Basicity – (ii) Resonance effect Aromatic amines (e.g., aniline) are weaker bases than the corresponding aliphatic and cyclic amines Boiling point Solubility Basicity Example: Cyclohexylamine Aniline pKb = 3.36 pKb = 9.42

Basicity – (ii) Resonance effect Aromatic amines are less basic Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.3 Basicity – (ii) Resonance effect Aromatic amines are less basic Boiling point The lone pair electrons of nitrogen atom are delocalised and overlapped with the aromatic ring π electrons system make it less available for bonding to H+ Solubility Basicity arylamines are stabilised due to the 4 resonance structures

Hoffmann’s degradation of amides Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.4 Reduction of nitro compounds Aromatic amines can be prepared by reduction of nitro compounds using Zn/H+ or SnCl2/H+ Reduction of nitro compound Reduction of nitriles Zn/H+ or SnCl2/H+ NO2 NH2 Reduction of amides nitrobenzene Aniline anline Hoffmann’s degradation of amides

Hoffmann’s degradation of amides Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.4 Reduction of nitriles Nitriles are reduced to primary amines by H2 / catalyst, LiAlH4 / H+ or NaBH4 / H+. Reduction of nitro compound Reduction of nitriles Reduction of amides Example : Hoffmann’s degradation of amides

Hoffmann’s degradation of amides Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.4 Reduction of amides Reduction of an amide using LiAlH4 / H+ or NaBH4 / H+ can yield a primary, secondary, or tertiary amine depending on the type of amide used Reduction of nitro compound Reduction of nitriles Reduction of amides Hoffmann’s degradation of amides

Hoffmann’s degradation of amides Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.4 Example : Reduction of nitro compound Reduction of nitriles Reduction of amides Hoffmann’s degradation of amides

Hoffmann’s degradation of amides Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.4 Hoffmann’s degradation of amides On warming a primary amide with bromine in solution of NaOH, a primary amine is formed. This reaction is used to synthesise primary alkyl and aryl amines. Reduction of nitro compound Reduction of nitriles Reduction of amides Hoffmann’s degradation of amides The elimination of carbonyl group is shortening the length of carbon chain by one carbon atom.

Hoffmann’s degradation of amides Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.4 Example : Reduction of nitro compound Reduction of nitriles Reduction of amides Hoffmann’s degradation of amides

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 Reaction with acyl chlorides Reaction with : 1° and 2° amines are acylated to form N-substituted amides Acyl chloride Acid anhydride Benzenesulphonyl chloride Nitrous acid Bromine water 3° amines are not acylated because they do not have a H atom attached to N atom. Formation of dye

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 Reaction with acid anhydride Reaction with : 1° and 2° amines are acylated to form N-substituted amides Acyl chloride Acid anhydride Benzenesulphonyl chloride Nitrous acid Bromine water 3° amines are not acylated because they do not have a H atom attached to N atom. Formation of dye

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 Reaction with benzenesulphonyl chloride Reaction with : Hinsberg’s test Acyl chloride This reaction is used to differentiate between 1°, 2° and 3° amines. Acid anhydride Benzenesulphonyl chloride Nitrous acid Bromine water Formation of dye

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 1° amines Benzenesulphonyl chloride reacts with a 1° amine to form a white precipitate (N-substituted sulphonamides) Reaction with : Acyl chloride Acidic hydrogen Acid anhydride Benzenesulphonyl chloride Nitrous acid Bromine water N-substituted sulphonamides have an acidic hydrogen, N-H. Formation of dye Therefore, it dissolve in aqueous NaOH.

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 2° amines Benzenesulphonyl chloride reacts with a 2° amines to form a white precipitate (N,N-disubstituted sulphonamide) Reaction with : Acyl chloride Acid anhydride Benzenesulphonyl chloride Nitrous acid Bromine water N,N-disubstituted sulphonamides do not have an acidic hydrogen, N-H. Formation of dye Therefore, it dissolve in aqueous NaOH.

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 3° amines 3° amine do not gives visible reaction with benzenesulphonyl chloride Reaction with : Acyl chloride Summary of Hinsberg’s test: Acid anhydride 1° amines  white precipitate  clear solution NaOH Benzenesulphonyl chloride 2° amines  white precipitate  do not dissolved NaOH Nitrous acid Bromine water 3° amines  do not give any visible change Formation of dye

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 Reaction with nitrous acid (NaNO2 + HCl) Reaction with : Nitrous acid (HNO2) is a weak and unstable acid. Acyl chloride It is always prepared in situ, by treating cold sodium nitrite (NaNO2) with an aqueous solution of a cold dilute hydrochloride acid (-5°C). Acid anhydride Benzenesulphonyl chloride Nitrous acid Nitrous acid reacts with all classes of amines Bromine water Nitrous acid test can be used to distinguish: 1° aliphatic and 1° aromatic amines 1° and 2° aliphatic amines Formation of dye

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 1° amines (Aliphatic) Primary aliphatic amines react with nitrous acid to yield highly unstable aliphatic diazonium salts Reaction with : Acyl chloride Acid anhydride Benzenesulphonyl chloride Nitrous acid Bromine water Observation : Formation of gas bubbles (N2) Formation of dye

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 1° amines (Aromatic) Primary arylamines react with nitrous acid to give arenediazonium salts Reaction with : Acyl chloride Acid anhydride Benzenesulphonyl chloride Nitrous acid Bromine water Formation of dye

1° aliphatic amines and 2° aliphatic amines Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 1° aliphatic amines and 2° aliphatic amines Reaction with : Primary aliphatic amines Form a mixture of alkenes, alcohols, alkyl halides and nitrogen gas. Secondary aliphatic amines Form secondary N-nitrosamines as yellow oil, which is stable under the reaction conditions. Acyl chloride Acid anhydride Benzenesulphonyl chloride Nitrous acid Bromine water Formation of dye

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties Identification test 19.5 Reaction with bromine water Reaction with : Aniline reacts with aqueous bromine to yield white precipitates Acyl chloride NH2 group is an activating and ortho-para directors group Acid anhydride Benzenesulphonyl chloride Nitrous acid Bromine water (2,4,6-tribromoaniline) Formation of dye Observation: White precipitate formed

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 Formation of dye Reaction with : Primary arylamines react with nitrous acid to give arenediazonium salts which are stable at 0 C Acyl chloride Acid anhydride Arenediazonium salts also undergo coupling reaction with aromatic compounds with strong electron donating group, such as –OH and –NR2 at the para position to yield azo compounds Benzenesulphonyl chloride Nitrous acid Bromine water Azo compounds are usually intensely coloured and relatively inexpensive compounds, they are used as dyes Formation of dye

Benzenesulphonyl chloride Chapter 19 : Amines 19.1 : Introduction 19.2 : Nomenclature 19.3 : Physical Properties 19.4 : Preparation 19.5 : Chemical properties 19.5 Reaction with : Acyl chloride Acid anhydride Benzenesulphonyl chloride Nitrous acid Bromine water Formation of dye