Amines 340 Chem 1st 1439

Outline Structure and Classification Nomenclature Physical Properties Preparation Reaction 340 Chem 1st 1439

Structure and Classification 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. 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. 340 Chem 1st 1439

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. Methylamine Benzyl methyl amine Trimethyl amine 340 Chem 1st 1439

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. 340 Chem 1st 1439

Naming Of Aromatic Amines Some common arylamines have the following names: Aniline (benzenamine) o-Toluidine m-Aminophenol p-Anisidine (4-methoxybenzenamine) 340 Chem 1st 1439

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

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

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 340 Chem 1st 1439

Amine’s 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-CN + 2 H2, Ni  RCH2NH2 Hofmann degradation of amides RCONH2 + KOBr  RNH2 340 Chem 1st 1439

1. Reduction of nitro compounds 340 Chem 1st 1439

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2. Ammonolysis of 1o or methyl halides 340 Chem 1st 1439

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SN2 Reactions of Alkyl Halides Ammonia and other amines are good nucleophiles 340 Chem 1st 1439

3. Reductive amination 340 Chem 1st 1439

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Reductive amination via the imine. 340 Chem 1st 1439

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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) 340 Chem 1st 1439

Examples 340 Chem 1st 1439

5. Hofmann degradation of amides 340 Chem 1st 1439

Outline possible laboratory syntheses for each of the following amines, starting with toluene. Use a different method for each compound. 340 Chem 1st 1439

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

Hofmann rearrangement deprotonation of the amide by the base to form an anion which then attacks the halogen to form a N-haloamide. 2. deprotonation by the base provides an anion that rearranges to an isocyanate intermediate and releases a halide anion. 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 340 Chem 1st 1439

Curtius rearrangement 340 Chem 1st 1439

Amine Reactions Reaction as Bases: Salt Formation Amide Formation Reaction with Nitrous Acid 340 Chem 1st 1439

Amine Reactions with Nitrous Acid Primary amines: Diazotization Secondary Amines: Nitrosamine formation Tertiary Amines: C-nitroso com 340 Chem 1st 1439

Mechanism of Diazonium salt formation 1 340 Chem 1st 1439

Mechanism of Diazonium salt formation 2 340 Chem 1st 1439

Diazonium Salt Reactions 340 Chem 1st 1439