Amines

• Amines are organic compounds derived by replacing hydrogen atoms of ammonia with alkyl/aryl groups
• Benadryl, an antihistaminic drug, contains a tertiary amino group
• In nature, amines occur among proteins, vitamins, alkaloids, and hormones
• Synthetic examples of amines include polymers, dye stuffs, and drugs
• Quaternary ammonium salts are used as surfactants
• Biologically active compounds like adrenaline and ephedrine, both containing secondary amino groups, are used to increase blood pressure
• Novocain, a synthetic amino compound, is used as an anaesthetic in dentistry
• Diazonium salts are intermediates in the preparation of aromatic compounds including dyes
• Amines are derivatives of ammonia obtained by replacing hydrogen atoms with alkyl and/or aryl groups
• Amines are classified as primary, secondary, and tertiary based on the number of hydrogen atoms replaced by alkyl or aryl groups
• In common system, aliphatic amines are named by prefixing alkyl group to amine, while in IUPAC system, primary amines are named as alkanamines
• Arylamines have the -NH2 group directly attached to the benzene ring
• Amines can be prepared by methods like reduction of nitro compounds and ammonolysis of alkyl halides
• Lithium aluminium hydride (LiAlH4) or catalytic hydrogenation produce primary amines
• This reaction is used for the ascent of amine series, preparing amines with one carbon atom more than the starting amine
• Reduction of amides with lithium aluminium hydride yields amines
• Gabriel synthesis is used for the preparation of primary amines
• Phthalimide on treatment with ethanolic potassium hydroxide forms potassium salt of phthalimide, which on heating with alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine
• Hoffmann developed a method for the preparation of primary amines by treating an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide
• Amines have different physical properties based on their structure and size
• Lower aliphatic amines are gases with a fishy odor, while primary amines with three or more carbon atoms are liquid
• Aniline and other arylamines are usually colorless but can get colored on storage due to atmospheric oxidation
• Amines are soluble in water due to hydrogen bonding but solubility decreases with an increase in molar mass
• Primary and secondary amines engage in intermolecular association due to hydrogen bonding
• Tertiary amines do not have intermolecular association due to the absence of a hydrogen atom available for hydrogen bond formation
• Amine salts on treatment with a base like NaOH regenerate the parent amine
• Amines react with acids to form salts
• Amines are engaged in intermolecular association due to hydrogen bonding
• Amines have an unshared pair of electrons on the nitrogen atom, making them behave as Lewis bases
• Amines behave as nucleophiles due to the presence of an unshared electron pair
• Amines salts are soluble in water but insoluble in organic solvents like ether
• The basicity of amines is related to their structure and stability of the cation formed
• Basic character of amines can be understood in terms of their Kb and pKb values
• The pKb values of amines determine their strength as bases
• The substituted ammonium ion formed from the amine gets stabilized due to the dispersal of the positive charge by the +I effect of the alkyl group
• Alkylamines are stronger bases than ammonia due to the electron-releasing nature of the alkyl group, which pushes electrons towards nitrogen, making the unshared electron pair more available for sharing with a proton
• The basic nature of aliphatic amines increases with the number of alkyl groups, following the order: tertiary amine > secondary amine > primary amine > NH3 in the gaseous phase
• In the aqueous phase, the order of basicity of amines is not regular and is influenced by the solvation effect and steric hindrance of the alkyl group
• Arylamines like aniline have a high pKb value due to the unshared electron pair on nitrogen being in conjugation with the benzene ring, making it less available for protonation
• Aniline is more stable than the anilinium ion due to its five resonating structures, leading to lower proton acceptability compared to ammonia