[27.1] amines
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what are amines?
organic compounds derived from ammonia, NH₃, where one or more H atoms in ammonia have been replaced by a carbon chain or ring
describe the 2 types of amines
• aliphatic - N atom is attached to at least one alkyl group (R) eg. CH₃NH₂ • aromatic - N atom is attached to an aromatic ring eg. C₆H₅NH₂
describe ammonia and the 3 classifications of amines
• ammonia - N surrounded by 3 Hs and 1 lone pair • 1ʸ amine - N surrounded by 2 Hs, 1 R group and 1 lone pair • 2ʸ amine - N surrounded by 1 H, 2 R groups and 1 lone pair • 3ʸ amine - N surrounded by 3 R groups and 1 lone pair • 4ʸ ammonium salts - NOT AMINES - N⁺ surrounded by 4 R groups and a negative ion
how do you name primary amines?
add suffix ‘amine’ to name alkyl chain eg. ethylamine, phenylamine
how do you name primary amines containing an amine group on another C?
use prefix ‘amino’ with a number to indicate position eg. 2-aminobutane
how do you name secondary or tertiary amines containing the same alkyl group?
use prefix di- / tri- eg. (CH₃)₂NH = dimethylamine, (CH₃)₃N = trimethylamine
how do you name secondary or tertiary amines where 2+ groups are attached to the N?
• as an N-substituted derivative of the larger group • name: CH₃NHCH₂CH₂CH₃, CH₃N(CH₂CH₃)CH₂CH₂CH₂CH₃ N-methylpropyl amine, N-ethyl-N-methylpropylamine
do amines dissolve in water?
amines which dissolve in water produce weak alkaline solution CH₃NH₂ (g) + H₂O(l) ⇌ CH₃NH₃⁺ (aq) + OH⁻ (aq)
how does solubility of amines change with carbon chain length and amine type?
• small amines are very soluble in water due to hydrogen bonds forming with water • after about 6 carbons, solubility decreases as carbon chain length increases • tertiary amines don’t have H bonding, so are less soluble than primary amines
how do amines behave as bases in their chemical reactions?
lone pair of electrons on N atom can accept a proton
when an amine accepts a proton, what bond is formed?
dative covalent bond is formed between the pair of electrons on the N atom and the proton
draw the equation for a reaction of an amine as a base
slide 16 of C27.1 amines ppt
what properties does the N lone pair determine?
• base strength depends on how well the N lone pair can accept a H+ • the higher the electron densitiy of the N lone pair, the stronger the base
what is the order of base strength of the different types of amines?
tertiary > secondary > primary > ammonia > aromatic
reactions of amines with acids
• produce salts • make sure to balance eg. ammonium sulfate salts • CH₃CH₂NH₂ + HCl -> CH₃CH₂NH₃⁺Cl⁻ • 2CH₃CH₂NH₂ + H₂SO₄ -> (CH₃CH₂NH₃⁺)₂SO₄²⁻
what happens when you add aqueous sodium hydroxide to an ammonium salt?
free base is liberated from its salt CH₃CH₂NH₃⁺Cl⁻ (aq) + NaOH (aq) -> CH₃CH₂NH₂ (l) + NaCl (aq) + H₂O (l)
name process rather than description of method how do you make aromatic amines?
reduction of nitrobenzene
name process rather than description of method how do you make aliphatic amines?
• nucleophilic substitution with haloalkane • reduction of nitrile
describe how to make aromatic amines
• nitrobenzene is heated under reflux with Sn / conc HCl to form the ammonium salt, phenylammonium chloride • this is reacted with excess NaOH to produce the aromatic amine, phenylamine • tin and HCl act as a reducing agent nitrobenzene + 6[H] -> phenylamine + 2H₂O
reagent, conditions, product, nucleophile making aliphatic primary amines: reaction of NH₃ with haloalkanes
• reagent - excess, alcoholic ammoina • conditions - reflux in excess, alcoholic solution under pressure • product - amine or its salt due to reaction with acid • nucleophile - ammonia (NH₃)
describe the role of ammonia in the production of amines
• ammonia attacks haloalkanes as it has a lone pair and is a nucleophile • the amine produced also has a lone pair so can also attack a haloalkane • this leads to the formation of substituted (secondary and tertiary) amines
why is excess ammonia used when making primary aliphatic amines?
ensures that all the haloalkane molecules with the ammonia before being able to react with any amines produced
how do you liberate the free base from its salt when making primary aliphatic amines?
add aqueous sodium hydroxide C₂H₅NH₃⁺Br⁻ (aq) + NaOH (aq) -> C₂H₅NH₂ (aq) + NaBr (aq) + H₂O (l)
describe how to make aliphatic primary amines from reduction of nitrile compounds
• react haloalkane with KCN (nucleophilic substitution) • reduce the nitrile form an aliphatic amine