Organic: Amines Flashcards
Naming amines?
- Name stem ends in -yl (propylamine) or can be propan-1-amine
- If another priority functional group is present as well as amine group , PREFIX -amino is used. (2-aminopropanoic acid - amino acid)
- If amine is secondary, each chain is named + smaller ALKYL groups attached is preceded by an -N
(N-methylpropylamine or N-methylpropan-1-amine (CH3CH2CH2NHCH3))
If chains are same length dont use -N - If tertiary amine : each alkyl group is given N
- PHENYLAMINE - if benzene ring and NH2 group
- If 2 amines groups - e.g 1,6diaminohexane or hexane-1,6-Diamine
What is an aliphatic and aromatic amine?
Aliphatic - if R group is an alkyl group (methyl,ethyl)
Aromatic - if R group is Aryl group (benzene ring/phenyl)
Primary aliphatic amines reaction with water?
small amines can form H bonds with water + dissolve readily
- as hydrocarbon part becomes longer, solubility decreases (phenylamine only slightly soluble)
BECAUSE : the bigger the amine, greater the LONDON forces between amine molecules + more energy needed to overcome
Larger carbon chain disrupt H bonding in water (cant form H bond with water)
Can also react with water to form ALKALINE SOLUTIONS :
CH3NH2 + H2O ⇌ CH3NH3+ + OH-
Primary aliphatic amines reaction with acids?
React with strong acids - form IONIC AMMONIUM SALTS - SOLID CRYSTALS which are soluble in acid
CH3NH2 (aq) + HCl (aq) → CH3NH3+Cl- (aq)
Methylamine Methyl ammonium chloride
adding NaOH to ammonium salt converts it back to amine
Primary aliphatic amines/phenylamine reaction with ethanoyl chloride?
(Acyl chloride)
Addition - elimination reaction (2 molecules join tgt , a small molecule is eliminated)
Acyl chloride —> SECONDARY AMIDE
Butylamine with ethanoyl chloride:
CH3COCl + CH3(CH2)3NH2 → CH3CONHCH2CH2CH2CH3 + HCl
Forms : N-butylethanamide + HCl
Reaction of Primary aliphatic amines with halogenoalkanes?
Nucleophilic substition reaction - electron deficient C atom on haloalkane and electron rich N atom on amine causes reaction
Butylamine + chloroethane —> SECONDARY AMINE + HYDROGEN HALIDE
CH3CH2CH2CH2NH2 + CH3CH2Cl → CH3CH2CH2CH2NHCH2CH3 + HCl
SECONDARY AMINE can react further with more HALOALKANE as it has electron rich N atom —> form TERTIARY AMINE
- reacts subsequently on to form QUATERNARY AMMONIUM SALT
HALOALKANE + primary aliphatic amine:
Reaction of secondary amine to form tertiary and subsequently quaternary ammonium salt?
Keep reacting with more haloalkane (in this case, (CHLOROETHANE)
FORMING TERTIARY: CH3CH2CH2CH2NHCH2CH3 + CH3CH2Cl → CH3CH2CH2CH2N(CH2CH3)2 + HCl
FORMING AMMONIUM SALT: CH3CH2CH2CH2N(CH2CH3)2 + CH3CH2Cl → CH3CH2CH2CH2N+(CH2CH3)3Cl-
(Doesn’t form HCl here, because requires loss of H from N atom in tertiary amine, but tertiary amine doesn’t have this)
Reaction of primary aliphatic amines with copper(II) ions?
Lone pair on nitrogen allows amines to act as ligands + form dative covalent bond with transition metal ions —> form coloured complex ions
(Similar reaction to when ammonia reacts with Cu)
[Cu(H2O)6]2+ + 2CH3CH2CH2CH2NH2 → [Cu(H2O)4(OH)2] + 2CH3CH2CH2CH2NH3+
Form blue precipitate
excess butylamine: precipitate dissolves to BLUE SOLUTION :
[Cu(H2O)4(OH)2] + 4CH3CH2CH2CH2NH2 → [Cu(CH3CH2CH2CH2NH2)4(H2O)2]2+ + 2H2O +2OH-
How to prepare amines?
- Reaction of HALOALKANE WITH AMMONIA
- REDUCTION OF NITRILES
Preparing primary aliphatic amines:
Reaction of halogenoalkane with ammonia?
Nucleophilic substitution
Ammonia is nucleophile + replaces halogen
Conditions: excess, hot ethanolic ammonia under pressure
PRIMARY AMINE FORMED
(NOT AS EFFICIENT for preparing HIGH YEILD OF primary amine, because further substitution reactions could occur)
Preparing primary aliphatic amines:
Reduction of nitriles?
-CN can be REDUCED TO -NH2 group
- Convert haloalkane to nitrile , USE KCN in aqueous ethanol (under reflux)
-
Nitrile vapour + H2 GAS passed over nickel catalyst
OR
LiAlH4 in dry ether used
E.g CH3CN + 4[H] —> CH3CH2NH2
Ethanitrile —> ethyl amine
FORM PRIMARY AMINE
(2 step reaction so may have LOW YIELD + KCN is toxic)
Why can ammonia and amines act as Bronsted-Lowry BASES?
N atom can accept a proton (H+ ION)
- act as Bronsted Lowry bases in aqueous solutions by DONATING its lone pair to PROTON - FORM DATIVE BOND
What is strength of a base dependent on?
Ability of lone pair on N ATOM to accept proton+ form dative bond
The more readily a proton is attracted, stronger the base is
Factors that affect the basicity of amines?
Positive inductive effect: some groups (like alkyl groups) donate electron density to N atom, causing lone pair of electrons to become more available —> INCREASE BASICITY
Delocalisation : presence of aromatic ring (benzene ring) cause lone pair of electrons on N atom to become delocalised in benzene ring
- lone pair less available to form dative bond with H+ —> DECREASE BASICITY
ORDER from strongest base to weakest base?
Secondary amines > Aliphatic amines > ammonia > aromatic amines
Secondary amines > primary - have more alkyl groups around N atom, in place of H atoms
More electron density pushed onto N ATOM (as inductive effect of alkyl groups > that of H atoms)
Primary aliphatic amine > ammonia - alkyl groups are electron releasing, pushing electrons towards N ATOM
Aromatic amines are weakest (DONT FORM BASIC SOLUTIONS) because: Nitrogen’s lone pair become delocalised in benzene ring - they’re less available to form dative bond with H+
