Amines

• Amines:

  • Amines are compounds derived from ammonia , that have a H replaced with an alkyl group
  • Can be classed as primary, secondary, tertiary
  • Often known for their pungent smells as well as their physiological effects
  • Amphetamine --> treats fatigue
  • Phenylephrine --> decongestant
  • Adrenaline --> stress hormone
• Naming amines:

  • Amines use the suffix '-amine' aftre the carbon chain prefix. E.g: methylamine
  • The prefix 'amino-' is for branched or more complex amines . E.g: 2- aminopropane

  
• • For secondary or tertiary amines each group from the amine group is named separately, the longest has the suffix -amine.
  • Secondary amines --> methylpropylamine
  • Tertiary amines --> Diethylpropylamine
• Amines as bases:

  • Amines act as weak bases due to the lone pair on the N atom being able to form a dative bond with a proton
  • They are proton acceptors
  • The salt formed is known as an ammonium salt

  
• Aliphatic amine synthesis:

  • To prepare aliphatic amines warm primary halogenoalkanes gently in excess ammonia, with an ethanol solvent
  • CH3CH2CH2Cl + NH3 --> CH3CH2CH2NH2 +HCl
  • Ethanol is used as water will protonate the ammonia (NH4+)
• • Many products ca be formed due to the ratio of amine to ammonia
  • 1 : 1 = primary
  • 2 : 1 = secondary
  • 3 : 1 = tertiary
  • 4 : 1 = quaternary (R4N+)
• • The HCl formed will react with any amine produced to form amine salts ( RNH2 + HCl --> RNH3+Cl-)
  • These salts can be removed by adding NaOH (aq)
• • Excess ammonia is often added to neutralise any HCl to form ammonium salts ( NH3 + HCl --> NH4+Cl-) & also minimises further substitutions with the amine products
  • CH3CH2CH2Cl + CH3CH2CH2NH2 --> (CH3CH2CH2)2NH + HCl
• • The formation of an amine from a halogenoalkane is a nucleophilic substitution reaction
  • The lone pair on the NH3 is attracted to the delta positive carbon in the carbon halogen bond
• • Amines can also be formed from the reduction of nitriles ( c=n) with either:
  • sodium & alcohol
  • Lithium tetrahydridoaluminate (LiAlH4)
  • RC=N + 2H2 --> RCH2NH2
• Aromatic amines:

  • Nitroarenes are reduced to form aromatic amines:
  • Tin and concentrated HCl act as a reducing agent & it is heated under reflux
  • Whilst the acid is added the mixture must be cooled, but once added the mixture is then heated
  • The amine formed will react with the HCl so the salt formed is removed by adding NaOH
  • Forming the amine, NaCl & water

  
• alpha - amino acids:

  • alpha amino acids contain both an amine and a carbonyl group that are separated by one carbon atom
  • They all share the general formula: RCH(NH2)COOH
  • Glycine is the simplest amino acid with an R- group of -H
  • The R group could be an alkyl, -OH, -SH, -COOH or -NH2

  
• Naming alpha - amino acids:

  • The carboxylic acid group takes priority, so the amine group will always be at position 2 in an alpha amino acid (2-amino)
• Zwitterions:

  • The carbonyl group is able to donate a proton to the amine group resulting in an internal salt, known as a zwitterion
  • They are the dipolar ionic form if an amino acid
  • Zwitterions have no overall charge as the charges cancel out
  • They form at the isoelectric point - a pH level unique to each amino acid due to the attached R -group

  
• Amides:

  • Amides are compounds with an amine group directly bonded with a carbonyl group
  • They can be calssified as either --> Primary (R - CONH2) or secondary (R - CONH-R')

  
• Secondary amide formation:

  • Secondary amides can be formed by the reaction of amines with carboxylic acids via a condensation reaction
  • Acid anhydrides or acyl chlorides could also be used

  
• Hydrolysis:

  • The secondary amide group can be hydrolysed under acidic conditions to form a carboxylic acid & an ammonium salt
  • The amine formed will react with the acid
  • Alkaline conditions to form a carboxylate salt and an amine --> the carboxylic acid formed will react with the alkali
• • stereoisomers are species with the same structure but a different arrangement of atoms in space
• E/Z --> restricted rotation around a c=c bond & 2 different groups bonded to each carbon
• Optical isomerism --> non - superimposable mirror images around a chiral centre
• Chiral centre:

  • A chiral centre is a carbon with 4 different atoms/ groups bonded to it ( so its asymmetrical) causing optical isomers to form
  • Also known as enantiomers
  • Enantiomers are non-superimposable images
  • To identify chiral centres look for the carbon that has 4 different groups on each of its bonds
• Properties of optical isomers:

  • Optical isomers rotate plane-polarised light in different direction i.e: on enantiomer rotates it clockwise
  • A racemic mixture contains equal proportions of each enantiomer will have no effect on plane-polarised light --> the rotations cancel out
• • condensation polymerisation is the joining of 2 monomers, with the elimination of small molecules e.g: H2O
• • Polyester are polymers that have monomers bonded via an ester link, i.e: that contained COOH and OH groups. E.g: Terylene & poly(lactic acid)
• • Polyamides are polymers that have monomers bonded via an amide link i.e: that contained COOH and NH2 groups. E.g: Nylon -6
• Polyesters:

  • There are 2 ways to form a polyester
  • 2 different monomers, a diol & a dicarboxylic acid. E.g: Terylene --> ethane -1, 2-diol + benzene 1,4 - dicarboxylic acid
  • one monomer with -OH and -COOH groups. E.g: poly(lactic acid) --> 2-hydroxypropanoic acid
• Terylene:

  • one mole of water is formed for each ester group formed

  
• PLA:

  
• Polymaides:

  • There are 2 ways to form a polyamide
  • 2 different monomers, a diamine & a dicarboxylic acid .E.g: Nylon -6
  • 1, 6 - diaminohexane + Hexane - 1,6 dioic acid
  • One monomer with - NH2 and -COOH groups. E.g: amino acids
• Nylon-6,6 :

  
• Kevlar:

  
• Polymer hydrolysis:

  • Polyesters can be hydrolysed by using either;
  • Aqueous HCl --> Alcohol + carboxylic acid (acidic conditions are much slower)
  • Aqueous NaOH --> Alcohol + carboxylate salt
  • Polyamides can be hydrolysed by using either:
  • Aqueous HCl --> Ammonium salt + carboxylic acid
  • Aqueous NaOH --> amine + carboxylate salt