2018 JC2 H2 Nitrogen Compounds Notes (upload for students)

H2 Chemistry 9729 Nitrogen Compounds P a g e | 1 E u n o i a J u n i o r C o l l e g e EUNOIA JUNIOR COLLEGE H2 CHEMISTRY (9729) ORGANIC CHEMISTRY TEACHERS’ COPY (2018 JC2) NITROGEN COMPOUNDS Name: ___________________________________________ Civics Group: _________ Recommended References: 1. A-Level Chemistry (4th ed), E.N. Ramsden 2. Organic Chemistry (6th ed), R.T. Morrison, R.N. Boyd 3. Organic Chemistry – Structure and Reactivity (4th ed), S.N. Eğe 4. Organic Chemistry (5th ed), F.A. Carey 5. http://www.chemguide.co.uk/organicprops/aminemenu.html Lecture Content Page 1. Introduction on Amines 2 2. Preparation of Amines 5 3. Basicity of Amines 7 4. Reactions of Amines 14 5. Introduction on Amino Acids 17 6. Reactions of Amino Acids 21 Learning Outcomes At the end of the lectures, you should be able to: (a) describe the formation of amines as exemplified by ethylamine (through amide and nitrile reduction) and by phenylamine (through the reduction of nitrobenzene) (b) describe the reaction of amines in the formation of salts (c) describe and explain the basicity of primary, secondary and tertiary amines in the gaseous phase (interpret as Lewis bases) (d) explain the relative basicities of ammonia, ethylamine and phenylamine in aqueous medium, in terms of their structures (e) describe the reaction of phenylamine with aqueous bromine (f) describe the formation of amides from the condensation reaction between RNH 2 and R’COCl (g) describe the acid/base properties of amino acids and the formation of zwitterions (h) describe the formation of peptide (amide) bonds between α-amino acids and, hence, explain protein formation (i) describe the hydrolysis of proteins

H2 Chemistry 9729 Nitrogen Compounds P a g e | 2 E u n o i a J u n i o r C o l l e g e 1 Introduction on Amines 1.1 Structure & Classification  General formula of primary (1) amines : RNH2  Functional Group : primary or secondary or tertiary amine  Amines may be classified as primary (1o), secondary (2o) or tertiary (3o) depending on the number of alkyl/aryl groups attached to the N atom. primary secondary tertiary quaternary ammonium salt 1.2 Nomenclature  Many aliphatic amines are named by specifying the alkyl groups attached to the N atom, following by the ending -amine.  Many aromatic amines are named as derivatives of the simplest aromatic amine, e.g. phenylamine (aniline). Examples: Alkylamines Arylamines CH3CH2NH2 ethylamine 2-pentylamine phenylamine cyclohexylamine (phenylmethyl)amine / benzylamine 5-bromo-2-ethylphenylamine dimethylamine trimethylamine diphenylamine 1 R group attached to N atom 2 R groups attached to N atom 3 R groups attached to N atom 4 R groups attached to N atom

H2 Chemistry 9729 Nitrogen Compounds P a g e | 3 E u n o i a J u n i o r C o l l e g e  For polyfunctional amines with other functional groups of higher priority, – treat the amine group as a substituent and add the prefix –amino to the parent compound E.g. H2NCH2COOH 2-aminoethanoic acid 4-aminophenol 1.3 Physical Properties of Amines (a) Boiling Point  Amines have higher boiling points than hydrocarbons with similar Mr due to stronger intermolecular hydrogen bonding.  However, amines have lower boiling points than alcohols of similar Mr due to the intermolecular hydrogen bonds in amines being weaker than those in alcohols since the N-H bond is less polar than O-H bond. Compound Mr b.p./ oC CH3CH2CH2NH2 (amine) 59 48.6 CH3CH2CH2OH (alcohol) 60 97 Quick Check Arrange the following compounds in order of increasing boiling points. Compound Mr (CH3)3N 59 (CH3)3CH 58 CH3CH2CH2NH2 59 Answer: (CH3)3CH < (CH3)3N < CH3CH2CH2NH2 N H R H N H R H N H R H + + – ||||||||||| Hydrogen bonds

H2 Chemistry 9729 Nitrogen Compounds P a g e | 4 E u n o i a J u n i o r C o l l e g e Compound Polarity Type of intermolecular forces of attraction (CH3)3N Polar Permanent dipole – permanent dipole attraction (CH3)3CH Non-polar Instantaneous dipole – induced dipole attraction CH3CH2CH2NH2 Polar Hydrogen bonding (b) Solubility in water Amines with small molecular size are soluble in water. Reason: Amines can form hydrogen bonds with water molecules. However, as the alkyl group(s) becomes bulkier/heavier , the solubility in water decreases because of the greater hydrophobic nature of the R group. Pen down your notes/ questions/ thoughts on this section in the space below OH H + + + - hydrogen bond NH H R ||||||||||| -

H2 Chemistry 9729 Nitrogen Compounds P a g e | 5 E u n o i a J u n i o r C o l l e g e LiAlH4 in dry ether r.t.p. LiAlH4 in dry ether r.t.p. 2 Preparation of Amines 2.1 Reduction of Nitriles General Equation: Reagents & Conditions: (1) LiAlH4 in dry ether, r.t.p. or (2) H2 with Ni catalyst, high temperature and pressure or (3) H2 with Pd or Pt catalyst, r.t.p. Type of reaction: Reduction Example Reduction of ethanenitrile CH3CH2CN + 4 [H] CH3CH2CH2NH2 2.2 Reduction of Amides General Equation: Reagent & condition: LiAlH4 in dry ether, r.t.p Type of Reaction: Reduction Example Reduction of ethanamide CH3CONH2 + 4 [H] CH3CH2NH2 + H2O 2.3 Ammonolysis of halogenoalkane General Equation: Reagents & Conditions: Excess c oncentrated ammonia in ethanol, heat in a sealed tube Type of reaction: Nucleophilic substitution

H2 Chemistry 9729 Nitrogen Compounds P a g e | 6 E u n o i a J u n i o r C o l l e g e Example Ammonolysis of 2-bromopropane: (CH3)2CHBr + NH3  (CH3)2CHNH2 + HBr In general, 3 2 2 3 4 quaternaryprimary secondary tertiary ammonium saltamine amine amine RX RX RXRX NH RNH R NH R N R N X       Example: Reaction of excess chloromethane with ammonia Predict with reasoning, the solubility of the end-product of the reaction in water. Answer: The ammonium salt is soluble in water. The ionic quaternary ammonium salt can form ion-dipole interactions with water molecules which releases energy that cause the detachment of ions from the crystal lattice for solvation. Note:  If an excess of NH3 is used, the main product formed is the 1 amine. Side-products can include the 2 and 3 amines as well as the quaternary ammonium salt.  If an excess of the halogenoalkane is used, the main product formed is the quaternary ammonium salt.

H2 Chemistry 9729 Nitrogen Compounds P a g e | 7 E u n o i a J u n i o r C o l l e g e 2.4 Reduction of Nitrobenzenes Reagents & Conditions: Sn in excess concentrated HCl, heat, followed with addition of NaOH (aq), r.t.p. Type of reaction: Reduction 3 Basicity of Amine