1. What do each of these have in common ? H 2 N C COOH H H

2. Amines L.O: To be able to describe and explain reactions of aliphatic and aromatic amines Homework: Activity – Paracetamol; an alternative to aspirin Due: Mon 22 nd Feb

3. Structure Contain the NH 2 group Classification primary (1°) amines secondary (2°) amines tertiary (3°) aminesquarternary (4°) ammonium salts Aliphaticmethylamine, ethylamine, dimethylamine Aromatic NH 2 group attached directly to benzene ring (phenylamine) R N : H H R H R R R + R N R R

4. Nomenclature Named after the groups surrounding the nitrogen + amine C 2 H 5 NH 2 ethylamine (CH 3 ) 2 NHdimethylamine (CH 3 ) 3 Ntrimethylamine C 6 H 5 NH 2 phenylamine (aniline)

5. Physical properties The LONE PAIR on the nitrogen atom in 1°, 2° and 3° amines makes them... LEWIS BASES - they can be lone pair donors BRØNSTED-LOWRY BASES - they can be proton acceptors RNH 2 + H + RNH 3 + NUCLEOPHILES - provide a lone pair to attack an electron deficient centre

6. Physical properties Boiling pointBoiling points increase with molecular mass Amines - higher boiling points than corresponding alkanes because of their intermolecular hydrogen bonding SolubilityLower mass compounds are soluble in water due to hydrogen bonding with the solvent. Solubility decreases as the molecules get heavier. Aromatic amines are only very slightly soluble in water. Soluble in organic solvents.

7. Basic properties BasesThe lone pair on the nitrogen atom makes amines basic; RNH 2 + H + RNH 3 + a proton acceptor Strength depends on the availability of lone pair and ability to pick up protons The greater the electron density on the N, the better it can pick up protons Affected by the groups attached to the nitrogen CH 3 N : H H C 6 H 5 N : H H Electron withdrawing substituents (benzene rings) decrease basicity as the electron density on N is lowered and the lone pair is less effective Electron releasing substituents (CH 3 groups) increase basicity as the electron density is increased and the lone pair is more effective

8. Preparation Aliphatic Amines can be prepared from halogenoalkanes ReagentAqueous, alcoholic ammonia ConditionsReflux in aqueous, alcoholic solution under pressure Product Amine (or its salt from reaction with the acid produced, which the amine is then liberated from with addition of NaOH (aq)) NucleophileAmmonia (NH 3 ) Equation C 2 H 5 Br + NH 3 (aq/alc) C 2 H 5 NH 2 + HBr ( or C 2 H 5 NH 3 + Br¯ )

9. Preparation Aromatic Amines can be prepared via reduction of nitrobenzene ReagentNitrobenzene, Sn metal, conc HCl ConditionsBoiling under reflux Product Aromatic amine salt (dissolve in the excess HCl). Free amine is liberated by addition of NaOH(aq) and then collected using steam distillation. Equation C 6 H 5 NO 2 + Sn + HCl C 6 H 5 NH 2

10. Reactions as weak bases Amines which dissolve in water produce weak alkaline solutions CH 3 NH 2 (g) + H 2 O(l) CH 3 NH 3 + (aq) + OH¯(aq) Amines react with acids to produce salts. C 6 H 5 NH 2 (l) + HCl(aq) C 6 H 5 NH 3 + Cl¯(aq) phenylammonium chloride This reaction allows an amine to dissolve in water as its salt. Addition of aqueous sodium hydroxide liberates the free base from its salt C 6 H 5 NH 3 + Cl¯(aq) + NaOH(aq) C 6 H 5 NH 2 (l) + NaCl(aq) + H 2 O(l)

11. Nucleophilic reactions Amines react as nucleophiles – why? Reagent Product Mechanism haloalkanes substituted aminesnucleophilic substitution acyl chloridesN-substituted amides addition-elimination

12. Nucleophilic substitution HALOALKANES Acting as a nucleophile, amines can attack halogenoalkanes to produce a 2° amine. This is also a nucleophile and can react further producing a 3° amine C 2 H 5 NH 2 + C 2 H 5 Br HBr + (C 2 H 5 ) 2 NH diethylamine, 2°amine

13. Amine reactions With acid C 2 H 5 NH 2 + H + (aq) C 2 H 5 NH 3 + (aq) The product is an ionic salt that will dissolve in water. The amine can be regenerated from the salt with the addition of STRONG ALKALI. With acid chlorides C 2 H 5 NH 2 + CH 3 COCl CH 3 CONHC 2 H 5 + HCl The product is a substituted amide.

14. Amino acids Amino acids contain 2 functional groups amine NH 2 carboxyl COOH They all have a similar structure - the identity of R 1 and R 2 vary H 2 N C COOH H H CH 3 H H 2 N C COOH R2R2 R 1

15. Amino acids – optical isomers Amino acids can exist as optical isomers If they have different R 1 and R 2 groups Glycine doesn’t exhibit optical isomerism as there are two H attached to the C atom H 2 N C COOH CH 3 H H 2 N C COOH H H GLYCINE 2-aminoethanoic acid

16. Amino acids - Zwitterions a dipolar ion has a plus and a minus charge in its structure amino acids exist as zwitterions give increased inter-molecular forces melting and boiling points are higher H 3 N + C COO¯ R2R2 R1R1

17. amino acids possess acidic and basic properties this is due to the two functional groups COOH gives acidic properties NH 2 gives basic properties they form salts when treated with acids or alkalis. H 2 N C COOH R2R2 R1R1 Amino acids

18. Basic properties: with H + HOOCCH 2 NH 2 + H + HOOCCH 2 NH 3 + HOOCCH 2 NH 2 + HCl HOOCCH 2 NH 3 + Cl¯ Acidic properties: with OH¯ HOOCCH 2 NH 2 + OH¯ ¯OOCCH 2 NH 2 + H 2 O HOOCCH 2 NH 2 + NaOH Na + ¯OOCCH 2 NH 2 + H 2 O