Amines

Question 1

What are amines?

Answer 1

• Derivatives of AMMONIA
• Where hydrogen atoms are replaced with an ALKYL group, -R

PRIMARY AMINE ~ RNH2 (one H replaced with an alkyl group)

SECONDARY AMINE ~ R2NH (two Hs replaced with an alkyl group)

TERTIARY AMINE ~ R3N (all three Hs replaced with an alkyl group)

Question 2

Naming Primary amines 1

Answer 2

• Alkyl group bonded to the nitrogen atom appears as a PREFIX
• e.g ethyl,propyl
• name ends with -AMINE

CH3CH2CH2NH2 ~ Propylamine

Question 3

Naming Primary amines 2 ~ when the amine group is on a carbon other than carbon 1

Answer 3

• amine is named with prefix -AMINO
• a number is used to indicate its position along the chain

CH3CH(NH2)CH3 ~ 2-aminopropane

• also used when there is MORE THAN ONE FUNCTIONAL GROUP present in the molecule

CH3CH(NH2)CH2NH2 ~ 1,2-diaminopropane

Question 4

Naming Secondary Amines

Answer 4

• TWO ALKYL GROUPS bonded to the nitrogen atom

SHORTER alkyl group:
- becomes the PREFIX
- Contains the N atom

• Name ends with -AMINE

CH3CH2CH2NHCH3 ~ N-methylpropylamine

Question 5

Naming Tertiary Amines

Answer 5

• THREE ALKYL GROUPS bonded to the nitrogen atom

SHORTER alkyl group:
- becomes the PREFIX
- Contains the N atom

• Name ends with - AMINE

CH3CH2(N)CH2CH3CH3CH2 ~ N,N-diethyl propylamine

Question 6

Like ammonia, amines behave as …

Answer 6

WEAK BASE:

• Lone pair of e- on the nitrogen atom ACCEPTS a proton, H+
• By forming a DATIVE covalent bond

RNH2 + H+ —— RNH3+

Question 7

What is PHENYLAMINE?

Answer 7

• An aromatic amine, where a phenyl group, or in general an aryl group, is bonded to the nitrogen atoms.

Question 8

The reactions of amines with acids

Answer 8

• Amines behave as bases as they are proton ACCEPTORS
• Reacts with an acid to form an ALKYLAMMONIUM SALT
• The ALKYLAMMONIUM ION replaces the PROTON in the acid to form a salt

Examples ~

Propylamine & HCl:

CH3CH2CH2NH2 + HCl —— CH3CH2CH2NH3+Cl- ( propylammonium chloride)

Phenylamine & HNO3:

C6H5NH2 + HNO3 ——- C6H5NH3+NO3-

Question 9

Preparation of Aliphatic Amines
(Type of reaction)

Answer 9

Haloalkane + NH3 + NaOH —– Amine + NaBr +H2O

• NH3 is a NUCLEOPHILE
• Br has been substituted by the NH3+ group

Type of reaction ~ Nucleophilic substitution

Question 10

Preparation of Aliphatic Amine:

(using bromoethane)

• Step 1
• Step 2
• Overall equation

Answer 10

Step 1: Formation of alkylammonium salt

CH3CH2Br + NH3 — CH3CH2NH3+Br-(ethyl ammonium bromide)

Step 2 : Formation of amine

CH3CH2NH3+Br- + NaOH — CH3CH2NH2 + NaBr + H2O

Overall equation:

CH3CH2Br + NH3 + NaOH —- CH3CH2NH2 + NaBr + H2O

Question 11

Further Substitutions ~ Reaction of ammonia with haloalkanes

Answer 11

When AMMONIA is added in excess:

• The formation of PRIMARY AMINES is favoured
• However, a mixture of primary, secondary & tertiary amines as well as quaternary ammonium salts are produced

When HALOALKANES is added in excess :

• Production of SECONDARY & TERTIARY AMINES and quaternary ammonium salts are favoured

Question 12

Preparation of Aliphatic Amines ~ REAGENTS & CONDITIONS
2 steps

Answer 12

1) Formation of alkylammonium salt:

EXCESS NH3:

• reduces further substitution of the amine group to form secondary & tertiary amines and quaternary ammonium salts

ETHANOL SOLVENT:

• an absence of water prevents the substitution of the haloalkane to produce alcohols
• and the protonation of NH3 to form NH4+

HEAT IN A SEALED TUBE:

• otherwise ammonia escapes as it is volatile

2) Formation of amine:

• NaOH

Question 13

Which is the STRONGER nucleophile, ethylamine or ammonia and WHY?

Answer 13

ETHYLAMINE:

• the ethyl group donates electron density to the nitrogen via hyperconjugation

Question 14

Reduction of NITROBENZENE to PHENYLAMINE (ANILINE)

Answer 14

Nitrobenzene + 6[H] – Phenylamine + 2H2O

REAGENTS & CONDITIONS:

• Sn & c.HCl
• heat under reflux

FOLLOWED BY:
- Excess NaOH(aq)