Classwork Series and Exercises {Chemistry- SS3}: Amines and Amides

AMINES

Amines are organic compounds that contain nitrogen and are basic. The general form of an amine is shown in Lewis form.

The different kinds of amines

Examples showing different ways to show condensed formula are:

Amines fall into different classes depending on how many of the hydrogen atoms are replaced.

Primary amines

In primary amines, only one of the hydrogen atoms in the ammonia molecule has been replaced. That means that the formula of the primary amine will be RNH₂ where “R” is an alkyl group.

Examples include:

The commonest name at this level is methylamine and, similarly, the second compound drawn above is usually called ethylamine.

Where there might be confusion about where the -NH₂ group is attached to a chain, the simplest way of naming the compound is to use the “amino” form.

For example:

There are other variants on the names, but this is the commonest and simplest way of naming these small secondary amines.

Tertiary amines

In a tertiary amine, all of the hydrogens in an ammonia molecule have been replaced by hydrocarbon groups. Again, you are only likely to come across simple ones where all three of the hydrocarbon groups are alkyl groups and all three are the same.

The naming is similar to secondary amines. For example:

Physical Properties of Amines

1. The first two members of amines are gases at room temperature and pressure
2. They have a strong smell of fish
3. They are very soluble in cold water like ammonia
4. They burn in air but ammonia does not.

Chemical Properties of Amines

1. Methylamine and ethylamine turn damp red litmus paper blue like ammonia
2. They form salts with mineral acids like ammonia

             C₂H₅NH_2(g) + HCl_(g)  ———-> C₂H₅NH₃⁺Cl^–

Uses of Amines

Amines can be use in making polyamides or nylon.

 AMIDES

Amides are derived from carboxylic acids. A carboxylic acid contains the -COOH group, and in an amide the -OH part of that group is replaced by an -NH₂ group.

So amides contain the -CONH₂ group.

Some simple amides

The most commonly discussed amide is ethanamide, CH₃CONH₂ (old name: acetamide).

Preparation of Amides

• Amides are prepared by the reaction of esters or acid chloride with concentrated aqueous ammonia e.g. propyl ethanoate and aqueous ammonia

            CH₃COOC₃H_7(aq) + NH_3(aq) ———> CH₃CONH_2(aq) + C₃H₇OH_(aq)

• Amide can also be gotten by dehydrating ammonium salts of carboxylic acids

            CH₃COONH_4(aq) <————-> CH₃CONH_2(aq) + H₂O_(l)

Physical Properties of Amides

1. The amides have high melting and boiling points than as expected because of the presence of hydrogen bonding between amide molecules.
2. Methanamide is liquid while the rest of the amides are crystalline solids.

Chemical Properties of Amide

1. When amide is hydrolyzed in the presence of mineral acids and alkalis as catalyst, it gives corresponding monocarboxylic acid.
2. Amides reacting with aqueous sodium hydroxide and bromine, yield the corresponding amines by dominating the carbonyl group

CH₃-CONH_2(aq) + Br_2(l) + 4NaOH_(aq) ——-> CH₃NH_2(g) + NaBr + Na₂SO₃ + H₂O

EXERCISES

Lets see how much you’ve learnt, attach the following answers to the comment below

1. What name should be given to the compound (CH₃)₂NCH₂CH₃? (a) ethylmethylamine (b) diethylmethylamine (c) ethyldimethylamine (d) butylamine
2. What element do amides and amines have in common, other than C and H? (a) O (b) S (c) N (d) P
3. How is this compound shown classified? (CH₃)₂NCH₂CH₃ (a) amide (b) tertiary (3°) amine (c) secondary (2°) amine (d) primary (1°) amine
4. Amines can be produced by: (a) Oxidation of amides (b) Reduction of amides (c)   Methylation of amides (d) Esterification of amides
5. Which of the following is not a primary amine? (a) 3-Hexylamine (b) 1-Butylamine (c) Cyclohexylamine (d) Diethylamine

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