Esters

Functional Group

Nomenclature

The carbon chain that came from the alcohol is given the suffix "-yl" as if it is a side chain.

The other carbon chain (containing the C=O bond) is given the suffix "-anoate". This is also the suffix for a salt made from a carboxylic acid.

Preparation

Esters can be made by reacting alcohols with either:

- carboxylic acids, with concentrated sulfuric acid and heat, OR

- acid chlorides

Reactions

HYDROLYSIS

Acidic and alkaline conditions can break the ester bond:

Acidic Conditions

Alkaline Conditions - note the different products!

SAPONIFICATION

This is a fancy name for making soaps. Fatty acids are esters, and can be hydrolysed to make soaps:

The IUPAC name for glycerol is 1, 2, 3 propan-triol.

AMIDE FORMATION

Esters can be used to make amides as well. Heat is required to complete the reaction.

POLYMERISATION

This will be a separate blog post. Polyesters are very useful polymers in the clothing industry, and to make drink bottles (PET).

Properties

Esters are insoluble in water. This is because they have a large non-polar part and cannot form hydrogen bonds with water. They do hydrolyse in water, forming the alcohol and carboxylic acid.

Their melting and boiling points are comparable to similar-sized aldehydes and ketones.

Amides

 Functional Group

The methyl groups can be replaced for any carbon chain.

Nomenclature

The suffix for amides in "-anamide".

Like other carboxylic acid derivatives, the amide is on the terminal carbon. Any other groups bound to the nitrogen atom (secondary and tertiary amides) are named as, for example, N-methyl.

N,N-dimethyl methanamide

Preparation

FROM CARBOXYLIC ACIDS

Heating is a critical step in this, to drive off the water and form the amide bond. This is called a condensation reaction.

FROM ACID CHLORIDES

Reactions

The only reaction we need to know about is hydrolysis (with an acid or a base):

Amides do not react with water. Instead, they dissolve as they can form hydrogen bonds with water molecules.

Acid Chlorides

Acid chlorides are much more reactive than their carboxylic acid counterparts. Therefore, they are often preferred for industrial processes.

Functional Group and Nomenclature

The suffix for acid chlorides is "-anoyl chloride"/

The functional group is always on the terminal carbon (numbered as "1").

Preparation

Acid chlorides are prepared by reacting a carboxylic acid with thionyl chloride:

Reactions

All reactions of acid chlorides produce HCl gas as a byproduct, except amide formation (which only liberates HCl gas when a primary amide is made, with heat provided).

WITH WATER

Acid chlorides do not dissolve in water because they react with water molecules instead:

ESTERIFICATION

Acid chlorides are a very efficient way to make esters, because the reaction is not reversible:

AMIDE FORMATION

Reacting with ammonia and heat will produce a primary amide, with ammonium chloride as a byproduct.

Reacting with amines will produce secondary and tertiary amides, with an amino salt as a byproduct.

Carboxylic Acids

Carboxylic Acids are another important organic compound. This is primarily because they give compounds characteristic properties (being that they are weak acids), and they are also important precursors to other useful organic functional groups (amides and esters, especially).

Nomenclature

The carboxylic acid functional group is always on the terminal carbon (the carbon that we number as "1"). We name the compound from that carbon chain length, and any additional functional groups and/or side chains:

Preparation

Carboxylic acids are prepared (made) by oxidising a primary alcohol under reflux.

This was already covered in this blog post: Oxidation of Alcohols

Reactions of Carboxylic Acids

Carboxylic acids have all of the same reactions as other acids:

• with metals to produce hydrogen gas and a metal salt (e.g. magnesium ethanoate)
• with oxides/hydroxides to produce water and a salt (neutralisation)
• with carbonates/hydrogen carbonates to produce water, carbons dioxide and a salt

Their reaction rates are low because they are weak acids (lower hydronium ion concentrations than strong acids).

Their organic reactions are:

1. CHLORINATION

The reaction with thionyl chloride will produce an acid chloride:

Like chlorination of an alcohol, this is an example of nucleophilic substitution. As two small molecules (sulfur dioxide and hydrogen chloride) are produced, it could also be considered to be a condensation reaction.

2. AMIDE PRODUCTION

Another form of condensation reaction produces and amide:

Note that there are two steps in this reaction. Without the additional heat, the reaction would stop at the production of the ammonium salt (ammonium propanoate).

3. ESTERIFICATION

There are two ways to make esters. Making them from carboxylic acids is the more difficult, but safer, way. This is another example of a condensation reaction, as a small molecule (water) is removed to make the compound:

Note: Concentrated sulfuric acid is used as it is a dehydrating agent. It removes the water, driving the equilibrium in the forward direction.