10.4 Carboxylic Acids and Esters

Carboxylic Acids

• These are compounds with a carboxyl group, which consists of a carbonyl group and a hydroxyl group (an OH group like in alcohols)

• The general structural formula is: O IIR - C - OH

• this can be written: R-COOH

Carboxylic Acids

• They are weak acids due to their slight ionization in water to release a hydrogen ion.

O O

II IIR - C - OH(aq) R - C - O-

(aq) + H+(aq)

Naming Carboxylic Acids

• In order to name these compounds: • First, identify the longest parent chain with

the carboxyl group. • Then drop the -e ending and add the

ending -oic and the word acid.

The first three Carboxylic Acids

• methanoic acid ethanoic acid propanoic acid

O O O II II II H - C - OH CH3 - C - OH CH3 – CH2 - C - OH

Polycarboxylic Acids

• You do not have to memorize these names and condensed formulas, all you must recognize is that these are carboxylic acids.

Properties of Carboxylic Acids

• Like other organic derivatives many of these compounds have common names, derived from the origin of the acid.

• Carboxylic acids are widely distributed in nature.

• They are present in all cells and are a component of fats.

• Fatty acids are carboxylic acids in fact.

Properties of Carboxylic Acids

• The common name for methanoic acid is formic acid since it is found in ants (the Latin for ant is formica).

• For ethanoic acid the common name is acetic acid, from acetum (Latin for sour wine, as in vinegar).

Properties of Carboxylic Acids

• Short chain carboxylic acids are volatile liquids with sharp, unpleasant odours such as sweaty feet, vomit and rancid butter.

• Tracker dogs follow the trail of carboxylic acid smell from the body odour of the subject.

• The polar nature of the carboxyl group allows these organic acids to be misable with water.

• Larger chain organic acids are waxy solids that are insoluble in water, but will dissolve in solvents such as ethanol or propanone.

Esters

• A compound called an ester is composed of an alcohol and a carboxylic acid.

• The process to create an ester is simply called esterfication.

Formation of an Ester

• Since water is eliminated in the process of this reaction, it may be called a condensation reaction.

Naming Esters

• We name esters by identifying the alcohol chain, dropping the -ol, and adding –yl.

• Then we name the acid by dropping the -ic acid and adding -ate.

Properties and Occurrence of Esters

• Lower molecular weight esters are colourless, volatile liquids that are soluble in water.

• Higher molecular weight examples are colourless, waxy solids that are insoluble in water.

• All esters have characteristic strong “fruity” smells and are soluble in non-polar organic solvents.

• Esters are themselves good organic solvents.

Properties and Occurrence of Esters

• Esters break down into their respective organic acid and alcohol from which they are formed.

• This process is called hydrolysis. • When sodium hydroxide is added to an

ester, for example to ethyl ethanoate, a salt, sodium ethanoate is formed along with ethanol.

Properties and Occurrence of Esters

• The reaction is shown below:

• Hydrolysis of an ester with an alkaline solution like sodium hydroxide is known as saponification.

• This reaction is used in the preparation of soaps from fats, which are esters of glycerol and fatty acids.

Properties and Occurrence of Esters

• Esters are found widely in nature as the flavour and odors of flowers, fruits and nuts.

• They are manufactured as artificial perfumes or scents and artificial food flavours that are added in many edible items like ice creams, soft drinks, sweets, etc.

• In industry, esters are used as solvents for making cellulose, fats, paints and varnishes and in the pharmaceutical industries. 

• Esters are also used as softeners in plastic and molding industries.

butan-1-ol

hexan-1-ol

octan-1-ol

2-methylpropan-1-ol

butan-2-ol

Alcohol Acid Ester produced Smell

Methanol Butanoic acid Methyl butanoate Pineapple

Methanol Benzoic acid Methyl benzoate Marzipan

Methanol Salicylic acid Methyl salicylate Wintergreen

Ethanol Methanoic acid Ethyl methanoate Raspberry/rum

Ethanol Ethanoic acid Ethyl ethanoate Pear drops/nail-varnish remover

Ethanol Butanoic acid Ethyl butanoate Pineapple

Propan-1-ol Ethanoic acid Propyl ethanoate Pear

Pentan-1-ol Ethanoic acid Pentyl ethanoate Banana

Pentan-1-ol Butanoic acid Pentyl butanoate Apricot/pear

Pentan-1-ol Pentanoic acid Pentyl pentanoate (Pine)apple

3-methylbutan-1-ol (isoamyl alcohol)

Ethanoic acid 3-methylbutyl ethanoate Banana/bee alarm pheromone

Octan-1-ol Ethanoic acid Octyl ethanoate Orange

Phenylmethanol (benzyl alcohol)

Ethanoic acid Benzyl ethanoate Peach