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 II R - 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 II R - 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 acidethanoic acidpropanoic acid O O O II II II H - C - OH CH 3 - C - OH CH 3 – CH 2 - 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

AlcoholAcidEster producedSmell MethanolButanoic acidMethyl butanoatePineapple MethanolBenzoic acidMethyl benzoateMarzipan MethanolSalicylic acidMethyl salicylateWintergreen EthanolMethanoic acidEthyl methanoateRaspberry/rum EthanolEthanoic acidEthyl ethanoatePear drops/nail-varnish remover EthanolButanoic acidEthyl butanoatePineapple Propan-1-olEthanoic acidPropyl ethanoatePear Pentan-1-olEthanoic acidPentyl ethanoateBanana Pentan-1-olButanoic acidPentyl butanoateApricot/pear Pentan-1-olPentanoic acidPentyl pentanoate(Pine)apple 3-methylbutan-1-ol (isoamyl alcohol) Ethanoic acid3-methylbutyl ethanoateBanana/bee alarm pheromone Octan-1-olEthanoic acidOctyl ethanoateOrange Phenylmethanol (benzyl alcohol) Ethanoic acidBenzyl ethanoatePeach