chemistry module 6 carboxylic acids and esters

when are carboxylic acids water soluble and why

when they have fewer than six carbon atoms per molecule. because water molecules can form hydrogen bonds with the functional group

what is produced when a carboxylic acid reacts with a metal

a salt and hydrogen gas

what is produced when a carboxylic acid is reacted with a metal oxide

a metal salt and water

what is produced when a carboxylic acid reacts with an alkali

salt and water

what is produced when a carboxylic acid is reacted with a carbonate

a metal salt, water, and carbon dioxide

nomenclature of esters

remove -oic acid from the carboxylic acid and replace with -oate, the alkyl chain attached to the oxygen atom of the -coo- group is then added as the first word in the name. eg methyl ethanoate

characteristics of esters

sweet and fruity smells

what is esterification

prepared from a condensation reaction between a carboxylic acid and alcohol with concentrated h2so4 as a catalyst.

reversible reaction.

slow reaction.

low yields

equation for propanol with ethanoic acid

hydrolysis of esters

Esters can be hydrolysed to reform the carboxylic acid and alcohol by either dilute acid or dilute alkali and heat

When an ester is heated under reflux with dilute acid (eg. sulfuric acid) an equilibrium mixture is established as the reaction is reversible

equation for ethyl propanoate and water

what happens if u heat the ester under reflux with dilute alkali

heating the ester under reflux with dilute alkali (eg. sodium hydroxide) is an irreversible reaction as the ester is fully hydrolysed

This results in the formation of a sodium carboxylate salt which needs further acidification to turn into a carboxylic acid

what are acyl chlorides

Due to the increased reactivity of acyl chlorides compared to carboxylic acids, they are often used as starting compounds in organic reactions

Acyl chlorides are compounds that contain an -COCl functional group and can be prepared from the reaction of carboxylic acids with liquid sulfur dichloride oxide

uses of acyl chlorides

Acyl chlorides are reactive organic compounds that undergo many reactions such as addition-elimination reactions

In addition-elimination reactions, the addition of a small molecule across the C=O bond takes place followed by elimination of a small molecule

examples of addition - elimination reactions

Hydrolysis

Reaction with alcohols and phenols to form esters

Reaction with ammonia and amines to form amides

hydrolysis of acyl chlorides

results in the formation of a carboxylic acid and HCl molecule

This is an addition-elimination reaction

A water molecule adds across the C=O bond

A hydrochloric acid (HCl) molecule is eliminated

formation of esters from acyl chlorides

Acyl chlorides can react with alcohols and phenols to form esters

The reaction with phenols requires heat and a base

why are acyl chlorides more useful in the synthesis of esters than carboxylic acids

reaction of carboxylic acids with phenol and alcohols is a slower reaction as carboxylic acids are less reactive and the reaction does not go to completion (so less product is formed)

formation of amides from acyl chlorides

Acyl chlorides can form amides from their condensation reaction with amines and ammonia

The nitrogen atom in ammonia and amines has a lone pair of electrons which can be used to attack the carbonyl carbon atom in the acyl chlorides

The product is a primary amide (when reacted with ammonia) or secondary amide (when reacted with primary amines)