4.5 Carboxylic Acids and their Derivatives

Functional group of carboxylic acids

COOH

Solubility of carboxylic acids

The COOH group is polar so it will undergo hydrogen bonding with water molecules

As carbon chain length increases solubility decreases

Acidity of carboxylic acids

Weakly acidic

Relative acidity of carboxylic acids, phenols and alcohols/water

Carboxylic acid > phenol > alcohol/water

Reaction of a carboxylic acids with metal

Forms a salt and hydrogen gas, seen as effeversence in solution

Reaction of carboxylic acids with bases

Forms a salt and water

Reaction of carboxylic acids with carbonates

Forms a salt, carbon dioxide and water

How to distinguish between a carboxylic acid and a phenol/alcohol

Aqueous sodium hydrogen carbonate

Carboxylic acid will produce bubbles of carbon dioxide gas, phenol will not

How to increase the acidity of a carboxylic acid or phenol

Addition of substituent groups e.g a halogen

How to form an aliphatic carboxylic acid

Oxidation of alcohols with acidified potassium dichromate

Heat and reflux

Observation of oxidising an alcohol with acidified potassium dichromate

Orange to green colour change

Aromatic carboxylic acid

The COOH group must be directly attached to the benzene ring

How to form an aromatic carboxylic acid

Oxidising an alcohol or aldehyde group that is directly attached to the benzene ring using acidified potassium dichromate

Oxidising an alkyl side chain using hot alkaline potassium manganate (alkaline due to the addition of NaOH)

Oxidising an alkyl side chain to produce an aromatic carboxylic acid

Irrespective of the length of the alkyl side chain, benzenecarboxylic acid will be produced

The alkaline potassium manganate is reduced to a brown-black sludge of manganese oxide

The sodium salt of the benzenecarboxylic acid forms, and HCL is added to reprotonate the salt to produce benzenecarboxylic acid

Reducing agent required to reduce a carboxylic acid

LiAlH4

Balanced equation for the reduction of carboxylic acids

Carboxylic acid + 4[H] ——> alcohol

Decarboxylation

The removal of carbon dioxide from a compound

Soda lime

A mixture of calcium hydroxide with sodium or potassium hydroxide

What does heating a carboxylic acid with soda lime cause

The removal of a molecule of CO2 resulting in an alkane that has 1 less carbon in its chain

How can decarboxylation occur without the use of soda lime

Using the calcium salt of an acid

Upon heating CO2 is removed, producing a ketone that has a longer chain length than the original salt

Conversion of carboxylic acids to esters

Carboxylic acid + alcohol

Warm under reflux with conc sulfuric acid catalyst

Forms ester + water

How to make an ester from acid anhydrides

Gently heat alcohol with acid anhydride

No need for acid catalyst

How to name an ester

First part relates to the alcohol

Second part relates to the carboxylic acid or acid anhydride

Ester functional group

C=O

I

O

Acid hydrolysis of esters

Heat ester under reflux with dilute sulfuric acid catalyst

Will produce the carboxylic acid and alcohol

Base hydrolysis of esters

Heat ester under reflux with aqueous sodium hydroxide catalyst

Leads to the production of the salt of the carboxylic acid due to the reaction between the acid and the base catalyst

How to produce a carboxylic acid from its salt

React with dilute acid to reprotonate the salt

Acid chloride functional group

C=O

I

Cl

Conversion of a carboxylic acid to an acid chloride

React carboxylic acid with SOCl2 under cold conditions and without the presence of water

Produce acid chloride and HCL

How to convert a carboxylic acid to an amide

React the acid with basic ammonia to give the ammonium carboxylate salt

Heat the salt, water is lost and the amide is produced

OR

Heat the acid with urea at 120 degrees C

Conversion of resulting amide to nitrile (C=-N)

Heat with P4O10

Formation of nitriles from halogenoalkanes

Heat the haloalkane with KCN under reflux

Acid chloride to amide

Add concentrated ammonia without heating

Hydrolysis of nitriles

Heat the nitrile under reflux with dilute acid

Hydrolysis of amides

Heat the amide under reflux with aqueous NaOH

Acidify to produce carboxylic acid with dilute acid

Reduction of nitriles to amines

Produces compounds with longer carbon chains

Using a solution of LiAlH4 in ethoxyethane