Carboxylic acids contain the carboxyl group
They are named after the alkane with the same number of carbon atoms. The ending -ane is changed to -anoic acid. Some examples are:
|Formula||Systematic Name||Common Name|
|HCO2H||Methanoic acid||Formic acid|
|CH3CO2H||Ethanoic acid||Acetic acid|
|HO2C-CO2H||Ethanedioic acid||Oxalic acid|
The C=O and the OH of the carboxyl group are so close that they modify each other's properties, hence carboxylic acids have many reactions which are different from those of both alcohols and carbonyl compounds. Aromatic carboxylic acids have many properties in common with aliphatic ones.
The C in the -CO2H group is always given the number 1 when naming substituted carboxylic acids, e.g.:
Carboxylic acids are soluble in water because they can form hydrogen bonds with water.
In water carboxylic acids form weak acid solutions. An equilibrium is set up:
Carboxylic acids are stronger acids than alcohols and phenols. It is the stability of the anion formed from the acid which decides how strong the acid is. If the negative charge on the oxygen can be shared with other atoms, the anion will be more stable and more of it will be made. The electric charge is spread out by delocalisation.
Benzoic acid is stronger than ethanoic acid because the negative charge on the carboxylate ion is delocalised in the benzene ring and hence the ion is stabilised more readily.
Carboxylic acids form salts with metals, alkalis and metal carbonates.
Here sodium ethanoate, CH3CO2Na, is formed.
The evolution of carbon dioxide from carbonates and hydrogencarbonates is used as a test to distinguish carboxylic acids from phenols.
Carboxylic acids react with alcohols in the presence of an acid catalyst, e.g. concentrated hydrochloric acid, to form esters.
(Ethyl ethanoate, CH3CO2C2H5, formed)
Carboxylic acids react vigorously with phosphorus pentachloride to produce an acyl chloride.
Carboxylic acids are reduced to alcohols by lithium tetrahydridoaluminate (lithium aluminium hydride), LiAlH4.
Amines are organic derivatives of ammonia. They are derived from ammonia by the replacement of hydrogen atoms in ammonia by alkyl or aryl groups. If one hydrogen is replaced, the amine is a primary amine; if two hydrogens are replaced, a secondary amine results; if three are replaced, a tertiary amine results.
The alkyl groups in secondary and tertiary amines need not all be the same.
The prefix amino is sometimes used to indicate the NH2 group, e.g.:
An aromatic amine has the nitrogen atom directly attached to the benzene ring.
The nitrogen atom in ammonia has a lone pair of electrons on it. The lone pair of electrons are responsible for ammonia being:
Amines similarly have a lone pair of electrons and have these properties too.
Amines can form hydrogen bonds with water.
Due to this strong attraction between amine molecules and water molecules, amines with small alkyl groups are soluble. Amines with larger alkyl groups are less soluble because the alkyl groups disrupt the hydrogen bonding in water.
The lone pair of electrons on the nitrogen can take part in dative bonding. It can accept a hydrogen ion, hence it acts as a base.
The presence of hydroxide ions makes the solution alkaline.
As amines are bases, they can react with acids to form salts.
Ammonia is an effective ligand because the lone pair of electrons on the nitrogen can dative bond to transition metal. Amines behave in a similar way.
Ammonia can act as a nucleophile with the lone pair of electrons attacking electrophiles such as halogenoalkanes.
Amines can act in a similar way:
Dimethylamine, (CH3)2NH, formed here.
Amines will also react with acyl chlorides to form an amide.
is an example of a secondary amide.
Amides contain the group:
Primary amides are formed when ammonia is reacted with an acyl chloride:
Secondary amides are formed when an amine is reacted with an acyl chloride:
Amides are hydrolysed when refluxed with either acid or alkali.
Part of this site was last updated on 21st January 2009.
This work is licensed under a Creative Commons Attribution-NonCommercial 2.0 England & Wales Licence.
Copyright © Article Gems 2006-09.