First things first we’re going to look at Bronsted-Lowry theory. This was an idea brought about by two guys called Johannes Nicolaus Bronsted and Thomas Martin Lowry.
According to their theory on acids and bases, a base is a compound that reacts with hydrogen ions to make a conjugate acid. And a Bronstead-Lowry acid-base reaction is characterised by the transfer of a proton.
According to Bronstead-Lowry a substance that can accept a proton is a base.
The strength of a base is characterised by the availability of the lone pair of electrons. When the electron density of the lone pair is high then the base is able to coordinate easily to a hydrogen ion and it is a stronger base.
A substance can be both a Bronstead-Lowry acid and base. This is possible if a molecule can both accept and donate protons. Water is a good example of this, being able to accept H+ and form an oxonium ion (H30+) or donate H+ and form a hydroxide ion (OH-).
Now let’s take a closer look at amines. Amines are weak bases as they have a lone pair on the nitrogen that can act as an H^+ acceptor.
A primary amine is molecule in which a nitrogen atom forms one bond to carbon.
As amines can act as bases, they form salts when reacted with acids. The amine salts are more soluble in water than the amine.
Amine molecules are useful in transition metal chemistry as they can form dative bonds.
Much like its basicity, the lone pair on N can form dative bonds with metal ions, allowing it to form complexes. This feature is particularly useful as it allows us to create multidentate ligands.
Amino acids are amphoteric. The amine group means amino acids can display basic behaviour, while the carboxyl group means they can be acidic.
Amino acids are also essential to almost all forms of life – and I mean essential!
They are the building blocks in proteins. DNA molecules code for individual amino acids that combine together in a string of peptide bonds to form a protein.
Proteins are the way in which DNA controls the body. The peptide bonding of amino acids is absolutely essential, because who knows where we would be without DNA!
Now let’s take a look at some examples and uses of amines.
Diazo compounds are commonly used for dyes. It is able to absorb light in the coloured part of the spectrum, and so we can make dyes.
Furthermore, by adapting the substituent groups (eg aromatic rings), we can change the wavelength of absorption and tune the colour.
To form diazonium ions, we need to react amines with nitrous acid; but nitrous acid is highly unstable. So we produce it in situ by adding sodium nitrite and dilute acid to the reaction vessel.
We react a diazonium with phenylamine or phenol in a coupling reaction. They are called coupling reactions as they involve bonding two aromatic rings via a diazo bridge.
Polyethenols might be very useful in clothes washing tablets. Polethenols are extremely useful as they are a moldable plastic that is soluble. We can contain washing powder within a polyethenol bag, which then dissolves when put in a washing machine – handy!