What is nitrous oxide?
One of the oxides of nitrogen.
Chemical formula: N₂O
Structural formula: N=N=O
Molecular shape: linear
Melting point: -90.86ºC
Boiling point: -88.48ºC
Molecular weight: 44.013 g/mol
Appearance: colourless gas
Density: 1.977 g/L
Enthalpy of Formation: +82.05 kJ/mol
History
It was first discovered by Joseph Priestley in 1772 - making it 251 years old in the year 2023. To put this into context, John Dalton discovered the ‘atom’ in 1808 when he found that chemicals always had whole number ratios of atoms (although the concept of being made of ‘tiny particles’ has been around since 400 B.C.). We didn’t even know ‘atoms’ existed when N₂O was discovered. He created it by heating ammonium nitrate in the presence of iron fillings, and then passing the gas that came off through water to remove unwanted by-products. Although this wasn’t Priestley’s only discovery - he was also the first to isolate gases such as carbon monoxide, oxygen, carbon dioxide, ammonia and sulphur dioxide.
Shortly after in 1799, Sir Humphry Davy (a chemist with numerous contributions to science) decided it was a superb idea to try inhaling N₂O. At the time they knew that an organism would suffocate in the absence of air, yet this wasn’t enough to put Sir Humphrey off. Fortunately for him, the gas wasn’t toxic in the short term. The effects were rather exciting: flushed cheeks, giddiness, intense pleasure, and vivid thoughts. Soon he was administering the gas to his patients, family, and friends and it wasn’t long before the gas was used as a form of entertainment at social gatherings. He recorded his findings in his publication: “Researches, Chemical and Philosophical, chiefly concerning Nitrous Oxide and its Respiration”.
Later, Gardner Quincy Colton (a medical school dropout) began hosting N₂O exhibitions around the US. It was at one of these that Dr Horace Wells (a dentist) noticed something peculiar: a man who had volunteered to inhale the gas injured his leg shortly after inhalation however it wasn’t
after some time had passed that he began to feel the pain. It occurred to Dr Wells that N₂O could possess painkilling properties. To further investigate, Dr Wells asked Colton if he could administer N₂O to him while another dentist (John Riggs) extracted one of Dr Wells’ molars. Success. Dr Wells felt no pain during the procedure. Subsequently in 1868, N₂O became an anaesthetic which is now used during childbirth, in ambulances and in dentistry.
Applications and Mechanism of Action
As said previously, it’s used as an anaesthetic. A key characteristic that N₂O has is its high lipid solubility which allows it to diffuse across the cell membranes of the cells lining the alveolus. The other gases present in the alveolus provide additional driving pressure for forcing the anaesthetic substance (N₂O) into the bloodstream. It is thought that N₂O interferes with GABA (Gamma-aminobutyric acid) receptors, these receptors are responsible for reducing the activity of neurones. High-dose exposure for up to 6 hours for purposes in clinical anaesthesia is rendered harmless when administered under the expertise of healthcare professionals.
Due to its unreactive nature, another use is in aerosols as a substitute for CFCs which have ozone-depleting qualities. When heated sufficiently N₂O can decompose into N₂ and O₂.
Misuse
In 2015, nitrous oxide was the second most popular recreational drug after cannabis. Side effects include dizziness, disorientation, weakness in the legs and loss of balance. In more serious cases, asphyxiation can occur due to the lack of oxygen supplied to the lungs.
N₂O also deactivates vitamin B12, consequently causing its deficiency. The deactivation occurs by N₂O irreversibly oxidising the cobalt ion at the centre of vitamin B12. Heavy use has also been associated with nerve damage and paralysis.
The Crime Survey for England and Wales found that 3.9% of 16-24 year-olds used N₂O in the year ending June 2022.
That’s around 230,000 people. You’ve almost definitely seen empty canisters of N₂O at some point. In 2016 selling N₂O for recreational use was made illegal, however, it’s argued that this can be difficult to prove especially for online vendors.
By Roshan