Although isopropyl alcohol and denatured alcohol have some similar uses, they belong to different alcohol groups.
As a result, they have distinct formulas, structures, reactions, and toxicity levels. In this post, we consider the differences between isopropyl alcohol and denatured alcohol in more detail, along with their respective uses and limitations.
In this post:
Isopropyl alcohol vs. denatured alcohol
Chemical structure and properties
Chemically speaking, all types of alcohol have a hydroxyl functional group attached to an aliphatic carbon in an alkyl group chain. Hence, the generic formula of alcohol is ROH. The R group can be any alkyl group or a radical form of alkane chain, which is missing hydrogen.
However, if we take a closer look at the structure and properties of both isopropyl alcohol and denatured alcohol, you’ll see there are some key differences.
Isopropyl alcohol (IPA)
Isopropyl alcohol, popularly known as rubbing alcohol, is concentrated isopropanol that has been blended with anywhere between 5% and 30% water. Its chemical formula is C3H8O. Unlike ethanol, IPA isn’t suitable for human consumption.
Isopropyl alcohol is the simplest example of a secondary alcohol, a type of compound where the carbon atom of the hydroxyl group is attached to 2 alkyl groups.
Discovered in 1920, it was the first commercially viable synthetic alcohol ever produced. Chemists working at the Standard Oil Company of New Jersey (later Exxon Mobil) synthesised it while studying by-products of petroleum. It’s now one of the most widely used solvents in the world.
Isopropyl alcohol can be produced from the chemical reaction between propylene and sulphuric acid, which is then followed by hydrolysis.
Denatured alcohol
Denatured alcohol is classified as a primary alcohol, which means the carbon atom of the hydroxyl group is only attached to one alkyl group.
It’s essentially ethanol (CH3CH2OH) that’s been treated with denaturants in order to become poisonous and repellent to humans. These additives include toxic or foul-tasting substances such as methanol, benzene, pyridine, castor oil, gasoline, acetone, and isopropyl alcohol. Sometimes dye is also added to make it easily distinguishable from drinkable alcohol.
Denatured alcohol typically contains around 90% pure ethanol and 5% toxic denaturants. It’s industrially used as a solvent, cleaning liquid, and fuel. The poisonous additives are mixed with ethanol to avoid paying beverage taxes, thereby reducing the cost.
Comparing toxicity and safety
Both isopropyl alcohol and denatured alcohol are unsuitable for human consumption. Even drinking small amounts can cause dizziness, nausea, confusion, blindness, coma, and even death.
While both of these alcohols are toxic, denatured alcohol is a more potent poison because it contains other dangerous additives.
Isopropyl alcohol
Although isopropyl alcohol is classified as a toxic substance, meaning that it’s dangerous to consume and behaves as a mild skin irritant, it’s generally safe to use.
Unlike denatured alcohol, isopropyl alcohol has not had anything but water added to it. However, IPA is toxic in itself and should never be ingested.
Denatured alcohol
Denatured alcohol isn’t toxic by nature – it’s deliberately made toxic by adding poisonous agents. Methanol is the most common chemical used to denature ethanol – this is why denatured alcohol is often referred to as ‘methylated spirit’.
Methanol is extremely toxic to humans. Whereas ethanol is metabolised by alcohol dehydrogenase in the body to create acetaldehyde, which is then quickly removed, the same enzyme metabolises methanol into a highly toxic poison called formaldehyde. This causes methanol poisoning, which can be lethal.
When it comes to inhalation and exposure risks, denatured alcohol is more dangerous than isopropyl alcohol. In this way, while IPA is a toxic substance and should not be consumed, denatured alcohol is more dangerous when it comes to inhalation and exposure risks.
Industrial and medical applications
Both isopropyl alcohol and denatured alcohol are used as disinfectants. However, only isopropyl alcohol is used as a rubbing alcohol and hand sanitiser, either in 40% or 70% concentrations by volume in water. This is because denatured alcohol can easily irritate and dry the skin.
Isopropyl alcohol is also commonly used to clean medical instruments such as scalpels and disinfect wounds or the skin before surgery, as well as in the preparation of tinctures of iodine for a more potent disinfectant.
Reagent-grade denatured alcohol can be as high as 95% ethanol and 5% methanol and other additives. This type of denatured alcohol is an effective solvent, which means it can be used in the manufacture of things like cosmetics, astringents, and anti-foaming agents. It’s also commonly used as an industrial cleaning agent and fuel for alcohol burners and camping stoves.
Limitations of isopropyl alcohol
Despite its many industrial and medical applications, isopropyl alcohol does have a few limitations.
For example, IPA isn’t suitable for mixing shellac, a natural resin that woodworkers use to give their pieces a lustrous finish. To ensure it’s fresh, carpenters often make the solution themselves by dissolving shellac flakes in denatured alcohol.
Isopropyl alcohol shouldn’t be used instead of denatured alcohol due to its lower concentration and water content (water may cause problems due to its slow evaporation rate).
Its toxicity also means isopropyl alcohol can’t be used in food preparation or food processing. And while IPA can technically be used for sample preservation, it has to be 90% concentration, which is generally difficult to obtain.
Limitations of denatured alcohol
While denatured alcohol makes an effective cleaning agent, it can’t be used as an antiseptic. Because denatured alcohol contains methanol, along with several other toxic chemicals, it can potentially cause skin irritation, severe reactions or even poisoning.
Denatured alcohol also has a few other limitations. For example, it shouldn’t be used to clean electronics (IPA is better suited to this job). This is because the chemicals that have been added to denatured alcohol could leave behind residues on the sensitive components after the ethanol has evaporated.
Legal and environmental considerations
You can legally keep small quantities of both isopropyl and denatured alcohol in your house – just make sure it’s out of reach of children and pets. It’s a good idea to store isopropyl rubbing alcohol in your medicine cabinet, while larger containers of denatured alcohol are best kept in a garage or workshop.
However, there are various legal and environmental issues to consider if you require bulk quantities of alcohol for industrial or manufacturing purposes. Whatever the intended use, always check the local or national regulations on environmental safety for storing and disposing of these chemicals.
For example, here in the UK, you may want to review HMRC’s Excise Notice 473 regarding the production, distribution, and uses of denatured alcohol. You should also read the product’s material safety data sheet (MSDS) carefully. At ReAgent, you’ll find safety data sheets for all of the chemicals we supply on our website.
We sell top-grade IPA and denatured alcohol products in a variety of batch sizes. Our chemicals are ISO-quality-approved and available for next-day delivery. Get in touch with our expert team today to see what we can offer you.
