Isopropyl alcohol and denatured alcohol both have a variety of applications in a range of industries. But what is the difference between these alcohols, and is it safe to use them interchangeably?
In chemistry, alcohols are organic compounds where the hydroxyl group (-OH) is attached to a carbon atom. Alcohol comes in many different structures and forms, but today we will only be looking at 2: isopropyl alcohol (IPA) and denatured alcohol.
Isopropyl alcohol and denatured alcohol belong to different alcohol groups. Therefore, they have different structures, formulas, and reactions. These differences are important to be aware of when thinking about their respective uses and whether one can be used instead of the other.
Difference in Structure
Denatured alcohol is classified as a primary alcohol because it is ethanol (CH3CH2OH) that has been treated with denaturants in order to become poisonous and repellent to humans. Primary alcohols are where the carbon atom of the hydroxyl group is only attached to one alkyl group.
Ethanol is a primary alcohol that is used in alcoholic beverages. Denatured alcohol can be made of around 90% pure ethanol and 5% toxic denaturants.
Secondary alcohols are where the carbon atom of the hydroxyl group is attached to 2 alkyl groups. Isopropyl alcohol is the simplest example of a secondary alcohol and is a slightly bigger molecule than ethanol, with the formula C3H8O. Unlike ethanol, IPA is not meant for human consumption – although it has not been treated with denaturants to make it this way.
Isopropyl alcohol is concentrated isopropanol that has been blended with anywhere between 5% and 30% water.
Difference in Toxicity
Although isopropyl alcohol is classified as a toxic substance, meaning that it is dangerous to consume and behaves as a mild skin irritant, it is mostly safe to use. Unlike denatured alcohol, IPA is toxic in itself. It has not had anything but water added to it, and is often used by doctors as a disinfectant and antiseptic.
While isopropyl alcohol is often referred to as a ‘surgical spirit’ because of its use in hospitals and other medical applications, denatured alcohol is referred to as a ‘methylated spirit.’ This sounds the alarm bells when thinking of its toxicity because it indicates that it includes methyl alcohol, also known as methanol.
Denatured alcohol isn’t toxic by nature like IPA – it is made toxic by being treated with poisonous agents like benzene and pyridine. Methanol is the most common chemical used to denature ethanol with, and it 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 formaldehyde, which is a highly toxic poison. This causes methanol poisoning which can be lethal. 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. Knowing this difference in toxicity is crucial when trying to identify whether uses of these 2 alcohols should be interchanged.
When Shouldn’t I Use Denatured Alcohol?
Its antibacterial properties make isopropyl alcohol an excellent antiseptic and disinfectant. As well as an efficient surface cleaner in a range of domestic, medical, and laboratory environments, isopropyl alcohol is also commonly used in hand sanitisers, surgical hand scrubs, and antiseptic solutions. It is a first-aid kit must-have for disinfecting minor cuts and scrapes. While it is a mild skin irritant, doctors still use IPA to swab your skin before an injection. This is because it is efficient at killing any surface bacteria. To read more about how this works, check out our blog on the uses of IPA.
While denatured alcohol can also be used as an effective cleaning agent, it cannot be used on skin as an antiseptic. The main reason for this is its toxicity. By containing methanol, denatured alcohol could cause dermatitis if skin is exposed to it. While IPA does have the propensity to be a skin irritant, this is only in circumstances where high concentrations have been left on the skin for long periods of time. Because denatured alcohol contains methanol, along with several other toxic chemicals which you may not be able it identify, it is generally unsafe to use as an antiseptic as it could cause severe reactions and even poisoning.
Although denatured alcohol can be used as a cleaning agent, it should not be used in place of isopropyl alcohol when it comes to cleaning electronics. 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. Comparatively, isopropyl alcohol is mostly pure and its high volatility means that no streaks or residue will be left behind after use.
As well as this, common denaturing agents like methanol, acetone, and pyridine are highly damaging to plastic. Since thin plastic coatings are often used to protect display screens, using denatured alcohol to clean them could cause damage to them after prolonged use.
When Shouldn’t I Use Isopropyl Alcohol?
While isopropyl alcohol can be used in many of the same applications as denatured alcohol, there are certain uses that denatured alcohol is more suited towards. In sample preservation, for example, IPA can be used but only in concentrations of 90% which is generally difficult to obtain.
Denatured alcohol is a more effective preserving agent for a few reasons. The presence of ethanol, for example, is able to drive out the water from the sample’s tissue. This makes it a more effective dehydrating agent which is vital in sample preservation. Because isopropyl alcohol is blended with water, it is not as efficient in this regard. To see what other uses denatured alcohol has, head over to one of our previous posts.
Shellac is used in woodwork as a lacquer. A natural resin, carpenters use shellac to give their pieces a lustrous finish, and they often mix the solution themselves to ensure that it is fresh. To do this, shellac flakes are dissolved in denatured alcohol. This creates a sticky substance which can then be easily wiped over the wood.
Denatured alcohol is used because it is extremely high proof. The typical denatured formula consists of 190-proof ethanol, 4% methanol and 1% other denaturants. This high concentration enables the denatured alcohol to dissolve the shellac flakes quickly and effectively. Isopropyl alcohol should not be substituted in this application for several reasons.
The main reason is that IPA is generally found in lower concentrations. The standard solution of 70% wouldn’t be effective as its evaporation rate would be slower, raising the chances of the shellac flakes clumping together and not completely dissolving. Isopropyl alcohol also contains water, which could also cause problems given its slow evaporation rate. Therefore, denatured alcohol shouldn’t be replaced with IPA when mixing shellac for woodwork.
Isopropyl alcohol and denatured alcohol can be alternated in some applications. Both can be used as cleaning agents, and as solvents in a variety of industries. The main difference is that IPA shouldn’t be used in certain applications because it won’t be as effective as denatured alcohol, whereas the latter shouldn’t be used to replace IPA because it is highly toxic and could be dangerous. Both alcohols have their benefits and drawbacks, and are widely used across many industries.
For comprehensive information about isopropanol, check out our Complete Guide to Isopropanol resource.
At ReAgent, 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. With ReAgent, you get to choose the packaging material, the label design, and even have the option for us to manufacture a bespoke blend for you so that all of your business needs are met at once. Get in touch with our expert team today to see what we can offer you.
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