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Name: Robert
Status: other
Grade: other
Location: CA
Country: USA

Can you tell me the difference between Amyl Alcohol and Isopropyl Alcohol and why the amyl is recommended for cleaning plastics over Isopropyl? Does the Isopropyl dry things out where the Amyl does not? Please clarify.


Both isopropyl and amyl alcohols are indeed alcohols (having a polar OH functionality). The difference is that isopropyl alcohol has three carbons and the OH is attached to the middle carbon. Amyl alcohol, on the other hand, is a class of alcohols having five carbons. These carbons can be attached together in a straight line with the OH at the end (n-pentyl alcohol) or the carbons could be arranged in all sorts of manner with the OH attached in many different carbon positions. As such, commercial amyl alcohol is most likely a mixture of different 5-carbon alcohols.

I am not sure as to why amyl alcohol is the preferred cleanser for plastics. I can only guess that some plastics are more soluble in isopropyl alcohol rather than the amyl alcohol mixture. As such, isopropyl alcohol may cause some damage to the surface of the plastic (the plastic will lose its sheen).

Greg (Roberto Gregorius)

Be aware that there are several different "amyl" alcohols. The general formula is:


but the carbons can be put together in a number of configurations. It has a lower vapor pressure than isopropanol, and is more hydrophobic than isopropanol. I am unaware of any general preference of one over the other. It depends upon what "plastic" is being cleaned and what is being removed from the surface of the plastic.

Vince Calder

Hi Robert,

I found your question a little puzzling. As an engineer with years of experience with a wide range of plastics, I have never once run across any recommendation to use amyl alcohol for cleaning purposes. For many plastics such as nylon, polyester, ABS, and especially solvent- sensitive polycarbonate (Lexan), isopropyl alcohol is recommended for cleaning purposes. In fact, because of polycarbonate's high solvent sensitivity, the only universally recommended cleaning solvent for this plastic is isopropyl alcohol.

The main difference between n-amyl and isopropyl alcohols (in this context) is the length of the hydrocarbon "backbone". N-amyl alcohol's carbon chain is 5 carbon atoms long, whereas isopropyl alcohol's carbon chain is only 3 carbons atoms long. The result is that isopropyl alcohol is more volatile and therefore evaporates faster after it is used for cleaning.

Neither of these alcohols "dries out" plastic, since there is no water (or any other substance) in plastic to "dry out" in the first place. Both of these alcohols act as both polar and non-aggressive non-polar solvents, which is very advantageous for cleaning. Acting as polar solvents, they are able to dissolve polar contaminants such as salts, and other water soluble contaminants.

Both of these alcohols are also able to dissolve non-polar contaminants such as oils and greases, with isopropyl alcohol acting as a somewhat more aggressive non-polar solvent because of its shorter carbon "backbone" and therefore lower molecular weight. Unlike many hydrocarbon solvents, neither of the two alcohols are damaging to any common plastics.

To summarize, when comparing the two, isopropyl alcohol is the cleaning solvent of choice for most plastics. Unlike normal-amyl alcohol, which is not easily available, 99% isopropyl alcohol is available at any drugstore. Isopropyl is better at removing oily deposits, and dries faster after use.

Bob Wilson

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