# Isopropyl alcohol forming peroxides

I read in many MSDS that Isopropyl alcohol tends to form peroxides (by reacting to air OR light) which may explode when they reach a given concentration.

For example: http://nj.gov/health/eoh/rtkweb/documents/fs/1076.pdf or http://www.hvchemical.com/msds/isal-70.htm as well as many others.

I own a few liters of isopropyl alcohol (a few bottles) and I'm getting concerned. It came in standard transparent (polypropylene I suppose) bottles with a plastic bag wrapped around it (I suppose to prevent contact with air). I only keep one bottle ready to use, all the others are as when I bought them (with plastic bag wrapped around it), stored in a relatively cool (<= 25°C) dark area of my house.

This is at home and I couldn't find any fire resistant storage cabinet in my area.

Now, I'm not sure if I understand the datasheet correctly, but as far as I understood the problem lies with the opened bottle (which I open and close regularly) and not with the air-tight never opened other bottles, right? Therefore a simple solution may be to say: after one year I empty the opened bottle, trash it away and buy another one. Should this be enough?

• Is it pure isopropanol? For example, most "rubbing alcohol" that you would by at the supermarket or pharmacy is 30-80% (the remainder water). The presence of water decreases the peroxide danger. – Ben Norris Apr 9 '13 at 1:01
• Pure. Isopropanol >= 99.9%. – user51166 Apr 9 '13 at 4:23

I think this may be an overreaction. First, MSDS are designed for workers working with industrial quantities in industrial conditions. Second, the danger comes from concentration of the peroxide from evaporation or, more typically, distillation. Small quantities of peroxides in solution are not usually an explosion hazard. Third, I have never seen isopropanol listed in lists of hazardous peroxide prone chemicals as used by lab safety departments (ethers are the typical risk here). The closest I have seen is sec-butanol, which is the secondary alcohol from butanol, and I've only seen this listed once, in a list that seemed much more cautious than some other lists. Isopropanol is the secondary alcohol from propanol. Given your storage, cool and dark, I think you are fine. Remember that 91% isopropanol is sold in drugstores, though these may contain stabilizers and you larger bottles may not.

But having said all this, Lighthart's brief answer is correct though probably unlikely. If you DO see any crystals, don't even try to open the bottle (crystals in the threads are the most common source of explosion). But again, seems unlikely.

If you are still concerned, there are peroxide test strips you can buy that are very easy to use and can tell you what concentration of peroxides are present.

• I bought my isopropanol directly from a chemical supply. It's isopropanol > 99.9%. Would your remark still apply? – user51166 Apr 9 '13 at 4:25
• Sure, and Ben Norris' answer essentially agrees with mine. Peroxides did form from ancient bottle after concentration by distillation. And he also recommended test strips. So at the moment, I'd say you're fine. – user467 Apr 9 '13 at 11:05
• Please pardon me if I sounded alarmist. Chemists work all day to make awesome crystals, and most are curious when some high quality crystals actually form. It is natural to investigate closely – Lighthart Apr 9 '13 at 17:08

Isopropanol is not one of the notorious peroxide formers, but it will eventually do so in the presence of oxygen (with or without light - the process is autocatalytic).

When I was a graduate student TA in an organic chemistry class, isopropanol was a distillation "unknown". However, the "unknown" bottle had probably been in existence for 20 years and was periodically refilled. Some of the isopropanol had been around in the presence of air for a long time. While the bottle never developed the crystals typical of ether peroxides, peroxides did form. Our proof was the explosion of three distillations using the stuff. Fortunately no one was injured.

There is a qualitative test for the presence of peroxides. Buy yourself some KI Starch test paper. KI reacts with oxidants to produce $\ce{KI3}$, which binds with starch to form a blue-purple complex. This chemistry is also the basis of the famous iodine clock reaction.

$$\ce{ROOH + 2H+ + 3I- -> ROH + H2O + I3-}$$ $$\ce{I3- + starch -> [I3-starch]^-} \ \ \text{(blue)}$$

• I assume therefore that never opened bottles are not a concern at all, right? Once opened a bottle lasts about a year so it should be fine from what you've been saying, right? – user51166 Apr 9 '13 at 18:23
• The unopened bottle has headspace. Unless otherwise labeled, that headspace is probably air. Unopened bottles can be dangerous, too. When in doubt, dispose of it. – Ben Norris Apr 9 '13 at 18:27
• There is a very small headspace. But if they're only 1-5 years old? – user51166 Apr 9 '13 at 18:48

Not quite enough. If you ever see crystals in the bottle, year old or otherwise, evacuate and call the bomb squad.

• It sounds alarmist; But I assume that you just left out that it is improbable that peroxide crystals form. (That's said elsewhere.) It is not alarmist to say that in case peroxide crystals did form, it's time to be alarmed. – Volker Siegel Sep 7 '16 at 0:57
• I give you my sincerest hopes you never see the crystals, yes. – Lighthart Sep 7 '16 at 4:15