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#1
Old 12-17-2011, 06:38 AM
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What's The Difference Between Isopropyl and Ethyl

OK the hand sanitizer I got at Walgreens says active ingredient 62% ethyl alcohol. Inactive ingredients fragerence, glycerin, isopropyl alcohol, purified water..."

The bottle says: 62% ethyl alcohol... antimicrobial

My rubbing alcohol says, 70% isopropyl alcohol and inactive ingredient: water

The rubbing alcohol says: antiseptic


So what exactly is the difference? Is it that the isopropyl won't kill microbes and the ethyel isn't antiseptic or what?

http://en.wikipedia.org/wiki/Isopropyl_alcohol

http://en.wikipedia.org/wiki/Ethanol

I read the above Wikipedia articles, but they are over my non-scientific head.

So basically if I want to use them to fight off the germs of a common cold on my hands or a desk, which to use? Or are they both ineffective? Obviously you don't drink either.

Thanks
#2
Old 12-17-2011, 06:52 AM
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Either will be moderately effective at killing germs on skin or other surfaces.

Ethyl alcohol actually is the same stuff that is in beer or wine or whatever to make you drunk, but if you buy it as hand sanitizer it will have something mixed in it to make it taste nasty (and that may be poisonous). It may be the isopropyl alcohol.

They are different chemicals. Just because both are classed as alcohols it does not follow that they are the same or will do the same thing. There are many different alcohols. Ethyl alcohol is the only one you want to have in your beer or whiskey.
#3
Old 12-17-2011, 07:46 AM
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Thanks makes sense, they add the isopropyl into the ethyl. Anyone know which would be better at killing a common cold germ?
#4
Old 12-17-2011, 09:01 AM
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Quote:
Originally Posted by BeaMyra View Post

So what exactly is the difference? Is it that the isopropyl won't kill microbes and the ethyel isn't antiseptic or what?

I'll try to clear up the chemistry and not make it complex. They're different chemical compounds, both composed of chains of carbon. The carbon chain in isopropyl is 3 carbons long and has the OH attached to the middle one. The carbon chain in ethanol is 2 carbons long. (Of course with only 2 carbons the OH is attached at the end since there's no other carbons.)

Oh interesting factoid, the mechanism your body uses to metabolize ethanol also metabolizes isopropyl alcohol and methanol. (Wood alcohol.) In those cases it turns them into acetone and formaldehyde. (Which are really toxic and are the things that hurt you if you were to drink either.)
#5
Old 12-17-2011, 09:16 AM
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they will both kill germs about the same for this situation. use both for their better application. though if you only would have one the isopropyl would be better.

the hand sanitizer is made for hands, it has some fragrance and fat in it. it might leave a residue on surfaces and be too stinky if used on everything. the ethyl alcohol in the sanitizer might harm some surfaces the isopropyl alcohol would not. it wouldn't leave as dry a feeling on your skin as isopropyl alcohol would.

the isopropyl alcohol is good for surfaces because it won't leave a residue and evaporate cleaner. it would likely be less harmful to surfaces that would be affected by alcohol chemically.
#6
Old 12-17-2011, 12:48 PM
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An important distinction

and speaking from personal experience, when one is an engineer visiting the Kingdom of Saudi Arabia and one has a bunch of supplies with him, including isopropyl alcohol, and one is trying to clear Saudi customs at Jeddah International Airport, and one is asked what this stuff is, the proper answer is cleaning solvent, not alcohol.
#7
Old 12-17-2011, 02:07 PM
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A minor hijack if I may ...

Isopropyl is commonly sold in pharmacies in (IIRC) 70% & 91% solutions with the remaining percentage of inactive ingredient being water.

For ordinary household disinfection or antiseptic use, is there any meaningful difference? It seems odd to offer two such similar products. What can 91% do that 70% can't? And why 91% versus 89, or 90, or 92%? I know isopropyl is very hygroscopic so there's a practical upper limit below 100%. But IIRC it's north of 91%.

Wiki was uninformative. Anybody got some insight?
#8
Old 12-17-2011, 03:10 PM
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At work, we use the 91% isopropyl as a shoe-stretch spray because it works better for that purpose than the 70% solution.

Other than that, I got nuthin'
#9
Old 12-17-2011, 03:49 PM
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91% isopropynol might harm some materials and a lesser strength should be used. it doesn't leave as much wetness.
#10
Old 12-17-2011, 04:23 PM
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I think that water and isopropanol codistill (and I know that water and ethanol do). I wonder if the 70% and 91% may be the concentrations that two different manufacturing methods can practically reach. Maybe there is an easy way to make 70% and then an additional step that costs more but will reach 91%.

Generally I think isopropanol and ethanol can do many of the same jobs including disinfection. Ethanol has the advantage that it is cheaper to make, but the disadvantage that you have to pay a special tax to sell it, unless you add something to make it poisonous - also known as "denaturing" it. At least this is how I understand it.
#11
Old 12-17-2011, 05:25 PM
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We can buy 100% ethanol in the lab, but for cleaning it's diluted down to 70%. I've been told that 70% is actually a better disinfectant than 100%, but I've never bothered to find out why.
#12
Old 12-18-2011, 10:15 AM
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Quote:
Originally Posted by Smeghead View Post
We can buy 100% ethanol in the lab, but for cleaning it's diluted down to 70%. I've been told that 70% is actually a better disinfectant than 100%, but I've never bothered to find out why.
Quote:
Intriguingly, 70% alcohol is a more effective antiseptic than 100% alcohol. Because alcohol causes protein to coagulate on contact, a 100% solution coming into contact with a microorganism creates a hardened protein wall around the outside of the organism, rather than permeating into its interior. Because microorganisms can be very resilient, this protein shell only causes dormancy rather than death. This can lead to revival and a continuation the cycle of reproduction under the right circumstances. At a purity of 70%, however, the alcohol causes coagulation to occur more gradually, slowing down the microorganism from the inside out.
http://wisegeek.com/why-is-alcoh...antiseptic.htm

And with "slowing down" they mean "kill", I hope.
#13
Old 12-18-2011, 12:30 PM
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IIRC from my chemistry days, the molecule of isopropyl alcohol is large enough to prevent it from being absorbed through the skin.

The molecules of methyl and ethyl alcohol are small enough to be absorbed through the skin and enter the blood stream, with undesired consequences.
#14
Old 12-18-2011, 01:09 PM
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Well, the individually prepackaged little cotton wipes they use to disinfect your skin before giving you a shot are isopropyl. I've noticed some hand sanitizer is ethanol, and some is isopropyl. They both claim "Kills 99.999% of germs" (I truly wonder about and am highly skeptical of that 3rd significant digit accuracy). I think they both kill germs, or at least bacteria, the same way. I've also heard that within a minute or two of using it the same amount of germs are back on your hands. Not sure if that's true or not... kinda hard to believe if it really kills 99.999% of them.

If my hands feel greasy/oily I find both work very well (at 70% or above concentrations) at dissipating said gunk ... I am practically addicted to the stuff because I always use it before any session on my iphone or ipad as it cuts down on screen smudges, fingerprints, etc. Oleophobic screens my ass. I highly recommend a squirt of either type of alcohol on your hands before your next session of Angry Birds.
#15
Old 12-18-2011, 02:56 PM
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Quote:
Originally Posted by kaltkalt View Post
They both claim "Kills 99.999% of germs" (I truly wonder about and am highly skeptical of that 3rd significant digit accuracy).
It seems to me that this is simply an artifact of the way infectivity is commonly measured.

http://en.wikipedia.org/wiki/Titer

Quote:
A titer (or titre) is a way of expressing concentration. Titer testing employs serial dilution to obtain approximate quantitative information from an analytical procedure that inherently only evaluates as positive or negative. The titer corresponds to the highest dilution factor that still yields a positive reading.

For example, positive readings in the first 8 serial twofold dilutions translate into a titer of 1:256 (i.e, 2−8). A specific example is a viral titer, which is the lowest concentration of virus that still infects cells. To determine the titer, several dilutions are prepared, such as 10−1, 10−2, 10−3,...,10−8.
So, when during testing, a disinfectant is found to reduce the virus titer in a solution from 1:10^6 to 1:10^1 (a 100,000-fold reduction), it could be said to kill 99.999% of virus present.
#16
Old 12-18-2011, 03:23 PM
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Quote:
Originally Posted by kaltkalt View Post
...
They both claim "Kills 99.999% of germs" (I truly wonder about and am highly skeptical of that 3rd significant digit accuracy).
...
You mean 5th significant figure of accuracy.
#17
Old 12-18-2011, 07:07 PM
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Also, given that bacterial growth is exponential, 99.999% isn't all that impressive. Canned and processed foods are required to go through some sort of sterilizing process that is known to kill at least 99.99999% of botulism spores, which are one of the most difficult bacterial cells to kill. That's a further two orders of magnitude, and I've been told that many facilities go beyond that to be on the safe side.
#18
Old 12-19-2011, 05:52 AM
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I have a bottle of 99% isopropyl alcohol. I have no idea what it's intended applications are, but it's recommended for a process of removing undesired bitter flavors from a tobacco pipe.
#19
Old 12-19-2011, 09:48 AM
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99% isopropyl alcohol is used as a solvent, often in cleaning applications. it has little water, it is an alcohol that has some strength but is not as aggressive a solvent as ethanol or methanol.
#20
Old 12-24-2012, 04:41 PM
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I'm glad this question was asked, as I have had it on my mind as well. However, maybe except for response #5, I don't feel very satisfied.

Not long ago, I was at the local pharmacy and they had bottles of "rubbing alcohol" (one was ethel alcohol, and one was isopropyl alcohol), at nearly the same price. Hmmm -- why might I prefer one of these over the other -- which one to buy (as the price difference was quite minimal)?

It seems from what I read on this board that isopropyl is "safer" on the skin (less absorption), and as a "cleaning agent" (leaving less residue). Both seem equal as disinfectants, as far as I can tell from what has been written here. Does this seem about right?
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