[iScience]

1.) Vinegar (Diluted Acetic Acid)

2.) Isopropyl Alcohol


What reactions do these chemicals undergo to make them expire?

[Hunter2]

Vinegar nothing, Isopropylacohole can be oxidised to Acetone.

I am also wondering about the general expiredating. Also chemicals like sodiumcarbonate, sodiumchloride etc. get this. Probably a law for storage conditions. Even the bottles or containers have expiredates.

[Arkcon]

Vinegar nothing, Isopropylacohole can be oxidised to Acetone.

And I was just going to say isopropanol nothing.  I was so shocked when the USP IPA stand said, "Keep in brown glass.  May polymerize"  And I was, "What?  What functional group is going to change into what?"  Wikipedia says that reaction requires an oxidizing agent.  But I have to assume, over years of time frame, some acetone is going to form from atmospheric oxygen.  And now the sample is contaminated, for some purposes.

But then, how are you so sure acetic acid won't change over the years?  Now I'm wondering about that too.

Either of them can absorb moisture from the air, and become diluted.  Again, this would be significant depending on the application.  Their use as standards or for organic reactions that must not have moisture.

Or they could evaporate.  I mean, its your job as a chemist to look at the bottles and not say, "I bought a gallon 10 years ago, that's plenty for my purposes," only to find you don't have it when you need it.  SO the manufacturer preempts it for you.  And gets frequent business, too.

And the sample may leach something from the bottle over time.

I am also wondering about the general expiredating. Also chemicals like sodiumcarbonate, sodiumchloride etc. get this. Probably a law for storage conditions. Even the bottles or containers have expiredates.

And this too.  Nothing lasts forever.

[orgopete]

I can see the suppliers adding an expiration date. Why not?

Where is the rate data from which expirations are calculated? I'm guessing this is going to be hard to find.

IPA polymerizing? I kind of doubt that. If it did, what was the polymerization agent? All of this suggests to me reactions that are not characteristic of the solvent or reagent itself. If so, then as the poster was asking, what is the reaction that is to be avoided? At what rate?

If you test chemicals you have in your laboratory for the presence of peroxides, you will be surprised how many will test positive. (As I recall we were using a horse liver peroxidase test strip???. This was years ago.) Opening bottles will alter how long you might keep them. If it is an aldehyde, use it fresh. The older it is of if opened, check before using.

I say, use some judgement. Some reagents such aldehydes, acid chlorides, moisture sensitive reagents, air sensitive reagents, etc., require your own judgement. Sodium chloride, isn't it mined or isolated from the oceans? What is the degradation rate on that?

[iScience]

Follow up questions!

Isopropylacohole can be oxidised to Acetone.

So basically water comes along and takes a hydrogen off the OH?


I'm going to continue assuming that IS what happens for my next questions, but someone please do confirm that that is what indeed happens.f Thanks~


Sounds like if i add a strong base in isopropylalcohol, equilibrium will shift towards acetone formation, and all i need to do with an expired bottle of IPA is to add some strong acid to get back IPA?

[discodermolide]

The conversion of isopropyl alcohol to acetone is an oxidation, this will NOT be reversed by adding a strong acid. And it is not an equlibrium process, it is irreversible.

[iScience]

i'm reading on wikipedia and it says the oxidation of IPA is done through . all these different chemicals; but the only thing listed under "ingredients" for IPA sold at cvs and walmart isopropyl alcohol and water. is this a lie?

[discodermolide]

What does this mean"the oxidation of IPA is done through"?
Oxidation of IPA by air is quite slow and acetone will only occur in small amounts after a few years. You would need a GC to detect it.

[billnotgatez]

I am even more confused now.
It has always been my understanding that expiration dates applied to unopened containers of a product and it would be assumed that an open container had a shorter shelf life.
I also thought that the shelf life included any reaction between the product and the container.
Also, it included the limits of the container to protect the product as well as the products ability to break down on its own over time.

I could see vinegar having trace compounds in it that may influence this issue, but IPA would never have been suspected by me.

[Corribus]

You guys are overthinking this. They put expiration dates on cans of beans, too, and those things will stay good forever. Do aspirin tablets suddenly lose effectiveness on the date printed on the bottle? Of course not. How long they have potency depends too many factors to capture effectively in a predetermined date.

I think at best it just serves as a reminder that if your chemical has been open for a while, it might be worth checking it to ensure it hasn't decomposed or absorbed contaminants from the environment. Probably it has some importance in industry as part of QC procedures. A good chemist will check all this anyway, date notwithstanding.

[billnotgatez]

@Corribus
Beans get mushy after a long while, but I get your point and mostly agree with you.
Butter gets rancid by its own internal enzyme activity, so being a sealed container is not enough.
I have seen where pineapple juice has eaten away the container it was stored.
Wine ages in the bottle and can turn into vinegar if not processed properly.
In any case as far as IPA and probably vinegar I would be more in agreement with you.

@iScience

i'm reading on wikipedia and it says the oxidation of IPA is done through . all these different chemicals; but the only thing listed under "ingredients" for IPA sold at cvs and walmart isopropyl alcohol and water. is this a lie?

Labeling of products is regulated but has leeway. Sometimes the regulators allow traces of stuff in products as long as it is under a certain level. Therefore the product maker is not technically (legally) misinforming when not including the traces of stuff in the label.

[DrCMS]

In reality a lot of expiry dates or shelf lives are just guesses.  Some are set based on test data but a lot are not.

[Corribus]

In reality a lot of expiry dates or shelf lives are just guesses.  Some are set based on test data but a lot are not.

Yes, I guess this was my point. Not that packaged goods (chemicals, foods, drugs) can't undergo changes during storage - just that sell-by or use-by dates are arbitrary and determined according to a set of idealized assumptions about how the goods are likely to be stored and transported. Obviously, a jar of olive oil stored above a stove is going to perish a lot more quickly than a jar stored in a cellar, regardless of what the date printed on the outside of the container is.