I made enough Pirhana to fill a 3L flask and was happily cleaning it out on our front porch where we have a moveable bench for doing things that
generate more vapor than our weak fans can handle. That's about to change but for the moment there it is... so after doing the cleaning I transferred
the solution, still hot, to another 3L flask. The flask I transferred it to had been cleaned with HCl/alcohol and rinsed once. The single rinse was
not enough becaue what happened next was scary. At first it seemed like a more vigorous reaction than the previous one but it continued to build. I
had the flask in a stainless bowl on a cork ring. The flask overflowed, the hot mixture went all over the bench and porch. At that point we got the
hose out and started washing everything down. The bowl is ugly the cork ring is burned to a crisp and there's big black circle in the bench where the
bowl sat. A little more alcohol residue and we could have had an explosion. If you use the stuff regularly you probably know all this but I
furthered by education on Pirhana solution yesterday. The condition was not addressed anyway. The flask looks like it has a residue in it but now I
think the previous owner screwed it with strong base. It looks like it's peeling inside. I've never seen this before.Formatik - 9-5-2008 at 10:50
Be careful with this stuff, it builds ozone just on standing. I've had to use it to eat burned carbon off the inside of a distillation flask, it took
a small amount of heat but eventually cleared it all. I wonder if it will oxidize sulfur? Though I've found hot toluene dissolves sulfur, so no need
for pirhana.ShadowWarrior4444 - 9-5-2008 at 12:31
Hmmm, peeling--what color is the residue? Does it appear that the glass itself is peeling?
Pirahna should do only one thing to glass itself: hydroxylate the surface by adding silanol groups, thereby making the glass more hydrophilic.
One thing that may be causing the residue is (if it is white-ish) that transition metals embedded in the glass catalyzed the creation of Caro's Acid.
(Peroxymonosulfuric acid.) As I'm sure you’re aware, *any* organic solvent has a very high likelihood of causing an explosion near piranha, this is
why piranha is usually mixed first, allowed to cool, then added slowly to the substrate to clean (just in-case.)
Other ancillary notes: Don’t use 50% or above peroxide, your chance for a violent decomp is much greater--30% is more than sufficient to eat
anything organic. Also, Piranha works to dissolve elemental carbon using singlet oxygen, so if the previous owner had anything especially to
susceptible to singlet oxygen in there, piranha will likely oxidize it.
Related: There is another piranha called "base piranha" that is a 3-to-1 mixture Ammonium Hydroxide and H2O2, unlike regular piranha; this mixture
must be heated to 60 Celsius for it to work. (30% NH4OH should be used, with 30% H2O2 in water) You may wish to use this piranha to start off, as the
NH4 should complex and dissolve any pesky transition metals. If there is still residue left, the acid Piranha can be used.
Quantity to use: Try not to use alot of piranha at once--it works quickly and visibly, so you only need add a small amount, then rotate the flask to
so the solution touches a wide surface area. During this time, you may wish to watch for bubbles, indicating that you should pause at a particular
place for more intensive cleaning. Lastly, if you are deathly afraid of an explosion, keep the flask to be cleaned cold, this should prevent the
thermal runaway of the H2O2. Cooling the freshly mixed Piranha to ambient before use will help too.
[Edited on 5-9-2008 by ShadowWarrior4444]vulture - 9-5-2008 at 17:43
The most important thing is disposing of it properly. Once it's all contaminated, it's very unstable. This is the point where people get hurt by
exploding containers of piranha waste because they screwed the lid on.The_Davster - 9-5-2008 at 17:47
Quote:
Originally posted by ShadowWarrior4444
Quantity to use: Try not to use alot of piranha at once--it works quickly and visibly, so you only need add a small amount, then rotate the flask to
so the solution touches a wide surface area.
I am not one to rant on the dangers of piranha, as I have used it regularly over a year with only one incident(a beaker frothed over and spilled
piranha in the hood dissolving and rusting stuff), but this is a very important note which should be applied in all circumstances it can be.
250-500mL of piranha in your flask would have worked in the same way, but by not filling it you have a LOT of room for screwups and chance
occurrences.MagicJigPipe - 9-5-2008 at 18:13
I still can't believe you wasted 3L of piranha! Why did you feel compelled to fill the entire flask? Was it A LOT of residue?
3 liters!!! Oh my god!chemrox - 9-5-2008 at 22:46
It was very wasteful! The plan was to clean a lot of flasks in succession oh well... back to the peeling @Shadow. The peeling pre-dates my ownership
of the flask and not attributed to the Pirhana. Until the Pirhana episode I thought the peeling might be a residue. Now I feel its damage to the
glass and I've asked the glassblower to make my another. I have others but none of this configuration; 4 X24/40 and a central 29/42. I have a 3 day
, multiple reductive am synthesis under Ar in mind. I need to stir with a geared motor .. stir bars won't do it. I need an opening for the powder
funnel, another for a liquid funnel and another for a septum. What would have done the peeling? Hot NaOH in high concentration??ShadowWarrior4444 - 9-5-2008 at 23:14
NaOH conc. and hot should simply etch off the very surface of the glass exposed, dissolving it as sodium silicate. Same with HF (sans the sodium
silicate part.)
Peeling of glass is likely caused by some sort of disruption in the composition of the glass--bromine seeping in...perhaps thermally induced tension
in the structure, though that should manifest as hairline cracks, maybe excessive chromic acid use by the previous owner deposited Cr in the glass
structure. This is of course assuming it is the glass that is peeling, and not something inorganic.
You best option for cleaning this particular flask is probably using hot conc. NaOH yourself, to remove the surface of the glass along with whatever
is causing the peeling. Temperature and timing should be carefully observed for this operation, but it is a common lab procedure when *absolutely*
clean glass in required. Measuring the thickness of the glass before and after may be advisable as well, but not necessary.
Also, if it is something fun absorbed in the glass, NaOH etching will likely neutralize it as well as remove it, especially in the case of
halogens.
P.S. Posting this apparently makes me a hazard to myself. *smirk*
[Edited on 5-10-2008 by ShadowWarrior4444]497 - 18-5-2008 at 02:19
A couple weeks ago some pihrana acid spewed onto my face. I was adding ~50% H2O2 to a maybe 50 ml azeotrope H2SO4 which promptly violently decomposed,
shot out of the flask and onto my face. What possessed me to do such an amazingly stupid thing I still do not know. I was extremely lucky, I was not
wearing goggles (funny how accidents always happen on the one rare occasion you're no protected..) but none got in my eyes and I was able to wash it
off within eight or ten seconds but it did a bit of damage. Its mostly healed now, but for a while it looked pretty bad, big scabs... Feeling the skin
on your face bubbling and being rapidly destroyed is an interesting sensation, very surreal. When I went back to the flask, there was just a little
sprinkling of acid around it, almost more of it went on my face than anywhere else.
So if you do work with this shit, I recommend not doing it in a flask, if I had used a beaker it would have been fine... better yet don't use it at
all. There might have been a few copper ions in there too, I'm sure that didn't help.Klute - 18-5-2008 at 03:20
Damn, be carefull people! Pirahna solutions are very dangerous as you surely have seen!
I really don't understand the point of makign such a huge amount! The stuff is very unstable even in small quantities, 3L can represent a enormous
hazard! You just need a small film, and gradually turn the flask to let the whole surface exposed... Even if planning on doing several flask, you
would be better out pouring a small amount in each of them, and grdaully exposing the surface..
It should be the last resort... Try ethanolic kOH, or even aqua regia before pirahna.. I usually only use it for carbon residu or very resistant
traces of tar.. and immediatly dilute with 5x water minimum when done.. Never mix the used solutions with anything possibly containing
nitrates/nitric acid... I had a very bad surprise with this!
And also always wash the glassware as much as possible before treating with pirahna: acetone, followed by water and soap and lots of scrubbing and
water again. Even though it eat through nearly every stain/residu possible, it isn't efficient when there is too much, and very little organic residu
can cause runaway ...
