From: ILPI Support <info**At_Symbol_Here**ilpi.com>
Subject: Re: [DCHAS-L] Storing Pyrophoric/Water-Reactive Reagents at low temperature
Date: Wed, 18 Nov 2015 11:53:43 -0500
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Just about everyone in the organometallic community routinely stores their Sure-Seal™ bottles in refrigerators. I've never seen anyone put metal alkyls in a freezer (except in an inert atmosphere glovebox) - you'd have to start worrying about solubility, precipitation and in the case of alkylmagnesiums, Schlenk equilibria.
The general interest in keeping the bottles cold is that chemical reactions follow a rule of thumb that reaction rates (in this case, degradation) double with each 10 =B0C increase in temperature. So if you can drop the temperature by 20 =B0C, your material should last 4x longer.
One could worry about what happens in a refrigerator as a punctured septum seal will inevitably begin to permit air and water through, which is why most labs have various rituals involving Parafilm™ sealing over the punctured septum. Although there are temperature (and thus, pressure) swings when you bring the material in and out, these are generally not going to appreciably accelerate moisture or oxygen getting into the bottle as most folks tend to have a slight nitrogen overpressure in their bottles and the vapor pressures of the solvents are rather significant.
So we have a balance - let the punctured bottle sit out warm and have it degrade at a faster rate versus the smaller possibility that fairly insignificant amounts of air and water might get into the bottle taking it in and out of the refrigerator.. If the bottle is used frequently and will be used up quickly, then refrigeration cycles could theoretically cause a tad more degradation. But if the bottle is used very occasionally, then it will do better sitting in a cold dark place.
Regardless, the contents of the bottle will degrade over time. Which is why a competent chemist will perform a titration before using such solutions - even solutions that are brand new and have never been opened regardless of how/where they are stored or what the alleged molarity is on the label. Most labs add a label to these bottles that records the various titration dates and molarities so you don't have to go through the bother if someone titrated it a few days prior to the next use.
A refrigerator has one general advantage for pyrophoric storage - it provides protection from fire sprinklers, fire hoses, water pipe breaks, popped condenser hoses etc. If you're storing pyrophrics or water-reactive substances outside the fridge, you need to have this kind of protection. In addition, secondary containment is also a necessity whether that's a spill tray in the refrigerator or an enclosed plastic tote or cabinet elsewhere.
Finally, the explosion-proof language you referenced is lawyer-inspired. An explosion-resistant refrigerator (one with no electrical contacts, lights, controls etc. in the interior) is sufficient, as we're talking about the threat inside the fridge, not outside. Even an explosion-proof fridge is essentially pointless in most laboratories unless you're prepared to address the dozens of other potential ignition sources (computers, hot plates, light switches, stereos, cell phones etc.)
Safety Emporium - Lab & Safety Supplies featuring brand names
Fax: (856) 553-6154, PO Box 1003, Blackwood, NJ 08012
I read some Protocols for Safe Use of Pyrophoric/Water-Reactive Reagents mentioned "When refrigeration of materials is required, materials must be stored in an approved explosion-proof refrigerator/freezer." As we all know, even the explosion-proof refrigerator/freezer cannot provide dry environment.
Can you share your experience on storing pyrophoric, flammable, and water-sensitive substances such as tBuLi solution in pentanes at low temperature? Great Thanks!
Zhen (Jenny) Fu, Ph.D., Sr. Safety Specialist, Environmental Health & Life Safety Administration & Finance / Dept. of Public Safety
Previous post | Top of Page | Next post