Other Time-Sensitive Chemicals

Potassium and Potassium-Sodium Alloy (NaK)

• Often called a “peroxide former”, though the term is not accurate and not used here.
• Reacts with oxygen and water during storage, causing a crust to grow, which may explode on disturbance (e.g., grabbing the potassium with tweezers) if sufficiently thick
  • Enough O₂ and H₂O can diffuse through mineral oil to allow a hazardous crust to grow on potassium stored in oil.
  • Polyethylene containers are permeable to O₂ and H₂O and are less suitable for potassium storage than glass vessels.
• Thin grey coating which does not obscure features of the metal surface (like scratches or imperfections) is generally not hazardous – see Figures 1 and 2.
• Crust which completely obscures the metal, is visibly thick, shows surface “fur” or excrescences, or is white, yellow, or very pale grey — potassium may be dangerous.
• Refer to the CHP (Section 7) for more information on the hazards and chemistry of crust formation on potassium.

Basic Rules:

1. Minimize inventory or seek safer alternatives (e.g. sodium, which does not generate a hazardous crust)
2. Date containers of potassium when received (or when filled, if potassium is transferred to a new container).
   • Potassium should be stored in non-combustible secondary containment (steel can)(if stored outside of a glove box). The secondary container shall be labelled with the contents, and if it is closed (i.e. has a lid) it shall also be dated.
   • Write expiration date on the bottle and enter expiration date into online inventory (EHSA or RSS) one year into the future.
3. Inspect potassium metal annually to catch incipient crusting.
   • If potassium is still in a safe condition (e.g., Figures 1 and 2):
     • Date the bottle, e.g., “Inspected on xx/xx/xxxx”
     • Update the expiry date in the online inventory one year into the future
   • If potassium is in a potentially unsafe condition, contact hazmat@usc.edu.
4. Whenever possible, store potassium and potassium alloys in containers impermeable to oxygen and water vapor (e.g., glass) rather than in plastic containers (e.g., polyethylene).

Potassium Amide (Potassamide; KNH2), Sodium Amide (Sodamide, NaNH2), and Other Alkali-Metal Amides

• Often called a “peroxide former”, though the term is not accurate and not used here.
• Highly reactive, combustible solids
• Reacts with oxygen very quickly to form nitrite and traces of hyponitrite which are oxidizers
• Brief exposure to air or longer exposure to oxygen traces (e.g. in underperforming glove box) may result in material becoming spontaneously explosive
• Hazard is not visible and material cannot be practicably tested for nitrite build-up
• Refer to CHP (Section 7) for more information on the hazards and chemistry of alkali metal amide / oxygen interactions, including literature references.

Basic Rules:

1. Alkali metal amides shall be purchased in the minimal quantities consistent with the work to be done.
2. Upon purchase, containers of alkali metal amides shall be dated and immediately transferred to an inert-atmosphere glove box. The containers shall be stored in the glove box for their lifetime.
   • The glove box shall keep oxygen levels at a small value (single digit ppm or lower). Improvised glove boxes, glove bags, etc., shall NOT be used to store alkali metal amides.
3. Containers of alkali metal amides shall be dated when first opened.
4. Containers of alkali metal amide shall not be opened outside of a glove box for any reason.
5. Containers of alkali metal amide shall not be stored outside of an appropriate glove box even if unopened.
   • Exception: Alkali metal amide sealed in glass ampoules may be stored outside of a glove box.
6. Labs using alkali metal amides shall have an SOP for safe use.
7. All manipulations of alkali metal amides shall be done in an appropriate glove box. These materials may be cycled out of the box only for immediate use and in sealed, inert atmosphere reaction vessels.
8. An alkali metal amide in a reliable glove box may be stored for a maximum of one year after opening, or a maximum of two years since purchase, whichever comes first.
9. Immediately notify EH&S Hazmat if alkali metal amide has been inadvertently exposed to air and may have become hazardous.

Hydrogen Peroxide

Hydrogen peroxide slowly decomposes over time with oxygen evolution.

• Store upright in the container in which it was purchased, which will have a vented lid if the hydrogen peroxide is of any appreciable concentration
• Impurities greatly catalyze decomposition and should be rigorously excluded.
  • Do NOT pour unused hydrogen peroxide back into the stock bottle!
• Storage in a refrigerator is recommended to prolong life.
• Hydrogen peroxide above 30% concentration is markedly hazardous and should not be purchased unless absolutely necessary (it is only needed for a very few uncommon chemical syntheses).

Formic Acid

Very concentrated formic acid (approx. > 90%) may slowly decompose to carbon monoxide on storage.

Either purchase less concentrated acid, fit the container with a vented lid, store in a plastic bottle, or loosen cap annually to relieve possible pressure and increment expiration date by a year after venting.

Further reading: Management of time-sensitive chemicals (II): Their identification, chemistry and management.

Chloroform

• Slowly oxidizes to form phosgene, an extremely toxic gas.
  • Phosgene concentrations in old chloroform can be well above that needed to cause deep lung damage.
  • Phosgene is highly reactive and there are several reports in the literature of unexpected experimental results being traced back to phosgene impurity in chloroform used as a solvent.
  • http://pubsapp.acs.org/cen/safety/19980302.html — Case where four researchers were sickened and numerous DNA experiments ruined by phosgene in chloroform.
  • Further reading: Management of time sensitive chemicals (I): Misconceptions leading to incidents and Management of time-sensitive chemicals (II): Their identification, chemistry and management.
• Always use chloroform in a chemical fume hood — Chloroform vapor is a significant chronic health hazard, in addition to the possible acute hazard from adventitious phosgene.
• Buy inhibited chloroform whenever possible, preferably the grade which is inhibited with ethanol.
  • Amylene-inhibited chloroform is available but may not be effective at reducing phosgene formation.
• Always store in the dark (phosgene generation is strongly driven by illumination).
• Recommended to not store chloroform for an excessive length of time
  • Ethanol-stabilized chloroform – Recommend to dispose three years from purchase date
  • Other chloroform – Recommend to dispose one year from purchase date
• Over-age chloroform – Recommend to dispose or test for chloroform.
• Less hazardous organic solvents are available which can substitute for chloroform in many applications.
• If needed to detect phosgene:
  • 5 ml chloroform is dissolved in 15 ml dry benzene and add one drop of p-phenetidine. Turbidity (due to formation of solid N,N´-di(4-ethoxyphenyl)urea particles) shows presence of phosgene. (Ref: p 132 of this review paper).
    • Original reference specifies benzene; suggest replacing with dry toluene.
  • Various colorimetric phosgene tests are also to be found in the chemical literature.

Hydrogen Bromide Gas and Anhydrous Hydrogen Fluoride

When stored in steel cylinders, anhydrous HF and HBr may slowly react producing hydrogen which raises the pressure. If this continues for a few years, the cylinder may spontaneously explode due to overpressurization. For example, a 14 year old lecture bottle of anhydrous hydrogen fluoride was found to have a pressure of around 2400 psig instead of the normal pressure of around 1 psig (reference). See here for example of an HF cylinder explosion.

Steel cylinders of HBr and HF:

• Date cylinder with purchase date.
• If the manufacturer provides an expiration date, makes sure this is clearly marked on the cylinder and entered into the online chemical inventory.
  • If no manufacturer’s expiration date, put expiration date two years after purchase date (write on cylinder and enter into online inventory).
• Once cylinder reaches expiration date, either return to vendor or test cylinder pressure.
  • If cylinder pressure significantly exceeds vapor pressure of contents (table below), the cylinder is starting to corrode internally and generate hydrogen and should be returned to the vendor.
  • If pressure is normal, write testing date on cylinder and increment expiry date in online chemical inventory one year into the future.

Anhydrous HF in Monel metal cylinders appears to be safe in prolonged storage.

Further reading: Management of time sensitive chemicals (I): Misconceptions leading to incidents and Management of time-sensitive chemicals (II): Their identification, chemistry and management.