How to Learn about and Detect a HazMat in an Ether and Minimize or Remove it

Diethyl ether and other peroxide forming ethers like Tetrahydrofuran (THF) or Ethylene glycol dimethyl ether (1,2-Dimethoxyethane or DME, MeO(CH2)2OMe) need to be avoided, and whenever used, are required to be handled with caution.


Peroxide forming ethers are HazMats (hazardous materials).

Unlike other alkyl ethers, Dimethyl ether (MeOMe) resists autoxidation. DME (not to be confused with 1,2-Dimethoxyethane, which is a peroxide forming ether, the acronym of which is also DME) is relatively non-toxic, although it is highly flammable. The HFR (health, flammability, reactivity) rating of DME is 241 as per NFPA (national fire protection association) 704 fire diamond. A potentially major application of DME is as a substitute for Propane in LPG (liquefied petroleum gas) used as fuel in household and industry. DME may also be used as a blendstock in Propane autogas/gas.

THF synthesis

 


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Red = Reduction

THF is a relatively acutely nontoxic solvent, with the median lethal dose (LD50) comparable to that for Acetone. However, chronic exposure is suspected of causing carcinogenesis. It is highly flammable. Reflecting its remarkable solvent properties, it penetrates the skin, causing rapid dehydration. The HFR rating of THF is 231 as per NFPA 704.

THF dissolves or penetrates most polymer glove materials fast; only LLDPE (linear low-density polyethylene) laminated gloves can protect against it for long time, similar to most ketones. PVA (polyvinyl alcohol) coated gloves may provide protection for nearly an hour, but since PVA is water soluble, they are only effective in low humidity and when working with anhydrous solvents. Even very thick nitrile or nitrile-neoprene gloves are degraded by THF in under 10 minutes.

THF is even more perilous as it tends to form an (unstable) peroxide upon reaction with aerial oxygen (accelerated by light, metal catalysts, and aldehydes):



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When the ether is shaken with a freshly prepared aqueous solution of Ferrous sulfate and Potassium thiocyanate, the presence of peroxide in ether is detected as shown below:


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Ox = Oxidation

Commercial supplies of THF are often stabilized with Butylated hydroxytoluene (BHT) to minimize this hazard as follows:


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EDG = Electron donating group, BDE = Bond dissociation energy

The presence of BHT in THF makes the chromatogram look worse though.

A long-term storage of THF without BHT is not recommended.

THF is purified before distillation. Distillation of THF to dryness is unsafe because the explosive peroxides may concentrate in the residue.

Removal of peroxide can be done by washing the ether with a solution of ferrous salt, which reduces peroxide to alcohol.

For laboratory scale, drying THF with Lithium aluminum hydride (LiAlH4 or LAH, which reduces peroxide to alcohol) or passing through molecular sieves is done to remove both water and peroxides.

Concentrated Sulfuric acid, a dehydrating agent, breaks the water-THF azeotrope, which helps remove water-soluble impurities and aromatic hydrocarbons. While effective at removing impurities, distillation with concentrated acids can be unintended or dangerous due to potential polymerization of THF or hazardous reactions with high levels of peroxides.



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Disclaimer: This post is written to promote learning and may be used as a guideline. Please follow the safety measures and prevent damage at your own discretion.

Harrowing HazMat❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com❗

References:

(1)    Wikipedia Contributors. Ether. Wikipedia. https://en.wikipedia.org/wiki/Ether.
(2)    Tetrahydrofuran. Wikipedia. https://en.wikipedia.org/wiki/Tetrahydrofuran.
(3)    Wikipedia Contributors. Dimethyl ether. Wikipedia. https://en.wikipedia.org/wiki/Dimethyl_ether.
(4)    Butylated hydroxytoluene. Wikipedia. https://en.wikipedia.org/wiki/Butylated_hydroxytoluene.

‌(5)    Graham, T. W.; Fryhle, C. B.; Snyder, S. A. Organic Chemistry.; Hoboken, Nj John Wiley Et Sons, Inc, 2016.

(6)    Brown, C.; Ford, M. Higher Level Chemistry, 2nd ed.; Pearson Education: Harlow, Essex, 2014.

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