Reagent preservation

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Although most chemical compounds and elements can be stored indefinitely (ex: sodium chloride, barium sulfate, oxalic acid, aluminium, etc.) in most if not all storage conditions, there are quite a lot of reagents that tend to undergo chemical changes, regardless of the storage. Even in the best storage conditions, they will degrade over long periods of time. To maintain the long shelf life of them, preservatives as well as other additives are added.

General

Many chemicals, such as ethers, tend to undergo autoxidation when in contact with air. Halogenated carbons will too suffer similar effects. Alkaline metals like potassium also build up dangerous peroxides in contact with oxygen.

Other compounds, such as sugar or citric acid will serve as nourishment for mold or other biological organisms. Alcohols, like ethanol, will not turn into their respective carboxylic acids (like acetic acid) if they're concentrated enough.

Some elements like silver will darken in prolonged contact with polluted air, even though silver resists atmospheric oxidation. Many other metals suffer similar effects. Some metals, like magnesium, zinc or lanthanides are relative stable in dry air, but will quickly tarnish if moisture is present.

Note that preservatives have poor efficiency if you do not store your reagents properly.

Reagents and preservatives used

Compound Preservative Notes
1,4-Dioxane Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), fresh copper, diphenylamine, hydroquinone
Acrolein Hydroquinone Does not always work, possibly due to impurities[1]
Barium ferrate Potassium hydroxide, sodium hydroxide
Benzyl chloride Propylene oxide Concentration 0.25-1%
Chloroform Ethanol, methanol, pentene (amylene) Accepted values of 1% for ethanol; 100 ppm for amylene[2]
Citric acid Biocides, like benzalkonium chloride Aqueous solutions and wet citric acid are prone to mold; solid or anhydrous citric acid less so
Dichloromethane Ethanol, methanol, cyclohexane, cyclohexene, amylene Accepted values of 100 ppm for amylene, cyclohexane, cyclohexene[3]
Diethyl ether Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), fresh copper, diphenylamine, ethanol, hydroquinone Accepted values 1-2% for ethanol[4]
Diisopropyl ether Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), fresh copper, diphenylamine, hydroquinone The amount of preservative added must be greater compared to other ethers
Formaldehyde Methanol For aqueous formaldehyde (Formalin) the concentration is 10-20%; Inhibts oxidation and polymerization
Hydrogen peroxide Phosphoric acid, EDTA
Isopropanol Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), fresh copper, diphenylamine, hydroquinone Only required if kept for more than 1-2 years in contact with air
Lead(II) azide Dextrin Generally used in Pb(N3)2 aqueous solutions and during production to inhibit the growth of large crystals
Lead(IV) acetate Anhydrous (glacial) acetic acid, acetic anhydride
Methyl iodide Copper or silver wire/powder
Natural rubber Ammonia 0.2 % m/m (short term storage) to 0.7 % m/m (long term storage)[5]
Pentaerythritol tetranitrate Urea
Potassium ferrate Potassium hydroxide
Schweizer's reagent Excess ammonia
sec-Butanol Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), fresh copper, diphenylamine, hydroquinone Only required if kept for more than 1-2 years in contact with air
Smokeless powder Diphenylamine
Sodium bisulfite Sulfur dioxide
Sodium ferrate Sodium hydroxide
Sulfur trioxide Antimony pentafluoride, Antimony pentachloride Concentration 0.5-1%; antimony pentafluoride gives a better performance than the pentachloride[6]
Tetraamine copper(II) complex Excess ammonia
Tetraaminecopper(II) persulphate Excess ammonia
Tetrahydrofuran Butylated hydroxytoluene (BHT), Butylated hydroxyanisole (BHA), fresh copper, diphenylamine, hydroquinone Accepted values of 100-300 ppm for BHT[7]

Storage atmosphere

Some materials that react with air are best or can only be safely stored under air-free atmosphere. While noble gasses like argon are commonly used, being relative cheap, other gasses like nitrogen, sulfur hexafluoride, most saturated perfluorocarbons can also be used. Carbon dioxide or gaseous saturated hydrocarbons (methane, ethane, propane, butane) can also be used in some cases. Some compounds like sulfur dioxide or ammonia are being used as preservatives themselves.

Compound Noble gasses Nitrogen Sulfur hexafluoride Perfluorocarbons Carbon dioxide Hydrocarbons Notes
Alkali metals Compatible Compatible, save for lithium Compatible Incompatible Incompatible Compatible Lithium is incompatible with SF6 at high temperatures
Alkali metal hydroxides Compatible Compatible Compatible Compatible Incompatible Compatible Calcium and strontium slowly react with nitrogen
Alkali earth metals Compatible Compatible Compatible Compatible Incompatible Compatible
Alkali earth metal hydroxides Compatible Compatible Compatible Compatible Incompatible Compatible
Bisulfites Compatible Compatible Compatible Compatible Compatible Compatible Incompatible with carbon dioxide in the presence of moisture
Chlorocarbons Compatible Compatible Compatible Compatible Compatible Compatible
Ethers Compatible Compatible Compatible Compatible Compatible Compatible
Sulfites Compatible Compatible Compatible Compatible Compatible Compatible

Safety

Reagents treated with preservatives must be inspected periodically for any signs of degradation, in the event said preservatives failed to do their job.

References

  1. https://www.youtube.com/watch?v=7oAcT4Duun4
  2. http://www.sigmaaldrich.com/chemistry/solvents/learning-center/stabilizer-systems.html
  3. http://www.sigmaaldrich.com/chemistry/solvents/learning-center/stabilizer-systems.html
  4. http://www.sigmaaldrich.com/chemistry/solvents/learning-center/stabilizer-systems.html
  5. Polymer Latices: Science and technology Volume 2: Types of latices, D.C. Blackley, p. 28
  6. https://www.google.com/patents/US2511072
  7. http://www.sigmaaldrich.com/chemistry/solvents/learning-center/stabilizer-systems.html

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