# What (simple) household chemicals react with oxygen?

I'm interested in making a small "preservation chamber" that I can basically use to store objects without the presence of oxygen. I have a resealable stainless steel canister and the plan is pretty much just to put whatever object I want to be preserved inside, together with a chemical/object/thing that absorbs the oxygen from the air inside the can, protecting the other item. I don't have access to anything fancy, so I need something is/can be made from household materials that will react with/contain oxygen.

Here's the catch: It CANNOT be a candle. The container has a plexiglass cover that will melt if it's exposed to the heat of a flame. (I tried it before; it worked, but the plastic almost cracked. I don't dare to do it again.)

• Use a candle but arrange it so the flame doesn't touch the cover? Use a different cover? – user253751 May 5 '19 at 23:37
• @immibis, I can't use a different cover. The cover is attached and has the seal. The problem wasn't the flame itself touching the cover, but the heat above it. I don't want to try anything with a hot flame because if it doesn't work out I very well might ruin the cover. – Rafael May 6 '19 at 1:06

You don't have to reinvent the wheel. Food industry already uses quite simple oxygen scavengers for decades, and one of the most affordable formulations include iron powder mixed with sodium chloride.

Typically, an oxygen scavenger is packaged in small packets (sometimes labeled as "oxygen absorber" or "antioxidant") that are added with the product inside the pact and sealed. The absorber itself consists of iron powder and an inert absorbent (sodium chloride, activated carbon, food-grade clay or a composite such as nylon 6/nanoclay). When placed inside a package with a product intended for storage, it begins to actively absorb oxygen and completely removes it within 12–96 hours. The drawback of using Fe is that it promotes rapid lipid oxidation, if it's leaked and gets in contact with the product. However, since you are already using stainless steel container, going with iron-based quencher seems like an optimal choice to me.

More historical background and interesting tech details can be found in Wiley's Encyclopedia of Packaging Technology [1, p. 845]:

[…] The iron-based oxygen scavengers are the most prevalent and they are examined first.

The iron technology is based on rapid oxidation of iron powders to prevent headspace oxygen from reacting with foodstuff components or to reduce oxygen permeation rates through container walls. Reduced iron powders (zero-valent iron $$\ce{Fe^0}$$) are highly reactive and possess a higher capacity to react with oxygen than partially oxidized ferrous iron ($$\ce{Fe^2+}$$) compounds. Large exposed surface area of iron powders per unit weight, which increases with reduction in mean particle size and especially when using highly porous "sponge" iron morphologies, promotes simultaneous oxidation at multiple reactive sites, resulting in faster rates of oxygen scavenging. Presence of electrolytes and an aqueous interface to facilitate electron transfer during oxidation is known to accelerate oxidation reactions of transition metals. This is exempliﬁed by rapid rusting of ferrous metals and steels exposed to road salt and salted seawater, in contrast with slow rates of corrosion in the dry climates. Ferrous and ferric iron oxides and hydroxides produced by oxidative reactions are basic. As a result, acidic environments promote oxygen scavenging by shifting equilibrium to iron oxides. At low pH values, oxidation of reduced iron proceeds in humid environments even in the absence of oxygen, by deoxygenizing water molecules and resulting in hydrogen gas formation.

Since low pH values and aqueous interfaces require the presence of water, water vapor diffusion and variation in relative humidity of the environment can be used to control activation of oxygen scavenging capacity of iron powders. The speciﬁc formulations are designed to trigger the activation at desired RH levels, control the reaction rate, achieve the full oxidative potential of the iron powder, maintain compatibility with various products, and ensure food safety. The reaction formula for complete oxidation of reduced iron to eventually form ferric oxide trihydrate complex (commonly known as rust) is

$$\ce{4 Fe^0 + 3 O2 + 6 H2O → 4 Fe(OH)3 → 2 (Fe2O3* 3 H2O)}$$

Many transition metals are recognized as being sufficiently oxidative to become candidates for an oxygen-scavenger formulation; however, iron does offer unique advantages that have driven the industry to general use of this medium. Iron has a relatively high afﬁnity to combine with oxygen on a per unit weight basis compared to most alternatives. Complete oxidation of 1 g of reduced iron removes 300 cm³ of oxygen at STP conditions. Elemental candidates that exceed it have drawbacks such as the odor problems with the use of sulfur and the propensity of aluminum to form an almost impermeable oxidized skin layer that limits further oxidation. Iron rust, on the other hand, ﬂakes off as it forms and it is highly permeable to further duffusion of water and oxygen. Of great importance is the food safety of iron powders, which are recognized as nutrients important for healthy blood and commonly used as food enrichments in milled flour, breads, breakfast cereals, and baby foods. The same cannot be said about copper, zinc, aluminum, and many other transition metals. The abundance and relatively low cost of producing elemental iron are also important, especially in comparison to choices such as palladium and platinum metals and catalysts based on them. Then there is the ready ability to manipulate reactive capability of iron powder formulations to adapt to a wide variety of applications for both the rate of oxygen scavenging and the activation by the moisture in a package headspace. One of the few drawbacks is that the oxidation of iron is a temperature-dependent reaction and normally slows dramatically as the temperature approaches freezing.

Electrolytes and acidifying agents in a scavenging formulation are commonly supplied by metallic salts […]. The practical considerations of food safety have dictated that common table salt ($$\ce{NaCl}$$) is often the best choice for the electrolyte, while various metal and organic salts of strong acids are often used to increase the acidity of the formulation. […] When the packaged product does not have a required water activity to fully activate an iron-based scavenger and provide the desired reaction rate, premoisturized silicas, zeolites, and activated carbons are used as self-contained water carriers in various proprietary formulations to provide a reliable activation.

### References

1. The Wiley Encyclopedia of Packaging Technology, 3rd ed.; Yam, K. L., Ed.; John Wiley & Sons: Hoboken, N.J, 2009. ISBN 978-0-470-08704-6.
• Very interesting answer! I'm thinking of using steel wool as the iron. I'm just a little confused about the water. Assuming I'll put the iron and salt in a cup, should just add a little water to dissolve everything? Or maybe not because it will then take oxygen from the water, not the air? – Rafael May 7 '19 at 1:37
• @Rafael AFAIK there is no need to use large amounts of water; I'd add it drop-wise if you think the air itself isn't humid enough. – andselisk May 7 '19 at 3:13