Difference between revisions of "Oxalic acid"

Revision as of 17:58, 2 August 2015

Oxalic acid dihydrate.

Oxalic acid is an organic compound with the chemical formula H₂C₂O₄. Along with formic acid, it is one of the most corrosive organic acids.

Properties

Chemical

Oxalic acid is very strong for an organic acid. It will react with manganese dioxide to form manganese oxalate and carbon dioxide.

MnO₂ + 2 H₂C₂O₄ → MnC₂O₄ + 2 CO₂ + 2H₂O

Physical

Oxalic acid is a colorless hygroscopic crystalline solid, with a snow-like aspect. It is soluble in water (143 g/L at 25˚C), more soluble in ethanol (240 g/L) but poorly soluble in ether (18 g/L). It has a weak smell and is irritating to skin. It has a melting point of 102 °C and sublimes between 149 - 160 °C.

Availability

Oxalic acid is sometimes available as wood bleach or as beehive disinfecting powder. It can also be bought online, such as from Amazon. "Bar Keepers Friend" is a very cheap multi-surface cleaner containing oxalic acid dihydrate, available at hardware stores.

Preparation

Oxalic acid can be made from the oxidation of sucrose, glucose, or ethylene glycol using nitric acid or air in the presence of vanadium pentoxide.

Below is a synthesis of oxalic acid found online, using nitric acid and sucrose:

10 g of sugar are added in a flat bottom flask and 50 ml of concentrated nitric acid and heat the flask in a water bath. The reaction will yield nitrogen oxide fumes, so it's best performed outside or in a fume hood. Stop the heating and remove the flask from the water bath. When the reaction subsides, add the hot solution into an evaporating basin. Wash out the flask with 10 ml of conc. nitric acid and evaporate the solution on the water bath until it has a volume of 10 ml. Add 20 ml of water to the solution and evaporate again to 10 ml. Cool the solution in a cooling bath to crystallize the oxalic acid. Dry the crystals.^[1]

Projects

• Purifying MnO₂ from old batteries
• Making formic acid by distillation of oxalic acid with glycerol
• Lanthanide purification
• Make pyrophoric iron
• Oxalate esters

Handling

Safety

Oxalic acid is corrosive to human tissues, so proper protection must be worn. It is not extremely volatile, so its vapors aren't usually a hazard. Oxalates are the notorious cause of kidney stones, so ingestion of both acid and salt should be avoided.

Storage

Should be stored in closed bottles.

Disposal

Oxalic acid and oxalates can be destroyed with hydrogen peroxide.^[2]

References

1. ↑ http://www.scribd.com/doc/45869039/preparation-of-Oxalic-acid
2. ↑ http://web.ornl.gov/info/reports/1981/3445605762877.pdf

Relevant Sciencemadness threads

• oxidation of diols
• Drying Oxalic Acid Dihydrate to Anhydrous