Oxalic acid is a chemical which is made up of two carboxylic acid groups bonded together.
It is two carboxylic acid groups bonded together. It is classed as a dicarboxylic acid and it is the simplest possible member of this group of organic compounds. It is a much stronger acid than ethanoic acid (acetic acid) is, and it has a strength three thousand times greater. Molecular oxalic acid is a reductant and its ionic form, the oxalate ion, can be used to chelate metallic ions. Oxalic acid normally exists in crystalline form associated with two molecules of water of crystallisation, which can be written as COOH-COOH.2H2O.
The synthesis of oxalic acid is typically carried out by oxidising carbohydrates, such as glucose, with either oxygen or nitric acid using vanadium(V) oxide as a catalyst. There is a range of alternative starting compounds that can be used in the place of glucose. Two such compounds include 2-hydroxyethanol and glycolic acid. A more recent technique for making oxalic acid is by carrying out a carbonylation reaction with alcohols in oxidative conditions. This is a condensation reaction (as water is also produced as a side product) which produces oxalic acid’s diesters. Oxalic acid can then be isolated by saponification of these diesters. In the region of 120 million kilograms of oxalic acid is made each year.
In most cases it is easier to buy oxalic acid than to synthesise it in a laboratory. It is, however, important for the accomplished lab technician to know how to make oxalic acid as part of their general proficiency. They can do this by simply adding a small quantity of vanadium pentoxide to a mixture of sugar and nitric acid. The solid that is left behind by this reaction is then fractionally distilled, though alternatively it can be decomposed by exposure to heat (pyrolysis).
Friedrich Wohler successfully synthesised ethanedioic acid in a laboratory by hydrolysing cyanogen (NC-CN).
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