ethanedioic acid, IUPAC name for oxalic acid.

Colourless, crystalline, toxic carboxylic acid found in many plants, especially rhubarb, wood sorrel, and spinach. Because it forms soluble chelates with iron, some of the iron in these plants is not available nutritionally. However, this property makes it useful for removing blood and rust stains, cleaning metals other than iron, and flushing car radiators. Oxalic acid and its salts (oxalates) are used in many chemical processes.

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Dicarboxylic acids are organic compounds that are substituted with two carboxylic acid functional groups. In molecular formulae for dicarboxylic acids, these groups are often written as HOOC-R-COOH, where R is usually an alkyl, alkenyl, or akynyl group. Dicarboxylic acids can be used to prepare copolymers such as nylon and polyethylene terephthalate.

In general, dicarboxylic acids show the same chemical behaviour and reactivity as monocarboxylic acids. The ionization of the second carboxyl group occurs less readily than the first one. This is because more energy is required to separate a positive hydrogen ion from the doubly charged anion than from the single charged anion.

A mnemonic to aid in remembering the order of the common nomenclature for the first six dicarboxylic acids is "Oh my, such great apple pie!" (oxalic, malonic, succinic, glutaric, adipic, pimelic).

When one of the carboxy groups is replaced with an aldehyde group, the resulting structure is called a "aldehydic acid".

Examples

Elementary dicarboxylic acids

Common name	IUPAC name	Chemical formula	Structural formula
Oxalic acid	ethanedioic acid	HOOC-COOH
Malonic acid	propanedioic acid	HOOC-(CH2)-COOH
Succinic acid	butanedioic acid	HOOC-(CH2)2-COOH
Glutaric acid	pentanedioic acid	HOOC-(CH2)3-COOH
Adipic acid	hexanedioic acid	HOOC-(CH2)4-COOH
Pimelic acid	heptanedioic acid	HOOC-(CH2)5-COOH
Suberic acid	octanedioic acid	HOOC-(CH2)6-COOH
Azelaic acid	nonanedioic acid	HOOC-(CH2)7-COOH
Sebacic acid	decanedioic acid	HOOC-(CH2)8-COOH
Phthalic acid	benzene-1,2-dicarboxylic acid o-phthalic acid	C6H4(COOH)2
Isophthalic acid	benzene-1,3-dicarboxylic acid m-phthalic acid	C6H4(COOH)2
Terephthalic acid	benzene-1,4-dicarboxylic acid p-phthalic acid	C6H4(COOH)2

See also

• Dicarboxylic acids
• Tricarboxylic acid