Mellitic acid

Mellitic acid

Skeletal formula
Ball-and-stick model Space-filling model
Names
Preferred IUPAC name Benzenehexacarboxylic acid
Other names Graphitic acid
Identifiers
CAS Number	517-60-2 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:41089 Y
ChEMBL	ChEMBL1231329 N
ChemSpider	2244 Y
DrugBank	DB01681 Y
ECHA InfoCard	100.007.495
PubChem CID	2334
UNII	P80QSP14DM Y
CompTox Dashboard (EPA)	DTXSID50199650
InChI InChI=1S/C12H6O12/c13-7(14)1-2(8(15)16)4(10(19)20)6(12(23)24)5(11(21)22)3(1)9(17)18/h(H,13,14)(H,15,16)(H,17,18)(H,19,20)(H,21,22)(H,23,24) Y Key: YDSWCNNOKPMOTP-UHFFFAOYSA-N Y InChI=1/C12H6O12/c13-7(14)1-2(8(15)16)4(10(19)20)6(12(23)24)5(11(21)22)3(1)9(17)18/h(H,13,14)(H,15,16)(H,17,18)(H,19,20)(H,21,22)(H,23,24) Key: YDSWCNNOKPMOTP-UHFFFAOYAB
SMILES O=C(O)c1c(c(c(c(c1C(=O)O)C(=O)O)C(=O)O)C(=O)O)C(=O)O
Properties
Chemical formula	C12H6O12
Molar mass	342.16 g/mol
Density	1.68 g/cm3, 2.078 (calc.)
Melting point	> 300 °C (572 °F; 573 K)
Boiling point	678 °C (1,252 °F; 951 K) (calc.)
Acidity (pKa)	5.0, 2.19, 3.31, 4.78, 5.89, 6.96
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Mellitic acid, also called graphitic acid or benzenehexacarboxylic acid, is an acid first discovered in 1799 by Martin Heinrich Klaproth in the mineral mellite (honeystone), which is the aluminium salt of the acid. It crystallizes in fine silky needles and is soluble in water and alcohol.

Structure

The stable conformation of this molecule has the carboxylic acid groups rotated out of the plane of the central benzene ring. The molecule adopts a propeller-like conformation in which the tilt of each carboxylic acid group relative to the central benzene ring varies due to intramolecular hydrogen bonding.

Preparation

Mellitic acid may be prepared by warming mellite with ammonium carbonate, boiling off the excess of the ammonium salt, and adding ammonia to the solution. The precipitated alumina is filtered off, the filtrate evaporated, and the ammonium salt of the acid purified by recrystallization. The ammonium salt is then converted into the lead salt by precipitation with lead acetate, and the lead salt is then decomposed by hydrogen sulfide. The acid may also be prepared by the oxidation of pure carbon, graphite or hexamethylbenzene, by alkaline potassium permanganate in the cold, or by hot concentrated nitric acid.

Reactions

It is a very stable compound; chlorine, concentrated nitric acid and hydriodic acid do not react with it. It is decomposed, on dry distillation, into carbon dioxide and pyromellitic acid, C₁₀H₆O₈; when distilled with lime it gives carbon dioxide and benzene. Long digestion of the acid with an excess of phosphorus pentachloride forms the acid chloride, which crystallizes in needles, and melts at 190 °C. By heating the ammonium salt of the acid to 150–160 °C while ammonia is evolved, a mixture of paramide (mellimide, molecular formula C
₆(CONHCO)
₃), and ammonium euchroate is obtained. The mixture may be separated by dissolving out the ammonium euchroate with water. Paramide is a white amorphous powder, insoluble in water and alcohol.

The high stability of mellitic acid salts and their presence as an endproduct of the oxidation of polycyclic aromatic hydrocarbons, which are present in the solar system, make them a possible organic substance in Martian soil.

Mellitates (and salts of other benzene polycarboxylic acids) of iron and cobalt have interesting magnetic properties.

See also

• Mellitic anhydride

Further reading

Henry Enfield Roscoe, Carl Scholemmer, "Mellitene Group", "A Treatise on Chemistry: V.III: The Chemistry of the Hydrocarbons and their Derivatives on Organic Chemistry: P.V:529. D. Appleton and Co. (1889).

This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Mellitic Acid". Encyclopædia Britannica. Vol. 18 (11th ed.). Cambridge University Press. p. 95.