Mellitic acid, also called graphitic acid or benzenehexacarboxylic acid, is an

acid An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...

first discovered in 1799 by

Martin Heinrich Klaproth Martin Heinrich Klaproth (1 December 1743 – 1 January 1817) was a German chemist. He trained and worked for much of his life as an apothecary, moving in later life to the university. His shop became the second-largest apothecary in Berlin, and ...

in the

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

mellite (honeystone), which is the

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

of the acid. It crystallizes in fine silky needles and is soluble in

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

and

alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...

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 Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...

salt, and adding

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

to the solution. The

precipitate In an aqueous solution, precipitation is the "sedimentation of a solid material (a precipitate) from a liquid solution". The solid formed is called the precipitate. In case of an inorganic chemical reaction leading to precipitation, the chemic ...

alumina Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium oxide. It is commonly ...

is filtered off, the

filtrate Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter ...

evaporate Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. A high concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when hum ...

d, and the ammonium salt of the acid purified by recrystallization. The ammonium salt is then converted into the

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

salt by precipitation with lead acetate, and the lead salt is then decomposed by

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

. The acid may also be prepared by the oxidation of pure

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...

or hexamethylbenzene, by

alkaline In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...

potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, which dissolves in water as K+ and ions to give an intensely pink to purple solution. Potassium permanganate is widely us ...

in the cold, or by hot concentrated

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

Reactions

Mellitic acid is a very stable compound;

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

, concentrated

and hydroiodic acid do not react with it. It is decomposed, on dry distillation, into

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

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 Phosphorus pentachloride is the chemical compound with the formula . It is one of the most important phosphorus chlorides/oxychlorides, others being and . finds use as a chlorinating reagent. It is a colourless, water-sensitive solid, althoug ...

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 ), 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. Heating ammonium mellitate

The high stability of mellitic acid salts and their presence as an endproduct of the oxidation of

polycyclic aromatic hydrocarbon A Polycyclic aromatic hydrocarbon (PAH) is any member of a class of organic compounds that is composed of multiple fused aromatic rings. Most are produced by the incomplete combustion of organic matter— by engine exhaust fumes, tobacco, incine ...

s, which are present in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

, make them a possible organic substance in Martian soil. Mellitates (and salts of other benzene polycarboxylic acids) of

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

and

cobalt Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...

have interesting magnetic properties.Kurmoo M, Estournes C, Oka Y, Kumagai H, Inoue K (2005) Inorganic Chemistry volume 44, page 217

Structure

Preparation

Reactions

See also

References

Further reading