Dimethylglyoxime
Overview
 
Dimethylglyoxime is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 described by the formula CH3C(NOH)C(NOH)CH3. This colourless solid is the dioxime
Oxime
An oxime is a chemical compound belonging to the imines, with the general formula R1R2C=NOH, where R1 is an organic side chain and R2 may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted oximes form a closely related family of compounds...

 derivative of the diketone diacetyl
Diacetyl
Diacetyl is a natural byproduct of fermentation. It is a vicinal diketone with the molecular formula C4H6O2...

 (also known as 2,3-butanedione). DmgH2 is used in the analysis of palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...

 or nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

. Its coordination complexes are of theoretical interest as models for enzymes and as catalysts. Many related ligands can be prepared from other diketones, e.g.
Encyclopedia
Dimethylglyoxime is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 described by the formula CH3C(NOH)C(NOH)CH3. This colourless solid is the dioxime
Oxime
An oxime is a chemical compound belonging to the imines, with the general formula R1R2C=NOH, where R1 is an organic side chain and R2 may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted oximes form a closely related family of compounds...

 derivative of the diketone diacetyl
Diacetyl
Diacetyl is a natural byproduct of fermentation. It is a vicinal diketone with the molecular formula C4H6O2...

 (also known as 2,3-butanedione). DmgH2 is used in the analysis of palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...

 or nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

. Its coordination complexes are of theoretical interest as models for enzymes and as catalysts. Many related ligands can be prepared from other diketones, e.g. benzil
Benzil
Benzil is the organic compound with the formula 2, generally abbreviated 2. This yellow solid is one of the most common diketones...

.

Preparation

Dimethylglyoxime can be prepared from butanone
Butanone
Butanone, also known as methyl ethyl ketone or MEK, is an organic compound with the formula CH3CCH2CH3. This colorless liquid ketone has a sharp, sweet odor reminiscent of butterscotch and acetone. It is produced industrially on a large scale, and also occurs in trace amounts in nature...

 first by reaction with ethyl nitrite
Alkyl nitrites
Alkyl nitrites are a group of chemical compounds based upon the molecular structure R-ONO. Formally they are alkyl esters of nitrous acid. They are distinct from nitro compounds ....

 followed b hydroxylamine
Hydroxylamine
Hydroxylamine is an inorganic compound with the formula NH2OH. The pure material is a white, unstable crystalline, hygroscopic compound. However, hydroxylamine is almost always provided and used as an aqueous solution. It is used to prepare oximes, an important functional group. It is also an...

 monosulfonate:

Ni(dmgH)2

Dimethylglyoxime is used as a chelating agent
Chelation
Chelation is the formation or presence of two or more separate coordinate bonds between apolydentate ligand and a single central atom....

 in the gravimetric analysis
Gravimetric analysis
Gravimetric analysis describes a set of methods in analytical chemistry for the quantitative determination of an analyte based on the mass of a solid...

 of nickel. The use of DMG as a reagent to detect nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

 was discovered by L. A. Chugaev
Lev Aleksandrovich Chugaev
Lev Aleksandrovich Chugaev was a Russian chemist. The Chugaev reaction, which he discovered during his work on thujene an terpene, is named after him. He was also active in the field of inorganic chemistry especially Platinum group complexes.In literature he is also known as Leo Aleksandrovich...

 in 1905. For qualitative analysis
Qualitative inorganic analysis
Classical qualitative inorganic analysis is a method of analytical chemistry which seeks to find elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous solution, so that materials in other forms may need to be brought into this state before using standard...

, dmgH2 is often used as a solution in ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

. It is the conjugate base, not dmgH2 itself, that forms the complexes. Furthermore, a pair of dmgH- ligands are joined through hydrogen bonds to give a macrocyclic ligand
Macrocycle
A macrocycle is, as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule." In the chemical literature, organic chemists may consider any molecule containing a ring of nine or more atoms to be a macrocycle...

. The most famous complex is the bright red Ni(dmgH)2, formed by treatment of Ni(II) sources with dmgH2. This planar complex is very poorly soluble and so precipitates from solution. This method is used for the gravimetric determination of nickel, e.g. in ores.


Cobaloximes

The nitrogen atoms in dmgH2 and its complexes are sp2 hybridized. Because of the planarity of the resulting ligand, the macrocycle [dmgH]22- resembles some biologically important macrocyclic ligands, as found for example in vitamin B12 and myoglobin. A well known family of model complexes, the cobaloximes, have the formula CoR(dmgH)2L, where R is an alkyl group and L is typically pyridine. In such complexes, L and R occupy “axial” positions on the cobalt, perpendicular to the plane of the (dmgH)2.
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