Salicylaldoxime is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

described by the formula C₆H₄CH=NOH-2-OH. It is the

oxime In organic chemistry, an oxime is an organic compound belonging to the imines, with the general Chemical formula, formula , where R is an organic Side chain, side-chain and R' may be hydrogen, forming an aldoxime, or another organic functional g ...

salicylaldehyde Salicylic aldehyde (2-hydroxybenzaldehyde) is an organic compound with the formula . Along with 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde, it is one of the three isomers of hydroxybenzaldehyde. This colorless oily liquid has a bitter almo ...

. This crystalline, colorless solid is a chelator and sometimes used in the analysis of samples containing

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. The lanthanide and actinid ...

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s, with which it often forms brightly coloured

coordination complex A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

es.

Reactions

Salicylaldoxime is the conjugate acid of a bidentate ligand: :2 C₆H₄CH=NOH-2-OH + Cu²⁺ → Cu(C₆H₄CH=NOH-2-O)₂ + 2 H⁺ In highly acidic media, the ligand protonates, and the

metal aquo complex In chemistry, metal aquo complexes are coordination compounds containing metal ions with only water as a ligand. These complexes are the predominant species in aqueous solutions of many metal salts, such as metal nitrates, sulfates, and perchlo ...

and aldoxime are liberated. In this way the ligand is used as a recyclable extractant. It typically forms charge-neutral complexes with divalent metal ions.

Analytical chemistry

In the era when metals were analysed by

spectrophotometry Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spe ...

, many chelating

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s were developed that selectively formed brightly coloured complexes with particular metal ions. This methodology has been eclipsed with the introduction of inductively coupled plasma methodology. Salicylaldoxime can be used to selectively

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 ...

metal ions for gravimetric determination. It forms a greenish-yellow precipitate with copper at a pH of 2.6 in the presence of

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...

. Under these conditions, this is the only metal that precipitates; at pH 3.3,

nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

also precipitates. Iron (III) will interfere. It has been used as an ionophore in

ion selective electrode An ion-selective electrode (ISE), also known as a specific ion electrode (SIE), is a simple membrane-based potentiometric device which measures the activity of ions in solution. It is a transducer (or sensor) that converts the change in the concent ...

s, with good response to Pb²⁺ and Ni²⁺.

Extraction of metals

Saloximes are used in the extraction and separation of metals from their ores. In one application of

hydrometallurgy Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy uses solutions to recover metals from ores, concentrates, and recycled or residual materials. Usually the extracti ...

, Cu²⁺ is extracted into organic solvents as its saloxime complex.{{cite journal, doi=10.1016/j.ccr.2007.03.014, title=Co-extraction of Cations and Anions in Base Metal Recovery , year=2007 , last1=Tasker , first1=Peter A. , last2=Tong , first2=Christine C. , last3=Westra , first3=Arjan N. , journal=Coordination Chemistry Reviews , volume=251 , issue=13–14 , pages=1868–1877

References

External links

Chemical data at NIST Chemistry WebBook
2-Hydroxyphenyl compounds Analytical chemistry Aldoximes