Salicylaldoxime is an organic compound described by the formula C6H4CH=NOH-2-OH. It is the oxime of salicylaldehyde. This crystalline, colorless solid is a chelator and sometimes used in the analysis of samples containing transition metal ions, with which it often forms brightly coloured coordination complexes.[1]
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| Names | |
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| IUPAC name
Salicylaldehyde oxime
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| Other names
Saldox; 2-[(E)-(hydroxyimino)methyl]phenol
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.002.140 |
PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| C7H7NO2 | |
| Molar mass | 137.138 g·mol−1 |
| Appearance | white to off-white crystals |
| Melting point | 59 to 61 °C (138 to 142 °F; 332 to 334 K) |
| 25 g L−1 | |
| Hazards | |
| NFPA 704 (fire diamond) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Reactions
editSalicylaldoxime 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 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
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In the era when metals were analysed by spectrophotometry, many chelating ligands 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 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. Under these conditions, this is the only metal that precipitates; at pH 3.3, nickel also precipitates. Iron (III) will interfere. [2] It has been used as an ionophore in ion selective electrodes, with good response to Pb2+ and Ni2+.[3]
Extraction of metals
editSaloximes are used in the extraction and separation of metals from their ores. In one application of hydrometallurgy, Cu2+ is extracted into organic solvents as its saloxime complex.[4]
References
edit- ^ Smith, Andrew G.; Tasker, Peter A.; White, David J. "The structures of phenolic oximes and their complexes" Coordination Chemistry Reviews 2003, volume24, pp. 61-85. doi:10.1016/S0010-8545(02)00310-7
- ^ SH Simonsen; HM Burnett (1955). "Spectrophotometric Determination Of Copper With Salicylaldoxime - Application To Analysis Of Aluminum Alloys". Analytical Chemistry. 27 (8): 1336–1339. doi:10.1021/ac60104a039.
- ^ EK Quagraine; VPY Gadzekpo (December 1992). "Studies Of Spectrophotometric Reagents In Some Transition-Metal And Lead Ion-Selective Electrodes". Analyst. 117 (12): 1899–1903. Bibcode:1992Ana...117.1899Q. doi:10.1039/an9921701899.
- ^ Tasker, Peter A.; Tong, Christine C.; Westra, Arjan N. (2007). "Co-extraction of Cations and Anions in Base Metal Recovery". Coordination Chemistry Reviews. 251 (13–14): 1868–1877. doi:10.1016/j.ccr.2007.03.014.