Acetaldoxime

Acetaldoxime is the chemical compound with formula C2H5NO. It is one of the simplest oxime-containing compounds, and has a wide variety of uses in chemical synthesis.

Acetaldoxime
Names
IUPAC name
N-ethylidenehydroxylamine
Other names
aldoxime, acetaldehyde oxime, ethanal oxime, ethylidenehydroxylamine
Identifiers
3D model (JSmol)
1209252
ChEBI
ChemSpider
ECHA InfoCard 100.003.164
EC Number
  • 203-479-6
RTECS number
  • AB2975000
UNII
Properties
C2H5NO
Molar mass 59.067 g mol−1
Appearance clear, colorless to yellow liquid
Density 0.97 g cm−3
Melting point 25 °C (77 °F; 298 K) (average of the α and β forms)
Boiling point 115.24 °C (239.43 °F; 388.39 K)
299 g L−1
Solubility in ethanol miscible
log P -0.13
Vapor pressure 13 mmHg
Acidity (pKa) 11.82
Hazards
Main hazards Flammable, harmful by ingestion, irritant
Safety data sheet External MSDS
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
2
0
Flash point 40 °C (104 °F; 313 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Properties

Acetaldoxime will often appear as a colorless liquid, or a white solid. Its solid can form two different needle-like crystal structures. The α-form melts at approximately 44 °C - 47 °C, while the β-form melts at 12 °C. The liquid is known to have a pungent odor, and is highly flammable. The compound can act as both an acid or a base, due to its acidic proton on the hydroxyl group and the basic nitrogen atom. The compound exists as a mixture of its Z and E stereoisomers (i.e. syn and anti, or cis and trans) in its normal form. The E stereoisomer can be isolated by slow crystallization of a distilled E/Z mixture.[1][2]

Production

Acetaldoxime can be prepared by combining pure acetaldehyde and hydroxylamine under heating in the presence of a base.[3]

Preparation of acetaldoxime from acetaldehyde and hydroxylamine

The use of CaO as a base in the preparation of oximes from various types of ketones and aldehydes under mild conditions also gave quantitative yields. [4]

Reactions

Alkylation

Deprotonation of acetaldoxime with 2 equivalents of n-butyllithium at -78 °C generates the dianion which reacts with benzyl bromide or 1-iodopropane to give excellent yields of α-alkylated (Z)-oximes.[5] α,α-Dialkylation by further alkylation in similar way has been achieved.[5] It is generally known that ketone oximes can be deprotonated and alkylated regiospecifically syn to the oxime hydroxy group.[6][7] It is essential to perform the deprotonation and alkylation at -78 °C as otherwise no α-alkylated oximes are isolated, the major byproducts being nitriles.[6]

Rearrangement to acetamide

Heating of acetaldoxime in xylene in the presence of 0.2 mol % nickel(II) acetate[1] or silica gel[8] as catalyst caused isomerization into acetamide.

Synthesis of heterocycles

Chlorination of acetaldoxime with N-chlorosuccinimide[9] or chlorine gas[7][10] in chloroform affords acetohydroxamic acid chloride, which suffers dehydrochlorination with triethylamine to give acetonitrile N-oxide. The latter 1,3-dipole undergoes 1,3-dipolar cycloaddition to alkenes giving 2-isoxazolines in a one-pot procedure.[9] This reaction is also suitable for the construction of more complex molecules such as the conversion of a 6-ethylideneolivanic acid derivative into the corresponding spiroisoxazoline.[10]

Uses

Aldoximes such as acetylaldoxime are using during chemical synthesis processes as intermediates for chemical reactions. It is especially notable for its commercial application as an intermediate for the production of pesticides.[11]

References
  1. Field, L.; Hughmark, P. B.; Shumaker, S. H.; Marshall, W. S. J. Am. Chem. Soc. 1961, 83, 1983.
  2. "Oximes - Encyclopedia".
  3. "Acetaldoxime".
  4. Sharghi, H., & Sarvari, M. H.. A mild and versatile method for the preparation of pximes by use of calcium oxide. J. Chem. Research, 2000, pp. 24—25.
  5. Gawley, R. E.; Nagy, T. TL. 1984, 25, 263.
  6. Kofron, W. G.; Yeh, M. K. J. Org. Chem. 1976, 41, 439.
  7. Mukerji, S. K.; Sharma, K. K.; Torssell, K. B. G. T. 1983, 39, 2231.
  8. Chattopadhyaya, J. B.; Rama Rao, A. V. T. 1974, 30, 2899.
  9. Larsen, K. E.; Torssell, K. B. G. T. 1984, 40, 2985.
  10. Corbett, D. F. J. Chem. Soc. 1986, 421.
  11. "Production of acetaldehyde oxime".
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