Aluminium isopropoxide

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Aluminium isopropoxide
One enantiomorph of Al4(OiPr)12
General
Systematic name Aluminium Isopropoxide
Other names Triisopropoxyaluminium
Aluminium isopropanolate
Aluminium sec-propanolate
Aluminium triisopropoxide
2-Propanol aluminium salt
AIP
empirical formula C9H21O3Al
SMILES CC(C)O[Al](OC(C)C)OC(C)C
Molar mass 204.25 g/mol
Appearance white solid
CAS number 555-31-7
Properties
Density and phase 1.035 g/cm³, solid
Solubility in water Decomposes
Solubility in isopropanol Soluble
Melting point Sensitive to purity:
138–142 °C (99.99+%)
118 °C (98+%)[1]
Boiling point @10 torr 135 °C (408 K)
Structure
Crystal structure monoclinic
Hazards
MSDS External MSDS
Main hazards Flammable (F)
NFPA 704

1
2
2
 
Flash point 16 °C
R-phrases R11
S-phrases S8, S16
RTECS number BD0975000
Supplementary data page
Structure & properties n, εr, etc.
Thermodynamic data Phase behaviour
Solid, liquid
Spectral data UV, IR, NMR, MS
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
Infobox disclaimer and references

Aluminium isopropoxide is the chemical compound usually described with the formula Al(O-i-Pr)3, where i-Pr is the isopropyl group (CH(CH3)2). This colourless solid is a useful reagent in organic synthesis. The structure of this compound is complex, possibly time-dependent, and may depend on solvent.

Contents

[edit] History and nature of the reagent

Aluminium isopropoxide was first reported as a reducing agent by Meerwein and Schmidt in the Meerwein-Ponndorf-Verley reduction ("MPV") in 1925.[2] The reverse of the MPV reaction, oxidation of an alcohol to a ketone, is termed the Oppenauer Oxidation. The original Oppenauer oxidation employed aluminium butoxide in place of the isoproxide.[3]

The structure of the metal alkoxides are often complex and aluminium isopropoxide is no exception. The complexity is also reflected in the disputed melting point for the material which could reflect the presence of trace impurities, such as water, slow oligomerisation ("aging") or both. The tetrameric structure was verified by NMR spectroscopy and X-ray crystallography. The species is described by the formula Al[(μ-O-i-Pr)2Al(O-i-Pr)2]3.[4] [5] The unique central Al is octahedral surrounded by three bidentate "[Al(O-i-Pr)4]-" ligands, each featuring tetrahedral Al. The idealised point group symmetry is D3. The tert-butoxide is a dimeric with the formula Al2(μ-O-t-Bu)2(O-t-Bu)4[6] It is prepared analogously to the isopropoxide.[7]

A widely accepted method for preparing aluminium isopropoxide was published in 1936 by Young, Hartung, and Crossley.[8] Their procedure entails heating a mixture of 100 g of aluminium, 1200 mL of Isopropyl alcohol, and 5 g of mercuric chloride at reflux. The process occurs via the formation of an amalgam of the aluminium. A catalytic amount of iodine is sometimes added to initiate the reaction, which can be quite vigorous. Young et al. achieved an 85-90% yield, after purification by distillation at 140-150 °C (5 mm Hg).

[edit] Reactions

In a MPV reduction, ketones and aldehydes are reduced to alcohols concomitant with the formation of acetone. This reduction relies on an equilibrium process, hence it produces the thermodynamic product. Conversely, in the Oppenauer Oxidation, secondary alcohols are converted to ketones[1], and homoallylic alcohols are converted to α,β-unsaturated carbonyls.[9] In these reactions, it is assumed that the tetrameric cluster disagregates.

Being a basic alkoxide, Al(O-i-Pr)3 has been also investigated as a catalyst for ring opening polymerization of cyclic ester]]s.[10]

[edit] References

  1. ^ Ishihara, K.; Yamamoto, H. "Aluminum Isopropoxide" in Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley. DOI: 10.1002/047084289X.ra084
  2. ^ Meerwein, H.; Schmidt, R. "Ein neues Verfahren zur Reduktion von Aldehyden und Ketonen" Justus Liebig's Annalen der Chemie 1925, Volume 444, Pages: 221-238
  3. ^ Oppenauer, R. V. “Dehydration of secondary alcohols to ketones. I. Preparation of sterol ketones and sex hormones.” Recueil des Travaux Chimiques des Pays-Bas et de la Belgique (1937), volume 56, pages 137-44.
  4. ^ Folting, K.; Streib, W. E.; Caulton, K. G.; Poncelet, O.; Hubert-Pfalzgraf, L. G. "Characterization of aluminum isopropoxide and aluminosiloxanes” Polyhedron 1991, volume 10, pages 1639-46.DOI:10.1016/S0277-5387(00)83775-4.
  5. ^ Turova, N. Y.; Fozunov, V. A.; Yanovskii, A. I.; Bokii, N. G.; Struchkov, Yu T.; Tarnopolskii, B. L. Journal of Inorganic and Nuclear Chemistry 1979, volume 41, p. 5.
  6. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  7. ^ Wayne, W.; Adkins. H. “Aluminum tert-Butoxide“ Organic Syntheses, Collected Volume 3, p.48 (1955).
  8. ^ Young, W.; Hartung, W.; Crossley, F. "Reduction of Aldehydes with Aluminum Isopropoxide" Journal of the American Chemical Society, volume 58, pages 100-2, 1936.DOI:10.1021/ja01292a033
  9. ^ Eastham, J. F.; Teranishi, R. "Δ4-Cholesten-3-one" Organic Syntheses, Coll. Vol. 4, p.192 (1963). http://www.orgsyn.org/orgsyn/pdfs/CV4P0192.pdf
  10. ^ Tian, D.; Dubois, Ph.; Jérôme, R. "Macromolecular Engineering of Polylactones and Polylactides. 22. Copolymerization of -Caprolactone and 1,4,8-Trioxaspiro[4.6]-9-undecanone Initiated by Aluminum Isopropoxide" Macromolecules,1997, volume 30, pages 2575 -2581. DOI:S0024-9297(96)01567-7 ma961567w S0024-9297(96)01567-7.

[edit] External links