Aluminum Ethoxide1

Al(OEt)3

[555-75-9]  · C6H15AlO3  · Aluminum Ethoxide  · (MW 162.16)

(reagent for reduction of aldehydes to alcohols;2 catalyst for conversion of aldehydes to esters3)

Physical Data: mp 157-160 °C; liq bp 200 °C/6-8 mmHg; mixture of oligomers in solution; physical properties drastically affected by traces of moisture.

Solubility: sol hot xylene, cholorobenzene, other high boiling solvents.

Form Supplied in: available as white powder.

Preparative Method: react Aluminum filings with absolute ethanol using small amounts of Mercury(II) Chloride or Iodine as catalysts.4

Handling, Storage, and Precautions: use in a fume hood; air and moisture sensitive; extremely destructive to tissue of the mucous membranes and upper respiratory tract, eyes and skin, and should be handled with appropriate caution. Contact via inhalation route is particularly hazardous.

Reductions.

The reagent, while commercially available, may be conveniently prepared prior to use.4 It has been used in Meerwein-Ponndorf-Verley reductions for the selective conversion of a-halo aldehydes and a,b-unsaturated aldehydes to the corresponding alcohols. For example, reaction of chloral with aluminum ethoxide in ethanol as solvent gives acetaldehyde and the aluminum salt of trichloroethanol. Subsequent treatment of the salt with sulfuric acid liberates trichloroethanol in excellent yield (eq 1).4 Similar high-yield reductions have been carried out on bromal, cinnamaldehyde, and various halogenated cinnamyl and crotyl aldehydes.2,5

Esters from Aldehydes.

When Tishchenko treated a variety of aldehydes with a catalytic amount of aluminum ethoxide in the absence of solvents, he obtained primarily esters derived from oxidation of one half of the aldehyde and reduction of the other half. Extensive studies later verified this early work.6 Although alkali metal alkoxides have been used successfully in the Tishchenko reaction for aldehydes lacking a-hydrogens,3b aluminum ethoxide is almost invariably the catalyst of choice in those cases where aldol condensations would otherwise predominate. For example, treatment of butanal, 2-ethylbutanal, or octanal with aluminum ethoxide (5% by weight relative to the aldehyde) gave the corresponding esters in good yield (eq 2).6b Crossed Tishchenko reactions generally give mixtures of products.

Aluminum ethoxide in xylene has also been used to polymerize terephthalaldehyde into high molecular weight chains in a Tishchenko-like process.7


1. (a) Mehrotra, R. C. JIC 1953, 30, 585. (b) Beuhler, C. A.; Pearson, D. E. Survey of Organic Syntheses; Wiley; New York, 1970; Vol. 1, pp 853-854. (c) Bersin, T. Newer Methods of Preparative Organic Chemistry; Interscience: New York, 1948; pp 125-158. (d) Wagner, R. B.; Zook, H. D. Synthetic Organic Chemistry; Wiley: New York, 1953; p. 494.
2. Meerwein, H.; Schmidt, R. LA 1925, 444, 233.
3. (a) Cichon, L. Wiad. Chem. 1966, 20, 641, 783. (b) Kamm, O.; Kamm, W. F. OSC 1941, 1, 104.
4. Chalmers, W. OSC 1943, 2, 598.
5. Dworzak, R. M 1926, 47, 11.
6. (a) Child, W. C.; Adkins, H. JACS 1923, 45, 3013. (b) Villani, F. J.; Nord, F. F. JACS 1947, 69, 2605.
7. Sweeney, W. J. Appl. Polym. Sci., 1963, 7, 1983.

Gary W. Morrow

The University of Dayton, OH, USA



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