ALUMINUM ETHOXIDE

1

Aluminum Ethoxide

1

Al(OEt)

2

[555-75-9]

C

6

H

15

AlO

3

(MW 162.16)

InChI = 1/3C2H5O.Al/c3*1-2-3;/h3*2H2,1H3;/q3*-1;+3/

rC6H15AlO3/c1-4-8-7(9-5-2)10-6-3/h4-6H2,1-3H3

InChIKey = JPUHCPXFQIXLMW-MHHMYNCNAZ

(reagent for reduction of aldehydes to alcohols;

2

catalyst for

conversion of aldehydes to esters

3

)

Physical Data:

mp 157–160

◦

C; liq bp 200

◦

C/6–8 mmHg; mix-

ture 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 conver-
sion of α-halo aldehydes and α,β-unsaturated aldehydes to the
corresponding alcohols. For example, reaction of chloral with alu-
minum 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

Cl

3

C

O

H

3

(1)

O

H

3

+

Al(OCH

2

CCl

3

)

3

+

Al(OEt)

3

2 Al(OCH

2

CCl

3

)

3

+

3 H

2

SO

4

6 CCl

3

CH

2

OH

+

Al

2

(SO

4

)

3

84%

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 ox-
idation 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 α-hydrogens,

3b

aluminum ethox-

ide 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 corre-
sponding esters in good yield (eq 2).

6b

Crossed Tishchenko reac-

tions generally give mixtures of products.

R

H

O

R

OCH

2

R

O

2

(2)

Al(OEt)

3

R = n-Pr
R = Et

2

CH

R = Me(CH

2

)

6

81%
70%
69%

Aluminum ethoxide in xylene has also been used to polymer-

ize terephthalaldehyde into high molecular weight chains in a
Tishchenko-like process.

7

1.

(a) Mehrotra, R. C., J. Indian Chem. Soc. 1953, 30, 585. (b) Beuhler,
C. A.; Pearson, D. E. Survey of Organic Syntheses; Wiley: New York,
1970; Vol. 1, p 853. (c) Bersin, T. Newer Methods of Preparative Organic
Chemistry

; Interscience: New York, 1948; p 125. (d) Wagner, R. B.;

Zook, H. D. Synthetic Organic Chemistry; Wiley: New York, 1953;
p. 494.

2.

Meerwein, H.; Schmidt, R., Justus Liebigs Ann. Chem. 1925, 444,
233.

3.

(a) Cichon, L., Wiad. Chem. 1966, 20, 641, 783. (b) Kamm, O.; Kamm,
W. F., Org. Synth., Coll. Vol. 1941, 1, 104.

4.

Chalmers, W., Org. Synth., Coll. Vol. 1943, 2, 598.

5.

Dworzak, R., Monatsh. Chem. 1926, 47, 11.

6.

(a) Child, W. C.; Adkins, H., J. Am. Chem. Soc. 1923, 45, 3013. (b) Villani,
F. J.; Nord, F. F., J. Am. Chem. Soc. 1947, 69, 2605.

7.

Sweeney, W., J. Appl. Polym. Sci., 1963, 7, 1983.

Gary W. Morrow

The University of Dayton, Dayton, OH, USA

Avoid Skin Contact with All Reagents