Potassium Hydroxide-Alumina


[1310-58-3]  · HKO  · Potassium Hydroxide-Alumina  · (MW 56.11) (Al2O3)

[1344-28-1]  · Al2O3  · Potassium Hydroxide-Alumina  · (MW 101.96)

(hydrolysis of esters; alkylation of alcohols, amides, and phenylacetonitrile)

Physical Data: see entries for Potassium Hydroxide and Alumina.

Preparative Methods: mixing neutral alumina and a KOH solution produces a nearly homogeneous adsorbate (reagent 1), referred to as basic alumina.1 Another form of basic alumina (reagent 2) is prepared by mixing dried neutral alumina (100 °C for 24 h) with solid KOH.2

Hydrolysis of Esters.

Cholestan-3b-yl 3,5-dinitrobenzoate and other steroidal and triterpenoid 3,5-dinitrobenzoate esters were readily hydrolyzed by adsorbing a benzene solution of the ester on a column of reagent (1) and eluting it with a 3:1 benzene-ether mixture to give the alcohol in good yield (eq 1).3

Reagent (1) gave slower reaction rates with less reactive esters3 and better results were obtained from reagent (2). Stirring a solution of n-decyl benzoate in ether with reagent (2) at rt for 48 h gave n-decyl alcohol and benzoic acid in 91% and 89% isolated yields, respectively (eq 2).2 Other esters were hydrolyzed in isolated yields between 80-100% for either the alcohol or acid product. Control experiments showed that a dried KOH/alumina reagent at 110 °C gave no reaction and a small amount of water was required for the hydrolytic activity.2

Various reactions of basic alumina (reagent 1) with several classes of organic compounds were reported in an early short review.4 Some of these reactions are presented in eqs 3-5. Treatment of allyl bromide or propargyl bromide with basic alumina in ether for 4 days gave diallyl ether and dipropargyl ether, respectively, in low yields (eq 3).4

Either 1-chloro- or 1-bromocyclohexanone was converted to 2-hydroxycyclohexanone in 64% yield after a few minutes upon treatment with basic alumina.4 The product dimerized slowly upon standing at rt (eq 4).

Preparation of b-ethoxycinnamaldehyde by the hydrolysis of the corresponding dimethyliminium perchlorate salt was achieved with basic alumina in nearly quantitative yield (eq 5).4

Selective a-Monoalkylation of Phenylacetonitrile.

Alumina impregnated with KOH acted as an efficient base for the selective a-monoalkylation of phenylacetonitrile with alkyl halides in benzene (eq 6). It was suggested that the reaction occurs predominantly in the pores of the KOH/Al2O3 solid base. The high selectivity towards monoalkylation in nonpolar solvents was explained by the tight adsorption of the anion of the initial monoalkyl product onto the wall of the pore, thus rendering it strongly sterically hindered for a second alkylation.5

Selective N-Monoalkylation of Amides with Alkyl Halides.

Selective N-monoalkylation of amides was carried out successfully using KOH-alumina (eq 7). The best solvent for this reaction was dioxane which gave consistently the highest mono:dialkyl ratio. Unlike the previous reaction, the use of a mixture of powdered KOH and alumina was superior to the use of the KOH-impregnated alumina in both yield and selectivity. Also, alkyl bromides were better than the iodides. Reported yields ranged from 56% to 80% with selectivity towards N-monoalkylation ranging between 82-99%.6

1. FF 1969, 2, 18.
2. Regen, S. L.; Mehrotra, A. K. SC 1981, 11, 413.
3. Castells, J.; Fletcher, G. A. JCS 1956, 3245.
4. Serratosa, F. J. Chem. Educ. 1969, 46, 302 and references listed therein.
5. Sukata, K. BCJ 1983, 56, 3306.
6. Sukata, K. BCJ 1985, 58, 838.

Ahmed F. Abdel-Magid

The R. W. Johnson Pharmaceutical Research Institute, Spring House, PA, USA

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