Organic Syntheses, CV 5, 379
Submitted by E. H. Larsen and S.-O. Lawesson
1.
Checked by M. R. Michalewich and William D. Emmons.
1. Procedure
Caution! This reaction should be carried out behind a safety screen. The solvent removal and product distillation steps should also be carried out behind a screen to minimize trouble if the product is contaminated with undetected peroxides.
Benzoyl peroxide should be handled with caution because it is impact-sensitive.
To a
1-l., three-necked, round-bottomed flask is added
7.2 g. (0.15 mole) of a 50% dispersion of sodium hydride in mineral oil (Note
1). The
sodium hydride is washed several times by decantation with dry
ether and is then covered with
300 ml. of dry benzene (Note
2). The flask is equipped with
dropping funnel, stirrer, and
reflux condenser.
Diethyl ethylmalonate (28.2 g., 0.15 mole) (Note
1) is added dropwise over a 5-minute period, and the reaction mixture is stirred for 2 hours until a clear solution forms. The solution is cooled in an
ice bath, and
24.2 g. (0.1 mole) of benzoyl peroxide (Note
3) in
300 ml. of dry benzene is added dropwise over a 1-hour period with continuous stirring. After another 30 minutes, a peroxide test (Note
4) is made to ensure that all the peroxide has reacted.
The porridge-like mixture is then poured into 300 ml. of water and vigorously shaken in a
1-l. separatory funnel. The
benzene phase is separated, and the water phase is extracted three times with
100-ml. portions of ether. The combined extracts are washed until neutral and are dried over anhydrous
sodium sulfate. The volatile solvents are evaporated at aspirator pressure, and the residue (Note
5) is distilled through a short
Vigreux column. After a fore-run of
diethyl ethylmalonate 23.3–24.1 g. (
75–78%) of
diethyl [O-benzoyl]ethyltartronate is obtained, b.p.
132° (0.1 mm.);
n20D 1.4885.
2. Notes
3. The
benzoyl peroxide is recrystallized from
chloroform and
methanol at room temperature. The checkers used the 96% purity commercial grade available from the Lucidol Division of Wallace and Tiernan without further purification.
4. A few drops of the reaction mixture are added to a dilute solution of
sodium iodide in glacial
acetic acid; if a brown ring is not formed, all peroxides have reacted.
5. A peroxide test on the residue is recommended before the distillation is begun.
3. Discussion
The present procedure is essentially that described by one of the submitters.
2
4. Merits of the Preparation
The reaction described is of considerable general utility for the preparation of benzoyloxy derivatives of β-carbonyl compounds. Thus O-benzoyl tartronates have been prepared, from which routes to diethyl tartronates and tartronic acids have been developed.
2 Ethyl benzoyloxy cyanoacetates have similarly been prepared and are of potential interest in connection with the chemistry of amino acid precursors.
3 Similarly the benzoyloxy group has been introduced into β-keto esters
4,5 and β-diketones.
6 Also a new method for the preparation of acyloins was found.
5 An extension of the method has led to certain types of
benzoyloxy γ-keto esters7 and
benzoyloxy δ-ketonitriles.
8 The method has been reviewed.
9
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