Org. Synth. 1965, 45, 37
DOI: 10.15227/orgsyn.045.0037
DIETHYL [O-BENZOYL]ETHYLTARTRONATE
[Malonic acid, ethylhydroxy-, diethyl ester, benzoate]
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
1.
The
sodium hydride is obtained from Metal Hydrides Inc., Beverly, Massachusetts; the
diethyl ethylmalonate from Eastman Organic Chemicals.
2.
Reagent grade benzene was dried over calcium hydride prior to use.
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.
24. 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
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Ethyl benzoyloxy cyanoacetates
benzoyloxy γ-keto esters
benzoyloxy δ-ketonitriles
acetic acid (64-19-7)
Benzene (71-43-2)
methanol (67-56-1)
ether (60-29-7)
chloroform (67-66-3)
sodium sulfate (7757-82-6)
sodium iodide (7681-82-5)
diethyl ethylmalonate (133-13-1)
benzoyl peroxide (94-36-0)
sodium hydride (7646-69-7)
calcium hydride (7789-78-8)
DIETHYL [O-BENZOYL]ETHYLTARTRONATE
Malonic acid, ethylhydroxy-, diethyl ester, benzoate (6259-78-5)
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