Org. Synth. 1953, 33, 20
DOI: 10.15227/orgsyn.033.0020
DI-tert-BUTYL MALONATE
[Malonic acid, di-t-butyl ester]
Submitted by Chittaranjan Raha
1
Checked by William S. Johnson and Rudolph W. Kluiber.
1. Procedure
2.
A. Malonyl dichloride. In a 250-ml. Erlenmeyer flask (Note 1) fitted by a ground-glass joint to a reflux condenser capped with a calcium chloride drying tube are placed 52 g. (0.5 mole) of finely powered, dry malonic acid (Note 2) and 120 ml. (about 1.65 mole) of thionyl chloride (Note 3). The flask is warmed for 3 days in a heating bath kept at 45–50° (Note 4). During this period the mixture, which is agitated occasionally by gentle swirling, gradually darkens to a deep brownish red or sometimes a blue color. Finally the mixture is heated at 60° for 5–6 hours. After cooling, it is transferred to a 125-ml. modified Claisen flask and distilled at reduced pressure (water aspirator). A calcium chloride guard tube is inserted between the vacuum line and the apparatus, and the flask is heated with a bath rather than a free flame. After a small fore-run of thionyl chloride, the malonyl chloride distils at 58–60°/28 mm. The pale yellow product amounts to 50.5–60 g. (72–85% yield), nD29 1.4572.
B. Di-tert-butyl malonate. A 1-l. three-necked flask is fitted with a thermometer, a mercury- or rubber sleeve-sealed mechanical stirrer, a reflux condenser protected by a calcium chloride guard tube, and a dropping funnel (either pressure-equalized or protected by a calcium chloride guard tube). A mixture of 100 ml. (about 1 mole) of tert-butyl alcohol, dried by distillation from sodium and 80 ml. (0.63 mole) of dry dimethylaniline (Note 5) is placed in the flask, the stirrer is started, and a solution of 28.0 g. (0.2 mole) of malonyl dichloride in about 60 ml. of dry, alcohol-free chloroform (Note 6) is added slowly from the dropping funnel while the reaction flask is cooled in an ice bath. The reaction is strongly exothermic, and the rate of dropping is regulated so that the temperature of the mixture does not exceed 30°. After the addition is complete (about 30 minutes) the light-greenish mixture is heated under reflux for 4 hours. The mixture is then cooled, 150 ml. of ice-cold 6N sulfuric acid is added with stirring, and the product is extracted with three 250-ml. portions of ether (Note 7). The combined ether extracts are washed once with 6N sulfuric acid, twice with water, twice with 10% potassium carbonate, and once with saturated sodium chloride, and are finally dried over anhydrous sodium sulfate to which a small amount of potassium carbonate is added. The ether is removed by distillation at reduced pressure (water aspirator), and the residue (to which a pinch of magnesium oxide is added) is distilled at reduced pressure from a modified Claisen flask (Note 8). The yield of colorless di-tert-butyl malonate, distilling at 65–67°/1 mm., 110–111°/22 mm., is 35.8–36.2 g. (83–84%), nD25 1.4159, m.p. about −6°.
2. Notes
1.
Better results are obtained by using a
flat-bottomed flask, which permits the insoluble
malonic acid to be distributed over a greater surface.
2.
The reaction mixture is heterogeneous at first, and if the acid is not finely powdered, some of it remains unreacted. Attempts to carry out the reaction on a larger scale resulted in some charring and lower yields.
3.
Eastman Kodak Company white label quality thionyl chloride is satisfactory.
4.
The temperature range is critical, and yields are lower if it is not controlled carefully. The use of
pyridine as a catalyst is not recommended as it produces charring even after relatively short reaction periods.
5.
J. T. Baker dimethylaniline (purified grade) is satisfactory without distillation.
6.
The
chloroform was dried over and distilled from anhydrous
calcium chloride just before use.
7.
The
dimethylaniline may be recovered from the aqueous layer where it is dissolved as the salt.
8.
Di-tert-butyl malonate, like most
tert-butyl esters, decomposes readily on heating in the presence of traces of acids. It is therefore desirable to give all glassware to be used for distillation of the material an alkali rinse before use. The addition of a small amount of
magnesium oxide also helps to inhibit the decomposition during distillation.
2 When decomposition starts, foaming is generally observed. In this event the addition of glass wool to the distillation flask helps to keep the product from foaming over.
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3. Discussion
Procedure I is a modification
2 of the method of Altschul
3 for preparing
tert-butyl esters.
Di-tert-butyl malonate also has been prepared by the reaction of
malonyl dichloride and
tert-butyl alcohol in the presence of a base,
4,5, and by the reaction of
carbon suboxide with
tert-butyl alcohol.
6 Procedure II is based on the former
4 method and developed from studies initiated by P. C. Mukharji of the University College of Science and Technology, Calcutta.
Malonyl dichloride has been prepared from
malonic acid and
thionyl chloride,
4,7,8,9,10,11 and from
carbon suboxide and anhydrous
hydrogen chloride.
12 The present procedure is adapted from that of Staudinger and Bereza
9 and of Backer and Homan.
4
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
calcium chloride (10043-52-4)
potassium carbonate (584-08-7)
sulfuric acid (7664-93-9)
thionyl chloride (7719-09-7)
sodium sulfate (7757-82-6)
dimethylaniline (121-69-7)
Malonyl dichloride (1663-67-8)
Malonic acid (141-82-2)
tert-butyl alcohol (75-65-0)
Di-tert-butyl malonate,
Malonic acid, di-t-butyl ester (541-16-2)
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