Org. Synth. 1952, 32, 68
DOI: 10.15227/orgsyn.032.0068
ETHYL ORTHOCARBONATE
[Orthocarbonic acid, tetraethyl ester]
Submitted by John D. Roberts and Robert E. McMahon
1.
Checked by William S. Johnson and William E. Loeb.
1. Procedure
This preparation should be conducted in a hood to avoid exposure to chloropicrin.
A solution of sodium ethoxide is prepared under nitrogen from 70 g. (3.04 g. atoms) of sodium and 2 l. of absolute ethanol (Note 1) in a 3-l. three-necked flask which is equipped with mechanical stirrer, efficient reflux condenser, dropping funnel, and a thermometer which dips below the level of the liquid in the flask. Chloropicrin (100 g., 0.61 mole) (Note 2) is placed in the dropping funnel, and the stirred solution is heated to 58–60° with a water bath. The chloropicrin is added at a rate of 30–35 drops per minute until the reaction becomes self-sustaining (about 20 minutes), at which point the water bath is removed and the balance of the chloropicrin is added at a rate sufficient to maintain the temperature at 58–60° (Note 3). When the addition, which requires nearly 2 hours, is complete, the stirrer is stopped and the mixture is allowed to stand overnight.
The flask is connected to a 2 by 50 cm. Vigreux column equipped with a total-reflux partial take-off head, and all but about 400 ml. of the ethanol is removed at 200 mm. pressure with a reflux ratio greater than 5:1 (Note 4).
The residue is cooled, diluted with 1.2 l. of water, and transferred to a 2-l. separatory funnel. The organic layer is separated, washed with 200 ml. of saturated salt solution, and dried over anhydrous magnesium sulfate. The aqueous layer is extracted with a total of 800 ml. of ether used in several small portions. The ethereal extracts are combined, washed first with 500 ml. of water then with 500 ml. of saturated salt solution, and finally dried over anhydrous magnesium sulfate. The ether is removed through a 1.8 by 25 cm. glass-helix-packed fractionating column with a total-reflux partial take-off head. The residue is combined with the balance of the crude product and distilled through the fractionating column at atmospheric pressure. The yield of ethyl orthocarbonate is 54–57.5. g. (46–49%); b.p. 158–161°; nD25 1.3905–1.3908.
2. Notes
1.
The
absolute ethanol was a good commercial grade and contained less than 0.1% of water according to the paraffin-oil test.
22.
Chloropicrin is a skin irritant and a lachrymator. No difficulty was experienced when the preliminary steps were carried out in a good hood.
3.
Care should be taken to regulate the temperature and rate of addition of chloropicrin as specified in order to avoid accumulation of unreacted
chloropicrin in the reaction mixture during the induction period; otherwise the reaction, which is strongly exothermic, may get out of control.
4.
A water bath should be used as a heat source to avoid over-heating, which leads to lowered yields. This distillation should be carried out carefully to prevent loss of product by co-distillation with the
ethanol.
3. Discussion
The above procedure is essentially that of Tieckelmann and Post.
3 Ethyl orthocarbonate has been prepared by the reaction of chloropicrin and
sodium ethoxide by Bassett
4 and Röse.
5 Thiocarbonyl perchloride has been reported
3,6 to react with
sodium ethoxide to give good yields of
ethyl orthocarbonate.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
chloropicrin
Thiocarbonyl Perchloride
ethanol (64-17-5)
ether (60-29-7)
nitrogen (7727-37-9)
sodium (13966-32-0)
sodium ethoxide (141-52-6)
magnesium sulfate (7487-88-9)
Ethyl orthocarbonate
Orthocarbonic acid, tetraethyl ester (78-09-1)
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