Checked by William S. Johnson and William E. Loeb.
1. Procedure
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.
2
2.
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
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