Checked by William S. Johnson and H. Wynberg.
1. Procedure
Sodium ethoxide is prepared from
12.0 g. (0.52 g. atom) of sodium and
300 ml. of anhydrous ethanol in a
1-l. three-necked round-bottomed flask fitted with a
reflux condenser carrying a
calcium chloride tube. After the
sodium has dissolved completely, the condenser is arranged for distillation under reduced pressure and the excess
ethanol is removed by heating the flask on a
steam bath while the system is maintained at the pressure obtained with an
ordinary aspirator (Note
1).
As rapidly as possible, after removal of the
ethanol, the flask is fitted with a
rubber-sealed stirrer, a
dropping funnel, a distilling head containing a
thermometer, and a condenser arranged for distillation into a flask protected by a calcium chloride tube. There are then added
300 ml. (292 g., 2.5 moles) of dry diethyl carbonate,
80 ml. of dry toluene, and
58.5 g. (0.50 mole) of phenylacetonitrile (Note
2). The flask is heated, with good stirring, and the cake of
sodium ethoxide soon dissolves. When distillation has started, dry
toluene is added dropwise at about the same rate that the distillate is collected. Approximately
200–250 ml. of toluene should be added in a period of 2 hours (Note
3) while stirring and distillation are continued.
The mixture is cooled and transferred to a
1-l. beaker. After addition of 300 ml. of cold water, the aqueous phase is acidified with
35–40 ml. of acetic acid. The layers are separated and the water solution is extracted with three
75-ml. portions of ether. The organic solutions are combined, washed with 100 ml. of water, and dried over anhydrous
magnesium sulfate. The low-boiling solvents are removed by distillation at atmospheric pressure, and the residue is distilled under reduced pressure through a
short (15-cm.) Vigreux column. After a 1–5 g. forerun, the product is collected at
125–135°/3–5 mm. (Note
4). The yield is
66–74 g. (
70–78%).
2. Notes
1. The success of this procedure is dependent upon the quality of the
sodium ethoxide. The
ethanol should be dried before use,
2 and the
sodium ethoxide should not be heated to a temperature higher than 90–100°. The dry material can be transferred, but in this case it is advisable to prepare it in the flask in which it is to be used.
3. Any
ethanol remaining in the
sodium ethoxide, together with the
ethanol produced during the reaction, is removed during this period. The progress of the carbethoxylation reaction can be followed by temperature readings. During the first half of the heating period distillation usually occurs at a vapor temperature of 80–85°, but as the reaction nears completion and the
ethanol is removed, the temperature rises to 110–115°. Near the end of the period, the
sodium salt of ethyl phenylcyanoacetate appears as a precipitate.
4. Other observed boiling points are
129–131°/3 mm.,
145–150°/7–8 mm. The product is a colorless liquid,
nD25 1.5012-1.5019.
3. Discussion
This procedure is a modification of the method of Wallingford, Jones, and Homeyer.
3 The carbethoxylation of
phenylacetonitrile is the only method of preparative value for this compound.
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