Organic Syntheses, CV 4, 801
Submitted by B. W. Howk and J. C. Sauer
1.
Checked by N. J. Leonard and S. W. Blum.
1. Procedure
Into a
300-ml. three-necked flask equipped with a
nitrogen inlet, a
thermometer, and a
short fractionating column (Note
1) are charged
74.1 g. (0.50 mole) of triethyl orthoformate,
51.0 g. (0.50 mole) of phenylacetylene (Note
2), and
3.0 g. of zinc iodide (Note
3).
Ethanol is slowly distilled from the reaction mixture, which must be heated to about 135° before refluxing in the still-head begins. A total of 29–35 ml. of distillate, b p. 65–88° (mostly 78°), is collected over a period of about 1 hour as the temperature of the reaction mixture gradually rises to 200° to 210° (Note
4). The reaction mixture is cooled to room temperature and filtered with suction. The flask and the small amount of precipitate on the
filter paper are washed with
5 ml. of ether. The filtrate and
ether washings are combined and distilled. After a small fore-run,
phenylpropargylaldehyde diethyl acetal is collected at
99–100°/2 mm. The yield is
73–80 g. (
72–78%),
nD25 1.5153–1.5158. The synthesis is applicable to the preparation of other propargyl aldehyde acetals (Note
5).
2. Notes
1. The checkers found a
12-inch Vigreux column satisfactory.
2. The checkers purchased
phenylacetylene (p. 763) from Gesellschaft für Teerverwertung mbH., Duisburg-Meiderich, Germany.
3. The submitters report that
zinc nitrate appears to be equivalent to
zinc iodide as a catalyst and that
zinc chloride (commercial anhydrous grade) is satisfactory but requires 2–3 hours of heating and gives
64–70% yield.
4. Yields are lower under forcing conditions of prolonged heating.
3. Discussion
The acetylenic acetals are easily hydrolyzed to the corresponding aldehydes in high yields in the presence of dilute acids.
3,4 Acetylenic acetals have also been of value in the synthesis of α,β-unsaturated ethylenic acetals or aldehydes by partial catalytic hydrogenation of the triple bond.
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