Organic Syntheses, Coll. Vol. 4, p.801 (1963); Vol. 39, p.59 (1959).
PHENYLPROPARGYLALDEHYDE DIETHYL ACETAL
[Propiolaldehyde, phenyl-, diethyl acetal]
1Submitted by B. W. Howk and J. C. Sauer.
Checked by N. J. Leonard and S. W. Blum.
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%), n25 D
1.5153–1.5158. The synthesis is applicable to the preparation of other propargyl aldehyde acetals (Note 5).
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.
25. The method has been applied by the submitters to the preparation of cyclohexylmethylpropiolaldehyde diethyl acetal (54% yield) from cyclohexylmethylacetylene and triethyl orthoformate; of phenylethynyl n-butyl dimethyl ketal (40% yield) from phenylacetylene and trimethyl n-orthovalerate; and of phenylethynyl methyl diethyl ketal (34% yield) from phenylacetylene and triethyl orthoacetate. n-Butylpropiolaldehyde diethyl acetal was isolated in 32% yield by heating an equimolar mixture of 1-hexyne and triethyl orthoformate containing catalytic amounts of a zinc chloride-zinc iodide catalyst under autogenous pressure at 190? for 3 hours.
2The described method of preparing phenylpropargylaldehyde diethyl acetal is that of Howk and Sauer. The method
3for synthesizing phenylpropargylaldehyde diethyl acetal previously published in Organic Syntheses involves three steps beginning with cinnamaldehyde; over-all yields are 49–62%. Other methods of preparative value are the interaction of the Grignard reagent of phenylacetylene with triethyl orthoformate, or the sodium derivative of phenylacetylene with
4either triethyl orthoformate or ethyl formate. These reactions are discussed critically by Raphael.
Phenylpropargylaldehyde diethyl acetal has also been made by the action of the phenyl Grignard reagent with the diethyl
5acetal of chloropropiolaldehyde.
The acetylenic acetals are easily hydrolyzed to the corresponding aldehydes in high yields in the presence of dilute 3,4acids. Acetylenic acetals have also been of value in the synthesis of α,β-unsaturated ethylenic acetals or aldehydes by
4partial catalytic hydrogenation of the triple bond.
References and Notes
1. Contribution No. 474 from the Central Research Department, Experimental Station, E. I. du Pont de Nemours &
Co. (Inc.), Wilmington, Delaware.
2. Howk and Sauer, J. Am. Chem. Soc., 80, 4607 (1958).
3. Org. Syntheses Coll. Vol. 3, 732 (1955).
4. Raphael, Acetylenic Compounds in Organic Synthesis, pp. 68–75, Academic Press, New York, 1955.
5. Zakharkin, Doklady Akad. Nauk S.S.S.R., 105, 985 (1955) [C. A., 50, 11237a (1956)].