Org. Synth. 1959, 39, 59
DOI: 10.15227/orgsyn.039.0059
PHENYLPROPARGYLALDEHYDE DIETHYL ACETAL
[Propiolaldehyde, phenyl-, diethyl acetal]
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.
5.
The method has been applied by the submitters
2 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.
3. Discussion
The described method of preparing
phenylpropargylaldehyde diethyl acetal is that of Howk and Sauer.
2 The method for synthesizing
phenylpropargylaldehyde diethyl acetal previously published in
Organic Syntheses3 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 either
triethyl orthoformate or
ethyl formate. These reactions are discussed critically by Raphael.
4 Phenylpropargylaldehyde diethyl acetal has also been made by the action of the phenyl Grignard reagent with the
diethyl acetal of chloropropiolaldehyde.
5The 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.
4
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
phenylethynyl n-butyl dimethyl ketal
phenylethynyl methyl diethyl ketal
zinc chloride-zinc iodide
sodium derivative of phenylacetylene
diethyl acetal of chloropropiolaldehyde
ethanol (64-17-5)
ether (60-29-7)
zinc chloride (7646-85-7)
cyclohexylmethylacetylene (17715-00-3)
triethyl orthoformate (122-51-0)
ethyl formate (109-94-4)
cinnamaldehyde
Phenylacetylene (536-74-3)
1-Hexyne (693-02-7)
Phenylpropargylaldehyde diethyl acetal (6142-95-6)
Propiolaldehyde, phenyl-, diethyl acetal
zinc iodide
zinc nitrate (13778-30-8)
cyclohexylmethylpropiolaldehyde diethyl acetal
triethyl orthoacetate (78-39-7)
trimethyl n-orthovalerate (13820-09-2)
n-Butylpropiolaldehyde diethyl acetal (18232-30-9)
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