Org. Synth. 1967, 47, 98
DOI: 10.15227/orgsyn.047.0098
PHENYLCYCLOPROPANE
[Benzene, cyclopropyl-]
Submitted by R. J. Petersen and P. S. Skell
1.
Checked by Thomas R. Lynch and Peter Yates.
1. Procedure
Caution! This reaction should be carried out behind a safety screen.
A 1-l. three-necked flask is fitted with a reflux condenser, an addition funnel, and a thermometer. It is charged with 450 ml. of 95% ethanol, 230 ml. (236 g.) of 85% hydrazine hydrate (Note 1), and several porcelain boiling chips. The solution is brought to reflux with a heating mantle. Cinnamaldehyde (200 g., 1.51 moles) (Note 2) is added dropwise over a period of 45 minutes to the refluxing solution, while the mixture turns orange because of the formation of cinnamalazine in a side reaction (Note 3). After an additional 30 minutes at reflux, the flask is fitted with a simple takeoff head, and ethanol, water, and hydrazine hydrate are slowly removed by distillation. After approximately 3 hours the pot temperature rises to 200°, and phenylcyclopropane begins to codistil with the last of the hydrazine hydrate (Note 4). The distillate from this point is collected in a 250-ml. receiver, the main fraction coming over at 170-80°. When the pot temperature exceeds 250°, the decomposition is essentially complete (Note 5), (Note 6).
The crude, cloudy distillate (110–130 g.) is washed twice with 100-ml. portions of water and dried over anhydrous potassium carbonate. Distillation at reduced pressure, b.p. 60° (13 mm.), 79–80° (37 mm.), through a 12-in. Vigreux column gives phenylcyclopropane pure enough for most purposes; yield 80–100 g. (45–56%), n25D 1.5309.
2. Notes
1.
Matheson, Coleman and Bell technical grade 85% hydrazine hydrate was used.
2.
Eastman Organic Chemicals cinnamaldehyde gave satisfactory results. If colorless crystals are present in the neck of the bottle or on the walls above the liquid, the
cinnamaldehyde is seriously contaminated with
cinnamic acid and should be distilled before use. A small amount of
cinnamic acid apparently does not affect the yield of
phenylcyclopropane.
3.
Reversal of the addition procedure results in formation of
cinnamalazine as a major product.
4.
Earlier investigators employed strong bases (
sodium hydroxide,
potassium hydroxide) or
platinum on asbestos to catalyze the decomposition of
5-phenylpyrazoline. These catalysts are not necessary and should be avoided because they also cause the reduction of
cinnamalhydrazone to
propenylbenzene.
Phenylcyclopropane can be freed from
propenylbenzene only with great difficulty.
5.
The checkers found in a full-scale run that the pot temperature had to be raised to close to 250° before the onset of reaction, which was then very vigorous.
6.
Pyrazoline vapors are known to be rather flammable. It is advisable, therefore, to cool the pyrolysis flask somewhat before dismantling the apparatus. The syrupy residue in the flask sets to a hard mass on cooling; it can be removed by heating under
dimethylformamide on a
steam bath overnight.
3. Discussion
Phenylcyclopropane has been prepared by the base-catalyzed decomposition of
5-phenylpyrazoline (
33%),
2 by the reaction of
1,3-dibromo-1-phenylpropane with
magnesium (
68%),
3 and by the reaction of
3-phenylpropyltrimethylammonium iodide with
sodium amide in liquid
ammonia (
80%).
4 However, the method frequently used at present is the reaction of
styrene with the
methylene iodide-zinc reagent (
32%).
5
4. Merits of the Preparation
The procedure outlined is much quicker and simpler than previous methods. Starting materials are readily available, and the preparation can be run on any scale in the length of a day. Because exclusion of a basic catalyst eliminates the Wolff-Kishner reduction of the cinnamalhydrazone, separation of the 5-phenylpyrazoline from cinnamalhydrazone, or of phenylcyclopropane from propenylbenzene, does not have to be effected. The present procedure can also be used to convert other ring-substituted cinnamaldehydes to the corresponding arylcyclopropanes.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
cinnamalazine
cinnamalhydrazone
ethanol (64-17-5)
potassium carbonate (584-08-7)
ammonia (7664-41-7)
sodium hydroxide (1310-73-2)
magnesium (7439-95-4)
platinum (7440-06-4)
potassium hydroxide (1310-58-3)
hydrazine hydrate (7803-57-8)
cinnamic acid (621-82-9)
cinnamaldehyde
styrene (100-42-5)
propenylbenzene
sodium amide (7782-92-5)
dimethylformamide (68-12-2)
Benzene, cyclopropyl-,
Phenylcyclopropane (873-49-4)
1,3-Dibromo-1-phenylpropane (17714-42-0)
5-phenylpyrazoline
3-phenylpropyltrimethylammonium iodide (2125-48-6)
pyrazoline
methylene iodide-zinc
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