Organic Syntheses Procedure

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Org. Synth. 1965, 45, 86

DOI: 10.15227/orgsyn.045.0086

PHENYLBROMOETHYNE

[Benzene, bromoethynyl]

Submitted by Sidney I. Miller, Gene R. Ziegler, and R. Wieleseck¹.

Checked by William E. Parham and James N. Wemple.

1. Procedure

To a 2-l. bottle equipped with a rubber stopper and immersed in a mixture of ice and water (slush) there is added a cold (about 0°) solution containing 300 g. (7.5 moles) of sodium hydroxide (Note 1) and 800 ml. of water. The mixture is swirled or stirred while 160 g. (2 moles) of bromine is added. Phenylacetylene (84 g., 0.82 mole) (Note 2) is then added to the yellow solution, and the resulting mixture is stoppered and shaken. The rubber stopper is wired down, the bottle is covered with opaque cloth or paper, and the bottle is then placed in a mechanical shaker for 60 hours at room temperature (Note 3).

The crude oil is then separated from the aqueous phase, dried with calcium chloride (Note 4). and fractionated (Note 5) at reduced pressure under nitrogen (Caution! (Note 6)). The distillation receiver should be cooled in an ice-salt or dry ice-acetone mixture. After a small fore-run of phenylacetylene, there is obtained 109–124 g. (73–83% yield) of water-white phenylbromoethyne, b.p. 40–41° (0.1 mm.) n²⁵D 1.6075 (Note 7).

2. Notes

1. Practical grade sodium hydroxide and bromine were used.

2. Commercially available phenylacetylene can be used. The checkers used material as obtained from Columbia Organic Chemicals co., Inc.

3. Vigorous shaking is essential. For this reaction rate = k[C₆H₅ C≡CH] [OBr⁻] [OH⁻] with k = 7 M⁻² sec.⁻¹ at 25°.² Since the solubility of phenylacetylene at 25° is 5.1 × 10⁻³ M in water (2.0 × 10⁻³ M in 2M sodium chloride), efficient mixing of the reagents is of paramount importance.² An ordinary motor-drive stirrer proved to be inadequate. Phenylbromoethyne gradually darkens when exposed to light or air. The product is best stored under nitrogen in a refrigerator and should be distilled within a few days of its preparation.

4. The checkers observed that the calcium chloride absorbs appreciable quantities of product. The crude oil was dissolved in peroxide-free ether (about 300 ml.) prior to drying with calcium chloride, or the calcium chloride was extracted with several 50-ml. portions of dry ether after use. The ethereal extracts were concentrated under nitrogen and added to the product before distillation.

5. The checkers distilled the product from a flask equipped with a Claisen head but no column.

6. No air should be allowed to come in contact with the hot pot liquid during the distillation, for an exothermic reaction may occur; at best this may fill the apparatus with tarry material and the room with noxious fumes; at worst, pressure built up may destroy all or part of the apparatus. As a precaution, this distillation should be carried out behind a safety shield.

7. The checkers observed that the refractive index of a sample stored for 5 days in the refrigerator in a stoppered tube wrapped in aluminum foil and cloth changed from n²⁵D 1.6074 to n²⁵D 1.6082.

3. Discussion

Phenylbromoethyne has been prepared by base-catalyzed dehydrobromination of 1,1- or 1,2-dibromostyrene;³ by the thermal decomposition of silver 1,2-dibromocinnamate;³ from phenylethynylmagnesium Grignard reagent and bromine;⁴^,⁵ cyanogen bromide,⁶ or benzenesulfonic anhydride;⁷ from phenylethynylsodium and cyanogen bromide⁵ or p-toluenesulfonylbromide⁸; from phenylethynylsilver and bromine in pyridine;⁹ and from phenylethynyllithium and N-bromoimides.¹⁰ The present method is a modification of one in which the hypobromite-phenylacetylene mixture is warmed for 1.5 hours in the presence of an emulsifying agent, 1% potassium stearate¹¹ or soap,¹² to give 88% yield of product.

4. Merits of the Preparation

The hypohalite route to 1-chloro-, 1-bromo-, or 1-iodoalkynes is both general and convenient. The purity of the reagents does not appear to be critical.

References and Notes

Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois.
R. R. Lii and S. I. Miller, J. Am. Chem. Soc., 91, 7524 (1969); R. R. Lii, Ph.D. Thesis, Illinois Institute of Technology, 1971.
J. V. Nef, Ann., 308, 264 (1899).
J. I. Iotsitch, J. Phys. Chem. Soc. (Russia), 35, 1269 (1903) [Bull. Soc. Chim. France, [3] 34, 181 (1905)].
V. Grignard and C. Courtot, Bull. Soc. Chim. France, [4] 17, 228 (1915); V. Grignard, E. Bellet, and C. Courtot, Ann. Chim. (Paris), [9] 4, 39 (1915).
C. Moureu and R. Delange, Bull. Soc. Chim. France, [3] 25, 99 (1901).
L. Field, J. Am. Chem. Soc., 74, 394 (1952).
R. Truchet, Ann. Chim. (Paris), [10] 16, 309 (1931).
T. Agawa and S. I. Miller, Unpublished result.
V. Wolf and F. Kowitz, Ann., 638, 33 (1960).
F. Straus, L. Kollek, and W. Heyn, Ber., 63, 1868 (1930).
M. Murray and F. F. Cleveland, J. Chem. Phys., 12, 156 (1944).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

peroxide-free ether

1,1- or 1,2-dibromostyrene

calcium chloride (10043-52-4)

ether (60-29-7)

sodium hydroxide (1310-73-2)

sodium chloride (7647-14-5)

bromine (7726-95-6)

nitrogen (7727-37-9)

aluminum (7429-90-5)

pyridine (110-86-1)

Phenylacetylene (536-74-3)

Cyanogen bromide (506-68-3)

Phenylbromoethyne,
Benzene, bromoethynyl (932-87-6)

silver 1,2-dibromocinnamate

phenylethynylmagnesium

benzenesulfonic anhydride (512-35-6)

phenylethynylsodium

phenylethynylsilver

phenylethynyllithium (4440-01-1)

potassium stearate

p-toluenesulfonylbromide

Notes

References/EndNotes

Article Compounds

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