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01-16-04 19:55
No 482862
(Rated as: excellent)
The Preparation of 2-Phenylethyl Halides
C. C. Lee and J. W. T. Spinks
Can. J. Chem. 32, 1005-1011 (1954) (../rhodium/pdf /2-phenylethy
Abstract
The 2-phenylethyl halides were prepared from the treatment of 2-phenylethanol with thionyl chloride alone, thionyl chloride in pyridine, 48% hydrobromic acid, 55% hydriodic acid, or phosphorus and iodine.
Experimental
Reaction with Thionyl Chloride
In a 100 ml. round-bottomed flask, cooled in an ice bath and fitted with a reflux condenser, was placed 5.00g of 2-phenylethanol. Fifteen milliliters of thionyl chloride was added slowly. The mixture was removed from the ice bath and refluxed gently for one half hour. The excess thionyl chloride was distilled off and the residue fractionated under reduced pressure. The yields of 2-phenylethyl chloride, bp 85-87°C at 17 mmHg (lit. bp 81-84°C. at 14 mm.), for the duplicate runs were 4.64 and 4.40 gm. (81 and 77%, respectively).
Reaction with Thionyl Chloride in Pyridine
To a solution of 5.00 gm. of 2-phenylethanol in 20 ml of pyridine in a 250 ml Erlenmeyer flask cooled in an ice-bath was added portionwise 10 ml of thionyl chloride. When the mixture was shaken and then heated on a steam bath for about five minutes (prolonged heating will cause extensive decomposition) a black solution resulted. The mixture was then allowed to stand at room temperature for one half hour before it was poured into ice water. The product was extracted with ether, the extract being washed successively with distilled water, dilute hydrochloric acid, 10% sodium bicarbonate solution, and distilled water. After the extract was dried over anhydrous sodium sulphate, the ether was removed from the extract and the residue distilled under reduced pressure. The yields of 2-phenylethyl chloride for the duplicate runs were 3.72 and 3.86 g (65 and 67%, respectively).
Reaction with Hydrobromic Acid
A mixture of 5.00g of 2-phenylethanol and 28g of 48% hydrobromic acid was heated under reflux, with occasional shaking, for two hours. After the resulting mixture was cooled to room temperature, it was poured into ice water and extracted with ether. The extract was washed with water and 10% sodium bicarbonate solution and dried over anhydrous sodium sulphate. The ether was evaporated off and the residue distilled under reduced pressure. The yields of 2-phenylethyl bromide, bp 110-113°C at 17 mmHg (lit. bp 108-112°C at 17 mmHg), for the duplicate runs were 6.30 and 6.05g (83 and 80%, respectively).
Reaction with Hydriodic Acid
2-Phenylethanol (5.00 g) and 55% hydriodic acid (38 g) were refluxed for two hours. The resulting mixture was worked up as described in the reaction with hydrobromic acid. The yield of 2-phenylethyl iodide, bp 115-118°C at 14 mm. (lit. bp 114-116°C at 12 mm), was 8.75g (92%). In a duplicate preparation using 4.00 gm. of the labeled alcohol, the yield of the iodide was 6.88 gm. (90%).
Reaction with Phosphorus and Iodine
To a mixture of 4.00 g of 2-phenylethanol and 0.35g of red phosphorus in a 100 ml. round-bottomed flask fitted with a reflux condenser was added 4.40 gm. of iodine in small portions with shaking at room temperature. A slight warming up of the reaction mixture resulted. After the addition of iodine had been completed, the mixture was heated over a steam bath for one hour. After the mixture was cooled, ether was introduced to dissolve the product. The ether solution was filtered through glass wool, washed with dilute sodium hydroxide solution and distilled water, dried over anhydrous sodium sulphate, and evaporated over a steam bath to give a residue which on fractionation under reduced pressure gave 2-phenylethyl iodide, bp 115–118°C at 14 mm. The yields for duplicate runs were 6.14 and 6.46g (81 and 85%, respectively).
Hydrocinnamic Acid from 2-Phenylethyl Halides
The phenylethylmagnesium halide was prepared in the conventional way and treated with excess solid carbon dioxide. The resulting reaction mixture was acidified and extracted with ether. After the solvent was evaporated off from the ethereal extract, the residue was taken up in dilute sodium hydroxide solution and washed with ether to remove any unreacted organic halide. The product was then precipitated by acidifying the washed sodium hydroxide solution and again recovered by extraction with ether. After the extract was dried over anhydrous sodium sulphate, the ether was removed from this final extract and the residue was crystallized from petroleum ether (bp 40–60°C). Colorless needles of hydrocinnamic acid were obtained which melted alone, or on admixture with an authentic sample, at 48–49°C. (lit. mp 48.6°C). The yields based on the various samples of 2-phenylethyl halides used ranged from 70 to 80%.
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