1-Butylbromide [109-65-9-A] C4H9Br
Procedure: In a 100 ml round-bottom flask, 16.5 ml (0.18 mol) of n-butanol is placed under ice cooling. Slowly, 5 ml (0.09 mol) of 98% sulfuric acid is added dropwise (1 drop/2 s) while stirring vigorously. The solution turns brown-yellow. Then, 31 ml (0.28 mol) of 48% hydrobromic acid is added dropwise (1 drop/s). The solution now turns red-brown. The ice bath is removed, the flask is dried, and a distillation bridge is set up. The reaction flask is heated with a heating mantle, and the temperature is gradually increased. The product is directly distilled into a 100 ml separatory funnel. The distillation is stopped at 95 °C. The product boils over at about 80 °C. In the separatory funnel, two phases are formed. The slightly cloudy organic phase (bottom) is drained, collected, and the upper aqueous phase is discarded. The organic phase is washed with 16 ml of ice-cold water, 18 ml of 10% sodium carbonate solution (gas evolution), and then twice with 18 ml of cold water. To dry the crude product, 1-2 g of Na2SO4 is added, and the solution is then filtered. The yield is 60-80% of the theoretical yield.
Source: Thread in the LambdaForum
Delivered by: Jackal
Last updated: 15/01/2009
Other name: 1-Bromobutane
1-Butylbromide [109-65-9-B] C4H9Br
Procedure: In a 1000 ml round-bottom flask, place 255 ml of water. While stirring, add 309 g of finely powdered NaBr (or 340 g of KBr) (1), 207 ml of 1-butanol, and 206 ml of concentrated sulfuric acid. Half of the sulfuric acid is slowly added to the reaction mixture, then a reflux condenser is set up, and the second half is added via a dropping funnel so that the reaction mixture does not boil too vigorously.
The mixture is then refluxed for 4 hours in an oil bath while stirring vigorously to avoid phase separation (2). After 4 hours, the reaction mixture is subjected to distillation (oil bath at 140 °C) until no more distillate is collected, forming two phases in the receiver. The lower organic phase is separated in a separatory funnel (4) and washed with water (5), sufficient concentrated sulfuric acid (6), a solution of 10 g sodium carbonate in 100 ml water, and finally again with water. It is dried over anhydrous calcium chloride (5 g), filtered from the drying agent, and distilled, collecting the pure product after a small fore-run (drying tube!) (7). The literature yield (according to "Organic Syntheses" - unmodified procedure) is 90% of the theoretical yield.
Notes: (1) The experimenter used KBr. Due to the poor solubility of potassium salts, a large amount of salt remains in the reaction flask when using potassium bromide, which hinders stirring. It is important to grind the salt well.
(2) When using KBr with a magnetic stirrer (but also with NaBr), stirring can be difficult at times. In this case, shake regularly by hand.
(3) This procedure was tested only for KBr.
(4) The organic phase is at the bottom, has the larger volume, and is usually slightly cloudy - visually it can easily be confused with the aqueous phase. It is best to always take a few drops from both phases and test for water solubility.
(5) If the first water wash is omitted, HBr and some bromine are produced during washing with concentrated sulfuric acid, causing small smoke clouds to escape during pressure equalization.
(6) Washing with sulfuric acid is very important as it removes unreacted 1-butanol. Enough sulfuric acid must be used to form two clearly separated phases with the sulfuric acid phase at the bottom. According to the synthesis protocol from "Organic Syntheses," the experimenter would have needed 22 ml of sulfuric acid. However, it was necessary to use 60 ml of sulfuric acid. Then, another 20 ml of sulfuric acid was added. Caution: The mixture heats up significantly when mixed with sulfuric acid - let it cool down!
(7) According to the synthesis protocol from "Organic Syntheses," the product boils between 101-104 °C; according to "Vogel, Arthur I. - A Text-Book of Practical Organic Chemistry," between 100-103 °C. According to the experimenter's thermometer, the product boiled at 99.0-99.5 °C after a small milky fore-run. Since a higher boiling point was expected, a large fore-run was initially collected, which was redistilled to recover more product. A total of 207 g of pure 1-butylbromide was obtained (63% of the theoretical yield). The product appears to be free of unreacted 1-butanol, as part of it was used for a Grignard reaction, which started very readily.
Source: Based on: Organic Syntheses, Coll. Vol. 1, p.25 (1941); Vol. 1, p.3 (1921) • Vogel, Arthur I. - A Text-Book of Practical Organic Chemistry, 3rd Edition, Longman, London 1974
Delivered by: Heuteufel
Last updated: 05/04/2013
