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 Synthesis of trans-4,4'-Dibromostilbene by a Double Heck Reaction of (Arylazo)amines with Vinyltriethoxysilane
  • Synthesis of trans-4,4'-Dibromostilbene by a Double Heck Reaction of (Arylazo)amines with Vinyltriethoxysilane
  • The synthetic process of (CAS NO. ) contains 2 steps. The synthetic route is as follows:

    A. Synthesis of 4-[(Bromophenyl)azo]morpholine. In a 500-mL Erlenmeyer flask equipped with a magnetic stirring bar are placed 4-bromoaniline (15.0 g, 87 mmol) and 6 N hydrochloric acid (HCl), 36.4 mL, 210 mmol ) and the mixture is warmed on a bath to make a clear solution. It is cooled to 0°C to produce a heavy precipitate. A solution of sodium nitrite (6.30 g, 91 mmol) in water (10 mL) is added dropwise over 10 min. Stirring is continued at 0°C for 20 min, and morpholine (8.3 g, 9.0 mL, 96 mmol) is added dropwise to the above solution over 10 min. Water (100 mL) is added followed by the dropwise addition of 10% aqueous sodium bicarbonate solution (130 mL). After the solution is stirred for a further hour, the precipitated solid is filtered, washed with water and dried in air. The solid is dissolved in hot light petroleum (60-80 fraction) (80 mL) and treated with activated charcoal (1.5 g). The mixture is filtered while hot and the filtrate concentrated to ca. 40 mL. Upon cooling to room temperature, shiny crystals of the pure triazene are obtained. The mother liquor is concentrated to give a second crop of crystals (combined yield 20.3 g, 85%).

    B. Synthesis of trans-4,4'-Dibromostilbene. A 500-mL round-bottomed flask equipped with a magnetic stirring bar is charged with the above triazene (14.3 g, 53 mmol) and methanol (125 mL). The stirred solution is cooled to 0°C and 40% tetrafluoroboric acid (HBF4, 23 mL, 106 mmol) is added dropwise over 10 min. After the addition is complete, the ice bath is removed and the reaction brought to room temperature. It is stirred for an additional 10 min and palladium acetate [Pd(OAc)2, 0.12 g, 0.53 mmol] is added followed by the dropwise addition of a solution of vinyltriethoxysilane (4.94 g, 5.5 mL, 26 mmol) in methanol(10 mL). A second lot of Pd(OAc)2 (0.12 g, 0.53 mmol) is added and stirring continued for a further 30 min at room temperature. The mixture is warmed to 40°C for 20 min and finally heated under reflux for 15 min. The solution is concentrated under reduced pressure to half its volume and water (150 mL) is added. The precipitated solid is filtered, washed with water and dried in air. It is then boiled with toluene (125 mL) and filtered while hot. The filtrate is concentrated to ca. 70 mL, warmed to 70°C and light petroleum (30 mL) is added. Upon cooling to room temperature, the product crystallizes (4.20 g). Concentration of the mother liquor gives an additional crop (0.70 g) of the product (combined yield 4.90 g, 46.5%).


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