Бромирование бромом в уксусной кислоте.

1. Процедура из ПиХКАЛ.

To a well-stirred solution of 24.8 g 2,5-dimethoxyphenethylamine in 40 mL glacial acetic acid, there was added 22 g elemental bromine dissolved in 40 mL acetic acid. After a couple of min, there was the formation of solids and the simultaneous evolution of considerable heat. The reaction mixture was allowed to return to room temperature, filtered, and the solids washed sparingly with cold acetic acid. This was the hydrobromide salt. There are many complicated salt forms, both polymorphs and hydrates, that can make the isolation and characterization of 2C-B treacherous. The happiest route is to form the insoluble hydrochloride salt by way of the free base. The entire mass of acetic acid-wet salt was dissolved in warm H2O, made basic to at least pH 11 with 25% NaOH, and extracted with 3x100 mL CH2Cl2. Removal of the solvent gave 33.7 g of residue which was distilled at 115-130 deg C at 0.4 mm/Hg. The white oil, 27.6 g, was dissolved in 50 mL H2O containing 7.0 g acetic acid. This clear solution was vigorous stirred, and treated with 20 mL concentrated HCl. There was an immediate formation of the anhydrous salt of 2,5-dimethoxy-4-bromophenethylamine hydrochloride (2C-B). This mass of crystals was removed by filtration (it can be loosened considerably by the addition of another 60 mL H2O), washed with a little H2O, and then with several 50 mL portions of Et2O. When completely air-dry, there was obtained 31.05 g of fine white needles, with a mp of 237-239 deg C with decomposition. When there is too much H2O present at the time of adding the final concentrated HCl, a hydrated form of 2C-B is obtained. The hydrobromide salt melts at 214.5-215 deg C. The acetate salt was reported to have a mp of 208-209 deg C.

2. Процедура из Лабораторного Журнала.

Получение 1-(2,5-диметокси-4-бромфенил)-изопропиламина (DOB).

К раствору ~300 мг 2,5-DMA в 2 мл ледяной уксусной кислоты прибавлялось
0.45 мл раствора брома в ледяной уксусной кислоте, содержащего 0.28 г брома.
Смесь оставлялась стоять на 3 часа, разбавлялась небольшим количеством
эфира и отфильтровывалась. Выход ~150 мг DOB.

См. также бромирование ваниллина.

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