Bromohexadiene

Elimination of hydrogen bromide from bromohexadienes with dunethyl-benzylamine, 41, 50... 

In an assembly similar to that used for the previous reaction, 90 g. (0.67 mole) of dimethylbenzylamine (Note 8), 0.13 g. of hydroquinone, and 500 ml. of water are stirred and heated at 50°. The crude bromohexadiene (107 g., 0.67 mole) is added in the course of 20-40 minutes, and stirring and heating are maintained at 50° for 2-2.5 more hours. The flask is then fitted for downward distillation, and the mixture is distilled at about 40-50° and 30 mm. until no more oil distils with the water. A total of 133— 200 ml. of distillate is collected. This is discarded. 

The moist crude bromohexadiene is quaternized in water without further purification. The submitters report that, if desired, the crude mixture may be dried over anhydrous calcium chloride and fractionally distilled through a 10-in. stainless-steel-packed column at reduced pressure. Crude bromohexadiene (220-230 g.) from 147 g. (1.50 moles) of l,5-hexadiene-3-ol was found to give the fractions listed in Table I. The yield of the... 

B. 1,3,5-Hexatrietie. In a 500-ml., three-necked, round-bottomed flask fitted with a mechanical stirrer, a thermometer, and a graduated dropping funnel are placed 114 g. (0.42 mole) of phosphorus tribromide (Note 6) and 2 drops of 48% hydrobromic acid. As the contents of the flask are stirred and maintained at 10-15° by means of an ice-water bath, 98 g. (1.00 mole) of 1,5-hexadien-3-ol is added in the course of 1.5 to 1.75 hours. The mixture is allowed to stir at 10-15° for 40 minutes and then to stand at room temperature overnight. The flask is cooled in an ice-salt bath for 20 minutes, and the upper organic layer is decanted from the residue while still cold. The organic layer is successively washed with three 40-ml. portions each of ice water, 5% sodium bicarbonate, and water. The crude bromohexadiene weighs 147-153 g. (91-95%) (Note 7). 

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