Addition of halogen to steroids

The products of addition of bromine to unsaturated steroids play a part, as intermediates, in steroid rearrangements. The reaction is carried out in glacial acetic acid, ether, or chloroform at temperatures below 20° and leads 

It is usually possible to add bromine to unsaturated alcohols in dilute solution at 0-25° without replacement of the hydroxyl group. 

Thus 2,3-dibromo-l-propanol is obtained57 by treating allyl alcohol in ten times its volume of CC14 with a solution of the calculated amount of bromine in double its volume of CC14. 

1 mole of bromine is dropped, at first slowly and then rapidly, into a vigorously stirred solution of 1 mole of ethyl vinyl ether in 4 moles of CHC13 at —15°. When decoloration is complete, the chloroform is distilled off, and fractionation of the residue gives 1,2-di-bromoethyl ethyl ether (88.5 %), b.p. 80°/20 mm. 

1 mole of this product, dissolved in 3.5 moles of absolute ethanol, is dropped into a solution of 1.8 moles of KOH in 8.5 moles of absolute ethanol, at 0° with stirring. The mixture was boiled for 5 min (water-bath), then poured on ice, and the bromo acetal layer was separated. The aqueous layer was extracted with ether and the bromo acetal layer was combined with the ether and the whole dried over K2C03. After removal of the ether and ethanol by distillation, fractionation in a vacuum gave 2-bromoacetaldehyde diethyl acetal (83 %), b.p. 63°/14 mm.63 

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