Weygand/Hilgetag Preparative Organic Chemistry

Addition of halogen or thiocyanogen to C-C multiple bonds 111
to the trans-addition that is customary in addition of bromine to C=C bonds.
The trans-di&xial dibromides that are the primary products can be rearranged
to the fraws'-diequatorial isomers. For discussion and references see Fieser and
Fieser. 55a It should, however, also be mentioned that iodobenzene dichloride,
C6H5IC12, in chloroform is a useful reagent for adding chlorine to unsaturated
steroids, e.g., to cholesterol. 56
6. Addition of halogen to unsaturated alcohols or ethers
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 obtained 57 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.
Addition of bromine to alkyl vinyl ethers is usually carried out in CC14 or
CHCI3 with cooling to -5° to 0°. The preparation of 1,2-dibromoethyl methyl
ether from methyl vinyl ether is described in detail in " Synthesen der organischen
Verbindungen", 58 as also is the strongly exothermic addition of chlorine.
1,2-Dichloroethyl ethyl ether is obtained from ethyl vinyl ether below 30°
(cooling with ice and salt). 59 This method, which has been studied with numerous
examples, 60 is generally applicable, but its preparative importance in any one
case depends on ready accessibility of the vinyl ether, e.g., from acetylene, the
alcohol, and KOH in an autoclave. 61 #,/?-Dihalogeno ethers are interesting
intermediates; e.g., with alcoholic KOH they yield a-halogeno aldehyde
acetals. 62
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-dibromoethyl
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 K2CO3. After removal of the ether and ethanol by
distillation, fractionation in a vacuum gave 2-bromoacetaldehyde diethyl acetal (83 %), b.p.
63714 mm. 63
55 L.F. Fieser and M. Fieser, "Steroids," Reinhold Publ. Corp., New York, 1959,
pp. (a) 35-41, (b) 280-294, (c) 321-325.
56 C. J. Berg and E. S. Wallis, /. Biol. Chem., 162, 683 (1946).
57 W. G. H. Edwards and R. Hodges, /. Chem. Soc, 1953, 3428.
58 M. F. Schostakowski and P. W. Tjupajew, "Synthesen der organischen Verbindungen,"
VEB Verlag Technik, Berlin, Porta-Verlag, Munich, 1956, Vol. 2, p. 81.
59 M. F. Schostakowski and F. P. Sidelkowskaja, "Synthesen der organischen Verbindungen,"
VEB Verlag Technik, Berlin, 1959, Vol. 1, p. 69.
60 M. F. Shostakovski, Zh. Obshch. Khim.t 13, 1 (1943); Dokl. Akad. Nauk S.S.S.R., 41,
124 (1943); Zh. Obshch. Khim., 14, 102 (1944); 17, 957 (1947); Chem. Abstr., 38, 330 (1944);
39, 905 (1945); 42, 4520 (1948).
61 A. Je. Faworski and M. F. Schostakowski, "Synthesen der organischen Verbindungen,"
VEB Verlag Technik, Beriin, 1959, Vol. 1, p. 40.
62 A. Je Favorski and M. N. Shchukina, Chem. Abstr., 40, 4347 (1946).
63 H. Baganz and E. Brinckmann, Chem. Ber., 86, 1320 (1953).