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Org. Synth. 1937, 17, 18
DOI: 10.15227/orgsyn.017.0018
BROMAL
Submitted by F. A. Long and J. W. Howard.
Checked by W. W. Hartman and G. L. Boomer.
1. Procedure
In a 2-l. three-necked, round-bottomed flask, fitted with a liquid-sealed mechanical stirrer, a dropping funnel, and an efficient reflux condenser, are placed 720 g. (230 cc., 4.5 moles) of bromine (Note 1) and 1.5 g. of sulfur (Note 2). A glass tube is connected to the top of the condenser to carry the evolved hydrogen bromide to a gas trap. Sixty-nine grams (69 cc., 0.52 mole) of dry paraldehyde (Note 1) is added slowly, with stirring, over a period of about four hours. The reaction proceeds under its own heat during the addition of the paraldehyde; subsequently the mixture is heated externally for two hours at 60–80°. The solution is distilled and a fraction collected over the range 155–175° (Note 3).
On redistillation under reduced pressure there is obtained 220–240 g. (52–57 per cent of the theoretical amount) of reddish yellow bromal, boiling at 59–62°/9 mm., or 71–74°/18 mm.
2. Notes
1. The bromine is dried by shaking with concentrated sulfuric acid; the paraldehyde is dried over calcium chloride.
2. The use of sulfur as a catalyst increases the yield 5–10 per cent and causes no trouble in the purification.
3. The fore-run amounts to 90–180 g. and consists mostly of bromine, bromoacetaldehyde, and dibromoacetaldehyde. An additional quantity of bromal may be obtained by treating this material with a small amount of bromine, heating for two hours at 60–80°, and distilling as before.
3. Discussion
Bromal has been prepared by brominating a solution of paraldehyde in ethyl acetate,1 by passing bromine vapor through absolute alcohol,2 and by treatment of chloral with a metallic bromide.3

References and Notes
  1. Pinner, Ann. 179, 67 (1875).
  2. Schäffer, Ber. 4, 366 (1871).
  3. Müller, U. S. pat. 2,057,964 [C. A. 31, 112 (1937)].

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

metallic bromide

alcohol (64-17-5)

calcium chloride (10043-52-4)

sulfuric acid (7664-93-9)

ethyl acetate (141-78-6)

hydrogen bromide (10035-10-6)

bromine (7726-95-6)

sulfur (7704-34-9)

Bromal (115-17-3)

dibromoacetaldehyde

chloral (75-87-6)

bromoacetaldehyde (17157-48-1)

paraldehyde (123-53-7)