Org. Synth. 1937, 17, 20
DOI: 10.15227/orgsyn.017.0020
[Benzaldehyde, p-bromo-]
Submitted by George H. Coleman and G. E. Honeywell.
Checked by W. W. Hartman and A. J. Schwaderer.
1. Procedure
In a 1-l. three-necked flask fitted with a mechanical stirrer, a reflux condenser, a thermometer, and a dropping funnel is placed 100 g. (0.58 mole) of p-bromotoluene (Org. Syn. Coll. Vol. I, 1941, 136). The stem of the dropping funnel and the thermometer should reach nearly to the bottom of the flask. The upper end of the condenser is connected to a gas absorption trap. The flask is heated with stirring in an oil bath until the temperature of the liquid reaches 105°. The liquid is illuminated with an unfrosted 150-watt tungsten lamp, and 197 g. (61.8 cc., 1.23 moles) of bromine is added slowly from the separatory funnel (Note 1). About one-half of the bromine is added during the first hour, during which time the temperature is kept at 105–110°. The rest is added during about two hours while the temperature is raised to 135°. When all the bromine has been added the temperature is raised slowly to 150°.
The crude product (Note 2) is transferred to a 2-l. flask and mixed thoroughly with 200 g. of powdered calcium carbonate. About 300 cc. of water is added and the mixture is heated cautiously (Note 3) and then refluxed for fifteen hours to effect hydrolysis. The product is then distilled in a rapid current of steam (Note 4); the distillate is collected in 500-cc. portions and cooled; and the p-bromobenzaldehyde is collected and dried in a desiccator. From the first liter of distillate 50–60 g. of p-bromobenzaldehyde melting at 55–57° is obtained. An additional 15–20 g. of product melting at 50–56° is obtained in about 2 l. more of distillate (Note 5). This may be purified through the bisulfite addition compound (Note 6) and yields 13–18 g. of product melting at 55–57°. The total yield of pure aldehyde is 65–75 g. (60–69 per cent of the theoretical amount).
2. Notes
1. The rate of addition of the bromine should be so regulated that a large excess of unreacted bromine does not accumulate in the reaction mixture. The amount of bromine present may be roughly estimated by the color of the solution and by the amount of bromine vapor carried into the condenser.
2. p-Bromobenzal bromide is a lachrymator and also produces a burning sensation on the skin. Washing the affected parts with alcohol gives relief.
3. In order to avoid breaking the flask the mixture is heated first on a water bath and then on a wire gauze over a flame with continuous shaking until the liquid begins to boil. The refluxing may then be continued without danger.
4. The inlet tube for steam should reach to the bottom of the distillation flask. A 16-mm. bulb on the end of this tube with four 0.8-mm. openings helps to ensure thorough mixing of the heavy residue. If this residue is not well stirred the aldehyde distils very slowly. It is well to connect the flask to the condenser through a large Hopkins still head in order to prevent the entrainment of foam during the distillation.
5. Five to ten grams of crude p-bromobenzoic acid can be obtained by acidifying the solution left in the distilling flask.
6. The material is triturated with saturated sodium bisulfite solution (2 cc. per gram), and after about three hours the pasty mixture is filtered with suction. The addition product is washed with absolute alcohol and then with ether and transferred to a flask fitted for steam distillation. Excess sodium carbonate solution is added and the aldehyde is distilled in a current of steam.
3. Discussion
p-Bromobenzaldehyde has been prepared by the oxidation of p-bromotoluene with chromyl chloride,1 by saponification of the acetal from p-bromophenylmagnesium bromide and orthoformic ester,2 by the oxidation of ethyl p-bromobenzyl ether with nitric acid,3 by the oxidation of p-bromobenzyl bromide with lead nitrate,4 by the hydrolysis of p-bromobenzal bromide in the presence of calcium carbonate,5 and by the procedure given on p. 442 which involves oxidation of p-bromotoluene with chromium trioxide in the presence of acetic anhydride, followed by hydrolysis of the resulting p-bromobenzaldehyde diacetate.
This preparation is referenced from:

References and Notes
  1. Wörner, Ber. 29, 153 (1896).
  2. Tschitschibabin, ibid. 37, 188 (1904); Bodroux, Bull. soc. chim. (3) 31, 587 (1904); Gattermann, Ann. 393, 223 (1912).
  3. Errera, Gazz. chim. ital. 17, 206 (1887).
  4. Jackson and White, Ber. 11, 1043 (1878); Am. Chem. J. 3, 32 (1881).
  5. Adams and Vollweiler, J. Am. Chem. Soc. 40, 1738 (1918).

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

orthoformic ester

ACETAL (105-57-7)

alcohol (64-17-5)

ether (60-29-7)

acetic anhydride (108-24-7)

nitric acid (7697-37-2)

sodium carbonate (497-19-8)

bromine (7726-95-6)

sodium bisulfite (7631-90-5)

calcium carbonate (471-34-1)

lead nitrate (10099-74-8)

chromyl chloride

chromium trioxide (1333-82-0)

p-Bromotoluene (106-38-7)

Benzaldehyde, p-bromo- (1122-91-4)

p-Bromobenzal bromide

p-bromobenzoic acid (586-76-5)

p-bromophenylmagnesium bromide

ethyl p-bromobenzyl ether

p-bromobenzyl bromide (589-15-1)

p-bromobenzaldehyde diacetate