A Publication
of Reliable Methods
for the Preparation
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Annual Volume
Org. Synth. 1932, 12, 12
DOI: 10.15227/orgsyn.012.0012
[Benzaldehyde, p-chloro-]
Submitted by W. L. McEwen
Checked by Henry Gilman and Chuan Liu.
1. Procedure
A 500-cc. two-necked, round-bottomed flask is provided with an air-cooled reflux condenser, 2 cm. in diameter and filled for a length of 60 cm. with 5–6 mm. glass pearls or rings (Note 1). Chlorine is to be introduced by means of a 4-mm. glass tube, inserted through a cork in a neck of the flask, extending close to the bottom of the flask and provided with a small bulb with fine perforations to break up the gas stream into small bubbles. The large quantities of hydrogen chloride formed can be disposed of by means of a gas absorption trap.
Into the tared flask are placed 126.5 g. (1 mole) of p-chlorotoluene (Org. Syn. Coll. Vol. I, 1941, 170) and 3.8 g. of phosphorus pentachloride. The flask is heated in a bath kept at 160–170° (Note 2), and while illuminated with direct sunlight or with an unfrosted 100-watt tungsten lamp a rapid stream of chlorine is introduced directly from a cylinder until the gain in weight is 55–66 (Note 3).
The pale yellow or yellow-green product is then transferred to a 4-l. wide-mouthed bottle containing 400 cc. of concentrated sulfuric acid, and stirred vigorously (Hood) for five hours (Note 4). The viscous mixture is then transferred to a separatory funnel and allowed to stand overnight, after which the lower layer (Note 5) is run slowly, with stirring, into a 3-l. beaker three-quarters filled with cracked ice. The cream-colored solid obtained when the ice has melted is filtered by suction, washed with water, pressed dry on the funnel, and divided into three equal parts. Each portion is dissolved in a minimum of ether, and the ether solution is repeatedly shaken with 2 per cent sodium hydroxide solution until acidification of the washings gives no precipitate of p-chlorobenzoic acid (Note 6).
After removal of the ether by distillation on a steam bath, the residue is distilled under diminished pressure from a Claisen flask. The yield of p-chlorobenzaldehyde distilling at 108–111°/25 mm. and melting at 46–47° is 76–84 g. (54–60 per cent of the theoretical amount).
2. Notes
1. The glass packing reduces the tendency of the stream of hydrogen chloride to carry away p-chlorotoluene as a spray.
If only one run is to be made, good-quality corks are satisfactory. If several runs are made, it is recommended that the corks be impregnated with sodium silicate solution to prevent excessive corrosion by the hydrogen chloride and chlorine.
2. The bath contains either oil or graphite.
3. The time required was four and one-half hours. In a larger run by the submitter, in which 750 g. of p-chlorotoluene and 23 g. of phosphorus pentachloride were used, the time required for a gain in weight of 330–360 g. was six to ten hours.
4. Vigorous stirring is necessary to prevent undue foaming. Most of the hydrogen chloride is evolved early in stirring.
5. The waxy upper layer is discarded.
6. The yield of p-chlorobenzoic acid is about 20 g. From the larger runs, starting with 750 g. of p-chlorotoluene, the yield of acid averaged 260 g.
3. Discussion
p-Chlorobenzaldehyde can be prepared from p-chlorobenzyl chloride or p-chlorobenzyl bromide with aqueous lead nitrate;1 from p-chlorotoluene and chromyl chloride;2 by the hydrolysis of p-chlorobenzal chloride;3 from p-aminobenzaldehyde by diazotization and subsequent treatment with cuprous chloride;4 from p-chlorophenylmagnesium bromide and ethyl orthoformate;5 from p-chlorobenzyl chloride with hexamethylenetetramine and subsequent hydrolysis;6 by conversion of p-chlorobenzonitrile to the iminochloride which is then hydrolyzed;7 by the action of carbon monoxide and aluminum chloride on chlorobenzene;8 and by the action of sodium carbonate on 2,5-dichlorobenzenesulfonyl-4-chlorobenzoylhydrazine.9
This preparation is referenced from:

References and Notes
  1. Beilstein and Kuhlberg, Ann. 147, 352 (1867); Jackson and White, Am. Chem. J. 3, 30 (1881).
  2. Law and Perkin, J. Chem. Soc. 93, 1636 (1908).
  3. Erdmann and Kirchhoff, Ann. 247, 368 (1888); Erdmann and Schwechten, ibid 260, 63 (1890); Kaeswurm, Ber. 19, 742 (1886).
  4. Von Walther and Raetze, J. prakt. Chem. (2) 65, 258 (1902).
  5. Bodroux, Bull. soc. chim. (3) 31, 587 (1904).
  6. Mayer and English, Ann. 417, 78 (1918).
  7. Stephen, J. Chem. Soc. 127, 1874 (1925).
  8. Boehringer and Sons, Ger. pat. 281,212 (Chem. Zentr. 1915, I, 178).
  9. McFadyen and Stevens, J. Chem. Soc. 1936, 584.

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

sulfuric acid (7664-93-9)

hydrogen chloride (7647-01-0)

ether (60-29-7)

sodium hydroxide (1310-73-2)

phosphorus pentachloride (10026-13-8)

carbon monoxide (630-08-0)

sodium silicate

sodium carbonate (497-19-8)

chlorobenzene (108-90-7)

aluminum chloride (3495-54-3)

chlorine (7782-50-5)

lead nitrate (10099-74-8)

cuprous chloride (7758-89-6)

p-Chlorotoluene (106-43-4)

Ethyl orthoformate

hexamethylenetetramine (100-97-0)

chromyl chloride


p-chlorophenylmagnesium bromide

Benzaldehyde, p-chloro- (104-88-1)

p-chlorobenzyl chloride (104-83-6)

p-chlorobenzoic acid (74-11-3)

p-chlorobenzyl bromide (622-95-7)

p-chlorobenzal chloride (13940-94-8)

p-Aminobenzaldehyde (17625-83-1)

p-chlorobenzonitrile (623-03-0)