A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1949, 29, 63
DOI: 10.15227/orgsyn.029.0063
[Benzaldehyde, m-methoxy-]
Submitted by Roland N. Icke, C. Ernst Redemann, Burnett B. Wisegarver, and Gordon A. Alles.
Checked by H. R. Snyder and Frank X. Werber.
1. Procedure
A. m-Hydroxybenzaldehyde. In a 2-l. three-necked flask, equipped with a mechanical stirrer, a thermometer, and a 250-ml. dropping funnel, 575 ml. of 6 N sulfuric acid is cooled to 0° by means of a salt-ice bath. The acid is stirred and maintained at 0° or below while 167 g. (1 mole) of m-aminobenzaldehyde dimethylacetal (p. 59) is added dropwise. The solution becomes deep orange or red. When the addition of the amino compound is complete, a solution of 71 g. (1 mole) of 97% sodium nitrite in about 175 ml. of water is introduced slowly while the temperature of the acid solution is maintained at 5°. Stirring at 5° is continued for 1 hour to complete the reaction.
In each of two 4-l. beakers are placed 450 ml. of water and 50 ml. of concentrated sulfuric acid, and the solutions are heated to boiling with large burners. The cold diazonium solution is divided into two approximately equal portions which are placed in 500-ml. separatory funnels suspended above the beakers containing the boiling acid. The two portions of the diazonium solution are run dropwise into the strongly heated acid at such a rate that boiling continues. The solutions are boiled for 5 minutes after the additions are complete. They are then allowed to cool to room temperature and are finally stored overnight in a refrigerator. The crude product separates as a dark oil which crystallizes (Note 1) and becomes lighter in color upon standing. It is collected on a Büchner funnel and used in part B without purification (Note 2).
Methyl sulfate is quite toxic. Caution! The methylation should be carried out in a good hood.
B. m-Methoxybenzaldehyde. The crude m-hydroxybenzaldehyde is dissolved in about 550 ml. of 2 N sodium hydroxide in a 2-l. three-necked flask equipped with a mechanical stirrer, a thermometer, and a 125-ml. dropping funnel. The dark-colored solution is stirred while 126 g. (95 ml., 1 mole) of methyl sulfate (Note 3) is added dropwise and the temperature is maintained at 40–45°. When the addition is complete the mixture is stirred for 5 minutes. A 275-ml. portion of 2 N sodium hydroxide (Note 4) is added in one lot, and then 63 g. (47.5 ml.) of methyl sulfate is added as before, except that the temperature is allowed to rise to 50°. Stirring at 50° is continued for 30 minutes, the mixture is cooled, and the organic layer is extracted with ether (Note 5). The ether solution is dried over anhydrous sodium sulfate for 8 hours, then filtered and concentrated by distillation. The residue is distilled under reduced pressure. The yield of m-methoxybenzaldehyde, a pale yellow liquid boiling at 88–90° /3 mm., is 86–98 g. (63–72%) (Note 6).
2. Notes
1. Seeding the mixture helps to initiate crystallization.
2. If m-hydroxybenzaldehyde is desired, the crude product may be purified as described elsewhere (p. 453).
3. A good technical grade of methyl sulfate was used.
4. The optimum amount of sodium hydroxide solution apparently varies according to the amount of acid remaining in the crude, wet hydroxybenzaldehyde employed in the methylation. The checkers found it advisable to increase the amount added at this point to 345 ml. It is wise to test the reaction mixture with litmus paper occasionally during the final heating period and to add alkali as necessary to keep the solution from becoming acid.
5. If the methylation is not complete, some m-hydroxybenzaldehyde will remain dissolved in the aqueous phase. This may be recovered by acidifying the alkaline solution and collecting any crystalline solid which separates.
6. As with other aromatic aldehydes, m-methoxybenzaldehyde is susceptible to air oxidation and should be stored in a bottle which will just hold the product, so that air space above the liquid is minimized.
3. Discussion
m-Methoxybenzaldehyde has been prepared by the reduction of m-methoxybenzoic acid,1 by the reaction of diazotized m-aminobenzaldehyde with methanol,2 by an acid hydrolysis of the phenylhydrazone which was obtained by oxidation of the hydrazine analog,3 and by the methylation of m-hydroxybenzaldehyde, with methyl iodide,4,5,6,7 and with methyl sulfate.2,7,8,9

References and Notes
  1. Asano and Huziwara, J. Pharm. Soc. Japan, 50, 141 (1939).
  2. Noelting, Ann. chim., (8) 19, 541 (1910).
  3. Grammaticakis, Compt. rend., 210, 303 (1940).
  4. Tiemann and Ludwig, Ber., 15, 2043 (1882).
  5. Pschorr and Jaeckel, Ber., 33, 1826 (1900).
  6. Staudinger and Kon, Ann., 384, 90 (1911).
  7. Späth, Monatsh., 34, 1998 (1913).
  8. Posner, J. prakt. Chem., (2) 82, 431 (1910).
  9. Livshits, Bazilevskaya, Bainova, Dobrovinskaya, and Preobrazhenskii, J. Gen. Chem. U.S.S.R., 17, 1671 (1947) [C. A., 42, 2606 (1948)].

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


sulfuric acid (7664-93-9)

methanol (67-56-1)

ether (60-29-7)

sodium hydroxide (1310-73-2)

sodium sulfate (7757-82-6)

sodium nitrite (7632-00-0)

hydroxybenzaldehyde (90-02-8)

Methyl iodide (74-88-4)

methyl sulfate (75-93-4)

m-Hydroxybenzaldehyde (100-83-4)

m-aminobenzaldehyde (1709-44-0)

m-Aminobenzaldehyde dimethylacetal (53663-37-9)

Benzaldehyde, m-methoxy- (591-31-1)

m-methoxybenzoic acid (586-38-9)