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).

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).