A. m-Nitrobenzaldehyde. In a 3-l. three-necked flask provided with a dropping funnel, a thermometer, and an efficient mechanical stirrer is placed 1.25 l. of technical concentrated sulfuric acid (sp. gr. 1.84). The acid is stirred during the fairly rapid addition of 167 ml. (250 g., 4 moles) of technical fuming nitric acid (sp. gr. 1.49–1.50), with sufficient cooling by an ice bath so that the temperature of the mixed acids does not exceed 10°. The mixture is maintained at 5–10° while 213 g. (2 moles) of U.S.P. benzaldehyde (Note 1) is added with good stirring over a period of 2–3 hours. At the end of the addition the ice bath is removed and the mixture is allowed to stand overnight at room temperature.

The mixture is poured carefully onto about 3.25 kg. of cracked ice in a 2-gal. crock (Note 2) with manual stirring. The yellow precipitate is collected on a large Büchner funnel, washed with cold water, and pressed as dry as possible (Note 3). Further removal of water is accomplished by dissolving the moist product in about 100 ml. of warm benzene and separating the water layer in a separatory funnel. The benzene solution is filtered (Note 4) into a 1-l. distilling flask and concentrated on a steam bath. Distillation is discontinued when benzene no longer comes over or when nitrous fumes (from incompletely removed nitric acid) appear. The residual m-nitrobenzaldehyde is sufficiently pure for use in the next step (Note 5).

B. m-Nitrobenzaldehyde dimethylacetal. The above crude product is dissolved in 750 ml. of technical anhydrous methanol, 1 ml. of concentrated hydrochloric acid is added if necessary (Note 6), and the solution is allowed to stand at room temperature for 5 days (Note 7). A solution of sodium methoxide in methanol is added until the solution is just alkaline to moistened litmus paper. The methanol is removed by distillation on a steam bath; the residue is cooled to room temperature and treated with cool water to dissolve the inorganic salts. The aqueous solution is extracted with two 50-ml. portions of ether, and the extracts are added to the crude acetal. The solution is subjected to a preliminary drying over anhydrous magnesium sulfate (or sodium sulfate), filtered, and then dried for at least 12 hours over anhydrous sodium carbonate. After the ether has been removed by distillation on a steam bath the residue is distilled under reduced pressure from a 500-ml. Claisen flask. The yield of the light-yellow liquid acetal, boiling at 141–143°/8 mm. (Note 8), is 300–335 g. (76–85%) (Note 9).