o-Nitro (CAS no ), which is also known as Benzaldehyde, o-nitro-, could be produced through the following synthetic routes.

A. o-Nitrobenzylpyridinium bromide. A 1-l. flask fitted with a reflux condenser is charged with 102 g. (0.744 mole) of o-nitrotoluene, 120 g. (0.675 mole) of N-, 1.0 g. of benzoyl peroxide, and 450 ml. of dry carbon tetrachloride. The mixture is heated under reflux until, after the refluxing is temporarily interrupted, all the solid is seen to float on the surface (usually 6–8 hours suffices).

The hot mixture is filtered with suction into a 1-l. round-bottomed flask through a Büchner-type sintered glass funnel provided with a ground joint. The solid on the funnel is washed successively with two 50-ml. portions of hot carbon tetrachloride. The solvent is removed from the filtrate under reduced pressure on a water bath. The flask is then fitted with a reflux condenser, and 400 ml. of commercial absolute ethanol and 65 ml. (0.81 mole) of good grade pyridine are added to the residue.

The solution is heated at the reflux temperature for 45 minutes and immediately transferred to a wide-mouthed Erlenmeyer flask. Crystallization begins at once, and, after the mixture is cooled, the crystals of nearly pure o-nitrobenzylpyridinium bromide are collected, washed with cold ethanol, and used in the next step.

B. N-(p-Dimethylaminophenyl)-α-(o-nitrophenyl)nitrone. The wet o-nitrobenzylpyridinium bromide, together with 100 g. (0.536 mole) of p-nitrosodimethylaniline hydrochloride and 800 ml. of ethanol are introduced into a 2-l. three-necked flask equipped with an efficient stirrer, thermometer, and a dropping funnel, and immersed in an ice-salt bath. The stirrer is started, and a solution of 54 g. (1.35 mole) of sodium hydroxide in 500 ml. of water is added at 0–5°. The color changes gradually from yellow to green, brown, and orange. The stirring is continued at 5–10° over a period of 1 hour. At the end of this time 500 ml. of ice-cold water is added to the flask, and the orange N-(p-dimethylaminophenyl)-α-(o-nitrophenyl)nitrone is collected on a large Büchner funnel, pressed well, and washed with cold water. The nitrone is used in the next step without further purification.

C. . The wet crude nitrone is placed in a 3-l. beaker. A solution of approximately 6N sulfuric acid is then added, and the mixture is hand-stirred with a spatula or a glass rod. Crushed ice is added after 10 minutes, and the crude solid o-nitrobenzaldehyde is filtered, washed successively with dilute sodium bicarbonate solution and water, and dried over calcium chloride in a desiccator.

The light brown material is best purified by distillation under reduced pressure. The yellow aldehyde is collected at 120–140° (3 mm.) and melts at 41–44°. This material weighs 48–54 g. (47–53% overall yield based on N-bromosuccinimide) and is sufficiently pure for most uses.