m-Chloro (CAS NO.: ), which is also known as Benzaldehyde, m-chloro-, could be produced through the following synthetic routes.

A solution of 450 g. (2 moles) of stannous chloride crystals in 600 cc. of concentrated hydrochloric acid is placed in a 3-l. beaker provided with an efficient mechanical stirrer and cooled in an ice bath. When the temperature of the solution has fallen to +5°, 100 g. (0.66 mole) of is added in one portion. The temperature rises slowly at first, reaching 25–30° in about five minutes, then rises very rapidly to about 100°. Stirring must be vigorous or the reaction mixture may be forced out of the beaker. During the reaction the nitrobenzaldehyde dissolves, and an almost clear, red solution is obtained. The solution is cooled in an ice-salt mixture until the temperature has fallen to about +2°. During the cooling, orange-red crystals separate and a pasty suspension results.

A 250-cc. separatory funnel is fixed so that its stem extends below the surface of the pasty suspension. A solution of 46 g. (0.67 mole) of sodium nitrite in 150 cc. of water is placed in the funnel and is slowly added to the well-stirred mixture until it shows a positive starch-iodide test for nitrous acid. The temperature of the mixture is maintained between 0° and +5°throughout the addition of the nitrite solution, which requires about ninety minutes. Usually, all but 5–8 cc. of the nitrite solution must be added before a positive test for nitrous acid appears.

During the latter part of the diazotization of the aminobenzaldehyde, a hot solution of cuprous chloride is prepared. In a 5-l. round-bottomed flask, 189 g. (0.75 mole) of powdered copper sulfate crystals and 161 g. of sodium chloride are dissolved in 600 cc. of hot water, and to this solution is added a solution of 41 g. (0.22 mole) of sodium metabisulfite (Na₂S₂O₅) and 27 g. (0.67 mole) of sodium hydroxide in 300 cc. of water. The final temperature of the resulting cuprous chloride solution should be about 75°.

The diazonium solution is added to the hot cuprous chloride solution while the latter is shaken by hand but is not cooled. After the solutions are thoroughly mixed, 840 cc. of concentrated hydrochloric acid is added and the mixture is allowed to stand overnight. The reaction mixture is steam-distilled to separate the , which is collected practically completely in the first 1.5 l. of distillate. The m-chlorobenzaldehyde is removed from the aqueous distillate by extraction with two 150-cc. portions of ether, and the ethereal solution is dried with 10–15 g. of anhydrous calcium chloride. After being decanted from the drying agent, the ether is distilled, and the residual liquid is distilled under diminished pressure. The m-chlorobenzaldehyde boils at 84–86°/8 mm., 107–109°/26 mm.. The yield is 70–74 g. (75–79 per cent of the theoretical amount).