Into a
2-l. round-bottomed flask fitted with a
mechanical stirrer are placed
400 cc. of concentrated sulfuric acid cooled to 0° and
204 g. (1.5 moles) of pure methyl benzoate (Note
1). The mixture is cooled by means of an
ice bath to 0–10° and then, with stirring, there is added gradually, by means of a
dropping funnel, a mixture of
125 cc. (1.96 moles) of concentrated nitric acid (sp. gr. 1.42) and
125 cc. of concentrated sulfuric acid. During the addition of the nitrating acid, which requires about one hour, the temperature of the reaction mixture should be kept within the range 5–15° (Note
2).
After the
nitric acid has been added, stirring is continued for fifteen minutes longer; the mixture is then poured upon 1300 g. of cracked ice. The crude
methyl m-nitrobenzoate separates as a solid and is filtered off by means of suction and washed with water. The product is placed in a flask and agitated with
200 cc. of ice-cold methyl alcohol in order to remove a small amount of
o-nitrobenzoic ester and other impurities that are present. The cooled mixture is then filtered by means of suction, washed with another
100-cc. portion of cold methyl alcohol (Note
3), and the solid dried. The yield is
220–230 g. (
81–85 per cent of the theoretical amount) (Note
4) of an almost colorless product melting at
74–76°. In order to obtain a product of maximum purity, which melts at
78°, it is advisable to recrystallize the ester from an equal weight of
methyl alcohol.