A solution of 50 g. (1.25 moles) of sodium hydroxide in 1.5 l. of water is prepared in a 5-l. flask, and the solution is heated to gentle boiling. To the hot solution is added, in small quantities, 330 g. (0.9 mole) of anhydro-2-hydroxymercuri-3-nitrobenzoic acid (p. 56) (Note 1). The mixture is stirred after the addition of each portion of about 50 g. until the material has gone into solution except for a small residue. The flask is then fitted with a stirrer and addition tube (Note 2) and with a connection to a reflux condenser. The material is heated to boiling and stirred vigorously. There is slowly added, with continuous stirring, 101 g. (85 cc., 0.95 mole) (Note 3) of concentrated hydrochloric acid (sp. gr. 1.19). Heating is discontinued at this point, and 31.5 g. (30 cc., 0.5 mole) of glacial acetic acid (sp. gr. 1.05) (Note 3) is added slowly. A curdy precipitate forms.

A solution of bromine is prepared by dissolving 103 g. (1 mole) of sodium bromide and 160 g. (50.2 cc., 1 mole) of bromine in 150 cc. of water (Note 4). The mixture is stirred, and the bromine solution is added as rapidly as possible through the shaft of the stirrer. The precipitate dissolves. The solution is heated to boiling for five minutes after the last of the bromine has been added. The solution is then made slightly alkaline by the addition of 20 g. (0.5 mole) of solid sodium hydroxide and filtered through a fluted filter. The filtrate is then made acid to Congo red, using about 150 cc. of concentrated hydrochloric acid. The precipitated 2-bromo-3-nitrobenzoic acid is filtered with suction and sucked as dry as possible. It is then crystallized from 1 l. of hot 30 per cent alcohol. The yield of product melting at 185–187° is 130–150 g. (53–61 per cent of the theoretical amount, based on the 3-nitrophthalic acid used). About 25 g. of material melting at about 175° can be recovered from the mother liquor.