CCXLV.—The condensation of aromatic o-aminosulphonic acids with isocyanic acid

4-Nitroaniline-2-Sulfonic Acid Preparation and Salt Formation. A New Class of Aphrogens

“…Potassium Salt. Previously identified by nitrogen analysis (Scott and Cohen, 1922), the salt is bright orange but it is brown when precipitated from a slightly alkaline solution. It is reversibly thermochromic (becoming yellow at 100°C) and decomposes at 350°C (Figure 1).…”

“…Crystallizes from water as small, orange rhombic crystals; solubility 13.0 grams per 100 ml water at 100°C and 2.0 grams at 5°C. The salt is described by Scott and Cohen (1922) who found it to char without melting. It decomposes rapidly at 300°C (Figure 1).…”

“…few cases was the acid isolated and then only in gram quantities. Fischer (1891), who first synthesized the acid, and others (Boyle, 1911;Scott and Cohen, 1922;Skrowaczewska, 1953) isolated the compound by treating its barium salt with sulfuric acid-a procedure generally applicable for isolating sulfonic acids but unsuitable for the quantities we required.…”

“…The commercial sodium salt has been listed as "2-amino-5-nitrobenzenesulfonic acid, paste," and "2-amino-5-nitrobenzenesulfonic acid, ammonium salt." The ammonium salt was isolated by Scott and Cohen (1922) who reported the compound to char without melting at 290°C. They also isolated the potassium salt identified by nitrogen analysis.…”

Ureas

“…/7-Ethoxyphenylurea (Preparation 2-1) has also been prepared by the reac tion of/?-potassium cyanate or/?-phenetidine hydrochloride [20] or/7-phenetidine acetate [21]. /7-Bromophenylurea has also been reported to be prepared by the reaction of potassium cyanate on/7-bromoaniline hydrochloride [22,23].…”