INTERMEDIATES FOR HAIR COLORS 145 of wavelengths from 6.4 to 7.3 v, indicate that differences do exist be- tween the crude and purified products but sufficient data are not avail- able to determine fully the exact nature of these differences. In the laboratory recrystallization of nitro-p-phenylenediamine from water, a mass of sticky material was removed during the hot filtration. This material was washed repeatedly, on the filter, with hot water, until the flitrate came through colorless. After drying at 50øC, and cooling, this black material became very hard. It melted at 98øC. The material had an ash content of 0.67% and an iron content of 0.52% determined and reported as ferric oxide. An infrared spectrogram of this sludge is shown in Fig. 4. 4000 30• 2000 1500 CM a 1000 900 800 700 IOO IOO 80 80 •6o •40 •.0 •- 20 •0 3 4 5 6 7 8 9 10 II 12 13 14 153 WAVELENGTH (MICRONS Figure 4. Sludge from nitro-p-phenylenediamine Nitro-p-phenylenediamine differs from nitro-o-phenylenediamine in that reducing agents are not used in its preparation its solubility in wa- ter, while still low, is about eight times that of the ortho compound it is recrystallized from water instead of alcohol and it is much more difficult to reduce to 1,2,4-triaminobenzene. The sludge from nitro-p-phenylene- diamine melted at 98øC, compared to above 335øC for the ortho com- pound. This fact, in conjunction with the infrared spectrograms of the sludges, indicates that the two compounds are vastly different. Although precipitation in the base solution, of the crude para product, takes longer than with the ortho compound, it does occur. However, recrystallization of the crude product does remove the material that is responsible for the development of a precipitate on ageing. The amount of material precipitated in the boiling experiment, pre- viously described, was 2.13% for the crude nitro-p-phenylenediamine and 0.10% for the purified.

146 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 4-,4 mino-2-nitrophenol 4-Amino-2-nitrophenol can be prepared by coupling diazotized sul- fanilic acid with o-nitrophenol and treating the azo dye thus formed (4-hydroxy-3-nitroazobenzene-4-sulfonic acid) with sulfurous acid which splits it at the azo group forming sulfanilic acid and 4-amino-2-nitro- phenol which is recrystallized from water (8). Its solubility at 25øC in aqueous solution at a pH of 9.7 is 2.97% (1). Comparable analyses of 4- amino-2-nitrophenol are given in Table III. Table III Analyses of 4-Amino-2-nitrophenol Purified Raw Purity, % 99.4 95.1 Ash, % Trace 0.82 Iron, ppm Trace 382 Melting point (Fisher-Johns), øC 136 130 In the ageing test, precipitation in the solution containing the crude product started after 13 days at 50øC and after 15 days at room tempera- ture, while no precipitate appeared in bottles containing the purified material after 4 weeks. No appreciable differences were noted in the in- frared spectrograms of the crude and purified 4-amino-2-nitrophenols. In the laboratory recrystallization of 4-amino-2-nitrophenol from wa- ter, a small amount of black material was removed during the hot filtra- tion. This material was washed repeatedly on the filter, with hot water, until the flitrate came through colorless. After drying at 50øC, this black material melted at 135øC. It had an ash content of 1.42%, all of which proved to be ferric oxide. An infrared spectrogram of this sludge is shown in Fig. 5. 4000 3(•00 2000 I$00 CM 4 10043 900 800 700 10C 100 8C 80 •6C 60 •4C 40 • 2C 3 4 .5 6 7 8 9 10 11 12 13 14 150 WAVELENGTH (MICRONS) Figure 5. Sludge from 4-mnino-2-nitrophenol