[. Soc. Cosmet. Chem., 22, 139-151 (Feb. 4, 1971) The Purification of Some Intermediates for Permanent Hair Colors HAROLD H. TUCKER, Ph.D., and IRWIN SCHWARTZ, M.S.* Presented May 27, 1970, New York City Synopsis--Even though the INTERMEDIATES currently used by the manufacturers of oxi- dation hair colors are relatively pure, certain defects in the finished formulations have been traced to the presence of IMPURITIES in these products. Reported in this paper are the results of PURIFICATION, by RECRYSTALLIZATION, of 4-nitro-o-phenylenediamine, nitro-p-phenylenediamine, 4-amino-2-nitrophenol, 2-amino-5-nitrophenol, and 2-amino-4- nitrophenol. It has been shown that the formation of a precipitate in a HAIR DYE base solution, on ageing, may be caused by impurities, other than iron, present in the NITRO intertnediates and that this defect can be corrected by recrystallization of these intermediates. INTRODUCTION During the past decade much more attention has been given to the purity o[ products used by the manu[acturers of permanent hair colors. Suppliers have been requested to furnish products meeting in- creasingly rigid specifications and the methods o[ control have become much more sophisticated. Even though the intermediates currently being used by the manu[acturers o[ hair colors are relatively pure, certain de[ects in the finished formulations have been traced to the presence o[ impurities in these products. Reported in this paper are the results ot• purification, by recrystallization, o[ 4-nitro-o-phenylenediamine, nitro- p-phenylenediamine, 4-amino-2-nitrophenol, 2-amino-5-nitrophenol, and 2-amino-4-nitrophenol. These are the five leading nitro intermediates used in both permanent and semipermanent hair colors. * Lowenstein Dyes & Cosmetics, Inc., 420 Morgan Ave., Brooklyn, N.Y. 11222. 139

140 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS EXPERIMENTAL To obtain meaningful results, it was necessary to establish a method of analysis that would give reliable and reproducible figures using the available analytical equipment. Titration of an aqueous hydrochloric acid solution of the intermediate with standard sodium nitrite at 0 to 5øC, using starch-iodide paper as an outside indicator, was tried as a method for determining the purity of these compounds. While fairly consistent results were obtained with nitro-p-phenylenediamine, the re- sults with the other four intermediates were far from satisfactory. Since all of these compounds contain high percentages of nitrogen (27.4 or 18.1%) it was decided to use a modified Kjeldahl method and base the % purity on the nitrogen content. It is necessary to reduce the nitro groups to amino groups before proceeding with the deter•nination. This is done by adding 2 g of granular zinc metal, 15 ml of deionized water, and 15 ml of concentrated hydrochloric acid to the accurately weighed sample in a Kjeldahl flask. It is treated over a low flame until the water has been driven off and the residue starts to splatter. The reduction is then complete and, after cooling, the balance of the determination is the regular Kjeldahl method with sodium alizarine sulfonate as the indica- tor. This gives total nitrogen. Volatile nitrogen is determined by add- ing/5 ml of 30% sodium hydroxide to a solution of the intermediate and determining nitrogen without digestion. This is necessary in order to correct for any ammonium salts that might be present. The value for volatile nitrogen is subtracted from the total nitrogen to give fixed ni- trogen from which the percentage purity of the intermediate is calcu- lated. The intermediates are also tested for the percentage ash and the iron content. Ash is determined by ignition in a platinum crucible and weight of the residue. Iron is determined by fusing the ash in a mixture of equal parts of borax glass, potassium carbonate, and sodium carbonate, and dissolving the mass in dilute hydrochloric acid solution from which the iron is determined gravimetrically and reported as parts of iron per million parts of sample. Each of the five compounds is reported separately. Because of the possible effect of the method of preparation on the impurities that might be found in the product, a brief description of a suitable method for manufacturing is given for each product. The solubility of each inter- mediate in aqueous solution at 25øC and a pH of 9.7, as previously re- ported in the literature (1), is also listed. This is the approximate pH at which these intermediates are applied in permanent hair coloring.