610 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Wilmsmann (2) has demonstrated that there exists a critical molec- ular size which is important for the penetration of hair. He showed that, under conditions used in hair dyeing, globular molecules having a diameter of more than 6 A are prevented from penetrating into the hair cortex by a barrier near the hair surface. The intermediates used in oxidative hair dyeing vary in diameter from 4.7 A for p-phenylenediamine to 5.6 A for p-aminodiphenylamine, well under this critical molecular size. Although the first patent for the use of p-phenylenediamine in dyeing hair was granted to Erdmann (3) in 1883, the commercial de- velopment of this class of dyes took place largely in the fur industry. Kass (4) has classified oxidation hair dyes as: i, primary inter- mediates which yield colors on oxidation ii, color couplers or modifiers which do not form dyes on oxidation but do produce color changes when used with primary intermediates and iii, nitro derivatives which do not depend upon oxidation for the production of color but are limited to shades of yellow, red, and orange. In this work the primary inter- mediates have been divided into derivatives of p-phenylenediamine, o-phenylenediamine, p-aminophenol, o-aminophenol, and diphenyl- amines and the color modifiers into derivatives of rn-phenylenediamine, rn-aminophenol, hydroxyphenols, and naphthols. The nitro compounds are included in the classification corresponding to their structure. An attempt has been made to include all of the important intermediates used for oxidative hair dyeing along with pertinent data, some of which were collected from the literature and the balance determined in this laboratory. METHODS AND RESULTS In order to determine standard practice in this country, ten com- mercially available black oxidation dye solutions, products of the recog- nized leaders in this field, were purchased. All of them were solutions of low viscosity which thickened upon the addition of the oxidizing agent. For nine of these products the user was directed to add an equal quantity of 6% hydrogen peroxide just prior to application. Directions for the tenth product called for the addition of a solid material from a packet which contained both the oxidizing agent and a thickening agent. Ac- cording to the directions furnished by the manufacturers, the dyeing times varied from five minutes to forty-five minutes. The pH of these products, after the addition of the oxidizing agent, varied from 9.,5 to 10.2, with an average of 9.7. It has therefore been concluded that, in this country, it is common practice in oxidation hair dyeing to use a pH

HAIR COLORING WITH OXIDATION DYE INTERMEDIATES {•11 of 9.7 and hydrogen peroxide at a concentration of 3• as applied to the hair. In the tables data are listed for each intermediate on patents, fade- ometer readings, solubility, and color produced. Patent information was obtained from the patent literature, from publications by Forster and Soyka (5) and Austin (6), and the Color Index (7). Additional data on toxicity may be found by consulting Heiling6tter (8). All fastness- to-light tests were run on a standard fadeometer. Most of the solubil- ities in water were determined by dissolving a weighed excess of the in- termediate in deionized water at 35 øC, adjusting the pH to 9.7 + 0.2 by the dropwise addition of ammonium hydroxide, and bringing the total volume to 100 cc. After the temperature had fallen to 25 øC, the solu- tion was filtered through a Gooch crucible and the solubility determined by difference. In a few cases where the solubility given in the literature far exceeded that used in hair dyeing this figure was used in the tables but always with the temperature recorded beside the solubility figure. In all cases the purest intermediates available were used. All dyeings were performed by immersion for forty-five minutes at room temperature, using natural white hair at a hair/liquor ratio of 1 to 50. For the primary intermediates, with the exception of the diphenyl- amine derivatives, 0.025 3//solutions of each dye were used. With the diphenylamine derivatives dye concentrations of 0.005 3//were used be- cause of their limited solubility and intense coloring power. For the mixtures of color modifiers and primary intermediates the concentration of each was 0.01 3//. In addition to the intermediates the solutions con- tained deionized water, 10% isopropyl alcohol, hydrogen peroxide at a concentration of 3% and sufficient ammonium hydroxide to adjust the pH to 9.7 q- 0.2 after the addition of the peroxide. After immersion for forty-five minutes the hair was rinsed in running water and dried. Dyeing with Primary Intermediates The effect of constitution on color, depth of shade, solubility, and light fastness of p-phenylenediamine derivatives is shown in Table I. Table II summarizes the results with o-phenylenediamine and its deriva- tives. The results with p-aminophenol and its derivatives are given in Table III. It was expected that the addition of an amino-group in the ortho- position of p-aminophenol would increase the depth o[ shade, as was the case with p-phenylenediamine. However, the opposite effect was ob-