COLORING WITH SEMIPERMANENT DYES Table XI Structure of Dyes that Passed the Three Tests 2 t 3 • 3 2 6 • 5 t 5 6 393 Dye 1' 1 2 3 5 6 A-11 A-13 B-11 B-12 B-13 C-9 C-12 C-13 C-14 --N(CHa)2 --N(CH,•)2 H --NCOCH• H --NCOCH:i H --NCOCHa --OH --OH --OH --OH --:NH . . . --NO s •NH OH --NO• •NH ... --NO s ::O ... --NO • -•NH --0 H --NO s •0 . . . --NH• •O ß ß ß --NO2 •NH --OH --NOs . . . --NOs ß . . ß . . --NO• ß . • ß . . --NO2 , . o rOH --OH --NH2 ß , . ß . ß --NHs ß ß o --NH• Dye D-1 (CH,,3s Although the proposed structures have been given in one form, it has been known, for many years, that the indophenols and indamines exist in two tautomeric forms in equilibrium as reported by Vittum and Brown (38). Certain of the indophenol type dyes behave as indicators, giving one color in alkaline solution and a different color in acid solu- tion. The 10 dyes listed above were tested by comparing solution colors at pH values of 4.0 and 11.0. With the exception of dye D-l, no signi- ficant differences in co]or of acid and basic solutions, of the same dye, were noted. However, the basic solution of D-1 was a very dark green-blue and the acid solution a dark bright wine-red, indicating that this dye is unsatisfactory for use in semipermanent colors. These 10 dyes may be recrystallized from isopropanol, but the yields were, in all cases, very poor. In fact, with some products the til- trate had to be concentrated before crystallization occurred. For this reason a series of 11 solvents, some of which had been reported in the literature as being suitable for indophenols and indamines, were tried on

394 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS each of these 10 dyes. These included: (a) li•oToin, (b) ethanol, (c) ethanol to which an equal volume of cold water was added after hot filtra- tion, (d) methanol, (e) methanol to which an equal volume of cold water was added after hot filtration, (f) n-butanol, (g) xylene, (h) propylenegly- col, (i) pyridine, (j) pyridine to which 3 volumes of cold water was added after hot filtration, and (k) water. Even though the 10 dyes that survived the three fastness tests (Table XII) are an insufficient sample upon which to postulate a theory, the ob- servation can be made that in eight of these dyes the position meta to the oxygen or imine group is substituted by a nitro or an amino group. It has been confirmed that substitution in the benzene ring has a definite effect on the stability of the indophenol and indamine dyes. Although nine of the dyes described in this paper might find a useful application in semipermanent hair coloring, it is hoped that a complete range of suit- able colors will be developed by further research with the indophenols and indamines. Table XlI Properties of Dyes that Passed the Three Tests Light Rccrystn. Color of Recryst. Fastness Melting Color of Dye- Dye No. Method Product (hr) Point (øC) ing on Hair A-11 j Black 14 163 Yellow-brown A-13 j Orange 17 220 D Yellow-orange B-11 k Medium brown 16 277 Red-orange B-12 c Black 12 189 Bright yellow B-13 d Orange 23 140 Bright orange C-9 e Black 14 240 Ash brown C-12 e Black 11 165 Yellow-gold C-13 e Dark brown 33 above 290 Red-orange C-14 e Black 13 192 Golden brown D-1 e Light brown 10 112 Red-gray SUMMARY A review has been given of the recent literature on semipermanent hair coloring. A method of application of these colors has been selected from these references and a series of tests proposed for evaluating semi- permanent hair dyes. Three factors led to the selection of indophenols indamines for this research. It had been established that penetration of the fiber can be increased by decreasing the size of the dye molecule. Indophenols and indamines are among the smallest dye molecules known but are of limited stability. It had been reported that their stability can