RATIONALE OF DYES SYNTHESIS PROGRAM 359 competition by the carbonyl chromophore for the electron pair in op- position to the primary chromophoric dye system. The technique of modifying auxochromes with groups that increase or decrease their ability to deepen shade is used quite commonly to obtain changes of shade for a given color, as in the above case from a bluish-red to a neutral red. If the chemist now returns to H-acid (from which he has already obtained two red colors), couples it with diazotized sulfanilic acid in an acid medium, and then with diazotized aniline in an alkaline medium, he lengthens the conjugated system to the point where a deep blue dye re- sults (Fig. 9c). If p-nitroaniline is used in place of aniline, a further deepening of shade to a blue-black dye is obtained (Fig. 9d). Using all the general devices of varying the kind, number, and posi- tion of chromophores and auxochromes, the chemist has completed an initial line of azo colors for evaluation on wool. Further variations could be carried out to give azo dyes encompassing almost every color desired--greens, violets, scarlets, browns, and so on, in an almost infinite range of nuances of shade. Before leaving the area of azo dyes, it will be of interest to point out another tool which the organic chemist employs to obtain a given color, viz., additivity. Instead of obtaining deeper shades by seeing ways to increase the molecule's conjugation and electron mobility, he can take two differently colored chromophores and combine them chemically by an insulating group, thereby synthesizing the additive color. If, for example, a yellow azo dye (Fig. 10a) and a blue anthraquinone dye (Fig. 10b) are linked together by a group (Fig. 10c) which is incapable of transmitting electronic effects from one dye to the other, a green dye (Fig. 10d) will result. A wide choice of such insulating groups is available to the dyes synthesist. CONCLUSIONS Although the above discussion has been limited to azo dyes, it must be thoroughly stressed that the same general principles and approaches used to synthesize azo dyes are employed no matter what structural class of dyes is being investigated. The absorption spectrum of the starting molecule, be it colorless or colored, is determined and a systematic study is carried out by the chemist using a combination of synthesis and literature perusal to determine the effects on the original absorption of various substitutions and changes in the molecule. The organic structures comprising dyes are indeed varied and com- plex and require considerable ingenuity in their synthesis. For this

360 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS reason, the field of dyes has always been of great interest to the organic chemist. It was here that aromatic synthesis chemistry and the early theories of structure were expressed and delineated. Although thou- sands of dyes have been synthesized over the years, no letup of effort is in sight for there are still many problems to be solved and new ideas to be tested. (Received October 11, 1967) REFERENCES (1) Kamlet, M. J., ed., Organic Electronic Spectral Data, Vol. 1, Interscience Publishers, New York, N.Y., 1960. (2) Turner, D. W., Spectrophotometry in the far-ultraviolet region. Part II. Absorption spectra of steroids and triterpenoids, J. Chem. Soc., 1959, 30. (3) Pickett, L. W., and Sheffield, E., The ultraviolet absorption spectra of dioxadiene and dioxene, J. Am. Chem. Soc., 68, 216-20 (1946). (4) Hirayama, K., Handbook of Ultraviolet and Visible Absorption Spectra of Organic Com- pounds, Plenum Press, N.Y., 1967. (5) Coates, E., Colour and constitution, J. Soc. Dyers Colourists, 83, 95-111 (March 1967). (6) Grammaticakis, P., Structure and medium ultraviolet absorption of the aminobenzene- sulfonic acids and their derivatives, Cornpt. Rend., 236, 610-2 (1953). (7) Kiprianov, A. I., and Ushenko, I. K., Color and planarity of molecules of organic dyes, Izv. Akad. Nauk SSSR, Otd. Khim. Nauk, 1960, 492-500.