COLOR REACTIONS OF OXIDATION DYE INTERMEDIATES 151 used alone, they have a pronounced effect on the resulting hair color when used in conjunction with primary dye intermediates, especially p-phenylene diamine. All of these compounds, with the exception of alpha naphthol, are polyhydroxy phenols and they include the following: resorcinol, pyro- gallol, hydroquinone, phloroglucinol, pyurocatechol, alpha naphthol and dihydroxynaphthalene. The color changes produced by the phenols were described by Kass (2) in 1956. The phenols are not only valuable color modifiers but can also act as stabilizers, antioxidants and chemical timers to control the rate of color development. Resorcinol is extensively used as a drabbing agent for p-phylene diamine which usually yields brown tones with a violet cast. When resorcinol is used more desirable drab or greenish brown tones result. Alpha naphthol, on the other hand, yields violet to purple shades with p-phenylene diamine but because of its higher molecular weight its use may result in low intensity dyeings. p-phenylene diamine, although very color sensitive to the presence of other aromatic compounds, is not unique in this respect. P-amino phenol dyeings can also be modified. This compound when used alone results in reddish blonde shades but in the presence of alpha naphthol, distinct pink shades result. THE META DIaMINES The meta compounds, particularly the meta diamines, are classified as color couplers. When oxidized in the presence of para diamines they couple or condense with the quinone-di-imine to form intense blue or purple indamine dyes which have a high affinity for hair. The purple dye formed when alpha naphthol and p-phenylene diamine are oxidized together is an indophenol dye. The blue or purple dye formed when a meta diamine and a para diamine are oxidized together is an in- damine dye. This latter reaction is extensively used to obtain such shades as platinum, silver, steel gray and smoke blondes. Unfortunately, these colors are not as stable as dyes resulting from the oxidation of primary inter- mediates alone. We are speaking now of color stability on the hair. The blue and purple shades resulting from oxidizing a para diamine such as p-phenylene diamine in the presence of a meta diamine such as m-phenylene or m-toluylene diamine tend to turn red on the hair. Several years ago, in the course of investigating this problem, hair dyeings were made using various combinations of para diamines and meta diamines. No attempt was made to stabilize the blue and purple dyeings. When examined many months later, they had all drastically changed color with several becoming bright red. A possible explanation of this may be of interest. When a para diamine is oxidized in the presence of a meta diamine, a blue or purple indamine dye results which can readily undergo further oxidation with ring

152 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS closure to form a red azine dye (eurhoidine) as in the following reaction: NHs NHs NHs NHs NHs NH % % % + Nits CHa CHa p-Phenylene m-Toluylene Blue Diamine Diamine Indamine NH• xT NH• CHa Red Azine (Toluylene Red) This may explain another problem that has long plagued manufacturers of oxidation dyes. This is the tendency of drab shades based on p-phenylene diamine such as black, ash brown and ash blonde, to develop an objection- able reddish cast on the hair. Para phenylene diamine may contain very small amounts of meta diamine and the small amount of blue dye resulting during oxidation actually contributes to the desired drab tone. However, this blue dye in the hair can slowly undergo further oxidation and end up as a red azine dye. Although the stability of the blue and purple in- damine dyes can be improved by the careful use of polyhydroxy phenols, there is considerable room for improvement. It is a popular belief that one of the great advantages of oxidation dyes is that they produce fast shades on hair. This is not quite true. As we pointed out, shades which make use of the meta diamine coupling reac- tion tends to fade or turn red on the hair. Drab shades tend to lose their drabness and some of the red shades fade out. A careful study of the prob- lem results in the conclusion that good color stability is achieved when all of the dyes formed in a hair shade are of the azine, oxazine or phenazine type. Here we have complete oxidation and ring closure. Poor color stability is found when the hair shade includes indamine or indophenol dyes which can undergo further oxidation. It must be remembered that it is possible to produce a specific hair shade with more than one combination of intermediates and certain combinations result in more stable shades. This is by no means a hit or miss project. A thorough understanding of the ac- tion of intermediates individually and in combination with other inter- mediates is necessary to successfully formulate hair dyes. One of the problems in the laboratory dyeing of hair is that the dyed hair swatches are not always stable over a long period of time. One cannot