ZINC PYRITHIONE PREPARATIONS 105 atom of one of the hydroxyl groups. It was concluded that the pri- mary amino nitrogen atom does not participate in forming the chelate structure. The experimental proof for this is that when the analogous compound without hydroxyl groups, N,N-diethyl-l,3-propanediamine, was tested for its solvent capacity on ZPTO, the solubility of ZPTO was reduced from well over 10% at 20øG to less than 1%. Diglycolamine The superior solvent power of diglycolamine could be ascribed to the formation of a tetradentate chelate structure with ZPTO (Fig. 5). •k• •.,• . . • ...... • DIGLY Figure 5. ZPTO-diglycolamine complex Diglycolamine, which may be thought of as a derivative of diethyl ether, was chosen as the solubilizing agent for ZPTO in several clear formula- tions (Table I). These formulations are limited by the low water concentrations that are required for clarity. Increasing the concentra- tion of the water causes the disruption of the ZPTO-diglycolamine com- plex permitting free ZPTO to be thrown out of solution. The proto- type hair-setting lotion formulation that was prepared (Table I) con- tains 0.2% ZPTO and is clear. When water is added it becomes cloudy due to liberated ZPTO. The pH of a 1:1 mixture with water is 8.8. The shampoo preparation shown in Table I has good foaming proper- ties due partly to the high diethanolamide content. As expected, the

106 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I Product Formulations Based upon the ZPTO-Diglycolamine Complex Clear Hair-Setting Lotion Sequence Ingredient 1 Polyvinylpyrrolidone K-30 1 Anhydrous ethanol 2 Perfume oil fZPTO 3 }Diglycolamine 4 3.7% hydrochloric acid Clear Shampoo Sequence Ingredient 1 70-30 lauric-myristic diethanolarnide 1 Isostearic acid 1 Propylene glycol fZPTO 2 } Diglycolamine Hair Gel Sequence Ingredient 1 Eracol CD-18 a 1 Glycerine 1 Propylene glycol 1 95% ethanol J'CarboFol 940 2 •Water JZeTO 3 }Diglycolamine Per Cent 2.0 91.7 0.1 0.2 1.8 4.2 Per Cent 23.8 17.0 42.2 1.7 15.3 Per Cent 10 0 10 0 30 0 25 0 0 6075 23 6925 0.07 0.63 Witco Chemical Co., New York, N.Y. addition o15 water precipitates the ZPTO. A 1:1 mixture o15 this shampoo with water has a pH ot5 9.5. The hair-grooming gel 15ormulation (Table I), based upon a poly- propoxylated triol, incorporates diglycolamine as both a solubilizer 15or ZPTO and as a neutralizing agent 15or Carbopol resin. This digly- colamine neutralized gel contains 700 ppm ZPTO and has a pH of 7.5. Figure 6 is a photograph that compares this gel with a simple Carbopol gel neutralized with a system containing 1% ZPTO dissolved in 28% ammonium hydroxide. This particular ammonium hydroxide-neu- tralized gel contains 200 ppm ZPTO and is cloudy at pH 7.6. Actually, the diglycolamine-neutralized gel was initially clear but a15ter several days, small, well-defined ZPTO crystals were observed dispersed within it. It appears that the re15ractive index o15 these crystals is closer to the re15ractive index o15 the surrounding media than the re15ractive indices