EVALUATION OF SUNSCREENING AGENT 89 pendent laboratory.* All the clinical and performance studies on humans and the comedogenicity study on rabbits were conducted by another laboratory.? EXPERIMENTAL Phase 1-Initial Screening The first phase of the research program concerned the synthesis of com- pounds, which were expected to absorb in the optimum uv region. Pro- poxylated ethyl p-aminobenzoate was selected for further development be- cause it absorbs in the correct uv region and exhibits desirable physical prop- erties. Infrared (ir) spectra, nuclear magnetic resonance (NMR) spectra, and gas chromatographic analysis (GCA) substantiate that propoxylated ethyl p-aminobenzoate is a mixture of 2 moles of N, N-dihydroxypropyl and 1 mole of N-monohydroxypropyl ethyl p-aminobenzoate. NMR spectra show that the hydroxypropyl moiety in the mono- and di-compounds contains both primary and secondary hydroxyls. To further substantiate the actual composition of propoxylated ethyl p-aminobenzoate, pure mono and di hydroxypropyl sub- stituted ethyl p-anfinobenz.oates were synthesized, analyzed, and reblended in various mole ratios. Ir spectra, NMR spectra, and GCA .of a 2 di to 1 mono blend matched propoxylated ethyl p-aminobenzoate exactly. The ir spectra of propoxylated ethyl p-aminobenzoate, N, N-dihydroxypropyl, and N-mono- hydroxypropyl ethyl p-aminobenzoate are shown in Figs. 2, 3, 4, respectively. Table I contains the important physical properties, and Table II contains solubility data on propoxylated ethyl p-aminobenzoate. It should be understood that it is not essential for a compound to exhibit maximum absorbance at 308 nm, but only that the absorption peak be suffl- ciently broad to encompass the sunburn range of 290. to 320 nm and narrow enough to transmit the tanning range. Figs. 5, 6, 7, 8, 9, and 10 compare pro- poxylated ethyl p-aminobenzoate absorption with other sunscreens. Propoxy- lated ethyl p-aminobenzoate exhibits maximum absorbance at 308 to 311 nm, xvhich is the region of the greatest burning intensity, and compares very favor- ably with the most active sunscreens in use today. It will be noted in Fig. 7 that PABA, which is generally recognized as a very effective screen, has a somewhat less favorable absorption at 310 nm, although it is very active at 290, where comparatively little burning and .tanning take place. The compari- son with 2-ethoxyethyl-p-methoxycinnamate (Fig. 10) does not tell the whole story until one exposes both compounds to direct sunlight for various periods of time. Fig. 11 shows the dramatic effect of solar energy on the cinnamate with the obvious resulting formation of new compounds. Propoxylated ethyl *Food and Drug Research Laboratories, Inc., Conshohocken, Penn. '• Ivy Research Laboratories, Inc., Philadelphia, Penn.

90 JOUBNAL OF THE SOCIETY OF COSMETIC CHEMISTS o o o