DESIGN OF COSMETIC SUN SCREENS 107 the meta isomer since they are located at nonconjugating positions in the molecule bottom of page 106. This transition is simila rto that of the simple benzoate esters, and to aniline. These considerations lead to the conclusion that the para isomers afford the optimum cosmetic screen. Substitutions of various groups on the amino radical of the para amino- benzoates lead to considerable modification of the transition possibilities, and hence change the screening characteristics of the original chomophore. Acetylation of the amino radical greatly reduces the basic character of the nitrogen atom and hence decreases its electron-releasing tendencies. Thus the probability of the transition o o II I1 NH--C--CHa •NH--C--CHa I c c //% 0 OR ©: 0 OR is smaller than that in the parent free amine, and requires greater energy. As a result, absorption maximum is lowered from 297.5 mu to about 270 mu, and resulting p-acetamidobenzoate ester is not a good cosmetic screen. Another method of modifying the amino group is through Schiff-base formation by condensation with an aldehyde group. NH2 N=CH--R• q- R•--CH:O --• + H20 I c c o OR O OR The resulting aldimino structure allows a transition to occur which lies within the erythematogenic range of energy, N:CH--R• N--CH--R• I I c c //N /% 0 OR ©: 0 OR

108 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS and the resulting activated state is resistant to oxidation. These Schiff bases are the newest development in commercially available cosmetic sun screens. Thus, ethyl-p-glucosylimidobenzoate is a screen (Escalol- 206*) which is highly selective in its activity. To a greater extent than even the p-aminobenzoate esters, such compounds absorb selectively in the erythematogenic range while they are nearly completely transparent in the higher ultraviolet. They permit the most complete transmission of the tanning radiation while providing efficient protection against erythemal radiation. z 2['0 aoeO 360 400 WAVELENGTH Thus a 2.7 per cent concentration of Escalol 206 in a clear or emulsified lotion transmits only 7.4 per cent of the erythematogenic radiation of sunlight, and 95.6 per cent of the radiation in the so-called tanning range, above 315 millimicrons. REFERENCE (1) Braude, E. H., "Chemistry of Carbon Compounds," Vol. 1A, Elsevier Publishing Princeton, N.J. (1951), pp. 71-93. * Van Dyk & Co., Inc.