FATTY ACIDS AND DERIVATIVES IN COSMETICS* By Vm•½ K. B^B^¾AN E. F. Drew • Co., Inc., Boonten, N. The field of fatty acids and d•rivatives is rather an extensive one. A number of excellent texts and brochures (1-10) a.re now available which cover their chemistry and characterization of the numerous products and pure chemical compounds which occur in nature or have been synthesized in the chemists' laboratory. Summarizing or abstracting from these texts would be a waste of your time. The many excellent papers at your meetings and the other related fields have covered such derivatives of fatty acids as soaps and detergents of many different types and classes. In this paper I wish to discuss one segment of the broad field of fatty derivatives, namely, the glycerides. Mono-, di- and tri-esters of glycerin are used extensively in the cosmetic industry whether they are in the natural occurring state or tailor-made for the need and performance of a specific formulation. Mono esters of glycerin, monoglycerides as they have come to be called in the industry, are utilized as dispersing agents and emulsifiers and on to such use• as skin conditioners, solvents, dye or pigment vehicles and opacifiers for creams and lotions. Feuge (11) determined the effect of monog]ycerides on the surface ten- sion of a water and oil system, establishing the fact that the interfacial tension is substantially a function of the monoglyceride content. The diglycerides do not contribute to this phenomenon. The percentage of monoglyceride, required, however, may be added in pure form or in con- junction with diglycerides as long as the required amount is met. The performance in each case will be identical. Gros and Feuge (12) studied the monoglycerides of saturated fatty acids Cs through C•$ along with the monoglycerides of unsaturated fatty acids. The decrease of the interfacial tension was found to vary depending on the system being studied. Whether the calculations were made on a molar basis or a weight to weight basis, the chain length of the fatty acid used in monoglycerides contributed substantially to its behavior in the mineral oil, vegetable oil or other solvent media. The startling results were definite * Presented at the December 15, 1955, Meeting, New York City. 225

226 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS enough to compel one to study a given media and then select the mono- glyceride which would give the best results for that system. Alsop and Percy (13) found the presence of coconut oil fatty acid mono- glyceride stabilized emulsions of water and mineral oil containing soap and detergent. Bennett (14) has indicated that broader possibilities exist in the use of monoglycerides based on the techniques employed in preparing oil-in-water or water-in-oil emulsions. In the industrial application of monoglycerides, however, many factors must be considered beyond those covered by the authors mentioned. Rancidity, viscosity and opacity, for example, are but a few other considera- tions which may govern the choice of the monoglyceride. The mono- glycerides used in industry are generally a compromise between the chem- ically pure products of'given composition with specific oriented structures and the products which can be manufactured economically and constituting a mixture of mono-, di- and tri-esters present in a higher or lower percent- age depending on the technique used. The major supply available are products having 40 to 50 per cent monoglycerides with the balance prima- rily diglycerides and small amounts of triglycerides, free glycerin, free fatty acids, and in some cases, fatty acid soaps. In order to study the over-all, general behavior of the monoglycerides, we considered taking a typical product of industry containing 40 to 42 per cent monoglyceride and arbitrary formulations in water, oil or water-and-oil combination, and observed the differences which demonstrated the role specific fatty acids can play in otherwise identical products, conditions and system. Using fatty acids of 95 per cent purity, we prepared the monoglycerides of the saturated fatty acids C•.o through C•8. In this list we included the monoglycerides of approximately 90 per cent purity oleic acid and mono- glyceride of mixed fatty acids such as lard or tallow. Each of these mono- glycerides was prepared under controlled conditions, giving almost identical monoglyceride and diglyceride content. These products were evaluated along with several commercially available monoglycerides of equivalent monocontent in the following systems: 1. 20 parts light mineral oil, 80 parts water, 5 parts monoglyceride. 2. 90 parts light mineral oil, 10 parts monoglyceride. 3. 90 parts RBF cottonseed oil, 10 parts monoglyceride. 4. 90 parts water of pH 9, 10 parts monoglyceride. In each case the oil phase and the monoglyceride were mixed and heated to 60øC., under agitation. Water was added slowly at 60øC., and allowed to cool to room temperature while the agitation continued. Usually it took about thirty minutes for the mixing. In the experiments of system No. 1 of water and oil, the glyceryl mono- palmitate and monomyristate proved to be superior from the standpoint