j. Soc. Cosmet. Chem., 32, 75-85 (March/April 1981) Formation of N-nitrosodiethanolamine from the peroxidation of diethanolamine JOHN T. H. ONG, BONNIE S. RUTHERFORD, and ALFRED G. WICH, Elizabeth Arden Research Center, Lilly Research Laboratories, 307 E. McCarty St., Indianapolis, IN 46285. Received October I6, I980. Presented at the Society of Cosmetic Chemists Annual Scientific Meeting, New York, NY, December I I- 12, 1980. Synopsis N-Nitrosodiethanolamine (NDE1A) was formed in aqueous solutions containing POLYSORBATE 20 and diethanolamine stored at pH 6 and 50øC under continuous aeration. The yield of NDEIA increased over a period of four weeks and was related to the PEROXIDE level in the solution. The peroxide was formed as a result of the AUTOXIDATION of polysorbate 20. However, no peroxide could be detected in polysorbate 20 solutions containing diethanolamine, indicating the reaction of the peroxide with diethanolamine. It is suggested that peroxidation of diethanolamine would yield nitrite or oxides of nitrogen which then nitrosated the remaining diethanolamine. The formation of NDE1A was enhanced at higher level of peroxide but inhibited effectively by the ANTIOXIDANT propyl gallate or butylated hydroxyanisole. Furthermore, NDEIA was also formed in aqueous solution of hydrogen peroxide and diethanolamine. Mono- or triethanolamine did not yield NDEIA under the same experimental conditions, although the formation of peroxide from polysorbate 20 was similarly inhibited. The implication of the results is discussed. INTRODUCTION N-Nitrosamines are a group of organic compounds that have attracted considerable amount of attention due to their carcinogenicity in laboratory animals (1--3). Recently, Fine et al. (4) and Rosenberg et al. (5) have developed analytical techniques which would allow the determination of non-volatile nitrosamines in the parts-per-billion level. Consequently, trace levels of N-nitrøsødiethanølamine (NDEIA) have been detected in several cosmetic products (6). Edwards et al. (7) have demonstrated that NDEIA is absorbed through the human skin from a contaminated facial cosmetics. It appears that the majority of cosmetic ingredients do not significantly contribute to the presence of NDEIA in the products (8). Rather, the contamination is generally believed to be caused by the chemical reactions between a nitrosating agent and the widely used di- or triethanolamine. Some of the known nitrosating agents are C-nitro compounds, nitrite, or the oxides of nitrogen. Schmeltz and Wenget (9) have assessed 75

76 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the role of the commonly used C-nitro preservative, 2-bromo-2-nitropropane-l,3-diol, as the precursor of nitrite. Factors that affect the rate of NDEIA formation in aqueous solutions of 2-bromo-2-nitropropane-l,3-diol and ethanolamines are pH, the presence of catalyst or inhibitor, and the kind and grade of the ethanolamine (10). Furthermore, Fan et aL (11) reported the nitrosation of morpholine by several C-nitro compounds in a non-aqueous system. With regard to nitrite or oxides of nitrogen, data to date have not shown their presence in many common cosmetic ingredients (8). The purpose of this study was to identify a potential source of nitrosating agent in the course of inhibiting the formation of NDEIA in cosmetics. It has been reported (12,13) that polyoxyethylene compounds can undergo autoxida- tion to form hydroperoxides with subsequent cleavage of the chain. The importance of this hydroperoxides formation in relation to drug stability was assessed by McGinity et al. (14,15). More recently, Donbrow et al. (16) reported a detail study of the autoxidation of polyoxyethylene sorbitan mono-fatty acid esters (polysorbates) leading to the formation of hydroperoxides and subsequent changes of the physical and chemical properties of the surfactants. In view of the frequent use of polyoxyethylene surfactants to enhance the stability of the ethanolamine-fatty acid emulsion systems, it was thought necessary to explore the possibility of NDEIA formation in such combination of surfactants. This study reports the interaction of ethanolamines with hydrogen peroxide or the hydroperoxides of polysorbate 20 that was subjected to accelerated autoxidation. EXPERIMENTAL MATERIALS The following materials were used as received: polysorbate 20 (I.C.I. United States, Inc.) hydrogen peroxide 3 percent (Baker Chemical Co., AR 1-2180) monoethanol- amine 95 percent (Aldrich Chemical Co., Inc. 11,016-7) diethanolamine (Baker Chemical Co., AR 9227) triethanolamines 85 percent (Ashland Chemical Co.), 98 percent (Dow Chemical Co.), and analytical reagent grades (Baker Chemical Co., AR 1-9468) antifoam AF-72 (General Electric Co.) and disodium EDTA (J. F. Henry Chemical Co.). Propyl gallate and butylated hydroxyanisole were used as Tenox S-1 and Tenox A (Eastman Chemical Products, Inc.), respectively. All other materials, unless otherwise specified, were of analytical grade. Water for Injection USP was used as the solvent throughout the study. ' .]i APPARATUS Figure 1 shows the system used in the autoxidation of polysorbate 20. The reaction vessel was a 100-ml two-neck round-bottom flask equipped with a 20-cm Liebig condenser and a fritted gas inlet connected to the air supply with Tygon tubing. The vessels were immersed in a constant temperature waterbath at 50 ___ 0.2øC (Magni- Whirl, Blue M Electric Co. or Precision Scientific Co.). The air flow was regulated by adjusting the clamps on the tubing such that the air bubbles caused a mild turbulent mixing evenly in each of the reaction mixtures. The system was continuously exposed • to the fluorescent light of the laboratory throughout the study.