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j. Soc. Cosmet. Chem., 31,153-159 (May/June 1980) Some factors affecting the rate of N-nitrosodiethanolamine formation from 2-bromo-2-nitropropane-l,3-diol and ethanolamines JOHN T. H. ONG and BONNIE S. RUTHERFORD Elizabeth Arden Research Center, P.O. Box 2046, Indianapolis, IN 46285. Synopsis The RATE of FORMATION of N-NITROSODIETHANOLAMINE (NDEIA) at 50øC in aqueous SOLUTIONS OF 2-BROMO-2-NITROPROPANE-1,3-DIOL and TRIETHANOLAMINE decreases as the pH is decreased from 6 to 4. No NDE1A is produced at pH 2 after 20 days at 50øC. Citrate buffer catalyzes the reaction, but propyl gallate in combination with disodium EDTA significantly inhibits the reaction. Sorbitol and sorbose have very slight catalytic effect. Technical grade triethanolamine (85%) yields concentrations of NDEIA approximately eight-fold greater than the reagent grade (99%) under the same experimental conditions. This increase could be attributed to the faster nitrosation rate of diethanolamine which is present in substantial amounts in the technical grade triethanolamine. Monoethanolamine (95%) also yielded NDE1A but at a slower rate than either di- or triethanolamine. INTRODUCTION The presence of N-nitrosodiethanolamine (NDE1A) in certain cosmetic products has been reported by Fan et al. (1). We subsequently studied the course of formation of NDE1A in a model system and explored approaches to inhibit NDE1A formation. Lijinsky et al. (2) have shown that either di- or triethanolamine, which are widely used in cosmetics as a part of the emulsifying systems, can be readily nitrosated to form NDE1A. Further, 2-bromo-2-nitropropane-l,3-diol, which is commonly used as a preservative for cosmetics, is able to nitrosate the secondary amine morpholine in an organic solvent (3) it thus seems conceivable that the 2-bromo-2-nitropropane-l,3-diol might also nitrosate di- or triethanolamine. The present study reports 1) the rate of NDEIA formation from various ethanolamines in aqueous solutions at 50øC and 2) some of the factors and compounds affecting that rate. EXPERIMENTAL MATERIALS All materials used were purchased. 2-bromo-2-nitropropane-l,3-diol (Bronopol, Inolex Personal Care Div.), (triethanolamine 85% grade (Ashland Chemical Co.) and organic 153