FORMATION OF NDE1A 157 1,3-diol, which is more stable at lower pH the result is a slower rate of NDE1A formation. At pH 2 the amount of nitrite produced would be negligible over the period of the experiment, as can be predicted from the data of Bryce et al. (5). Furthermore, the concentration of the unprotonated triethanolamine in the acid-base equilibrium (eq 3) was so low (ca. 0.66 ng/ml) that the nitrosation reaction, if any nitrite were present, would not yield a detectable level of NDE1A in this study. The effects of some additives are seen on Table II. At pH 4 citrate buffer catalyzed the overall reaction by three-fold, presumably through a general acid-base mechanism involving the decomposition of 2-bromo-2-nitropropane-l,3-diol and, to a small extent, the nitrosation reaction itself (9). Alkyl polyhydroxy compounds such as sorbose and sorbitol had very slight catalytic effect. However, propyl gallate in combination with disodium EDTA showed significant inhibition of the overall rate of NDEIA formation. At pH 5 the reduction of the rate was eight- to ten-fold, while the pH 4 up to 25-fold reduction was evident. As noted with other phenolic antioxidants, propyl gallate served as a scavenger by removing the N20 3 produced by the decomposition of 2-bromo-2-nitropropane-l,3-diol in the solutions (eq 5). HO HO%COOC3H7N203--•+HO (5) o O%COOC3n 7 -¾ 2NO + H20 HO The NO produced in the above reaction could be converted into another nitrosating agent NO * in the presence of heavy metal ions (eq 6). NO + M n+ • NO + + M (n-•)+ (6) Challis et al., (10,11) have reported metal ion catalysis in the nitrosation reaction by NO. In the present study the EDTA was incorporated to chelate any heavy metal ions and prevent the formation of NO + . Table III shows the effect of the grade and kind of ethanolamine on the rate of NDE1A formation. Reagent grade triethanolamine (99%) yielded about 13% as much NDEIA as the technical grade (85%). This difference could be attributed to the presence of a larger amount of diethanolamine in the technical grade, for which the suppliers specify a maximum of 15% diethanolamine. The results show that at pH 4 the rate of NDEIA formation from diethanolamine was 10 to 20 times faster than that from the reagent grade triethanolamine (99%) under the same experimental conditions. Also, at pH 5 the rate of formation of NDE1A using diethanolamine was ten times faster than that from the technical grade triethanolamine (85%). Tertiary amines nitrosate at a slower rate than secondary amines because the former reaction involves a nitrosative dealkylation limiting step to yield a secondary amine which is then available for further nitrosation (12).

158 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table III Effect of the Grade and Kind of Ethanolamine on the Rate of NDE1A Formation • NDEIA Formed (ng/ml) at 50øC After the Following Heating Time (Days) pH Ethanolamine 6 13 20 4.0 Triethanolamine 99% 182 250 450 Triethanolamine 85% 291 3,320 3,260 Diethanolamine 1,960 6,120 7,980 Monoethanolamine 95% n.d. 2 300 210 5.0 Triethanolamine 85% 663 3,220 3,190 Diethanolamine 8,740 11,200 14,300 •Solutions contained 2-bromo-2-nitropropane-l,3-diol (0.1%) and ethanolamine (2%). 2None detected. Monoethanolamine (95%) yielded some NDE1A but at a slower rate than either tri- or diethanolamine. The NDEIA might be produced from diethanolamine present as impurity in the monethanolamine. Gas-liquid chromatography analysis indicated a diethanolamine level of approximately 0.3 mg/g. In addition, primary amines could also be nitrosated to form a diazonium ion which then reacts with the primary amine to yield a secondary amine. This later reaction is very unfavorable in strongly acidic solution due to the low fraction of the unprotonated amine (12). On the other hand, a mildly acidic or neutral medium would not favor the diazonium ion formation. These factors contribute to the low yield of NDE1A fi'om monoethanolamine. ACKNOWLEDGMENTS The authors are very grateful to Drs. J. E. McCullough and E. Farkas for their encouragement. Thanks are also given to Mr. H. F. Hugar for his technical assistance in the analytical work. REFERENCES (1) T. Y. Fan, U. Goff, L. Song, D. H. Fine, G. P. Arsenault and K. Biemann, N-nitrosodiethanolamine in cosmetics, lotions and shampoos, Food Cosmet. Toxicol., 15,423-430 (1977). (2) W. Lijinsky, L. Keefer, E. Conrad and R. Van de Bogart, Nitrosation of tertiary amines and some biologic implications,J. Nat. Cancer Inst., 49, 1239-1249 (1972). (3) T. Y. Fan, R. Vita and D. H. Fine, C-nitro compounds: a new class of nitrosating agents, •bxicol. Lett., 2, 5-10 (1978). (4) W. Fiddler, R. C. Doerr and E.G. Piotrowski, Observations on use of thermal energy analyzer as a specific detector for nitrosamines, in E. A. Walker, L. Griciute, M. Castegnato and R. E. Lyle, "Environmental aspects of N-nitroso compounds," IARC Scientific Publications No. 19, Interna- tional Agency for Research on Cancer: Lyon, France, 1978 pp 33-40. (5) D. M. Bryce, B. Croshaw, J. E. 1-Hall, V. R. Holland and B. Lessel, The activity and safety of the antimicrobial agent Bronopol (2-bromo-2-nittopropane-l,3-diol), J. Soc. Cosmet. Chem., 29, 3-24 (1978). (6) A.M. Unrau, Reaction of 2-methyl-2-nitro-l,3-propanediol with alkali, Can. J. Chem., 42, 1741-1745 0946). (7) I. Schmeltz and A. Wenget, 2-Bromo-2-nitropropane-l,3-diol as a nitrosating agent for diethanolam.- ine: a model study, Food Cosmet. Toxicol., 17, 105-109 (1979).