A Comparative Study On The Formation Of N-nitrosamines In Relation To Alkonolamide Surfactants

Alkanolamide surfactants are thickeners and foam boosters with excellent performance,which are widely used in daily chemicals such as cosmetics,personal care products and household cleaning products,which are also used in food detergents such as dishwashing detergents,vegetarian food cleaning agents and food processing machinery cleaners.Alkanolamide surfactants are usually prepared from natural oils,fatty acids or their methyl esters and ethanolamines,such as monoethanolamine and diethanolamine.Fatty acid diethanolamide is restricted globally for use because more studies have shown that diethanolamine was easily nitrosated to carcinogenic N-nitrosodiethanolamine.Fatty acid monoethanolamide and methylethanolamide have been gradually accepted in the market as alternatives,however,which form N-nitrosamines compared with fatty acid diethanolamide has been seldom studied.To investigate the feasibility of replacing fatty acid diethanolamide by monoethanolamide and methylethanolamide in surfactant production and application,in this study,N-nitrosamines were prepared from three ethanolamines by tert-butyl nitrite,and identified to reveal nitrosation mechanisms and used as base materials to establish quantitative detection method by ultra performance liquid chromatography.Secondly,this method was used to evaluate the easiness of nitrosation among three ethanolamines,which is also used to investigate the related nitrosation of among three alkanolamide surfactants in production and application.The main experimental procedures,results and conclusions of this paper are as follows:?1?The structure identifications of FT-IR,ESI-MS,¹H-NMR and ¹³C-NMR of three ethanolamine nitrosation products showed that diethanolamine and methylethanolamine were directly nitrosated to N-nitrosodiethanolamine and N-nitrosomethylethanolamine,therein N-nitrosomethylethanolamine was enantiomers maintained at a fixed ratio of about 4:1;however,monoethanolamine was disproportionated to form diethanolamine,and then nitrosated to N-nitrosodiethanolamine.A quantitative detection method based on UHPLC with UV detection has been established.The condition for N-nitrosodiethanolamine was C18 reversed phase column with acetonitrile water mixture?2:8?and UV detector at 230 nm.Under this condition,the linear range was 0.0055⁰.11 mg/mL,the limit of quantitation and detection were 0.54 and0.18?g/mL.The condition for N-nitrosomethylethanolamine was C18 reversed phase column with acetonitrile water mixture?1:9?and UV detector at 234 nm.Under this condition,the linear range was 0.005⁰.1 mg/mL,the limit of quantitation and detection were 0.24 and 0.08?g/mL.Both methods are good linear correlation,repeatability and accuracy.?2?The pH significantly affected the nitrosation reaction between ethanolamines and nitrite.The optimum pH was 3.4,and the yields of N-nitrosamines increased with pH between2.3 and 3.4 and decreased with pH between 3.4 and 7.2,which was consistent with the literatures.The results of nitrosation reaction of raw material ethanolamines all indicate that methylethanolamine and monoethanolamine are more difficult to form N-nitrosamine than diethanolamine,moreover monoethanolamine is the most difficult.On the one hand,due to ethanolamines structure,monoethanolamine is the weakest nitrosation reactivity as a primary amine,while diethanolamine is more prone to nucleophilic substitution reaction because of higher electronegativity than methylethanolamine,on the other hand,due to the different stability of N-nitrosamines,N-nitrosodiethanolamine is more likely to form internal hydrogen bond compared with N-nitrosomethyl ethanolamine,so it is beneficial to form products and increase stability.The results of experiments in simulated physiological environments indicate that it is the least likely to form N-nitrosamines in simulated sweat,which is further revealed that products containing alkanolamide surfactants are more safe to apply to skin.?3?The results of related nitrosation on alkanolamide surfactants showed that N-nitrosamines were not detected in same production and simulated actual application;but in simulated enhanced application,N-nitrosodiethanolamine formed by diethanolamine was detected in simulated gastric juice.These results reveal that there are no evidence about forming corresponding N-nitrosamines in three alkanolamide surfactants conventional production and there are no evidence that N-nitrosamines are detected in three alkanolamide surfactants normal application;the results in simulated enhanced application indicate that fatty acid methylethanolamide and monoethanolamide can reduce harmful N-nitrosamines compared diethanolamide,therefore,it is feasible to substitute fatty acid diethanolamide by monoethanolamide and methylethanolamide.The results and conclusions in this article support the current tendency to substitute fatty acid diethanolamide by fatty acid methylethanolamide or monoethanolamide in surfactant production and applications;however,the solid form of fatty acid monoethanolamide,its insolubility and the instability of its thickened product have affected the acceptance of daily chemical manufacturers;previous results in our laboratory showed that fatty acid methylthanolamide has the same thickening and foam stability as fatty acid monoethanolamide and diethanolamide;Considering the easiness of forming N-nitrosamines,practicability and thickening and foam stability,this article recommends that fatty acid methylethanolamide is the first choice for commercial alkanolamide surfactants as thickeners and foam boosters.