Synthesis And Properties Of N~ε-Lauroyl Lysine

N^ε-lauroyl lysine（LL）is a functional powder derived from lysine,which is insoluble in most solvents,such as water and oil,and has no irritation to the skin.Besides,it has good biodegradability,strong antioxidant property and stability.Its flake crystal structure endows LL with the characteristics of easy adhesion and high lubricity,making them attractive to be applied as ingredients of cosmetic bases or skin feel modifiers.Lysine has two amino groups,the public method of its derivative LL has many synthetic steps and cumbersome purification.The current supply of LL still depends on imports.In this context,LL was synthesized by a one-step method,in which the purification steps were simplified,and the lysine residue in the reaction solution could be recovered.Then the effect of LL as a particle emulsifier in stabilizing Pickering emulsion was explored,and the effect of LL and sodium dodecyl sulfate（SDS）synergistically stabilizing emulsion was explored.Finally,LL was applied to specific cosmetic formulas.The main research contents and conclusions were as follows:Based on the Schotten-Boumann condensation reaction,lysine and lauroyl chloride were used as raw materials,a one-step method was used to synthesize LL,and the optimal synthesis conditions were explored through single-factor experiments and orthogonal experiments.The results showed that when using methanol as the solvent,with the p H being controlled at 7-8during reaction using the sodium hydroxide,it was beneficial to the synthesis and purification of LL.When the molar feed ratio（n（lauroyl chloride）:n（lysine））was 3:1,the concentration of lysine was 0.02 mol/150 m L,and the reaction temperature was 30℃,the best yield was 53.3%.The lysine in the reaction solution under the optimal conditions was recovered,and the recovery rate was 36.2%.Finally,the structure of LL was characterized by IR,MS and ¹H NMR,and the thermal decomposition temperature of LL was measured to be 263.5℃.The influence of the crystallization temperature on the particle diameter of LL was explored,and the influences of the operating parameters on the preparation of Pickering emulsions under the smallest particle diameter were investigated.The results showed that the optimal temperature of LL crystallization was 30℃,and the diameter of the prepared particles was（1347.4±156.9）nm.The oil-water-LL contact angle was measured to be 142.9°±1.6°,and the type of prepared emulsion was W/O.The optimal preparation conditions for the emulsion were a homogenization rate of 11000 r·min^-1,an emulsification temperature of 20℃,a particle concentration of 2 wt%,and an oil-water volume ratio of 5:5.The average droplet size of the emulsion prepared under these conditions was（23.5±1.5）μm,the emulsification rate was 91.7vt%after storage for 7 days,and the initial viscosity was 2449 Pa·s.In addition,LL had good tolerance to water phases of different p H.In the subsequent standing experiment,it was found that the emulsion system stabilized by LL had good long-term stability.The synergistic effect of LL-SDS to stabilize the emulsions and the effect of inorganic salt on the synergistic effect of two emulsifiers were explored.The results showed that the addition of the SDS to the LL could enhance its performance to improve the stability of the emulsions.When the concentration of the SDS reached a certain value,the phase of emulsions was reversed.This is because the hydrophobic tail chains of SDS molecules were adsorbed on the particles,the hydrophilicity of the particles was improved.The decrease of contact angle increased the curvature of the emulsion droplet interface and the adsorption strength of the particles on the interface.The system formed W/O type Pickering emulsions dominated by particles.Then the increase of the SDS concentration led to a competitive behavior between two emulsifiers,and the emulsification of the system failed.As the concentration of SDS continued to increase,the system eventually reversed to form O/W emulsions.Based on the synergistic stabilization of the two emulsifiers,different concentrations of inorganic electrolytes were added to the water phase.The addition of Na Cl improved the surface activity of SDS.As the concentration of Na Cl increased,the range of the SDS concentration that could stabilize the W/O emulsions narrowed to disappear,and finally forming the O/W emulsions.LL was further applied to the formulas of isolation emulsion and moisturizing cream.The results showed that the samples had good appearance and smell.The p H of moisturizing cream was 6.58;the viscosity of isolation emulsion and moisturizing cream were 8582.85 m Pa·s and37695.06 m Pa·s,respectively.Afterwards,the temperature stability test were performed on the samples,and the color stability test was performed on the isolation emulsion,the results showed that two samples remained stable,and the color of the isolation emulsion remained consistent.The sensory evaluation of the isolation emulsion revealed that the sample had good spreadability and transparency,which could meet the needs of use.