Synthesis And Properties Of N-Fatty Acyl Threoninate

In recent years,more and more researchers have paid attention to green surfactants.Among them,amino acid surfactants are the one of green surfactants,which have good safety and biodegradability,and are widely used in household,personal care chemical industry and other fields.Threonine,as one of the amino acids used in fodder,is mature in domestic production technology and has achieved large-scale mass production,which provides rich raw material support for the research of threonine-based surfactants,and there are few reports on threonine-based surfactants.Therefore,in this paper,four kinds of N-fatty acyl threonine（C_nThr,n=12,14,16,18）with different carbon chain lengths by using threonine and neutralized by alkali,and we established a new method for determining C₁₂Thr by using high-performance liquid chromatography.Then we studied the effect of hydrophobic tail chain length on the properties of surfactants;Considering the degreasing power of amino acid surfactant is poor,we built a microemulsion with threonine-based surfactants as surfactant,and made full use of the excellent solubilization ability of microemulsion to indirectly improve the degreasing power of amino acid surfactant.Within the scope of this paper,the main research contents and conclusions are summarized as follows:（1）Synthesis and structural characterization of sodium lauroylthreoninate（C_nThrNa,n=12,14,16 and 18）.A series of threonine-based surfactants including C₁₂ThrNa,C₁₄ThrNa,C₁₆ThrNa and C₁₈ThrNa were synthesized by using long chain fatty acids（dodecanoic acid,tetradecanoic acid,hexadecanoic acid and octadecanoic acid）as raw materials,The structure of the product was characterized by FT-IR,¹H NMR and ESI-MS,and it was demonstrated that the products were the target products.（2）Purity analysis of C₁₂ThrUsing bromocresol green as indicator,Hamming 1622 as cationic titrant.the purity of C₁₂ThrNa was determined by two-phase titration method.but it is difficult to distinguish the titration end point due to emulsification.Finally,HPLC-RID method was established to analyze the purity of C₁₂Thr.As the results,this method could also detect the baseline separation of C₁₂Thr,LA and Thr.was achieved.the purity of C₁₂Thr was about 98.98%.The detection limits of LA and C₁₂Thr were 4.12×10^-3 g L^-1 and 4.32×10^-3 g L^-1,respectively.The RSD of both LA and C₁₂Thr samples were less than 2%.The average recovery rate of LA and C₁₂Thr were 99.47±0.16%and 99.55±0.18%,respectively,and the RSD of LA and C₁₂Thr were0.14%and 0.16%,respectively.（3）Structure-performance relationship of C_nThr Me（Me=Na,choline cation,n=12,14,16 and 18）Krafft temperatures of C_nThrNa（n=12,14,16 and 18）surfactants were measured by visual method.It is found that the Krafft temperatures of C₁₂ThrNa,C₁₄ThrNa,C₁₆ThrNa and C₁₈ThrNa were 22.82±0.16℃,36.30±0.10℃,50.70±0.21℃and 62.09±0.06℃,respectively.With the increase of alkyl chain,Krafft temperatures of samples increase gradually.In order to increase the water solubility of C_nThrNa（n=12,14,16,and 18）,we obtained a series of C_nThr-Ch（n=12,14,16,and 18）by using hydroxylcholine.The micellization behavior of C_nThr-Ch was studied by surface tension method,fluorescent probe method and interfacial tension method.The study found that the cmc values of C₁₂Thr-Ch,C₁₄Thr-Ch,C₁₆Thr-Ch and C₁₈Thr-Ch measured by surface tension method were 4.27 mmol L^-1,1.17 mmol L^-1,0.240 mmol L^-1 and 0.055 mmol L^-1,respectively,The cmc values of C_nThrNa（n=12,14,16,and 18）tested by different methods had unity.The foam properties,emulsification properties,solubilization properties and wetting ability of C_nThrNa（n=12,14,16 and 18）were tested.It was found that with the increase of alkyl chain,the foaming height decreased gradually,the foaming stability increased gradually,the emulsion droplets tend to be more homogeneous and stable.,the stability of the emulsion is enhanced,the solubility of n-octane and n-octanol increased gradually,and the solubility of n-octane was better than that of n-octanol.Moreover,the wetting ability of C_nThr-Ch decreased gradually with the increase of alkyl chain.（4）Microemulsion system based on C₁₂ThrNaThe construction and physicochemical properties of microemulsion were studied by using C₁₂ThrNa as surfactant and using short-chain alcohol as co-surfactant.The properties of microemulsion system were studied by using Shah titration method to construct quasi-ternary phase diagram.The influence of co-surfactants,the mass ratio of co-surfactants and surfactants（K_m）and oil phases on the construction of microemulsion system was studied.The results showed that n-butanol is co-surfactant,K_mis 2.3,isopropyl myristate is oil phase,and the area of microemulsion in single phase is the largest.The types of microemulsion were analyzed by conductivity method,including O/W,B.C and W/O.It was found that the particle size of the microemulsion decreased with the increase of water content by using Dynamic Light Scattering（DLS）in the particular range of the water content which belongs to O/W microemulsion.