Preparation Of Naphthyl-based Surfactants And Their Application In Chloromethylation Of Aromatic Compounds

Chloromethylation of aromatic compounds are very important reactions in organic synthesis.Traditional chloromethylation procedures exit problems such as low selectivity and high environmental hazards.The application of micellar catalysis to the chloromethylation of aromatic compounds can significantly increase the reaction rate and selectivity,and the aqueous medium in the reaction system can effectively avoid the generation of carcinogens（chloromethyl ethers）.Therefore,the chloromethylation reactions of aromatic compounds carried out in micellar catalysis system are environmentally-friendly chloromethylation methods,and have good application prospects.Recent years,the application of gemini surfactants in micellar catalysis attracted more and more attentions due to their lower CMC and higher solubilization to organic compounds.In this paper,in order to develop a green and environmentally friendly process for the chloromethylation of aromatic compounds,two kinds of naphthyl-based quaternary ammonium salts were synthesized,and catalytic performance of these two surfactants in chloromethylation of aromatic compounds were also investigated.In this paper,two naphthyl-based quaternary ammonium surfactants Naph-GS and Naph-MS were synthesized by reaction of 1-chloromethyl naphthalene and bis（chloromethyl）naphthalene with N,N-dimethyl long-chain alkyl tertiary amine.The purified products were characterized by FT-IR and ESI-HRMS.The critical micelle concentration（CMC）and surface tension(γ_CMC)at the critical micelle concentration of Naph-MS and Naph-GS are 3.70 mmol/L,27.90 m N/m;0.89 mmol/L and 31.60 m N/m,respectively.Both Naph-MS and Naph-GS can effectively reduce the surface tension of the solution,the CMC of Naph-MS is about four times higher than that of Naph-GS.The sizes of most micelles of Naph-MS and Naph-GS aqueous solution at 1.1 CMC are both below 1 nm.While at the concentration of 11 CMC,most of Naph-MS and Naph-GS micelles aggregate forming particles with an average size of 1.2 nm and 10 nm,respectively.Compared with the Naph-MS,Naph-GS aqueous solution can form larger micelles when the concentration is at the same multiple of CMC.The micellar effects of Naph-MS and Naph-GS on the chloromethylation of naphthalene in H₂SO₄-Na Cl-paraformaldehyde chloromethylation system were investigated,the results indicated that the gemini surfactant Naph-GS has better catalytic performance than conventional surfactant Naph-MS.The optimal reaction conditions of Naph-GS micellar catalysis chloromethylation of naphthalene are:Naph-GS:0.53 mol%（10 mmol/L）,naphthalene:17 mmol,paraformaldehyde:21.3 mmol,H₂SO₄:8 m L（110 mmol）,saturated Na Cl solution:5 m L,cyclohexane:4 m L,reaction at 70 ^oC for 12 h.Under this condition,the conversion of naphthalene is up to 90%,and the position selectivity ofα-chloromethyl naphthalene can reach 94.8%.The inorganic phase of this chloromethylation system can be recycled by simple separation,and the conversion of naphthalene can still remain at 85%after 5 cycles.Naph-GS was also used to catalyze the chloromethylation of OP-10.The conversion of OP-10 can reach 88%when the reaction was catalyzed by Naph-GS（10 mmol/L）at mole ratio of OP-10/paraformaldehyde being 1.0:4.1 at 85°C for 12 h.Then,the quaternary ammonium salt modified OP-10 was synthesized by reaction of chloromethylation OP-10and triethylamine.The surface activity and application prospects of this quaternary ammonium salt modified OP-10 are being further explored.