Design, Preparation Of Eco-friendly Hydroxylamine Ionic Liquid Salts And Their Application In Clean Synthesis Reaction

Hydroxylamine?NH₂OH?is normally existed in the form of inorganic acid salt.How to solve the environmental problems caused by these salts and obtain clean hydroxylamine products is a serious challenge in the development of hydroxylamine salts.The present research aims to utilize green acid ionic liquids as alternatives to conventional inorganic acids in hydroxylamine stabilization,leading to the formation of several eco-friendly hydroxylamine ionic liquid salts,and investigate their applications in clean synthesis of caprolactam?CPL?,phenol and aniline.The preparation,characterization and density functional theory?DFT?calculations of hydroxylamine 1-sulfobutyl-3-methyl imidazole hydrosulfate salt and its application in CPL synthesis was investigated from cyclohexanone?CYC?under solvent-free conditions.?1?By using acid ionic liquid?[HSO₃-b-mim]?HSO₄?as alternative to conventional inorganicacidsinhydroxylaminestabilization,anewkindof green chemical-hydroxylamine1-sulfobutyl-3-methylimidazolehydrosulfatesalt??NH₂OH?₂·[HSO₃-b-mim]?HSO₄?was prepared for the first time.Its structure and composition were characterized by melting point,element analysis,FT-IR,Raman and NMR.DFT calculations were further performed to verify its structure.That is,one NH₂OH was combined with the H⁺released by-SO₃H in the cation of[HSO₃-b-mim]?HSO₄ to form NH₃OH⁺.Another NH₂OH was stabilized by network of H bonds or bonded forms formed among the H,O and N atoms in the?NH₂OH?₂·[HSO₃-b-mim]?HSO₄.?2?The one-step synthesis of CPL from?NH₂OH?₂·[HSO₃-b-mim]?HSO₄ and CYC under solvent-free conditions was studied.The suitable reaction conditions were as follows:n?CYC?:n??NH₂OH?₂·[HSO₃-b-mim]?HSO₄?:n?ZnCl₂?=1:2:2,reaction temperature of150?,reaction time of 2 h.The CYC conversion and CPL selectivity were 100%and91.0%,respectively.?3?The thermal stability of?NH₂OH?₂·[HSO₃-b-mim]?HSO₄ was better than?NH₂OH?₂·H₂SO₄ and NH₂OH·HCl.Furthermore,when the reaction was completed,the ionic liquid combined in the?NH₂OH?₂·[HSO₃-b-mim]?HSO₄ could be recovered.Hence,the environmental and safety problems caused by the conventional hydroxylamine inorganic acid salts could be avoided by using?NH₂OH?₂·[HSO₃-b-mim]?HSO₄.The extended preparation of hydroxylamine ionic liquid salts and their reactivity in direct synthesis of CPL was studied from CYC under mild conditions.?1?Three relatively low-cost acid ionic liquids were used in NH₂OH stabilization.Accordingly,three novel hydroxylamine ionic liquid salts were obtained.They are hydroxylamineN,N,N-trimethyl-N-sulfobutylhydrosulfatesalt??NH₂OH?₂·[HSO₃-b-N?CH₃?₃]?HSO₄?,hydroxylamine 1-sulfobutyl pyridine hydrosulfate salt??NH₂OH?₂·[HSO₃-b-Py]?HSO₄?and hydroxylamine N-imidazolium hydrosulfate salt??NH₂OH?₂·[H-mim]?HSO₄?,indicating that NH₂OH stabilization by acid ionic liquids to form hydroxylamine ionic liquid salts has a certain universality.?2?One-step synthesis of CPL from?NH₂OH?₂·[HSO₃-b-mim]?HSO₄ and CYC under mild conditions was realized,with ZnCl₂ as the catalyst and acetonitrile as the solvent.The optimalreactionconditionswereasfollows:CYC5mmol,n?CYC?:n??NH₂OH?₂·[HSO₃-bmim]?HSO₄?:n?ZnCl₂?=2:1:3,acetonitrile 10 mL,reaction temperature 80?,reaction time 4 h.The conversion of CYC was 82.5%,and the selectivity of CPL was 96.3%.Compared with the solvent-free conditions,the reaction temperature was remarkably decreased from 150 to 80?when acetonitrile was used as the solvent,which was helpful to improve the characters of the recovered ionic liquid.?3??NH₂OH?₂·[HSO₃-b-N?CH₃?₃]?HSO₄ demonstrated better reactivity than other three hydroxylamine ionic liquid salts and conventional hydroxylamine inorganic acid salts.Under the above mentioned suitable conditions,the CYC conversion and CPL selectivity were 99.1%and 92.0%,respectively.The preparation,characterization and DFT calculations of hydroxylamine Br?nsted-Lewis?B-L?acid ionic liquid salts and their application in CPL synthesis under mild conditions was investigated.?1?To avoid the separation of catalyst ZnCl2 and acid ionic liquid,ZnCl2 was implanted into the acid ionic liquid to form the B-L acid ionic liquid,which was then used to stabilize NH2OH to obtain a series of hydroxylamine B-L acid ionic liquid salts with adjustable number of NH₂OH?[H-mim]Cl-ZnCl₂-NH₂OH?1:3:y??.Their structure and composition were verified by characterizations as well as DFT computations.The maximum number of NH2OH could be stabilized by[H-mim]Cl-ZnCl2?1:3?was 6,which obviously increased the number of NH₂OH,meanwhile reduced the amount of acid ionic liquid.?2?One-step synthesis of CPL from[H-mim]Cl-ZnCl2-NH2OH?1:3:y?and CYC under mild conditions was investigated.When[H-mim]Cl-ZnCl2-NH2OH?1:3:3?was used,the yield and selectivity of CPL were 91.3%and 96.7%,respectively.The application of hydroxylamine ionic liquid salts in hydroxylation?amination?of benzene to phenol?aniline?was studied.?1?A new route with hydroxylamine ionic liquid salts as the hydroxylation agents to replace the?NH2OH?2·H2SO4,meanwhile the acid ionic liquids as the alternative media to H2SO4,was proposed for direct hydroxylation of benzene to phenol.The suitable operating conditionsweredescribedasfollows:Benzene5.63mmol,n?Benzene?:n??NH₂OH?₂·[HSO₃-b-N?CH₃?₃]?HSO₄?=1:1,?NH₄?₆Mo₇O₂₄ 0.1 mmol,CuCl₂0.1 mmol,6 mL HAc and 1.5 mL[HSO₃-b-N?CH₃?₃]?HSO₄ as the solvent,reaction temperature of 80?and reaction time of 4 h.Under these conditions,the phenol yield and selectivity were 11.2%and 100%,respectively.Furthermore,the ILs-Mo-Cu catalytic system could be recycled at least three times.?2?Hydroxylamine could not only be used as the hydroxylation reagent,but also as the amination reagent.By changing the reaction conditions,the products could be adjusted to aniline from hydroxylamine salts and benzene.When?NH2OH?2·H2SO4 was used as the raw material,benzene 5.63 mmol,n?Benzene?:n??NH₂OH?₂·H₂SO₄?=1:1,?NH₄?₆Mo₇O₂₄0.15 mmol,4 mL HAc and 6 mL[HSO₃-b-N?CH₃?₃]?HSO₄ as the solvent,reaction temperature of 80?and reaction time of 4 h,the product was only aniline.The yield and selectivity of aniline were 62.0%and 100%,respectively.Moreover,when?NH₂OH?₂·[HSO₃-b-mim]?HSO₄ was used as the amination reagent,the solvent was changed to 6.65 mL HAc and 3.35 mL[HSO₃-b-mim]?HSO₄,the amount of?NH₄?₆Mo₇O₂₄was 0.1 mmol,the yield and selectivity of aniline were 58.3%and 100%with other conditions unchanged.