Study On The Unit Reactions Of The Fine Synthesis In Ionic Liquids

Room temperature ionic liquids, which have very low vapor pressure and arethermally stable, have been recognized as a possible environmentally benignalternative to volatile solvents in the chemical industry. The application oftask-specific ionic liquids with specific functional groups, which can be used as bothof reagent and medium, but also catalyze special reactions, further enhances theversatility of ionic liquids. Development of new procedures in organic synthesis usingtask-specific ionic liquids as solvents and catalysts has become a novel research areain recent years.In this dissertation, several environmentally benign reaction procedures, such asesterification, nitration, condensation and oxidation, with or without the presence of atask-specific ionic liquid have been developed. A acidiC ionic liquid, [Hmirn][HSO₄],was prepared and used as solvent and catalyst in the esterification of acetic acid andalcohols. The esterification products could be easily separated in high yield from thereaction system via simple phase separation. The acidic ionic liquid phase afterremoval of water could be reused. The effect of reaction conditions on product yieldfor the esterification between acetic acid and n-butanol was studied. Butyl acetatewith a yield of 97% was obtained under optimal conditions. The acidic ionic liquid[Hmim][HSO₄] was recycled 5 times and the yield of butyl acetate did not decreaseremarkably. The structure of the acidic ionic liquid [Hmim][HSO₄] was characterizedby ¹H NMR, IR, and elemental analysis, and it was found that [Hmim][HSO₄] existedas monohydrate. Acidity determination of aquoes solutions of [Hmim] [HSO₄] showedthat [Hmim][HSO₄] possessed stronger acidity than [Hmim][CF₃COO]. The apparentkinetics of esterification for acetic acid with benzyl alcohol were investigated. It wasfound that the reaction was first order with acetic acid and benzyl alcohol respectively.The activation energy and preexponential factor were 89.27KJ·mol^-1 and 19.50,respectively. Nitration of alkyl benzenes and halo benzenes in ionic liquids were alsostudied. The weak nitrating agent NH₄NO₃/TFAA could mono nitrate alkyl benzenesand halo benzenes in the presence of [Hmim][CF₃COO] or [Hmim][HSO₄] as dualsolvent and catalyst. High para selectivity was observed in the nitration ofbromobenzene with NH₄NO₃/TFAA in acidic ionic liquid [Hmim][HSO₄] and theisomer ratio of 4-nitro product was 90% at 0℃. [H₃N⁺-CH₂-CH₂-OH][CH₃CH(OH)COO^-] with weak basic character weresynthesized and used as catalysts in the Knoevenagel condensation reaction ofaromatic aldehydes with ethyl cyanoacetate or malononitrile. Most of thecondensations took place at room temperature. The reactions were complete forperiods ranging from several to sixty minutes to provide good yields (81-98%) ofα,β-unsaturated carbonyl compounds, only the E-isomers were detected.Mannich condensation reactions of aromatic aldehydes, aromatic amines andaromatic ketones in ionic liquid [Bmim][BF₄] or solvent free conditions were studied.It was found that acidic ionic liquids [Py][CF₃COO] or [Py][Tsa] can catalyze thereaction effectively in solvent free conditions. [Py][CF₃COO] was observed to bemore effective than [Py][Tsa] as catalyst, and 90% product yield was isolated with[Py] [CF₃COO] as catalyst.The side chain oxidation of toluene, 2,4-Dimethynirobenzen and 4-nitrotouene tothe corresponding acids in ionic liquid [Bmim][BF₄] or traditional organic solventswith oxygen was studied. Oxidation of toluene with oxygen in ionic liquid[Bmim][BF₄] in the presence of catalytic amount of [Bmim]₃[PO₄(W(O)(O₂)₂)₄] orTEMPO-[Bmim][PF₆]/CuCl gave the unreacted reactant. Oxidation of2,4-dimethylnitrobenzene with molecular oxygen catalyzed by cobalt acetate in aceticacid in the presence of an initiator gave 3-methyl-4-nitrobenzoic acid in 51% yield.4-Nitrobenzoic acid was prepared in 75% yield by manganese sulfate catalyzed liquidphase oxidation of 4-nitrotoluene with oxygen.