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Asymmetric Epoxidation of Olefins Synergically Catalyzed by Cyclodextrins and Dioxiranes

Author: XiaoZiSheng
Tutor: LanZhiLi
School: Hunan Normal University
Course: Organic Chemistry
Keywords: Olefins Cyclodextrins Inclusion complex Dioxiranes Epoxidation Synergistic catalysis
CLC: O621.25
Type: Master's thesis
Year: 2007
Downloads: 104
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Abstract


The asymmetric epoxidation of olefins synergically catalyzed bycyclodextrins （CDs） and dioxiranes has some advantages over pastresearch results. The synthetic method using water as solvent can avoidthe environmental pollution from organic solvents and metal catalysts.The reaction condition is moderate and the operation is convenient andsimple. The synthetic route is straightforward and the consumption ofenergy resources is low.In this thesis, we investigated the asymmetric epoxidation of olefinsincluded by CDs. In the reaction, CD is acted as a kind of chiralultramicroreactor and dioxirane is oxidant which is generated fromketones and potassium peroxymonosulfate (Oxone?) in situ.The asymmetric epoxidation of styrene with dimethyldioxirane inthe presence ofβ-cyclodextrin （β-CD） has been discovered. However, theenantiomeric excess of 1,2-epoxyethylbenzene was only up to 29%. Inthe thesis, The synergistic catalytic reaction rule of CDs and ketones wasstudied and mechanism of asymmetric epoxidation of olefins wasdiscussed. The research results are as follows:（1） An inclusion complex of styrene andβ-CD was prepared bysaturated solution method. The influences of the inclusion conditionswere studied and the optimum preparation process was established byorthogonal experiments. The formation of styrene-β-CD complex wasconfirmed by FT-IR, TG-DTA, XRD, 1HNMR. The association constantsof styrene and CDs were determined by UV. The recovery of inclusioncomplex prepared with the optimum inclusion condition was 71.85% and the content of styrene was 82.62 mg·g-1. The inclusion complex of CDsand styrene are more suitable for asymmetric epoxidation.（2） The asymmetric epoxidation of styrene included by CDs withdioxiranes produced from ketones and Oxone? in situ has been achieved.The various factors, such as reaction time and temperature, molar ratio ofmethyl isobutyl ketone （MIBK） to complex and the amount of NaHCO3,that control the enantioselectivity of the process have been examined. Theexperimental results indicate thatβ-CD has good ability of chiralrecognition to dioxirane which was generated from MIBK and Oxone? insitu. The maximum enantiomeric excess of 1,2-epoxy ethylbenzene wasup to 46%. A series of CD derivants were prepared according to theliteratures. The effects of different CD derivants and ketones onasymmetric epoxidation of styrene have been investigated. The possiblemechanism has been proposed and effect of CD’s hydroxyl and hydrogenbond have been suggested.（3） Some olefins were selectively epoxidated to the correspondingoptical epoxides, which can offer a new synthetic methodology of opticalepoxides. The reaction of asymmetric epoxidation ofα-methylstyrenewas performed by using 3-pentanone/Oxone? as oxidants andβ-CD as anultramicroreactor. The maximum enantiomeric excess ofα-methylstyreneepoxide was up to 59%.The synthetic method expands new application of the inclusioncomplexes ofβ-CD in organic synthesis. The research results of thisthesis not only enriched cyclodextrins chemistry but also offered a greensynthetic method, which have good prospect in theory and application.

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CLC: > Mathematical sciences and chemical > Chemistry > Organic Chemistry > Organic Chemistry general issues > Properties of organic compounds > Chemical properties of organic reactions
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