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Published byCharity Hood Modified over 8 years ago
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EPOXIDE FORMATION AND CLEAVAGE
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EPOXIDE Epoxides are cyclic ethers Three-membered ring compound Also known as oxiranes
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Epoxidation Epoxidation is an electrophilic addition Involves NGP Preparation: Peroxy oxidation of alkenes Base promoted cyclization of vicinal halohydrins
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Epoxidation: Syn addition Oxidation of Alkene Most widely used method Reaction of an alkene with an organic peroxy acid (peracid).
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C O bonds in the epoxide are not perfectly axial or equitorial Requirement Diaxial and trans position of leaving groups Epoxidation –single step process & stereospecific. Doesn’t involve a free carbocation. (i.e) Reactant Product Cis Cis Trans Trans
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Axial Equitorial Pseudo axial Pseudo equitorial Axial Equitorial Pseudo axial Pseudo equitorial
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Ring Opening Ring opening due to ring strain Regioselectivity of opening depend on condition Acid Catalysis Acid catalysis Nu - attack more substituted carbon atom (if unsymmetrical)
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Ex: acid catalysis B is the major product
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Base Catalysis Base catalysis Nu - attack less substituted carbon atom Ex:
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Conclusion Epoxides unlike ethers are reactive because of ring strain Most often used peoxy acids for epoxidation MCPBA (Meta chloroperoxy benzoic acid) MMPP (Magnesium monoperoxyphthalate)
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Transition state is similar for both formation and cleavage
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Reference Organic Chemistry (Clayden, Greevs, Warren,Wothers) Fundamentals of Organic Chemistry (Solomons & Graham) Stereochemistry Conformation and Mechanism ( P.S.Kalsi)
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