CHEM 203 Lecture Notes - Lecture 30: Peroxy Acid, Meta-Chloroperoxybenzoic Acid, Epoxide
Document Summary
The epoxidation reaction of alkenes: their conversion into epoxides. Concerted mechanism of peroxyacid epoxidation of alkenes: the epoxide forms in a single kinetic step though a mechanism that involves no radical or ionic intermediates: Presumed mechanism of peroxyacid epoxidation of olefins; e. g. , with mcpba: Strictly syn course of the epoxidation of alkenes with peroxyacid reagents: both c o bonds form from the same face of the olefinic system. Retention of olefin geometry during epoxidation reactions; e. g. o. These reactions are driven by release of strain: Regiochemical course of sn2 cleavage of unsymmetrical epoxides with basic nucleophiles: attack at the less sterically hindered position (more accessible *c o orbital). Inversion of configuration in the above reactions (the nu: interacts with the *c o orbital) Principle: weak, nonbasic nucleophiles (= conjugate bases of acids with pka < 0) such as h2o, alcohols, etc. react with epoxides only upon e. g. , protonic activation of the epoxide oxygen. Approximate pka of a protonated epoxide: 3.
