Feb 2, 2015 · Epoxides treated with aqueous acid will open to form trans diols. The mechanism resembles the opening of bromonium, chloronium, and mercurinium ions.

Epoxides may be cleaved by hydrolysis to give trans-1,2-diols (1,2 diols are also called vicinal diols or vicinal glycols). The reaction can be preformed under acidic or basic conditions which will provide the same regioselectivity previously discussed.

Thus, 1,2-epoxypropane reacts with HCl to give primarily 1-chloro-2-propanol, but 2-methyl-1,2-epoxypropane gives 2-chloro-2-methyl-1- propanol as the major product. The mechanisms of these acid-catalyzed epoxide openings are more complex than they initially appear.

In this article, we will focus on the reactions of hydroxides and alkoxides as good nucleophiles together with the ring-openings under acidic conditions. Let’s first mention what is common in the ring opening of epoxides with good and poor nucleophiles.

Feb 10, 2015 · Ring-opening of epoxides with basic nucleophiles. If a chiral center is at this carbon, its stereochemistry will be inverted. A simple way to remember this is to think of epoxide opening under basic conditions as proceeding much like an S N 2 reaction. Table of Contents: Understanding Separate Quench Steps: 1) Add this 2) THEN add this! 1.

When an asymmetric epoxide undergoes solvolysis in basic methanol, ring-opening occurs by an S N 2 mechanism, and the less substituted carbon reacts with the nucleophile under steric considerations and produces product B in the example below.

Unsymmetrical epoxides react with weak nucleophiles at the more substituted carbon atom. With this said, let’s dive into the regiochemistry, the stereochemistry, and the mechanistic aspects of the epoxide ring-opening reactions.

Jan 26, 2015 · Epoxides (oxiranes) are cyclic ethers that have unusually high reactivity due to ring strain (about 13 kcal/mol). The 3-membered ring of epoxides can be opened under both acidic and basic conditions. Epoxides can be synthesized from alkenes via epoxidation with a peroxyacid like m-CPBA, or from halohydrins via treatment with base. Table of Contents

Epoxides can open three-membered ring and this can be achieved with base or acid. As an acid can be used hydrogen halide acid (HCl, HBr, HI). As other nucleophiles can be used water or alcohol with a small amount of acid (often sulfuric acid) which catalyzes the reaction. This mechanism involves two steps: STEP 1.

Epoxides from Halohydrins • Addition of HO-X to an alkene gives a halohydrin • Treatment of a halohydrin with base gives an epoxide • Intramolecular Williamson ether synthesis