Question

Ethylene oxide is the starting material for the synthesis of 1,4 -dioxane. Propose a mechanism for each step in this synthesis. 1,4-Dioxane

Short answer

Question: Briefly describe the reaction mechanism for the synthesis of 1,4-dioxane from ethylene oxide using a Lewis acid catalyst. Answer: The synthesis of 1,4-dioxane from ethylene oxide involves four main steps. First, ethylene oxide reacts with a Lewis acid catalyst (e.g., AlCl3) to form a reactive intermediate. Next, a second ethylene oxide molecule nucleophilically attacks the positively charged oxygen of the intermediate, forming a dioxetane ring. Then, an intramolecular nucleophilic attack causes ring expansion and the formation of the desired 1,4-dioxane with aluminum still coordinated. Finally, the removal of the Lewis acid by a chloride ion regenerates the catalyst and yields 1,4-dioxane.

Step-by-step solution

Formation of the intermediate

Ethylene oxide (CH2OCH2) will react with a Lewis acid catalyst (such as Aluminum chloride or AlCl3) to form a more reactive intermediate. This intermediate will have a positive charge on the oxygen atom and the aluminum will be coordinated to the oxygen.

Nucleophilic attack by a second ethylene oxide molecule

The positively charged oxygen of the intermediate will act as an electrophile. A second molecule of ethylene oxide will act as a nucleophile, attacking this electrophilic center and forming a new C-O bond between the two ethylene oxide molecules. This leads to the formation of a four-membered ring dioxetane with a positive charge on one of the oxygen atoms and the aluminum still coordinated.

Ring expansion and intramolecular nucleophilic attack

The positive charge on the oxygen atom will cause the ring to expand, breaking one of the C-O bonds and allowing the negatively charged aluminum to attack one of the carbons of the ring. This intramolecular nucleophilic attack will lead to the formation of a six-membered ring - the desired 1,4-dioxane with aluminum still coordinated to one of the oxygen atoms.

Removal of the Lewis acid

In the final step, a chloride ion (Cl-) from the aluminum chloride will attack the aluminum, removing it from the 1,4-dioxane molecule and regenerating the AlCl3 catalyst. The final product, 1,4-dioxane, is now formed, and the reaction mechanism is complete.