What is Oxirane ?

Oxiranes 

Cyclic ethers with three membered rings are known as expoxides or oxiranes (IUPAC nomenclature). Check out Chemistry Formulas and NCERT Solutions for class 11 Chemistry prepared by Physics Wallah. 

Structure of oxiranes

Preparation of oxiranes

a) Oxidation of ethylene : In presence of Ag2O

b) Expoxidation: Most important method of formation. It is the reaction in which an alkene is reacted with an organic peroxy acid or peracid such as per benzoic acid (C6H5CO—O—OH) or peracetic acid (CH3CO—O—OH).

Reactions of Oxirane

The epoxy bond angle is lower than that of normal tetrahedral bond angle (109°28′).

∴ There is strain in the ring due to the unstability. Due to this, epoxides are highly reactive towards nucleophilic substitution reaction (unlike ethers). They undergo ring opening reaction so as to release the strain. Epoxides undergo acid catalysed and base catalysed opening of the ring.

Acid catalysed opening of oxiranes

The acid reacts with epoxides to prooduce a protonated epoxide. The protonated epoxide reacts with the weak nucleophile (water) to form protonated glycol , which then transfer a proton to a molecule of water to form the glycol and hydronium ion.

Base Catalysed opening of oxiranes: Epoxides can also undergo base - catalysed ring opening provided the attacking nucleophile is also a strong base such as an alkoxide or hydroxide ion.