Question

Draw a stepwise mechanism for the reaction of an alcohol with an isocyanate to form a urethane.

Short answer

Answer

Mechanism of the reaction

Step-by-step solution

Isocyanate

The organic compound with a functional group that bears nitrogen, oxygen, and carbon is called isocyanate. This is a highly dangerous chemical substance that causes significant health issues.

About the mechanism

The lone pairs of electrons present in the methanol attack the carbon atom of the isocyanate functional group leading to the formation of the cation. This ion has resonance stabilized structures. The mechanism is shown below.

Formation of cation

Addition of another methanol molecule

Another methanol is added to the above species that result in the formation of species in which nitrogen bears a negative charge. On rearrangement, the target urethane molecule is obtained. The mechanism is shown below.

Formation of the product