NOTE: Important charges and non-bonding electrons are shown throughout the animation except during the transition state phase.
In this initial step a nucleophilic attack is made on the azoformaldehyde to produce a anion intermediate that can be stabilised by one of the formaldehyde groups.
Click the structures and reaction black arrows in sequence to view the 3D models and animations respectively
T. Y. S. But and P. Toy, Chem. - An Asian J., 2007, 2, 1340–1355.