Cross Cannizzaro and Intramolecular Cannizzaro

[andyrk]

While I was going through my course material of Aldehydes and Ketones, I came across Cannizzaro Reaction. It is of 3 types, namely: Self Cannizzaro, Cross Cannizzaro and Intramolecular Cannizzaro. I understood the Self one but was unable to understand the other two. In the Cross one,why is always Formaldehyde (HCHO) used and reduced? And in Intramolecular one, how do we know which part of the dicarbonyl group will get reduced and which will get oxidised? Or is Intramolecular Cannizzaro meant for only a few dicarbonyl compunds like: Phenyl glyoxal, Pthaladehyde, Glyoxal? Because I saw only these with which Intramolecular Cannizzaro was done and shown. What about other dicarbonyl compounds?

 

[andyrk]

Anyone there?

 

[AGNuke]

Intramolecular Cannizzaro reaction generally takes place in molecules having two aldehyde groups and if they do undergo intramolecular Cannizzaro, they are expected to form a stable ring compound (6 membered).

As for Cross Cannizzaro, the reason behind using Formaldehyde as a reductant[\b] lies behind its mechanism and kinetics. Formaldehyde has little problem getting oxidized to formate (or I was taught so...) that the reaction largely go to that direction.