Re: Why does heat destroy vitamin C?

Increased temeprature favors the enolized form of the molecule, because heat increases deprotonation and enables the tautomer to form more readily. The enol-form has the tendency to form a diketone. That is a degraded form.

Heat increases the rates of the electron transfer across already formed bonds. It also increases the rates at which the bonds will break, and those breakages can result in degradation.

The structures are shown here.
http://en.wikipedia.org/wiki/Ascorbic_acid