Isotopic labelling studies pyrolysis

It is curious that there have been more fundamental developments in 1,3,5-triazine synthesis by this method than in any of the other sections, yet it is the oldest of all the synthetic routes. Cyanuric acid was originally prepared by the pyrolysis of uric acid (7) (see Section 2.20.1.2). The mechanism was proposed by Brandenberger and coworkers on the basis of isotopic labelling studies, and was reviewed by Modest (B-61MI22000, p. 706). The rearrangement of pyrimidines to 1,3,5-triazines is the most important advance in this area. 

The same products are formed by pyrolysis of the o-, m-, or p-methylbenzaldehyde p-toluenesulfonylhydrazones. Suggest mechanisms that could account for these skeletal rearrangements. Are any of your mechanisms consistent with the following isotopic labeling study ... 

Perez Locas C., Yaylayan V.A. Isotope labeling studies on the formation of 5-(hydroxymethyl)-2-furaldehyde (hmf) from sucrose by pyrolysis-GC/MS. Journal of Agricultural and Food Chemistry, 56, 6717-6723... 

---