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Tautomeric forms of Oxy‐ and Oxo‐derivatives of 1,3,5‐Triazine. Part VI. Isomerization mechanism and thermal stability of the methyl esters of cyanuric acid
Author(s) -
Paoloni L.,
Tosato M. L.,
Cignitti M.
Publication year - 1968
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570050415
Subject(s) - chemistry , tautomer , isomerization , cyanuric acid , molecule , ionic bonding , computational chemistry , thermal stability , triazine , medicinal chemistry , organic chemistry , ion , catalysis , melamine
Previous investigations of the kinetics and the mechanism of the thermal isomerization C 3 N 3 (OMe) 3 → C 3 (NMe) 3 O 3 have been continued with a study of the isomerization mechanism of the mixed O,O,N ‐ and O,N,N ‐trimethyl esters of cyanuric acid. A full discussion of the overall process is given, in which it is assumed that the above mixed esters are intermediates. It is shown that the tautomeric transformation occurs as the consequence of the attack of Me + cations on the ring nitrogen of the neutral molecules. The presence of such cations in the melt was established by ionic exchange with the H + of the molten acids. It is also shown that the tautomeric transformation in solution proceeds with the same mechanism. An explanation is proposed for the thermal instability of the mixed esters (which isomerize even in the solid state, more than 20° below their melting point), which is based on the high polarity of these molecules. This property is discussed in terms of electronic structure calculations carried out with the Pariser‐Parr‐Pople approximation of the A.S.M.O., S.C.F., method.