Photoinduced and Thermal Denitrogenation of Bulky Triazoline Crystals: Insights into Solid-to-Solid Transformation

Abstract

The photoinduced and thermal denitrogenation of crystalline triazolines with bulky substituents leads to the quantitative formation of aziridines in clean solid-to-solid reactions despite very large structural changes in the transition from reactant to product. Analysis of the reaction progress by powder X-ray diffraction, solid-state (13)C CPMAS NMR, solid-state FTIR spectroscopy, and thermal analysis has revealed that solid-to-solid reactions proceed either through metastable phases susceptible to amorphization or by mechanisms that involve a reconstructive phase transition that culminates in the formation of the stable phase of the product. While the key for a solid-to-solid transformation is that the reaction occurs below the eutectic temperature of the reactant and product two-component system, experimental evidence suggests that those reactions will undergo a reconstructive phase transition when they take place above the glass transition temperature.

Following a Photoinduced Reconstructive Phase Transformation and its Influence on the Crystal Integrity: Powder Diffraction and Theoretical Study

“…[3] There are examples, however, of irreversible photoamorphization and/or melting reactions. [4] In between these two reaction types exist the so-called reconstructive phase transformations (RPTs).…”

Polyaddition of Azide‐Containing Norbornene‐Based Monomer through Strain‐Promoted 1,3‐Dipolar Cycloaddition Reaction

“…The results from both MS and NMR confirmed the labile nature of triazoline, which is very advantageous in the design of new reactive polymer architectures, for example, through photodenitrogenation process to obtain aziriding‐containing polymer, and aziridine has been reviewed very recently as a very powerful functional group in transformation by ring‐opening reaction . It is noted that the detailed mechanism of denitrogenation and possible complex products, including aziridine, enamine, imine, pyrrole, polymer, etc., as found from the study of model compounds of small molecular weight have been an interesting topic to date . It is generally agreed that the formation of biradical by elimination of molecular nitrogen has been involved in the process.…”

“…But, triazoline is not stable and subjected to decomposition at intermediate temperatures to eliminate N 2 molecule . For example, Garcia‐Garibay and co‐workers applied photo‐ and thermal‐induced denitrogenation on the solid state of crystalline triazoline, the quantitative formation of aziridines could lead to reconstructive phase transition as an interesting example of solid‐to‐solid transformation . Recently, Li et al took advantage of this unique feature to obtain aziridine‐containing polymer in poling process for electrooptic application .…”

Crystal structure analysis of molecular dynamics using synchrotron X-rays

“…34,35 The first is the transition to an equivalent stable crystalline phase, which has the same periodicity and is formed without crystal deterioration. 34,35 The first is the transition to an equivalent stable crystalline phase, which has the same periodicity and is formed without crystal deterioration.…”

“…38 The third is the transition to a new stable phase. 34,35 The three phenomena described above can be involved in the photochemical phase transition. 39 The last is the transition to an isotropic phase such as amorphous 34 or melt phase.…”