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2-R-1 H -1,3-Benzazaphospholes (R-BAPs) are an interesting class of σ 2 P heterocycles containing PC bonds. While closely related 2-R-1,3-benzoxaphospholes (R-BOPs) have been shown to be highly photoluminescent materials depending on specific R substituents, photoluminescence of R-BAPs has been previously limited to an example having a fused carbazole ring system. Here we detail the synthesis and structural characterization of a new R-BAP (3c, R = 2,2′-dithiophene), and compare its photoluminescence against two previously reported R-BAPs (3a, R, R′ = Me and 3b, R = 2-thiophene). The significant fluorescence displayed by the thiophene derivatives 3b ( φ = 0.53) and 3c ( φ = 0.12) stands in contrast to the weakly emissive methyl substituted analogue 3a ( φ = 0.08). Comparative computational investigations of 3a–c offer insights into the interplay between structure–function relationships affecting excited state relaxation processes.
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This content will become publicly available on August 1, 2026
Transformation of cyclic amides and uracil-derived nitrogen heterocycles during chlorination
Nitrogen heterocycles are important structural components in biomolecules and anthropogenic chemicals, yet their transformation during chlorine disinfection remains poorly understood. This study investigated chlorination kinetics and product formation for six nitrogen heterocycles of increasing structural complexity, including cyclic amides (2-piperidone, glutarimide, 5,6-dihydrouracil) and uracil derivatives (uracil, uridine, and 1,3-dimethyluracil) to determine how structural variations influence reaction pathways. Apparent second-order rate constants varied widely from 9.2 × 10–3 M-1 s-1 (2-piperidone) to >103 M-1 s-1 (uracil, uridine), largely influenced by the nitrogen pKa values. Chlorination proceeded through initial N-chlorination, forming organic chloramides. While most organic chloramides were transient, that derived from 2-piperidone persisted for days under excess chlorine conditions. For saturated heterocyclic imides (glutarimide, 5,6-dihydrouracil), hydrolysis of the organic chloramides between the imide nitrogen and an adjacent acyl group rapidly formed ring-opened organic acids. Among uracil derivatives, chlorine added across the double bond. For uracil, the resulting 5-chlorouracil rapidly fragmented between the C-4 and C-5 position to release trichloroacetaldehyde at ∼100 % yield. Substitution at heterocyclic nitrogens in uridine and 1,3-dimethyluracil limited such fragmentation, forming more stable C-chlorinated heterocyclic or ring-opened products. The reaction patterns observed for these six nitrogen heterocycles were further validated using phthalimide and thymine, demonstrating the broader applicability of the identified reaction trends. These findings enhance our understanding of nitrogen heterocycle chlorination mechanisms and their implications for drinking water disinfection, offering insights into minimizing the formation of potentially harmful DBPs during chlorination.
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- Award ID(s):
- 2402425
- PAR ID:
- 10600906
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Water Research
- Volume:
- 282
- Issue:
- C
- ISSN:
- 0043-1354
- Page Range / eLocation ID:
- 123639
- Subject(s) / Keyword(s):
- Nitrogen heterocycles Chlorination Reaction kinetics Disinfection byproducts Nucleobases
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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