Tetrazole ethers from lignin model phenols: synthesis, crystal structures, and photostability
Bibliographic record
Abstract
The phenolic OH moiety in lignin is one of the key functional groups responsible for the photo-induced yellowing of mechanical wood pulps and papers. To evaluate new protective groups for the stabilization of lignin phenols, the model compounds, 2-methoxy-4-propylphenol (1) and 4-hydroxy-3-methoxyacetophenone (2) were reacted with 5-chloro-1-phenyl-1H-tetrazole to give the corresponding tetrazole ethers 1' and 2', respectively, that were then studied for their photostability. The synthesis of these ethers was more efficient than that of alkyl ethers because of less hydrolysis of the alkylating agent under the reaction conditions. Compounds 1' and 2' were fully characterized, including X-ray crystal structure analyses. Crystals of 1' and 2' were monoclinic of space groups P21/c and P21/a, respectively. For 1': a = 9.8679(6), b = 16.708(1), c = 10.2841(6) Å, β = 109.732(5)°, Z = 4. For 2': a = 7.7212(2), b = 27.350(5), c = 14.569(3) Å, β = 101.30(2)°, Z = 8. The structures were solved by direct methods and refined by full-matrix least-squares procedures to R = 0.039 (Rw = 0.046) for 2029 reflections with I [Formula: see text] 3σ(I) (for 1'), and to R = 0.055 (Rw = 0.073) for 3634 reflections with I [Formula: see text] 3σ(I) (for 2'). Compound 2' was much more photostable than the precursor phenol on exposure to strong fluorescent light, while 1' was only slightly more stable than the precursor phenol.Key words: alkylation, ethers, lignin model compounds, methylation, phenols, yellowing inhibition.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".