Aerobic Oxidation of β-1 Lignin Model Compounds with Copper and Oxovanadium Catalysts
Bibliographic record
Abstract
The reactivity of homogeneous oxovanadium and copper catalysts toward aerobic oxidation of phenolic and nonphenolic β-1 lignin model compounds has been investigated. Aerobic oxidation of diastereomeric, nonphenolic β-1 lignin models ( 1T, 1E ) using the six-coordinate vanadium complex (HQ) 2 V V (O)(O i Pr) (HQ = 8-oxyquinolinate) as a precatalyst in pyridine afforded ketone ( 3 ) and dehydrated ketone ( 4 ) derived from oxidation of the secondary alcohol. In contrast, using CuOTf/2,6-lutidine/TEMPO (OTf = trifluoromethanesulfonate, TEMPO = 2,2,6,6-tetramethyl-piperidin-1-yl-oxyl) in toluene for the same reaction afforded 3,5-dimethoxybenzaldehyde ( 5 ) and 4-methoxybenzaldehyde ( 6 ) as major products resulting from C α –C β bond cleavage. Reactions of the corresponding phenolic lignin model compounds ( 2T, 2E ) with 10 mol % CuOTf/2,6-lutidine/TEMPO gave ketone ( 9 ) as the major product, whereas 10 mol % (HQ) 2 V V (O)(O i Pr) or a stoichiometric amount of CuOTf/2,6-lutidine/TEMPO yielded 2,6-dimethoxybenzoquinone ( 10 ) as the major product, arising from cleavage of the C aryl –C α bond. Different selectivity was observed in the oxidation of 2T, 2E using the five-coordinate complex (dipic)V V (O)(O i Pr) (dipic = dipicolinate), with α,β-unsaturated aldehyde ( 14 ) as the major product (formed from oxidation of the primary alcohol and dehydration). The key differences in chemoselectivity between the vanadium and copper catalysts in the oxidations of these phenolic and nonphenolic β-1 lignin models are discussed.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".