Polymer and Silica Supported Tridentate Schiff Base Vanadium Catalysts for the Asymmetric Oxidation of Ethyl Mandelate – Activity, Stability and Recyclability
Bibliographic record
Abstract
Abstract Homogeneous tridentate Schiff base vanadium catalysts derived from salicylaldehydes and tert‐leucinol or tert‐leucine are known to be excellent catalysts for the asymmetric oxidation of α‐hydroxy esters including ethyl mandelate. Herein, new analogous supported, semi‐soluble and insoluble catalysts are synthesized and their activities relative to the homogeneous catalyst are reported. The new catalysts are characterized by 1H and 13C NMR spectroscopy, mass spectrometry (EI, ESI, FAB), X‐ray crystallography, elemental analysis, gel permeation chromatography (GPC), Fourier transform infrared (FT‐IR) spectroscopy, and nitrogen physisorption. The effects of support material, synthesis procedure, and reaction solvent are examined to probe the utility of these catalysts. Linear poly(styrene) supported catalysts are partially soluble under the reaction conditions, and it is shown that the soluble species contribute significantly to the catalytic reactivity. Insoluble catalysts based on the same vanadyl complexes supported on cross‐linked poly(styrene) resin or mesoporous silica allow for catalyst recovery and recycle, showing equivalent selectivities over multiple reaction cycles. The mesoporous silica supported catalyst exhibits greater selectivity than the analogous homogeneous and polymer supported catalysts. Rigorous recycle studies show a loss of activity in each recycle, which is attributed to the decomposition of some portion of the vanadyl complexes in each cycle.
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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 | 0.000 |
| 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".