La<sup>3+</sup>-Catalyzed Methanolysis of Phosphate Diesters. Remarkable Rate Acceleration of the Methanolysis of Diphenyl Phosphate, Methyl <i>p</i>-Nitrophenyl Phosphate, and Bis(<i>p</i>-nitrophenyl) Phosphate
Bibliographic record
Abstract
The interaction of La(3+) with diphenyl phosphate, methyl p-nitrophenyl phosphate, and bis(p-nitrophenyl) phosphate (4, 5, and 3) and the ensuing catalysis of methanolysis has been studied in methanol under completely homogeneous conditions of known pH. (31)P NMR shows that phosphates 3 and 4 are each associated with La(3+) as a rapidly interconverting mixture of complexes having 2:1, 1:1 (or 2:2), and 1:2 stoichiometry. At [La(3+)] > 2 x 10(-4) M, the kinetically dominant species in the pH regions of interest are phosphate-bound La(3+) dimers having 2-5 associated methoxides. Potentiometric titration reveals that 4 mM La(3+) alone in MeOH exhibits two apparent pK(a)s at 7.86 and 10.44 consuming 1 and 1.5 CH(3)O(-) per metal, the suggested structures being La(3+) dimers with first two and then five associated methoxides. In the presence of 0.5 equiv of 4 the potentiometric titration reveals strong complexation of 4 to La(3+) and a profile with apparent pK(a)s at 7.8 and 11.1 consuming 1 and 1.5 CH(3)O(-) per metal corresponding to phosphate-bridged La(3+) dimers with first two and then five associated methoxides. Methanolysis of 3-5 is strongly accelerated by La(3+). At pH 8.9 or 11.1, respectively, as little as 5 x 10(-4) M La(OTf)(3) accelerates the methanolysis of 3 or 4 by 10(10)-fold relative to the background reaction. Detailed kinetic studies of the methanolysis of 5 at varying [La(3+)] and pH indicate that both La(3+) monomers and dimers with associated methoxides are reactive species. The rate constants for La(3+) monomer and dimer catalysis of the methanolysis of 5 are dependent on pH, the slopes of the log plots being 0.35 and 0.5, respectively. A scheme is proposed to account for the non-first-order dependence on [CH(3)O(-)] wherein the La(3+)(CH(3)O(-))(x) + 5 <--> La(3+)(CH(3)O(-))(x):5 and (La(3+))(2)(CH(3)O(-))(y) + 5 <--> 5:(La(3+))(2)(CH(3)O(-))(y) equilibria are driven to the left with increasing numbers of associated methoxides and that attack on these complexes, whether by external or metal-associated methoxide, is slower due to the reduced net positive charge on the complex.
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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 | 0.001 |
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".