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 distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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 teacher head, 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".