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Titolo:
La3+-catalyzed methanolysis of phosphate diesters. Remarkable rate acceleration of the methanolysis of diphenyl phosphate, methyl p-nitrophenyl phosphate, and bis(p-nitrophenyl) phosphate
Autore:
Neverov, AA; Brown, RS;
Indirizzi:
Queens Univ, Dept Chem, Kingston, ON K7L 3N6, Canada Queens Univ KingstonON Canada K7L 3N6 Chem, Kingston, ON K7L 3N6, Canada
Titolo Testata:
INORGANIC CHEMISTRY
fascicolo: 14, volume: 40, anno: 2001,
pagine: 3588 - 3595
SICI:
0020-1669(20010702)40:14<3588:LMOPDR>2.0.ZU;2-C
Fonte:
ISI
Lingua:
ENG
Soggetto:
DINUCLEAR COBALT(III) COMPLEX; METAL-IONS; LANTHANIDE IONS; HYDROLYSIS; CLEAVAGE; CATALYSIS; ACID; RNA; COORDINATION; REACTIVITY;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
51
Recensione:
Indirizzi per estratti:
Indirizzo: Brown, RS Queens Univ, Dept Chem, Kingston, ON K7L 3N6, Canada Queens Univ Kingston ON Canada K7L 3N6 ston, ON K7L 3N6, Canada
Citazione:
A.A. Neverov e R.S. Brown, "La3+-catalyzed methanolysis of phosphate diesters. Remarkable rate acceleration of the methanolysis of diphenyl phosphate, methyl p-nitrophenyl phosphate, and bis(p-nitrophenyl) phosphate", INORG CHEM, 40(14), 2001, pp. 3588-3595

Abstract

The interaction of La3+ 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 (s)(s)pH. P-31 NMR shows that phosphates 3 and 4 are each associated with La3+ as a rapidly interconverting mixture of complexes having 2:1, 1:1 (or 2:2), and 1:2 stoichiometry. At [La3+] > 2 x 10(-4) M, the kinetically dominant species in the (s)(s)pH regions of interest arephosphate-bound La3+ dimers having 2-5 associated methoxides. Potentiometric titration reveals that 4 mM La3+ alone in MeOH exhibits two apparent (s)(s)pK(a)s at 7.86 and 10.44 consuming 1 and 1.5 CH3O- per metal, the suggested structures being La3+ 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 La3+ and a profile with apparent (s)(s)pK(a)s at 7.8 and 11.1 consuming 1 and 1.5 CH3O- per metal corresponding to phosphate-bridged La3+ dimers with first two and then five associated methoxides. Methanolysis of 3-5 is strongly accelerated by La3+. At (s)(s)pH 8.9 or 11.1, respectively, as little as 5 x 10(-4) M La(OTf)(3) accelerates themethanolysis of 3 or 4 by 10(10)-fold relative to the background reaction. Detailed kinetic studies of the methanolysis of 5 at varying [La3+] and (s)(s)pH indicate that both La3+ monomers and dimers with associated methoxides are reactive species. The rate constants for La3+ monomer and dimer catalysis of the methanolysis of 5 are dependent on (s)(s)pH, the slopes of thelog plots being 0.35 and 0.5, respectively. A scheme is proposed to account for the non-first-order dependence on [CH3O-] wherein the La3+(CH3O-)(x) 5 reversible arrow La3+ - (CH3O-)(x):5 and (La3+)(2)(CH3O-)(y) + 5 reversible arrow 5:(La3+)(2)(CH3O-)(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.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 29/03/20 alle ore 12:09:48