ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The kinetics and mechanisms of the reactions of aluminium(III) with pentane-2,4-dione (Hpd), 1,1,1-trifluoro pentane-2,4-dione (Htfpd) and heptane-3,5-dione (Hhptd) have been investigated in aqueous solution at 25°C and ionic strength 0.5 mol dm-3 sodium perchlorate. The kinetic data are consistent with a mechanism in which aluminium(III) reacts with the β-diketones by two pathways, one of which is acid independent while the second exhibits a second-order inverse-acid dependence. The acid-independent pathway is ascribed to a mechanism in which [Al(H2O)6]3+ reacts with the enol tautomers of Hpd, Htfpd, and Hhptd with rate constants of 1.7(±1.3)×10-2, 0.79(±0.21), and 7.5(±1.6)×10-3 dm3 mol-1 s-1, respectively. The inverse acid pathway is consistent with a mechanism in which [Al(H2O)5(OH)]2+ reacts with the enolate ions of Hpd, Htfpd, and Hhptd with rate constants of 4.32(±0.18)×106, 5.84(±0.24)×103, and 1.67(±0.05)×107 dm3 mol-1 s-1, respectively. An alternative formulation involves a pathway in which [Al(H2O)4(OH)2]+ reacts with the protonated enol tautomers of the ligands. This gives rate constants of 2.79(±0.12)×104, 3.86(±0.16)×105, and 8.98(±0.25)×103 dm3 mol-1 s-1 for reaction with Hpd, Htfpd, and Hhptd, respectively. Consideration of the kinetic data reported here together with data from the literature, suggest that [Al(H2O)5(OH)]2+ reacts by an associative or associative-interchange mechanism. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 257-266, 1998.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
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