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Kinetics and mechanisms of the reactions of aluminium(III) with β‐diketones in aqueous solution
Author(s) -
Tomany Claire T.,
Hynes Michael J.,
Schmid Thomas
Publication year - 1998
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1998)30:4<257::aid-kin3>3.0.co;2-r
Subject(s) - chemistry , enol , reaction rate constant , protonation , tautomer , sodium perchlorate , aqueous solution , kinetics , ionic strength , medicinal chemistry , perchlorate , reaction mechanism , inorganic chemistry , ion , organic chemistry , catalysis , electrochemistry , physics , electrode , quantum mechanics
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(H 2 O) 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 dm 3 mol −1 s −1 , respectively. The inverse acid pathway is consistent with a mechanism in which [Al(H 2 O) 5 (OH)] 2+ reacts with the enolate ions of Hpd, Htfpd, and Hhptd with rate constants of 4.32(±0.18)×10 6 , 5.84(±0.24)×10 3 , and 1.67(±0.05)×10 7 dm 3 mol −1 s −1 , respectively. An alternative formulation involves a pathway in which [Al(H 2 O) 4 (OH) 2 ] + reacts with the protonated enol tautomers of the ligands. This gives rate constants of 2.79(±0.12)×10 4 , 3.86(±0.16)×10 5 , and 8.98(±0.25)×10 3 dm 3 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(H 2 O) 5 (OH)] 2+ reacts by an associative or associative‐interchange mechanism. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 257–266, 1998.