B. Pal, P. Sen, K. Gupta
Mar 20, 2007
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ChemInform
Abstract
The review narrates the electron transfer reactions of some chloroaurate(III) complexes in acid medium reported since 1970 onwards. The reactions involving inorganic substrates and gold(lll) were studied mostly in HCl medium whereas the oxidations of different organic substrates were investigated in sodium acetate-acetic acid buffer medium. Increase in [H + ] decreases the rate of reactions. At higher concentrations of [H + ] (ca. ≥ 0.5 mol dm -3 ), AuCl 4 - or HAuCl 4 is the reactive gold(III) species whereas when the reactions were studied in much lower acidities of [H + ] (« 0.5 mol dm -3 ) or in sodium acetate-acetic acid buffer medium, AuCl 4 - , AuCl 3 (OH 2 ) and AuCl 3 (OH) - are the reactive species which oxidize the substrates. Kinetic evidence for the participation of AuCl 4 - , AuCl 3 (OH 2 ) and AuCl 3 (OH) - is provided. The reactivity of these different gold(III) species follow the order: AuCl 3 (OH) - > AuCl 3 (OH2) > AuCl 4 - . Influence of ionic strength was noticed in the oxidations of some inorganic and organic compounds by gold(III). The rates in the presence of different salts like NaCI, NaClO 4 and Na 2 SO 4 at constant ionic strength was found to be same in the oxidations of a number of inorganic compounds indicating that anions do not have any influence on the rate. The rates were found to depend not only on the ionic strength but also on the concentration and nature of the cations. The pseudo-first-order rate constant increases in the order Li + < Na + < K + . < Rb + < Cs + in the oxidation of a number of inorganic substrates. The reactions exhibit diverse mechanistic behavior. Kinetic and mechanistic features associated with such reactions have been discussed and analyzed. An attempt has been made to correlate mainly our experimental observations.