Kinetics Of Oxidation Of Dihydric Alcohols & Amino Acids By Ag(Ⅲ) Spectrophotometrically

In this paper, kinetics and mechanism of oxidation of dihydric alcohols, ethylene glycol monoethyl ether , amino acids by Ag(III) in alkaline medium were studied by spectrophotometry. The change of k_obs with different [R], [OH],[IO₄^-], Ionic Strength μ were studied, the determining-step rate constants (k) and activation parameters were evaluated at 298.2 K.We think that [Ag(OH)₂(H₂IO₆)₂]^5- was the existent form in the alkaline medium, and the activation center was [Ag(OH)₂(HIO₆)]^3-. The kinetics and mechanism from our theory were in accordance with our experiment result.Through the experimentation, we find that the reaction rate changed with the position of hydroxyl group and the length of carbon chain, when the reaction of the similar compounds oxidation by Ag(III). At the same temperature, the reaction rate constant of the determining-step has such a sequence: ethylene glycol >L-aspartic acid >l,2-butylene glycol >1,3- butylene glycol > ethylene glycol monoethyl ether. The ortho-compound formed penta cyclic compound was more stable that the meta-compound formed hexa cyclic compound, so the reaction rate of the ortho-compound is larger. In addition, the carbon chain of butylene glycol was longer than that of ethylene glycol, so the spatial hindrance of butylene glycol was bigger than that of ethylene glycol, so the reaction rate of butylene glycol was longer than that of ethylene glycol. Ordinarily the reaction rate of amino acids is faster than that of glycols, but the carbon chain of ethylene glycol is very short, the reaction rate of L-aspartic acid was longer than that of ethylene glycol.Because the existent form in aqueous periodate solution is very complex, which is connected with change of [OH^-]. In the system of 1,2-butylene glycol and L-aspartic acid oxidation by Ag(III), the reaction rate decrease with the increase in [OH^-], After a point, it increased with the continuous increase in [OH^-]. So we brought forward the two different mechanism at the different alkaline value, which can explain our experiment result.