Kinetics and mechanism of the oxidation of proline by periodate

Abstract

ROSA PASCUAL, MIGUEL A. HERRAEZ, and EMILIO CALLE. Can. J. Chem. 67, 634 (1989).The kinetics of oxidation of proline by periodate has been studied at pH 1.40-8.83 and 30.0°C. The reaction rate is first order in both periodate and amino acid, and the overall reaction follows second-order kinetics. There was no evidence for the formation of an appreciable amount of intermediate. The reaction rate is highest at pH 4-7 and the oxidation is catalysed by HP@-ions. The pH dependence of the reaction rate can be explained in terms of reaction of periodate monoanion and the protonated and dipolar forms of the amino acid. The mechanism proposed and the derived rate law are consistent with the observed kinetics. The rate constants obtained from the derived rate law are in agreement with the observed rate constants, thus justifying the rate law and the proposed mechanistic scheme.Key words: oxidation of proline, oxidation by periodate.

Kinetics and Mechanism for Oxidation of L‐Proline by Bis(hydrogen periodato)argentate(III) Complex Anion

“…Oxidation of L-proline by periodate in the pH range of 2.10-5.0 has been studied and reported, 14 and the oxidation reaction also follows an overall second-order rate law, first-order in both periodate and proline. The second-order rate constants, measured at 30 ℃, are about 1/10000-1/1000 of those we obtained for the Ag(III) oxidation in the present work.…”

“…Since periodate-proline and Ag(III)-proline reactions have been studied in different pH ranges, the interaction between periodate and proline should be checked in the alkaline medium we used. Reactions between periodate (1-2 mmol•L -1 ) and L-proline (10-20 mmol•L -1 ) at [OH -]＝0.030 mol•L -1 and 30.0 ℃ were followed spectrophotometrically at 310 nm, the wavelength used for kinetic measurements by Pascual et al 14 Following the reactions for several hours, no significant absorbance changes were observed, indicating that the reaction between periodate and proline was either extremely slow or did not proceed at all in the alkaline medium.…”

“…This is also consistent with the negative test results by Nessler's Reagent for ammonium and by DNPH for aldehyde/ketone. Corresponding peaks of other possible products such as 1-pyrroline-2-carboxylic acid and 2-pyrrolidinone, formed in oxidations of proline by enzyme 12 and IO 4 -, 13,14 were not found on the mass spectra.…”

“…7 This remarkably catalytic property of proline has since generated a world-wide interest; currently, catalytic syntheses of various asymmetric organic compounds by using proline (or its derivatives) either alone or in combination with metal ions are being vigorously pursued. [8][9][10][11] A number of kinetic and mechanistic studies on the oxidation reactions of proline by various oxidants have been reported; the oxidants include enzymes, 12 non-metallic small molecules [13][14][15][16][17] and metal ions/complexes. [18][19][20] It is of interest to notice that the oxidation reactions have been shown to take place via diverse mechanisms and depending on the nature of oxidants several oxidation products of proline have been identified.…”

“…[18][19][20] It is of interest to notice that the oxidation reactions have been shown to take place via diverse mechanisms and depending on the nature of oxidants several oxidation products of proline have been identified. [13][14][15][16][17][18][19][20] In view of the general interest of proline as discussed above, we have undertaken a mechanistic study on the oxidation reaction of L-proline by bis(hydrogen periodato)argentate(III) complex anion, [Ag(HIO 6 ) 2 ] 5-. The formula and crystal structure of [Ag(HIO 6 ) 2 ] 5were well-established and reported earlier; [21][22][23][24] the complex has a typical square-planar geometry around the metal center.…”