The mechanism of oxidation of α-glycols by periodic acid. Part X. The oxidation of pinacol, and a general discussion of the stability of periodate esters and their role in the mechanism of oxidation

Abstract

The kinetics of oxidation of pinacol by periodate have been studied a t 0" and 25" over the range pH 0-1 3. The kinetics are second order except a t 0" and pH > 11. Under the latter conditions, with excess pinacol, the kinetics are those of consecutive first-order reactions, showing that an intermediate is being formed in appreciable concentration. Several features of the kinetics resemble closely those observed for the formation of the cyclic ester from propane-1.2-diol and periodate. It is concluded that the oxidations of pinacol and propane-1.2-diol by periodate proceed via a mechanism which is probably common to all oxidations of 1.2-diols by periodate, viz. the formation of a periodate monoester, followed by ring-closure to a cyclic ester, then decomposition of a monoanion of the cyclic ester to the reaction products. The stages of the mechanism are discussed in detail, and it is shown that the different types of pH dependence observed in the oxidation of 1.2-diols by periodate can be readily accommodated by this mechanism. The stability of the periodate esters is discussed, and it is concluded that the general order of stability of esters containing six-co-ordinated iodine is : cyclic triester > cyclic diester (5-membered ring) > cyclic diester (6-membered ring) > monoester. A comparison of the acid strengths of H6108 and cyclic periodate esters suggests that the periodiate di-and tri-anions are appreciably dehydrated in aqueous solution to H1052-and 4 S. Senent-Perez and P. Escudero, Anales red. SOC. espafi.

Mild Protocols for Generating Molecular Complexity: A Comparative Study of Hetero‐Domino Reactions Based on the Oxidant and the Substitution Pattern

“…20% combined yield), thus corroborating a cyclic complex formation, such as 54 (Scheme 4), similar to the periodic acid mechanism proposed by Buist and Bunton. [26] Analogous results were obtained starting from the diastereomeric mixture 19, the byproduct being the keto-enol form (53) of the diketone 52, along with a small amount (Ͻ5%) of the allylic oxidation product as above.…”

Development of a Hypersensitive Periodate‐Cleavable Amino Acid that is Methionine‐ and Disulfide‐Compatible and its Application in MHC Exchange Reagents for T Cell Characterisation

“…Chemocleavage of the conditional peptide lodged in the peptide binding groove should demand accessibility of the amino alcohol moiety to periodate anions, as well as an orientation of the vicinal amino alcohol that sterically allows the formation of the cyclic periodate ester intermediate 17. In view of the constrained conformation of the peptide ligand in the MHC groove, we investigated (by HPLC analysis) whether the loaded ligands p*AA syn or p*AA syn / anti would show differential reactivities towards periodate.…”

Aerobic Oxidation of Vicinal Diols Catalyzed by an Anderson-Type Polyoxometalate, [IMo6O24]5

“…This finding would tend to discount the possibility of a cyclic-intermediate mechanism as was suggested for periodic acid-catalyzed reactions. [15] The products of 1,2-cyclohexanediol are initially only cyclohexanone-2-ol, with increasing quantities of 1,2-cylohexanedione being formed as a function of time, that is the ratio 1,2-cylohexanedione/cyclohexanone-2-ol increases as a function of time. On the other hand in the hydrobenzoin oxidation, the benzaldehyde/benzil ratio is~9 and more or less constant as a function of time.…”