www.bacpl.org/j/pcc Physical Chemistry Communications, Volume 3 Issue 1, April 2016
Kinetics and Mechanism of Oxidation of Erythritol by Permanganate Ions in an Alkaline Solution Manjanath B. Patgar, Sharanappa T. Nandibewoor, Shivamurti A. Chimatadar* P. G. Department of Studies in Chemistry, Karnatak University, Pavate Nagar, Dharwad 580003, India Corresponding author: Tel.: +91‐836‐2771606; Fax (Off): 91‐836‐2771275 *E‐mail address: schimatadar@gmail.com Abstract The oxidation of erythritol (ERT) by permanganate ion ( MnO-4 ) in aqueous alkaline medium and a constant ionic strength of 6.0×10‐2 mol dm‐3 were studied spectrophotometrically at 25oC. The reaction between erythritol and MnO-4 in alkaline medium exhibits 1:4 stoichiometry. The product, 2, 3, 4‐ trihydroxybutanoic acid, was isolated and identified with the help of TLC and characterized by FT‐IR and GCMS. The other product MnO42‐ was confirmed by UV‐Vis spectral studies. The order of the reaction with respect to MnO-4 and ERT concentrations were found to be unity and less than unity respectively. The rate of the reaction increased with increase in []. The effect of ionic strength, dielectric constant and added product on the rate of reaction was also studied. Based on the experimental results, the probable mechanism was proposed. The activation parameters with respect to slow step of the mechanism were computed and discussed. Thermodynamic quantities were also calculated. Keywords Kinetics; Oxidation; Mechanism; Erythritol; Alkaline Permanganate; Thermodynamic Parameters
Introduction Potassium permanganate is widely used as an oxidizing agent as well as an analytical reagent and also as disinfectant. These reactions are governed by the pH of the medium. Among six oxidation states of manganese from +2 to +7, permanganate, Mn(VII), is the most potent oxidation state in acid as well as in alkaline media. The oxidation by permanganate ion finds extensive application in organic synthesis [1, 2]. During oxidation by permanganate, it is evident that permanganate is reduced to various oxidation states in acidic, alkaline, and neutral media. In a strongly alkaline medium, the stable reduction product [3, 4] of permanganate ion is magnate ion, MnO42-. The process can be divided into a number of partial steps and examined separately. The MnO2 appears only after a long time, that is, after the complete consumption of MnO -4 . The kinetics of oxidation of sugars is subject of extensive research in recent years. This is attributed to the economic and biological importance of carbohydrates to living organisms. The oxidations have been reported out in both acidic and alkaline media using such oxidants as transition metal ions, inorganic acids, organometallic complexes and enzymes [5‐12]. Despite much work already done on the oxidation of sugars, very little attention was given to the use of permanganate anion [6]. The present study is therefore undertaken to clarify the mechanism of oxidation of erythritol by permanganate anion in alkaline medium as a follow up of the previous studies in the literature on the oxidation of sugars with chromium(VI) and iridium(IV) ions [13, 14]. OH HO
OH OH
Erythritol
Erythritol is a four‐carbon sugar alcohol with sweetness intensity varying from 0.6 to 0.8 [15]. Erythritol is the only sugar alcohol produced commercially by fermentation [16]. Blood glucose and insulin levels do not increase when erythritol is administered orally to normal male subjects [17]. From the results of acute and subchronic studies in animals, erythritol can be classified as non‐toxic [18]. In addition, erythritol is also noncariogenic [19]. The Food
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