Base-catalyzed oxidation of poly (ethylene glycol) by alkaline permanganate: Part II. Kinetics and mechanistic of decomposition of coordination intermediate complex

• Main Authors: Refat M. Hassan, Suzan A. Sayed, Samia M. Ibrahim
• Format: Article
• Language: English
• Published: Elsevier 2021-09-01
• Series: Egyptian Journal of Petroleum
• Subjects: Poly (ethylene glycol); Permanganate; Oxidation; Decomposition of intermediate complex; Acid-derivative-PEG
• Online Access: http://www.sciencedirect.com/science/article/pii/S1110062121000131

The kinetics of decomposition of coordination polymer poly (ethylene glycol) intermediate complex [PEG-MnVIO42-] which was formed during the progression of the relatively fast first stage for the oxidation of poly (ethylene glycol) (PEG) by alkaline permanganate have been investigated by conventional spectrophotometer. Pseudo first -order condition in the presence of [PEG] substrate as a synthetic polymer in large excess over [MnO4-] was showed first-order overall reaction kinetics. The influence of the alkali concentration on the decomposition rate constants indicated that the oxidation rates were increased with increasing the alkali concentration, therefore, the decomposition process was considered of base-catalyzed nature. The rate constant of decomposition was found to be 2.3 x10-4 s−1, whereas the deprotonation constant was 2.88 dm3 mol−1 at 45 °C. The activation parameters have been calculated and found to be ΔH≠ = 34.93 kJmol−1; ΔS≠ = −176.2 Jmol-K−1 and ΔG≠ = 90.96 kJmol−1. The chemical structure of such synthesized acid-derivative of PEG was elucidated by elemental analysis and spectral data. The negative results of 2,4-dinitrophenyl hydrazine and hydroxylamine identified investigations along with (FTIR) spectra results indicated that the oxidation product is the acid derivative of poly (ethylene glycol) (ADPEG). The synthesis procedure of the acid-derivative of PEG (ADPEG) as the final oxidation product was described in detail. The product yield was found to be ~ 98%. It is found that the oxidation product (ADPEG) has a high tendency for chelation with most polyvalent metal ions in particularly the divalent metal ions forming their corresponding coordination polymer complexes. Therefore, this distinct property of the product renders it to be used as a chelating agent of high performance, non-toxicity and low cost compared with the chelating agents available in the markets. A suitable reaction mechanism for the decomposition in terms of electron-transfer nature was suggested and discussed.